Showing posts with label Eaglecrest. Show all posts
Showing posts with label Eaglecrest. Show all posts

Friday, October 31, 2014

Eyes in The Night!

In honor of all things spooky, we've been running a feature called 'Eyes In The Night' over on our facebook page. So far, we've seen raccoon, deer, opossum, bobcat, hare, great horned owls, skunk, great crowned night herons, and bullfrogs. We've watched them forage, hunt, eat, and very occasionally interact with one another under IR light, which they can't see. It's fascinating to see just how many animals are busy after dark!

Animals can be classified as nocturnal (primarily active at night), diurnal (primarily active during the day), cathemeral (sporadically active during the day or night), and crepescular (primarily active at dawn and dusk). Whether nocturnal, cathemeral, or crepescular, animals that are active under low-light conditions may have bigger eyes and ears, darker colors, more distinct vocalizations, and quieter movements than their strictly diurnal counterparts.

Seeing
Opossum at Eaglecrest 
Why do the animals and birds we watch after dark have such large glowing eyes? Because their eyes:
  • Tend to be larger and more protruding than those of diurnal or daytime animals. 
  • Often have pupils that open more widely than those of diurnal animals.
  • Often have slit rather than round pupils. Slit pupils are more efficient at opening and closing quickly.
  • Usually have more rods than cones. Rods work better in low light, detecting motion and basic visual information, while cones work better in bright light, registering detail and detecting color. Some nocturnal animals have no cones at all.
  • May have a special light gathering structure called a tapetum, which amplifies the amount of light that reaches the retina. The tapetum reflects light that has already passed through the retina back through the retina a second time, giving it another chance to strike the light-sensitive rods. The animals we watch can't see IR light, but their widely dilated eyes certainly reflect it!

Hearing
Deer are crepuscular, or active at dawn and dusk.
Their large, moveable pinna give them excellent
directional hearing. 
Why do the animals we watch after dark spend so much time listening? Many nocturnal animals rely on their hearing as much or more than their vision. How are their ears different from those of diurnal animals? They might have:
  • Enlarged pinnae (the outer part of the ear), facial disks, or other features that help them gather and condense sound.
  • Directional location. Think of ears as a microphone. In some animals (bobcats, for example), pinnae can be moved to funnel sound into the inner ear, helping localize the source of sound. Other animals, like owls, have offset ears that provide a precise x/y prey point based on a sound’s location.
  • Inner ear structures that maximize high frequency sounds (like mice rustling in the leaves). This might include denser, shorter auditory hairs, and denser auditory nerves. All the better to hear you with, my dear! 
  • Ultrasonic hearing. Bats are famous for echolocation, but some moths and nocturnal butterflies have ultrasound-sensitive ears on their wings to help them escape. 

Smelling 
Opossum flehvening at Eaglecrest
Why do the animals we watch spend so much time smelling things? In a low to no-light world, scent conveys important information about potential mates, rivals, predators, and dinner. Nocturnal animals:
  • Often have a larger olfactory epithelium, which improves their sense of smell. The sense of smell is most highly developed in nocturnal mammals, although some nocturnal birds also have a sense of smell. An improved sense of smell helps nocturnal animals find food and avoid becoming dinner under low-light to no-light conditions.
  • Often communicate via scent marking and smell. Scents intimidate rivals, attract mates, convey information about health, and provide information about numbers and types of animals in any given place. 

Touching
Nocturnal animals are very sensitive to touch. Many of them have special adaptations to help maximize touch in low-light or no-light situations, including:
  • Vibrissae, or whiskers that serve as tactile organs. While many animals have vibrissae, they tend to be more prominent on nocturnal animals or animals that hunt in low light. Vibrissae may be found on an animal’s face, forelegs, or feet. 
  • Sensory maps that maximize the input from vibrissae, antennae, and other tactile sensors. A study by biologist Dennis O’Leary found that a mouse’s sensory map is dominated by clusters of neurons that process whisker signals. A cluster for one whisker is bigger that the cluster of neurons dedicated to the mouse’s entire foot. 
  • A higher percentage of the cerebral cortex dedicated to touch. For example, almost two-thirds of the area responsible for sensory perception in a raccoon's brain is specialized to interpret touch. 
In a dark world, special adaptations help animals find food and mates, avoid predators, and defend their territories. I am grateful to have a chance to see them, spooky or not! Every time I step outdoors after dark now, I think about all of the animals that might be active around me.
Did you know...
While we don’t understand all of the ways touch works, image maps called cortical homunculi help map tactility. Check it out:
Links that helped me understand this:


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Wednesday, April 02, 2014

Big Jump at Eaglecrest

The Big Jump happened at Eaglecrest on April 1 at 4:42PM PDT, although it didn't go quite as expected. We believe that Wilma laid seven eggs of her own and incubated four additional eggs laid by Trudy, the intruder goose. Six goslings hatched. Of those six, four jumped at roughly 24 hours and two were unable to rise to their feet. All four that jumped made it safely to the pond.

Canada goslings are precoccial birds. They require very little direct parental care or feeding following hatch. Their parents will protect them from predators and other geese and help them find food, but they don't incubate the young after hatch or bring food to them in the nest. Canada goslings need to be able to get on their feet quickly, since the entire family leaves the nest roughly 24 hours after hatch starts.

The goslings that didn't jump were never able to get to their feet or move significantly from one place, which indicates they experienced some kind of damage during development in the egg. One of the goslings had already completely dried off, indicating hatching had happened some time ago. The other, while still wet, was unable to get up or propel itself at all. Canada goose hatchlings should be able to come to their feet very quickly once hatched. That those two didn't indicated something was wrong.

So why did two of the embryos fail to develop properly? We don’t know for sure. The eggs could have been injured in the struggles between Wilma and Trudy or damaged because Wilma couldn’t incubate, turn, or aerate all eleven eggs properly. From our point of view, two goslings died without reaching their feet and one egg failed to hatch. But from the goosey point of view, four goslings survived to fledge. Would waiting another twelve to twenty hours have saved the two goslings that failed to rise? No, but it might have harmed the successful hatchlings, who needed nourishment they couldn't get in the nest. Fred and Wilma gave their healthy, living offspring an excellent chance at survival by jumping when they did.

Some video of the goslings from Eaglecrest:

New goslings – MsDebbiB: http://youtu.be/DAp15Xu_rm8
Gosling leg stretch – Eaglewhisperer18: http://youtu.be/QsOIW3VKG2g
Wilma’s little goslings – Mocha Mama: http://youtu.be/uxnIZVrAzGU
The Jump! – Mocha Mama: http://youtu.be/sUHSmVge3-0
Waddle to the pond – Mocha Mama: http://youtu.be/C91I5Pl_pqA
Goslings swim - MsDebbiB: http://youtu.be/LijKt2jfczc

To learn more about incubation and heat/cold damage, follow this link:
http://www.brinsea.com/customerservice/poweroff.html

To learn more about the differences between altricial and precoccial birds, click here:
http://goo.gl/qC70ut
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Monday, March 24, 2014

Canada Goose Update

The goose and the hawk. Hawks drive the
intruder from their nest.
In the last blog, I speculated that Wilma's nest intruder could have been dumping eggs. It looks like she dumped not one, but two! From Eaglecrest:

Canada goose Mom Wilma is incubating NINE EGGS...seven of her own and two laid right in her nest by a female intruder. The two "foreign" eggs were laid on 3-15 and 3-22. In both cases, Wilma relentlessly attacked the intruding goose until she left. We may not have seen the last of her. The two intruder eggs will not hatch with Wilma's...they are eleven days or more behind schedule. Wilma began full time incubation of her SEVEN eggs on Tuesday, March 4th. We will expect the little goslings to hatch around March 31st...with the "big jump" about April 1st. Mate Fred is in constant protection mode, as usual.

We've been asked why this goose is behaving so strangely. Why is she dumping eggs? Why is she trying to sit in a hawk nest? I'm speculating that our invader is responding to the recent death of her mate. I haven't seen her accompanied by a male, which is extremely uncommon. Mated male geese are almost always hovering around their nesting mates, protecting them from predators and other geese. A study done at Horicon March in 1959 indicated that reduced breeding productivity was almost entirely connected with goosey social behavior. The authors of the paper wrote: 

"Over half the birds assumed to be capable of breeding failed to make nests in which they laid and incubated eggs; one-fifth of the birds failed even to pair up effectively. The nine pairs that failed to lay eggs in nests were involved in unusually frequent territorial clashes, and most of them were unable to maintain stable territories for any length of time. Four of the 5 pairs (and perhaps all 5) that lost their clutches did so because of disturbance to the female from other geese, related to a lack of effective male defense."

So our unknown intruder doesn't have a male to help safeguard her nest from other geese, who can be very disruptive to laying and sitting. What seems like erratic behavior is really an attempt to produce young under extremely difficult circumstances. While the intruder's eggs won't survive this spring, she'll most likely pair up with a new male goose to try again in 2015. There is no shortage of geese at Eaglecrest!

Geese have an elaborate, shifting hierarchy ruled by ganders with large families. I'll write a little more about the importance of family once the eggs start hatching. To watch Eaglecrest live, go to http://www.ustream.tv/eaglecresthawks. We anticipate hatch in Wilma's nest at the end of March or very early in April. 


Resources

Social Behavior and Breeding Success in Canada Geese (Branta canadensis) Confined under Semi-Natural Conditions
Nicholas E. Collias and Laurence R. Jahn
The Auk
Vol. 76, No. 4 (Oct., 1959), pp. 478-509
Published by: University of California Press
Article Stable URL: http://www.jstor.org/stable/4082315

Some of what we're seeing could also be a response to crowding, which impacts reproductive and social behavior. As California's drought reduces water resources, birds and other animals crowd more densely around those that remain. We'll explore the impact of crowding in a future blog.

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Monday, March 10, 2014

Canada Geese: Precocial versus Altricial

Three Canada geese at Eaglecrest are currently sitting on eggs. "Wilma", in the home tree, has laid seven eggs to date. She started full incubation on March 4th, which puts her hatch between March 27 and March 31. Betty has three or more eggs in the east pond nest, and Lucy has two or more eggs in the elevated pond nest.

The most common question about Eaglecrest's Canada geese is probably "How will the parents feed so many young?". While large broods are fairly common in many kinds of birds, Canada geese don't have to feed their young. Read on to learn more!

Precocial versus Altricial
From Stanford University:  A precocial bird is "capable of moving around on its own soon after hatching." The word comes from the same Latin root as "precocious." Altricial means "incapable of moving around on its own soon after hatchling." It comes from a Latin root meaning "to nourish" a reference to the need for extensive parental care required before fledging in altricial species. 

 So what's the big difference? Precocial birds like Canada geese lay energy-rich eggs to support the greater in-egg development of their young, who hatch ready to go. Their large, energy-rich eggs may contain almost twice the calories per unit weight than the eggs of altricial birds, which means that precocial females must obtain abundant food resources before laying eggs. Altricial birds like bald eagles, barn owls, and peregrine falcons do not have such large nutritional demands before egg-laying, but they have to find sufficient food once their helpless young hatch. While individual precocial birds are vulnerable to predation, it is much less likely that an entire brood will be eaten or destroyed. Altricial young cannot leave the nest prior to fledging, while precoccial young leave the nest quickly and have some ability, even when very young, to avoid predation.

Stanford University also tells us that there seems to be a trade-off in bird brain sizes related to the the degree of precocity. Precocial species have relatively large brains at hatching, but their adult brains are smaller relative to body size (the brain/body-mass index) than those of altricial birds. While altricial young hatch with smaller brains, they have highly efficient digestive tracts and a rich, parent-provided diet. Post-natal brain development is great and adults have proportionally larger brains than precocial species. Is this because they have more energy available to grow larger brains, or is something else going on? We're still trying to figure it out. This abstract hypothesizes that delaying brain development (by lengthening childhood) gives brains a longer period of time to grow and become more complex: http://goo.gl/sNw3xe.

At any rate, our hatchlings face very different challenges. Precocial Canada geese are relatively mature and mobile from the moment of birth, unlike altricial Bald eagles, Barn owls, and Peregrine falcons. Eagle, owl, and peregrine parents bring food into the nest for their young, often caching or storing prey for later consumption. Their young don't need to leave the nest or procure food until they fledge. The young goslings leave the nest within 24 hours of hatching and do not return to it. While their parents continue to provide protection and care, the goslings feed themselves.

The precocial goslings are also able to thermoregulate right away, unlike the eaglets and owlets. Altricial birds require their parents (or a parent) to apply warmth until their down feathers are developed enough to insulate them. The eagle parents and mother owl will spend a great deal of time huddling over their young after they have hatched, but the Eaglecrest geese will take to the water quite quickly, with no huddling required.

Eaglecrest offers a plethora of wildlife, including Canada geese, for watching. Visit http://www.ustream.tv/eaglecresthawks to see them! Again, we are anticipating goose hatch some time between March 27 and March 31.


Resources

Stanford University, Altricial and Precocial: http://www.stanford.edu/group/stanfordbirds/text/essays/Precocial_and_Altricial.html

Patterns of Metabolism and Growth in Avian Embryos
Carol Masters Vleck, David Vleck and Donald F. Hoyt
American Zoologist , Vol. 20, No. 2 (1980) , pp. 405-416
Published by: Oxford University Press
Article Stable URL: http://www.jstor.org/stable/3882403

The Evolution of Parental Care in Birds
A. Ar and Y. Yom-Tov
Evolution , Vol. 32, No. 3 (Sep., 1978) , pp. 655-669
Published by: Society for the Study of Evolution
Article DOI: 10.2307/2407731
Article Stable URL: http://www.jstor.org/stable/2407731

Developmental Modes and Developmental Mechanisms can Channel Brain Evolution
http://openi.nlm.nih.gov/detailedresult.php?img=3037498_fnana-05-00004-g003&req=4
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Friday, October 25, 2013

Red-Tailed Hawks and Social Play

Eaglecrest facilitator mochamamma has captured several videos of young red-tailed hawks squabbling, chasing, and stealing food from one another.
At first we thought they might be nest mates – although Stitch and Spot hatched just one young hawk, there are other nests in the area. But as the hawks piled up – three, four, five, eight – it became increasingly clear they weren’t related. What was going on?

We had a couple of ideas. Eaglecrest’s pond is a hot spot for local wildlife. Well over 30 species of animals have been captured on camera, including reptiles, amphibians, several mammals, and many birds. Large concentrations of raptors have been recorded at watering holes in Africa, Australia, the American Southwest, and other arid places. The young hawks at Eaglecrest were probably drawn in from the surrounding area by the pond’s abundant food and water supplies. But are they competing for limited resources or engaging in play and social interaction? Maybe a bit of both is happening.

I tend to think of red-tailed hawks as fairly solitary creatures. They chose a mate, build a nest, and defend their territory from interlopers, including other red-tailed hawks. But researcher Charles Preston observed red-tailed hawks in winter communal roosts of four to six members. These roosts sometimes included ferruginous hawks and at least one was close to a large communal roost of bald eagles.  Red-tailed hawks will also concentrate in higher numbers based on prey availability, which is probably why I start noticing them in larger numbers mid-fall. Like many other birds, red-tailed hawks are far less territorial when they aren’t breeding, although it might be a stretch to call them social. Yet juvenile red-tailed hawks engage in social play.

Play is well-documented among juvenile red-tailed hawks. They have been observed playing with inanimate objects like rocks and sticks – stalking them on the ground, pouncing on them, and dropping and catching them in flight. Play seems to have evolved in most species that provide prolonged periods of parental care, and red-tailed hawks are no exception. As Charles Preston notes, the young birds “may gradually broaden their range of hunting methods and increase their skills by learning from their parents or other red-tailed hawks.”

The young red-tailed hawks at Eaglecrest chase one another, steal prey, and mock fight. They spread their wings, assume striking poses, mantle food, stalk through the undergrowth, and wrestle, pinning each other down before walking away. It is interesting to speculate that this ‘flocking’ behavior might help the young, inexperienced hunters capture food, even if they risk having it stolen out from under them. More eyes are more likely to find food, especially when the hunters are young and inexperienced. The sheer number of young hawks might help flush prey out, although any successful hunter will need to defend his or her dinner against the rest. Although the pond is a rich environment, the young hawks are still learning to hunt and compete for prey. A little musing: we know the hunting skills they acquire will help them procure food. Will social skills like posturing and wrestling help them acquire mates and defend territory from other red-tailed hawks?

Presumably, our hawks will spend several weeks together honing hunting, social, and other survival skills prior to dispersal (or forced eviction by adult residents). I hope the skills they have acquired through social play will help them survive.

We still don’t know how common this kind of aggregation is, although I intend to do more reading and research in the weeks to come. Is this common outside of hot spots like the Eaglecrest pond? I have no idea. More questions: we have watched young eagles and vultures play, although those birds were pre-fledging. How does pre-fledging play inform post-fledging play? How is play different and alike in different species? Do parents play with young? Why is play so prevalent in juveniles? These are worthy and important questions to ask. Even TED plays attention to the importance of play: http://www.ted.com/talks/stuart_brown_says_play_is_more_than_fun_it_s_vital.html
So get out and play! 
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Wednesday, September 04, 2013

Golden Eagles

Eaglecrest's nesting golden eagles normally appear only at a distance. But on August 31, an immature eagle decided to show up in camera range. Viewers were treated to amazing views of the eagle's golden feathers, large talons, nictitating eyelids, and overall plumage. Video highlights can be found here:


Golden eagles get their name from the golden or tawny wash of feathers on their head and neck feathers. Adult American gold eagles are otherwise dark (or chocolate) brown in plumage, with 'marbled' flight feathers on their wing and tail. They range from 26 to 40 inches in length. Overall size is a complicated issue - while American gold eagles tend to be smaller than their counterparts in Eurasia, the largest gold eagle ever recorded was a female banded and released in Wyoming in 2006. Although bald eagles are a little bit longer on average than golden eagles (34 inches in length versus 33 inches in length), the difference is small enough that some golden eagles will be longer than some bald eagles. Confusing the issue even further, golden eagles (unlike bald eagles) don't appear to follow Bergmann's rule: one study found that golden eagles in Idaho were larger than those from Alaska. We can confidently say that they have a larger wingspan than bald eagles: North American golden eagle wingspans range from 6 feet to 7.2 feet according to Animal Diversity Web.

The eagle's nictitating membrane protects its eye
Look at that face! The nictitating membrane found in all birds is clearly visible. This membrane protects and moistens a bird's eye while allowing it to see. It also helps protect the young eagle's eye from scratches administered by struggling prey animals. The golden eagle lacks the baffles or 'jet cones' in a peregrine's nose, probably because golden eagles don't dive as fast as falcons do. Golden eagles achieve speeds of 28-32 miles per hour in an unhurried soaring flight, although they can achieve 120 miles per hour in a fast glide, and 150 miles per hour in a stoop. Its curved beak has sharp cutting edges for tearing meat, but lacks a falcon's tomial tooth. The tomial tooth, a small projection on the outer edge of the upper mandible, allows falcons to bite through cervical vertebrae and sever the spinal column of prey, quickly dispatching it. Golden eagles, however, deal death with their talons.

Check those legs and talons out! Unlike bald eagles, adult golden eagles are 'booted' - that is, their feathers cover their entire legs down to the toes. This may help protect their legs from bites and scratches inflicted by struggling prey. Golden eagles eat more kinds of prey than I can list here, since over 400 vertebrate species have been recorded as golden eagle prey. Although golden eagles appear to have food preferences, they are highly opportunistic hunters that will predate most reasonably-sized animals. They aren't going to wait for rabbits if ground squirrels are available!

Talons. 'He clasps the crag with crooked hands...'
The long, powerful talons of the golden eagle make escape extremely unlikely once prey is contacted. They can be up to three inches long and exert approximately 440 pounds per square inch of pressure. Small prey might be crushed, while larger prey might die from blood loss, shock, or collapse of the lungs following multiple punctures. Although the argument about how much weight golden eagles can carry rages on (Teenagers! Whole cows! Adult wolves!), the general consensus among people who study golden eagles is that prey much over 4.5 pounds would need highly favorable wind conditions for lift. So if a large golden eagle had plenty of momentum, and if the wind was right, and if it was able to swoop down and catch prey in its talons without stalling out, it might be able to lift more. But how much more is a matter of debate. Very large prey is simply eaten in place.

With their short, wide tails and long, broad wings, golden eagles are built to soar. They cock their wings in a slight 'V', somewhat like turkey vultures, and hold their wing tips wide open, flapping only when necessary. Unsurprisingly, they prefer open country and like to nest up high. Jumping off something high to attain lift is much less work than dead-lifting from the ground and height may, in some cases, make it easier to get prey to the nest. At Eaglecrest, the resident golden eagles nest in a large tree. Their large stick nest (smaller than a bald eagle's nest, on average, but still pretty large) is lined with grass and other soft vegetation when in use.

The flash of white indicates an immature eagle
Golden eagles are territorial. Given that this was a juvenile (its feet were not fully booted, it reveals a flash of white at the base of its tail when flying, and it has a lot of white patches), it was most likely a 2013 fledgling that hadn't yet dispersed. Like bald eagles, golden eagles appear to disperse from the natal sites, wander (fairly) widely, and return to their natal region, if not nest, as they approach maturity. I hope our young golden eagle will survive to adulthood and return to contribute yet more magnificent golden eagles to the area. What a wonderful sight to see!

Things that helped me write about this topic:

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Thursday, August 22, 2013

Getting Wet!

We talk about weather quite a bit. From wind in the tree to ice and snow on an eagle's back, we watch birds face difficult weather conditions. As our followers know, eagles and peregrine falcons have highly insulative waterproof feathers that protect them from wet, cold weather. However, some birds specialize in getting wet.

This double-breasted cormorant was caught on camera at Eaglecrest. The cormorant is a marine bird that specializes in eating fish, although it will also sometimes eat insects, amphibians and crustaceans (thank you, Animal Diversity Web and Wikipedia). They generally feed in shallow water (less than 8 meters or 24 feet deep), which may explain why they like Eaglecrest's pond. David McDonald, Eaglecrest's owner, also keeps it well stocked with fish.

Even many waterfowl tend to avoid actually getting wet. Like many birds, ducks and geese have feathers that 'zip' together and trap air, forming a water-resistant coat of sorts. They coat their feathers with oil from their preen glands, further helping repel water. Dabbling ducks (like the mallard and wood ducks at Eaglecrest) spend most of their time on the water's surface, tipping butt-up every once in a while to nibble passing food. Wet feathers would weigh them down, causing them to ride lower in the water. This in turn would lead them to expend more energy while searching for food - a bad trade off all the way around. Dabbling ducks want buoyancy.

But the cormorant has a different hunting strategy. A cormorant's outer feathers are water permeable, which weighs the cormorant down and helps it remain underwater. There is some debate about whether this has to do with feather structure or its preen gland. Some sources claim that cormorants produce less preen oil, aiding feather permeability, while others believe that feather structure plays a more dominant role. Whatever the cause of permeability, dry feathers next to the cormorant's skin trap air. Its unique feathers reduce buoyancy while retaining warmth. For all practical purposes, the cormorant is wearing a sort of home-grown dry suit. Unlike its cousin the Anhinga, which soaks all the way through, cormorants can handle cold water. I've seen them in shallow water on the south side of Lake Superior, near the Apostle Islands, where summer surface water temperatures may not climb much above the mid-sixties - and that is in the warm part of the Big Lake! The cormorant's long tail and cyclical paddling also help reduce buoyancy. All of these things
keep the cormorant underwater longer at a lower metabolic cost, which pays off in more food opportunities and reduced energy loss.

Dabbling ducks spend a lot of time floating on the surface of the water. But once a cormorant has secured dinner, it tends to leave. It is a diver and swimmer, not a leisurely floater. It spreads its wet wings to dry until the next time it goes hunting underwater.

Some cultures fish with trained cormorants. Click here for a video that shows cormorant fishing: http://youtu.be/Me3J0K1Qd5o. Note how much lower they ride in the water even when floating. Scuba divers should check this link out - at least scuba divers that also enjoy reading about birds. This is the first time I've found a reference to Boyle's Law in a bird book. And finally, some people believe that the cormorant's wing spreading may serve social or thermoregulatory purposes as well.

Some more things that helped me learn about this topic:


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Thursday, May 30, 2013

IR Reflective Feathers and Facial Disks


While creating owl highlights this morning for our Eaglecrest site, I came across some very close-up footage of a fledgling owl's face. As the capture above shows, the young owl has a lovely ring of IR reflective feathers around its facial disk. I was curious, so I did a little research. If owls can't see IR light, why would they have IR reflective feathers? Although I wasn't able to find much on IR and feathers, it seems most likely that the ring is produced by melanin, which fluoresces under IR light. Melanin not only produces colors ranging from dark black to reddish brown and pale yellow, it also makes feathers stronger, stiffer, and more resistant to wear.

While many birds have some amount of melanin in their feathers, especially stiff wing primaries, owls instead have porphyrin, a pigment that doesn't stiffen feathers. Soft, serrated feathers aid an owl's silent flight by breaking up turbulence. An angry peregrine falcon whooshes by you, but you won't hear an owl coming (cue creepy music here). Owls are the only birds known to use porphyrin in their wing feathers.

The rigidity of a material also impacts the way it reflects sound. Rigid materials reflect sound better and more quickly than softer ones. To quote: "The speed of sound in a medium is determined by a combination of the medium’s rigidity and its density. The more rigid the medium, the faster the speed of sound." A wall or canyon might produce an echo, but a pillow won't. I tried it myself, just to make sure.

So soft feathers are wonderful for silent flight, but they don't reflect sound nearly as well as rigid feathers. I am speculating that our little barn owl has a ring of stiff, melanin-producing feathers around its facial disk. The stiff feathers channel sound better and more quickly than soft ones would - absolutely crucial for an animal that hunts in little or no light. The contrast between the owl's porphyrin and melanin laden feathers produces a ring effect that might not be noticeable in a bird with more melanin. It is interesting to speculate that 'echoes' produced by the irregularly shaped ring might also aid directional hearing. Changes in the speed of sound might help owls gauge prey distance and location much as bats use echolocation (aside: this might be the most hilarious video about echolocation ever made).

We know that an owl's facial disk is special in many ways, and that barn owls in particular seem to be well-adapted for low to no-light hunting. This looks like another example of owl adaptation in action.


Thanks to the camera operators at Eaglecrest for the wonderful video! The following things helped me learn about this topic:

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Wednesday, May 22, 2013

Camouflage!

In addition to being silent flyers, owls are remarkably cryptic. This photo shows a barn owl, possibly mother Tess, perched just outside the nest cavity. She has flattened herself against the tree and is holding one wing down. Her barred wings break up her outline, making her difficult to see against the tree's rough bark.

Camouflage exists in two basic forms: crypsis and mimesis. Cryptic camouflage makes animals hard to see, while memesis, or mimetic camouflage, disguises them as something else.

Visual crypsis can be achieved in many different ways. When Tess is perched as she is above, her colors and patterns resemble a natural background. Owls are adapted for exceptional camouflage when roosting and hunting. Many species have colors and patterns that mimic the bark of preferred trees, which may explain the incredibly variety of color and pattern morphs seen in many widely distributed owl species.

Disruptive patterns use strongly contrasting, non-repeating markings such as spots or stripes to break up outlines. Tess's barred wings, plumage, and dark spots help break up her outline, making her difficult to see. Her spots also make her more attractive to male barn owls, who exhibit a clear preference for spotted females. The bigger and darker the spots, the better!

Cryptic patterns and coloration don't work as well when an animal is moving. While the fledgling owls aren't acting particularly cryptic, adult owls have very cryptic behavior. They perch quietly and hunt stealthily. Their soft feathers reduce turbulence, muffling the sound of air flowing over their wings. As the young owls learn how to fly and hunt, they will become increasingly cryptic as well.

The combination of stealthy coloration, disruptive patterns, and cryptic behavior make owls very cryptic, or hard to see. But some people believe that kestrels practice mimetic camouflage. The picture to the right shows the kestrels nesting at Xcel Energy's Pawnee Station earlier this year. The male is on the left and the female is on the right. They are facing forward, so we can see the dark 'eye spots' on the back of their heads. This mimetic false face might confuse predators into thinking that the back of a kestrel's head is actually its front.

Like many ground-nesting birds, Killdeer lay very cryptic eggs. I find it extremely difficult to see the Killdeer egg in this video, even though she lays it right in front of us (it can briefly be seen about 52 seconds into the video). Both of the adults are quite cryptic against the gravel road. However, they also practice a distraction display that disguises a healthy bird as an injured one and helps protect the nest. When a threat approaches the nest, the killdeer holds it wing in a position that simulates an injury and emits a distress call. The 'injured' killdeer lures the predator away from the nest by appearing to be easy prey. Once the predator is far enough away from its nest, the killdeer flies away. This behavior also strikes me as mimetic, since a healthy bird is mimicking an injured one.

Can you see the Killdeer egg in this picture?


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Tuesday, May 21, 2013

Barn Owls Fledging at Eaglecrest

The barn owls began fledge at Eaglecrest on 5/19/13, when the first barn owl decided it was time to leap from the nest. We wondered how fledge would work, since the nest was so tight. The internal diameter of the hole is roughly a foot and a half, yielding a total area of about 1.76 feet (A=pr2) for four to five rapidly growing owls. In general, the birds we watch spend time wingercizing and hopping before fledging, learning about their wings and building some muscle prior to their first flight. But the size of the nest cavity prohibited the young barn owls from getting wing practice in. Would the lack of wingercizing present a problem? The answer appears to be 'No'. After sticking its wing out of the hole and clambering back in, the fledgling owl stuck its feet outside the hole, looked around, lowered its head, and leaped out into the night. This video shows the owl rapidly winging away from the tree, while three or four siblings watch from the hole. Actual fledge happens at 8:35 into the video.



Over the last two nights, we have watched the young owls begin to learn the basics of flying. They hop on branches, clamber up and down the trunk, and spend time practicing on the former canada goose nest, hopping and flying from the trunk to the nest and back again. We've also seen them scanning, moving their heads back and forth as they look at and listen to the world around them. Earlier this year, I was talking to one of my children about her navigational skills. "Mom," she protested, "why would I know how to navigate?  I've lived in the same place my whole life, and I don't drive yet." I think the young owls may be having a similar experience. They've spent their entire lives to date in a small, crowded hole where their wings and directional hearing weren't really needed. They have roughly five weeks of diminishing parental care to learn  flying, pouncing, hovering, hunting, and capturing prey. While flying and hunting are instinctual, proficient flying and hunting must be learned. A few video highlights from the first couple of nights:


According to the Barn Owl Trust, the amount of food each owl receives from its parents diminishes to zero by 14 weeks. There is some disagreement about dispersal, which may or may not happen after 14 weeks. We'll see what this family does.

Not a night owl? I am freeing up video from each night on a daily basis. To watch video, go to  Eaglecrest's Ustream site. Social stream will most likely be open. Click the Video tab just left of the Social  Stream tab above SS to view video.
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Friday, April 26, 2013

Red-Tailed Hawks, Nest Greenery, and Ants

First Meal
The hatchling red-tailed hawk at Eaglecrest ate its first meal yesterday afternoon. Like bald eagles, red-tailed hawks eat an extraordinary variety of prey. I thought I detected some fur on baby's first meal, but red-tailed hawks also eat birds, reptiles, insects, fish, and carrion. Eaglecrest's wonderful wildlife resources will provide plenty of food for the rapidly growing hawks.

We also saw the hatchling nibbling at the green leaves lining the bottom and sides of the nest bowl. Watchers know that Stitch and Spot regularly replenish the sprigs of small leaves placed haphazardly around the nest. As pretty as it looks, the hawks aren't bringing in greenery for decoration. The aromatic blue oak leaves may mark active territory, discourage parasitic insects such as fleas, ticks, fly maggots, and lice, or perform both functions at the same time.

Repelling Insects
We know that blue oak leaves release a wide variety of volatile organic compounds. A number of them have been identified as possible insect repellents, including isoprene, an oil that reduces thermal stress and repels insects. At least two mechanisms have been suggested for isoprene's repellent properties:
  • Number one: Isoprene hides host plants and animals by interfering with an insect's ability to smell a host. Parasites can't locate hosts hidden in an isoprene haze.
  • Number two: Isoprene repels insects. As the isoprene outgasses from the freshly cut leaves, it ozidizes to terpene, an insecticide. Many insects actively avoid terpene.
Whatever the mechanism, a number of animal species use greenery in and around their nests, burrows, and dens, including twenty-six members of the order falconiformes. Many of them choose highly aromatic leaves and/or bark, suggesting that appearance or appetite alone do not account for the regular delivery of fresh greenery to their homes. We've watched birds go to amazing lengths to build nests and protect their young. Why wouldn't they try to repel parasites and insects? 

Ants
Having said that, the leaves don't appear to work on ants. We periodically witnessed ants on and around the nest on April 25, although they didn't appear to be unduly disturbing the hawks. I'm no ant expert, but they appeared fairly small to me. Ants both migrate and swarm, so while may have been attracted to the nest by prey leavings, they also may have been simply passing through. I haven't been able to find much evidence that ants are especially harmful to birds, outside of a few highly specialized species. Some birds even allow themselves to become covered with ants - a practice known as anting that may be yet another defense against parasites. 

Enjoy watching the wildlife at Eaglecrest!

There is some debate about whether or not birds use greenery to repel or reduce parasites. Although I found the evidence to be pretty compelling, a few writers and researchers listed other possibilities, including that hawks are programmed to snip greenery in much the same way they are programmed to build nests, that hawks like greenery in the nest, and that the greenery is the result of hawks snipping branches away to improve sight lines in the nest.

 Things that helped me write about this topic:
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Thursday, April 25, 2013

Hatch at EagleCrest

We have the first hatch for Stitch and Spot Sr. at Eaglecrest. Here's a video thanks to mochamama22. A few special moments from the video:


  • 4:38: Stitch's 'funny' feather
  • 6:54: Stitch bites the eggshell
  • 7:04: Dad visits the nest
  • 7:07: We see the hatchling 
  • 7:44: Mom covers the hatchling



Follw this link to watch the hawks: http://www.ustream.tv/eaglecresthawks
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Sunday, April 14, 2013

Meet Stitch the Red-tailed Hawk

Eaglecrest begins hatch watch for Red-tailed Hawk 'Stitch' and her eggs on April 17th. Stitch is a buteo, a genus of birds of prey noted for broad wings, sturdy builds, and soaring flights. Her eggs are estimated to begin hatching on April 19th. To watch Stitch, visit Eaglecrest's Ustream site: http://www.ustream.tv/eaglecresthawks

Once her eggs hatch, Stitch will provide most of the brooding while mate Spot provides the family with food. Red-tailed hawks eat a wide variety of live prey, including mice, gophers, voles, chipmunks, squirrels, shrews, bats, quail, corvid birds, reptiles, and even insects and earthworms. Although Red-tailed hawks have been observed eating carrion, they prefer live prey.

Life in the nest will follow a familiar pattern for altricial birds. When the nestlings are small, Mom Stitch will spend a lot of time brooding and tearing food for them. As they become able to thermoregulate, the young hawks will be less interested in brooding and more interested in exploring the nest. Developmental stages include standing, food tearing, playing and interaction, and wingercizing.  The young hawks will fledge beginning at roughly 42 days of age. They will begin to catch their own prey six to seven weeks after fledging and will become independent of their parents at about four months of age. Since Red-tailed hawks tend to return to breed in the area they were born or hatched, it is likely that Spot and Stitch's progeny will settle nearby. Spot and Stitch's linage may have occupied Eaglecrest for a very long time. Although they weren't modern Red-tailed hawks, the fossil record shows that Accipitrine hawks had evolved by the beginning of the Pleistocene epoch. Some of those fossils were found at the La Brea tar pits, roughly 250 miles away from Eaglecrest.

We might enjoy watching Red-tailed hawks now, but for much of the past century, they were a maligned bird. In 1932, Dr. Thomas S. Roberts wrote:

"Thirty-four of the forty-eight states have laws that variously discriminate between the beneficial and supposedly harmful species of Hawks and Owls and make provision for the former group. Potection, however, was removed from all species in 1925...Since that time, a general and wholesale slaughter of these birds has been going on...Both Hawks and Owls are so greatly reduced in numbers as nesting birds that they have become somewhat of a rarity."

As has been noted elsewhere, the Red-tailed hawk made a spectacular comeback from the dark days of bounty hunting and shoot on sight. Now protected by the Migratory Bird Treaty Act, the bird is a very common sight along open fields and roads, where it hunts for small rodents. The Red-tailed hawk comes in a variety of sizes and plumage colors and patterns, but all adult Red-tailed hawks are easily identifiable by their bright red tails, which molts out in the hawk's second year of life.


What's happening in the eggs right now? Probably something like this: http://raptorresource.blogspot.com/2012/03/we-are-getting-lot-of-questions-about.html

RTH eggs are lightly-speckled to whitish ovals. Take a look at this video for a peek at the eggs, which can be seen at 8:29 into the video: http://youtu.be/SgQiZFioTj0


We are looking forward to hatch!

Things that helped me learn and write about this topic:
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Monday, April 08, 2013

Tess, the Count, and Larry the Lizard: Adventures in Symbiosis


Eaglecrest watchers might be familiar with Larry the Lizard, who periodically appears at the mouth of the Barn Owl nest, sunning and catching insects. I'm no lizard expert, but I think 'he' - we don't actually know the gender - might be a northwestern fence lizard. Larry resembles a northwestern fence lizard, lives in fence lizard range, and acts like a fence lizard.

Observers have noticed that Larry and the owls appear to have a symbiotic relationship. While barn owls prefer rodents, they will eat reptiles. However, they don't bother Larry. Is it because he eats ants and other bothersome bugs before they enter the nest? As David McDonald, Eaglecrest's owner, put it, "They look at him, but they don't bother him. He keeps ants and other bugs out of their nest."

Symbiosis has not been documented between northwestern fence lizards and barn owls, but it is known to occur between screech owls and blind snakes in the southwestern United States. Screech owls bring blind snakes - a sightless underground insect hunter that looks somewhat like a long earthworm - into their burrows, where they eat the pests that compete with nestlings for stored owl prey, as well as ants and other insects that could harm the young birds. Some people believe that the owls intentionally use the snakes as nest maids, while others believe that the snakes are dropped during the parent-chick handoff and simply find the burrow a good place to live. Fred Gehlbach, a biologist from Baylor University in Texas, found that snake-occupied screech owl nests produce more and healthier fledglings than do snake-free nests. Once the owl family leaves, the snake crawls down the tree and returns to its underground home. According to Gelbach, blind snakes are common guests of at least four owl species. The snakes we've seen slipping in and out of the nest at Eaglecrest might be performing a similar function.

So it seems at least possible that Larry and the snakes are engaged in a mutually symbiotic relationship with the owls - a relationship between individuals of different species that benefits both. The ants and other pests attracted to the nest's prey remains provide Larry with a steady diet, while the owls reap the benefits of built-in pest control. The snakes may be performing a similar function inside the owls' burrow. As scary as snakes might look to some of us (human) watchers, it is quite possible that they and the lizards are welcome guests.

Thanks to Eaglecrest for giving us a look at Larry!

Symbiosis may be much more common than we think. It comes in a number of different flavors, including:
  • Mutualism:  a relationship between individuals of different species that benefits both.
  • Commensalism: a relationship between individuals of different species in which one species benefits and the other is neither harmed nor helped.
  • Parasitism: a relationship between individuals of different species in which one species benefits and the other is harmed.
We've seen all three of these at the Decorah Bald Eagle nest. I'll return to this subject in a later post. 

Things that helped me learn about this topic: 
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Saturday, March 23, 2013

Barn Owl Hatch at Eaglecrest!


It appears the first barn owl egg have hatched at Eaglecrest this morning! Tess laid 7 eggs between 2/19 and 3/04. Assuming all of them hatch, we should have barn owl eggs hatching over the next 13 days. A video: http://youtu.be/n-AtdPhYRSA.

You can watch the nest at: http://www.ustream.tv/eaglecresthawks. I especially love to watch the owls at night, when the IR light does a wonderful job of illuminating the nest cavity.

We often try to determine when hatch happened. This can be difficult, since hatching is not an on/off event, but rather a process that occurs over a period of time, as this time-elapsed video of a barn owl egg hatching at Hawk Creek Wildlife Center shows: http://youtu.be/uPACjB14Nww

For more about eggs and egg hatching, read this blog post: http://raptorresource.blogspot.com/2012/03/we-are-getting-lot-of-questions-about.html

Congratulations, Tess!

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Thursday, February 21, 2013

Barn Owls at Eaglecrest

The barn owls at Eaglecrest laid their first egg on 2/19/13. They are nesting in a hole in the tree just below the nest tray that the geese are using. The Countess (also called 'Tess) will most likely lay four to six small eggs that should begin hatching after roughly 33 days, or on March 24. Unlike the geese, barn owls are asynchronous layers - that is, they don't delay incubation to assure that all of the eggs hatch at roughly the same time. The eggs will hatch in  the order they were laid, and there may be an age difference of up to three weeks between the youngest and the oldest nestling. The young birds are brooded for about two weeks and fledge in 50 to 55 days.

Here is a look at egg #1

Barn owls are one of two living lineages of owls. Most owls are classified as Strigidae, or typical owls - a name that appears to have derived from the Greek word strix, meaning screecher. Barn owls are Tytonidae, derived from tyto, a word that means either owl or honored. I've already done a blog post on the features and adaptations that all owls share: facial disks, large forward facing eyes, 'soft' feathers, round heads, distinctive facial markings and/or ear tufts, talons and a 'hawk-like' beak. However, there are also some differences between the two.


 Tytonidae have...
Heart-shaped faces
Large heads and long legs
Hunt at night
Are cavity nesters
No feathered ear tufts
Strigidae have...
Round faces
Smaller heads and shorter legs
Some kinds hunt during the day
Nest in a variety of ways and places
Feathered ear tufts

The heart-shaped facial disk of a barn owl has different directional properties than that of its round-faced cousins. If it were a microphone, we'd call it cardioid. The heart shape isolates sound sources and concentrates sound in front of the owl, obscuring sound from the sides and rear. Like its uneven ear holes, this helps it pinpoint prey. Its large head also means a larger facial disk with which to pick up sound. These specialized adaptations help barn owls hunt in very low light to complete darkness: a critical skill for barn owls, since many nocturnal animals curtail their activities to dens and burrows when the moon is full.

A barn owl's long, sparsely feathered legs help it catch mice, shrews, and voles in deep vegetation and underneath snow. Its third toe has a split talon that can be used as a comb. Perhaps their long legs aid in grooming, or help them avoid bites and scratches from prey. Or maybe tytonidae owls really like tall, long-legged mates. We know that dark spots on a female barn owl attract males - the larger and darker her spots, the more interested male owls get. Could long legs serve a similar function?

The lack of feathered tufts is also a mystery. Since some but not all Strigidae have ear tufts, I'm guessing - and this is a guess - that the common ancestor of all Tytonidae and all Strigidae did not have ear tufts (which are not at all related to ears or hearing). Therefore, the question should be 'why did some Strigidae develop ear tufts?'. Researchers have proposed camouflage, species recognition, and signaling under low-light conditions, but no one knows for sure. Barn owls are at the very low end of the avian acuity and contrast sensitivity spectrum. Perhaps they never developed ear tufts because they aren't likely to benefit from whatever visual cues, sexual attractiveness, or camouflage ear tufts provide to owls that have them.

Eaglecrest makes it possible for us to watch great horned owls and barn owls in the same territory. You can see why barn owls have been called 'ghost owls' and 'night owls' - their silent flight and vocalizations can seem a little eerie. They are very different from their louder, showier Strigidae cousins. Barn owls nest in cavities, returning to the same cavity year after year to lay eggs and raise young. Great horned owls commonly usurp the stick nests of other birds, while a barn owl makes a simple nest of her own regurgitated pellets, shredded with her feet and arranged into a cup. I'll be watching for more differences as they incubate eggs and raise young.

Barn owls are more effective than poison and traps at controlling rodent populations. If you have suitable habitat and are interesting in building a barn owl box, click here for directions from the Missouri Department of Conservation.

Things that helped me learn more about barn owls:




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Wednesday, February 20, 2013

Canada Geese at EagleCrest

Check out the video: http://youtu.be/8hT_Cg551_0
The Canada Geese laid their first egg at Eaglecrest on February 19th between 5:05pm and 6:18pm PST. Mother goose Wilma won't begin full incubation until most of her eggs are laid, which helps assure that the young goslings are all at about the same stage of development. I don't want to guess at a hatching date right now, but this is roughly what nesting looked like last year:
  • 1st egg: February 26
  • 2nd egg: February 28
  • 3rd egg: March 1
  • 4th egg: March 4
  • 7th and last egg: March 10
  • Hatching: April 6th
  • Nest Leave Taking: April 7th 
If the geese follow the same pattern this year, we should see an egg roughly every two days, with full incubation beginning about the time the last egg is laid. Hatch should start 24-28 days later: last year took 27 days. The goslings will jump from the nest within about 24 hours of hatch. We'll be able to watch the family swimming in the pond, but they will not come back to the nest once they've left it. 

People expressed a lot of concern about these three things last year: 
  1. Mother goose isn't spending enough time on her eggs
  2. The goslings will starve when they hatch
  3. The goslings will die when they jump from the nest
So let's talk about them, shall we? 

Incubating the Eggs
Mother goose won't begin full incubation until around the time her last egg is laid. Embryonic growth and development is a fast-paced chemical process that requires heat. By delaying incubation, mother goose delays the onset of embryonic development  and assures the synchronous hatching of fertilized eggs. Synchronous (closely-timed) hatching is especially important in the case of Canada geese and similar birds, which leave the nest roughly 24 hours after hatching. Unhatched eggs or birds too young to follow their parents die. 

I used to think that eggs would die if birds stopped sitting on them for even brief periods of time. Not true! Embryos are less sensitive to cold than to heat, particularly before incubation has started, and few birds incubate continuously. Wilma will regulate the temperature of her eggs by varying the amount of time she sits on them, and the tightness of her sit. If the weather is warm and sunny, she may spend a great deal of time off the eggs. We also might see her cover the eggs with soft nesting material.

Feeding the Goslings
I'm going to drop some words on you readers. Canada geese are precocial - that is, the young are relatively mature and mobile from the moment they hatch. They are born with their eyes open and can swim, run, and jump shortly after leaving the egg. This is important, since precocial species are normally nidifugous, meaning they leave the nest shortly after birth or hatching. 

Just before hatching, the goslings will consume whatever yolk and albumen remains in their eggs. This provides enough food energy for the next 24 to 48 hours. Once they've jumped from the nest, their parents will lead them to water and protect them from predators. Wilma and Fred do not need to provide food in the nest, and the goslings will find food (mostly) on their own once they reach the water. 

Jump!
Roughly 24 hours after hatching, Wilma will leave the nest and the goslings will jump after her. While this seems scary, it is very normal for geese. Canada geese have been documented nesting on heron nests, osprey nests, cliffs, and man made structures. Nesting in high places helps protect eggs and very young babies from ground-bound predators including raccoon, coyotes, opossums, cats, and dogs.

The jump is over very quickly. Dad Fred will be waiting on the ground below to help protect his family. Wilma will fly down from the nest and honk for the goslings, who will quickly follow her out of the nest. Their  light weight and downy bodies will help protect them from injuries when they land on the soft grassy surface below the nest, and Eaglecrest staffer Ramblin' Raptor will also put out straw or grass to help cushion their landing. Once the goslings have landed, their parents will lead them directly to the pond, honking and hissing all the way.

To see just how fast the jump goes, watch this video from 2012:

I've often heard Bob say that birds wouldn't do it if it didn't work. Successful behaviors lead to more offspring to pass those traits on to. Geese that are good at synchronous incubation will have better offspring survival rates than those that aren't. Geese that nest high will lose fewer eggs and young to ground-based predators, offsetting potential losses caused by landing injuries. Whatever we might think as human watchers, Fred and Wilma are following a way of life that has produced more winners than loosers. Mama (goose) knows best.
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