Showing posts with label Red-tailed hawks. Show all posts
Showing posts with label Red-tailed hawks. Show all posts

Thursday, April 30, 2015

Red-tailed hawk growth and development in the nest

Eaglets aren't the only thing growing right now! The two eyas red-tailed hawks at Eaglecrest are morphing into adults right before our eyes. Like bald eagles, different parts of their bodies grow at different times and different rates, reflecting developmental priorities and impacting behavior. How will hawks EC2 and EC3 (also known as Speckle and Snickers on the Eaglecrest Wildlife facebook page) grow?

  • 0-7 days: the culmen achieves maximum growth. Red-tailed hawks hatch with a culmen (the dorsal ridge of the upper mandible) that is about 30% of the maximum size it is likely to achieve in the nest. During a red-tailed hawk's first week of life, its already large culmen nearly doubles in length, going from an average of 6.9 mm in length to an average of 12.3 mm in length. Since the consumption of food is the root of all else besides, the hawk's food-consuming apparatus is given developmental priority. While the culmen continues to grow after week one, its rate of growth slows dramatically, becoming almost flat by week five. Bald eagles follow a similar pattern, although they have almost twice the growing time in the nest that red-tailed hawks do and their developmental milestones reflect that.  
  • 7-14 days: third toe and tarsus achieve maximum growth. Eating has priority, but movement isn't too far behind. A young hawk needs to move to build muscle and feed once it is past the point where Mom and Dad simply stuff food into its waiting mouth. In the second week of life, a red-tailed hawk's third toe and tarsus are given developmental priority. The third toe is the real stand out here, nearly doubling in length from 16.9 to 27.9 millimeters. With longer toes and thicker, longer tarsi, the hawks are better able to sit up, move around the nest on their feet and knees, and interact with one another. We see a similar pattern with bald eagles, who reach asymptotic mid-toe and tarsus size about half-way through their nestling period - 40 days, in their case. 
  • 14 to 21 days: body weight achieves maximum growth. With food intake well in hand, young hawks gain weight rapidly. While they've been growing all along, weight gain is the biggest actor in week three. The young hawks spend a great deal of time eating and sleeping as their weight increases. 
  • 21 to 24 days: weight gains decline, independence increases. During the fourth week, weight gain declines, the nestling hawks begin feeding independently, and feather growth takes over. The hawks have the strength and physical structures they need to stand upright on their feet, manipulate food, and feed on their own. At about day 24, the length of primary seven overtakes weight as the best indicator of age.  At this point, fledge is just two or three weeks away. 
  • 24 to 35 days: Feathers take front and center. As fledge comes closer, developmental energy is channeled into growing feathers. The primaries enter their maximum growth phase during weeks four and five, the two weeks prior to fledging. The young hawks will also be growing sub-adult feathers elsewhere, including their backs, their tails (which won't become red until molt two, in their second year of life), and their chests. 
  • 36 to 44 days: Time to fly! Feather growth will slow, but the growth of flight-related muscles is happening in leaps and bounds. Wingercizing will take front and center stage as they young hawks practice for the big event by flapping, wing-hopping, hovering, and eventually taking flight! 
Both red-tailed hawks and bald eagles allocate developmental energy into producing weight and structure first (day 0 to day 24), and feathers second (day 24 onward). While feathers often seem light and simple, these two distinct periods of growth point to the incredible amount of energy needed to produce a proper 'coat' of feathers. Enjoy the hawks now, since they will be leaving the nest soon. It takes just 44-46 days to grow a red-tailed hawk from hatchling to fledgling! 


Resources
Did you know?
Red-tailed hawks are excellent falconry birds. While their are many excellent falconry organizations, I'm most familiar with NAFA. Interested in falconry? Follow this link: http://n-a-f-a.com/
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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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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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