Monday, May 04, 2015

Can Bald Eagles Get Avian Influenza?

Can bald eagles get avian influenza? That question is increasingly being asked of us at Ustream and on Facebook. The short answer: We don't know. But let's take a quick look at the landscape so far.

What is avian influenza?
To quote the USDA: "Worldwide, there are many strains of avian influenza (AI) virus that can cause varying degrees of clinical illness in birds. AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be a natural reservoir for the less infectious strains of the disease.

AI viruses can be classified as highly pathogenic (HPAI) or low pathogenic (LPAI) strains based on the severity of the illness they cause. HPAI is an extremely infectious and fatal form of the disease that, once established, can spread rapidly from flock to flock."

There are at least two different HPAI strains circulating right now: EA/AM-H5N2 and EA-H5N8. The USDA tells us that: "The H5N8 virus originated in Asia and spread rapidly along wild bird migratory pathways during 2014, including the Pacific flyway.  In the Pacific flyway, the H5N8 virus has mixed with North American avian influenza viruses, creating new mixed-origin viruses.  This is not unexpected.  These mixed-origin viruses contain the Asian-origin H5 part of the virus, which is highly pathogenic to poultry.  The N parts of these viruses came from North American low pathogenic avian influenza viruses." The same thing appears to have happened in the Mississippi flyway with H5N2. It is generally believed that waterfowl migrating north carried the virus into Minnesota, although it isn't known how it spread to confined poultry. They most likely contracted the virus while wintering in areas shared with infected Pacific flyway birds.

At present, the USDA reports that:

  • 114 avian flu detections have been reported.
  • 21,644,473 animals have been affected. The vast majority have been on commercial poultry farms that raise chickens, turkeys, mixed poultry, and pheasants.
  • The first detection was reported on 12/19/14 and the last detection was reported on 05/01/15.
While most of the detections have been reported in commercial poultry, wild birds can contract H5N2 as well. The vast majority of cases have been reported in waterfowl, including wigeon, canada geese, mallard ducks, wood ducks, northern shovelers, and teal. Unfortunately H5N2 has also been reported in birds of prey, including:
  • Coopers hawks
  • Red-tailed hawks
  • Gyrfalcons
H5N8 has been reported in:
  • Peregrine falcons
  • A bald eagle
  • A great horned owl
  • Gyrfalcons
On April 30th, Minnesota Public Radio reported that a Cooper's hawk in Yellow Medicine County was the first Minnesota wild bird to test positive for the avian influenza virus H5N2. However, a positive test from a dead raptor only means the bird was exposed to the virus, not that the virus killed it or that the bird spread the virus to other birds. In this case, it was killed when it flew into a window and the virus was found after the carcass was sent to The National Veterinary Service Laboratory in Ames, Iowa.

So what can we make of all this? Based on what we know now, the eagles in Decorah and Fort St. Vrain don't appear especially likely to succumb to H5N2 avian influenza.
  • While H5N2 can be spread through consuming infected prey, it has tended to spread in domestic animals after direct contact with fecal droppings or respiratory secretions of infected birds. This is less likely to happen in a highly dispersed bird like the bald eagle. The virus has only been reported in one bald eagle and a small handful of wild raptors.
  • No large die-offs of raptors have been reported in Minnesota, Iowa, or Wisconsin. All three states are conducting surveillance programs to identify to what extent the virus is present in wild birds.  
  • While waterfowl can carry the virus, it seems to primarily affect domestic large-scale operations. Backyard flocks of chickens have not been infected to nearly the same degree. The USDA has identified just 12 cases in backyard flocks, including five in Washington in January and February, plus others in Idaho, Kansas, Minnesota, Montana, Oregon and Wisconsin. Wild and backyard birds could have been exposed over time to low pathogenic versions of bird flu and developed stronger immunity as a result.
It is believed the virus will die as temperatures warm up and ultraviolet light increases.  In the meantime, I suggest the following links for more information, including influenza updates: 
How are states responding?
News Articles

Did you know?
In Minnesota, the DNR is working to identify the virus in wild birds. The agency is collecting waterfowl fecal samples throughout Minnesota; asking turkey hunters from Kandiyohi, Pope, Meeker, Swift and Stearns counties to submit their harvested wild turkeys for testing; and collecting dead birds of various species reported by the public. 

The DNR has collected 29 dead birds of varying species; nine have tested negative for the virus and 20 results are pending. Test results also are pending on the 37 samples from hunter-harvested wild turkeys. The agency has collected 2,749 waterfowl fecal samples – nearing its goal of 3,000 – and more than 2,200 have tested negative; results for the rest are pending. The waterfowl fecal sampling effort is designed to determine with 95 percent confidence whether the virus is present on the landscape in at least one percent of the waterfowl population. They really want to know if you find a dead turkey or raptor. Go to for more information.

The Raptor Resource Project has offered to collect samples while banding this year. I'm guessing the answer will hinge on whether or not we start seeing problems in the wild population. We will keep you informed if anything happens.

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! 

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:

Wednesday, April 08, 2015

A Four Recap

Earlier this week, a follower asked us for a recap of eagle Four’s life. Four was one of three eaglets that hatched in 2014. While early life in the nest was fairly ordinary, gnats and record-breaking rain interfered with fledging. For the first time that we know of, only one of the 2014 Decorah alumni successfully transitioned to life in the wild. One of Four’s siblings was injured and went to SOAR, where he  remains. The other sibling died of electrocution from a high voltage transmission line not far from the hatchery.

Four’s transition from fledge to flight was a bumpy one. During her first month on the wing, Bob rescued her from a location at the side of a highway, a fence, some deep woods, and a corn field. She roosted on the ground, traveled only short distances, and remained in the vicinity of the nest longer than any other eaglet we are aware of. We were starting to ask ourselves if Four would ever go when, on October 19, she abruptly left. Between June 22, 2014 and March 1, 2015, we received 302 valid fixes on Four. She traveled a total of 686 miles, averaging 2.2 miles a day. She achieved her furthest distance from home on January 8, 2015, when she was tracked 159 miles south of her natal nest. Her longest contiguous flight took place on December 1st, when she traveled 34.8 miles between the Maquoketa River and a roost near Lake McBride. She was electrocuted on March 2nd, roughly 130 miles south of N2.

After Four was electrocuted, we documented her death and reported it to the US Fish and Wildlife Service. We also contacted Alliant Power with photos of the pole under which Bob found her. When we were told it was up to code, Bob decided to get a second opinion. Contact number two told us that several things needed to be fixed to make the pole safe for birds. We passed the information back to Alliant Energy and decided to survey the area for more eagles. Two Ustream mods volunteered to conduct the survey for us. They didn’t find any eagles, but they did learn about another electrocution. They provided photos of that pole and several others. Alliant stated that they would fix the fatal poles and others like them. Thank you very much to IzzySam and Faith for taking this on for us.

We plan to take a trip back into the area where Four died to see whether Alliant fixed the poles as promised. The code we used to follow the travels of our eagles will be repurposed to map electrocutions and identify problem spots. While not every pole can be immediately protected, we can make dangerous poles a priority. Four touched a lot of hearts during her brief life. It is our hope that her death will bring about a safer environment for eagles and other birds.

Four's data is retained here:

What can you do?

  • Find out whether your utility has an avian protection plan. If they don't, they should consider adopting one. An APP helps keep animals, equipment, and people safe.
  • Report electrocuted birds and other animals to your power company. Electrocutions are deadly to animals, harmful to equipment, and potentially dangerous to human beings. 
  • Report collisions to your power company. While our eagles have been electrocuted perching on poles, collisions are also deadly. Swan diverters and other deterrents can be installed.
  • If you are a member of an electric cooperative, make your concerns known to the board. I know of at least one electric cooperative in the process of retrofitting all their poles are safe. Electrocutions destroy equipment, require unscheduled repair time, and are expensive. 

Tuesday, March 24, 2015

Egg Colors and Shapes

The Chicago Peregrine Program inspired me to write a quick blog on the colors and shapes of eggs. Bald eagles have white eggs, peregrine falcons have eggs that range from light cream through brick red, and red-tailed hawks have pale eggs that are lightly splotched with brown. How and why do the birds we watch lay differently-colored eggs?

In general, female birds inherit egg colors and patterns from their female parents, who are ZW heterogametes. Egg-shell is made primarily of calcium carbonate, a white material, so the default color of all eggs could be considered white. As an egg moves down a female bird's oviduct, it squeezes or presses against glands that produce colored pigments from the breakdown of hemoglobin. Some colors (blues and greens) are applied very early on in the shell forming process, while others (brown) are applied quite late. Color may be applied relatively evenly or in drips and drabs depending on the bird and the speed of the egg through the female's oviduct. If the egg is stationary or moving very slowly, it may be solid, blotched, or spotted. If it is in motion, it will be streaked.

Coloring eggs carries a metabolic cost, so why aren't all bird eggs white? It's believed that birds with white or nearly white eggs have nesting strategies that hide their eggs from predators without the use of color. They might nest in cavities like barn owls, cover their eggs in vegetation like geese, or begin incubation immediately, like bald eagles. Since the eggs aren't visible to predators, camouflage colors and/or cryptic markings don't provide a survival advantage. Birds that lay colored eggs tend to nest in places or ways that are more visible to predators. Peregrine falcons, for example, don't usually begin full incubation until after their third egg is laid. The red color and light speckling helps conceal peregrine eggs when Mom and Dad aren't sitting on them and could make the eggs harder for nest invaders like raccoon to find. Ten or 20 seconds might buy enough time for enraged parents to drive nest intruders away.

So why do red-tailed hawks lay lightly speckled eggs while eagles lay white, highly visible eggs? Both birds begin full incubation right away and nest in fairly similar ways. We don't know for sure, although eagles in general are highly visible (giant nests, flashy black and white colors, six-foot wing spans) while hawks tend to be more concerned with concealment. The differences in egg-coloration might reflect some aspect of their lives we don't understand, but either way, egg-coloration is driven by survival. Hawks must need to conceal their eggs where eagles do not.

Predators aren't the only problem birds face. Some birds commonly lay or dump eggs in the nests of other birds. Splotched, spotted, or streaked eggs may help individual birds recognize their own particular markings and reject eggs that don’t match. So why don't Canada geese, which egg-dump, lay patterned or marked eggs? In general, I suspect that dumped eggs don't impact the survivability of original eggs very much in Canada geese. They are precoccial, so young require less parental investment once the eggs hatch. Canada geese also time hatching quite tightly, so an egg dumped at the wrong time won't survive.

How about egg shape? Peregrine falcons, Bald eagles, and Red-tailed hawks lay differently colored eggs, but the eggs of all three species are elliptical or oval in shape. Elliptical eggs nestle nicely in a scrape or nest cup where they sit side by side or in a line. However, the eggs of cavity-nesting birds like the Barn owls at Eaglecrest may be almost spherical. These eggs tend to cluster at the bottom of the tree hole. Their shape makes stacking a little easier, which helps the female incubate all of them. We tend to think of eggs as neat ovals, but some birds, like the killdeer at Eaglecrest, lay pyriform eggs. These oddly-shaped eggs are tapered, which causes them to roll in a tight circle. In the case of ledge-nesting birds, pyriform eggs are less likely to roll off, while killdeer eggs tend to stay in the nest scrape instead of rolling across gravel or stones where they could break.

In general, egg color and shape is influenced by survival. Female birds that produce more young will out-compete female birds that don't. Egg-color and shape may be influenced by overall health (healthier birds tend to lay more vibrant eggs), metabolic cost, the need to hide from predators, the need to identify one's own eggs, and the incubation advantage shape confers in any given circumstance. In all cases, our parents have demonstrated egg-ceptional egg-care. We look forward to hatching soon!

Things that helped me learn and write about this topic:

Sunday, March 08, 2015

Decorah Eaglet Four Electrocuted

We are sorry to announce that Four, the single remaining bird from the 2014 Decorah alumni to remain in the wild, was electrocuted on Tuesday, March 2nd. This is the fourth eaglet from Decorah that we know of to die from electrocution. Bob and a good friend picked her carcass up on Thursday after the Eagle Valley team notified us that they received a mortality ping. Bob and Brett examined her on Saturday and verified the cause of death.

Bob found her lying underneath a utility pole. He took photographs and sent them to a consultant, who told us the pole was unsafe and made suggestions to improve the safety of this pole and other poles in the area. We brought them forward to Alliant Energy/Interstate Power and Light and are waiting for a response from them.

Why do the eaglets keep perching on power poles? Bob theorizes there is a behavior difference between urban and rural eagles. Rural eagles are programmed to perch in trees because that is what they have available. But urban eagles, including our beloved Decorah family, are exposed to power poles and other man-made structures from the beginning. There are vast amounts of power poles serving our needs.  With eagles beginning to nest in close proximity to man - something new for both species - he believes electrocution will be an increasing concern for urban-fledged eagles and utility companies.

What can you do?

  • Find out whether your utility has an avian protection plan. If they don't, they should consider adopting one. An APP helps keep animals, equipment, and people safe.
  • Report electrocuted birds and other animals to your power company. Electrocutions are deadly to animals, harmful to equipment, and potentially dangerous to human beings. 
  • Report collisions to your power company. While our eagles have been electrocuted perching on poles, collisions are also deadly. Swan diverters and other deterrents can be installed.
  • If you are a member of an electric cooperative, make your concerns known to the board. I know of at least one electric cooperative in the process of retrofitting all their poles are safe. Electrocutions destroy equipment, require unscheduled repair time, and are expensive. 

We will continue our work with the electric distribution industry to address this issue and are researching deterrents for the poles near the nest and elsewhere.

Bob with Four

Monday, February 23, 2015

Eggs, eggs, eggs!

Egg Questions and Answers

How long does it take a bald eagle egg to hatch?
There are two ways to think about this: from egg laying to hatch, and from pip to hatch
  • From egg-laying to hatch: Most experts say 35 days, give or take a few. In Decorah, hatches have ranged from 35 to 39 days after lay, with the first egg usually taking the longest. I'd look for first hatch to occur about 38 days after lay, so we're looking at March 28.  In Fort St. Vrain, hatches have ranged from 36 to 40 days after lay, with the first egg usually taking the longest, so we're looking at March 25th. But it could be a little earlier or a slightly later than that.
  • From pip to hatch: Pipping occurs when the baby eagle's egg tooth first breaks through the eggshell. It can take as long as a day for the chick to fully hatch. 
How big is an eagle's egg?
Bald eagles lay white, oval shaped eggs. Size-wise, they are just a tad smaller than a tennis ball, although tennis balls are round, not oval. They weigh approximately 125 grams or 4.4 ounces, and are on average about 2.9 inches long and 2.2 inches wide.

How many eggs will the eagles lay? Will all of their eggs hatch?
Although the most common clutch size for eagles is two eggs, the Decorah Eagles and Fort St. Vrain  have a history of laying three eggs. The breakdown among bald eagles in general is as follows:
  • 79% of clutches have two eggs
  • 17% of clutches have one egg
  • 4% of clutches have three eggs
Both sets of eagles have hatched all of their eggs to date; however, fertilized eggs can fail to develop due to extreme cold, soft shells, or microorganisms. We are hopeful they will have another great year, but we won't know until it happens.

What is in those eagle eggs?
At this point, the developing embryo is still quite small. It is surrounded by the amnion, a fluid-filled bag that helps protect it from jarring and sloshing. The yolk and albumin provide nourishment and additional cushioning, the allantois filters out waste products from the kidneys, and the chorion provides ventilation.  Inner and outer shell membranes help safeguard the embryo from bacterial contamination and keep the egg's insides from leaking out through its highly porous surface.  Embryo, fluids, and membranes are all enclosed in a chalky membrane that strengthens the egg, providing an additional layer of protection from punctures and pressure. An outer cuticle on the chalky membrane (what we think of as the shell) gives texture and even more protection to the eggs.

How do eagle parents care for eggs?
Eagle parents ensure optimal temperature and humidity by alternately incubating, getting off, and rearranging their eggs. While turning eggs might be a matter of instinct, it also prevents the embryos from sticking to the insides of their eggshells, and it optimizes membrane growth. They move very carefully around the eggs, often balling or partially closing their long, sharp talons to keep from puncturing the eggs. Concerned about the amount of time the eagles are spending off the eggs?
Read this blog:

The following resources helped me learn and write about this topic:
  • Bald eagle egg size and color:
  • What's inside that egg?
  • The importance of egg-turning:
  • Previous blogs at this site.
Did you know?
Some birds bury their eggs in compost heaps to incubate them. Meet the megapodes!

Tuesday, February 17, 2015

Sex determination in birds

Humans, other mammals, and some insects genetically determine sex via X and Y chromosomes. In the XY sex-determination system, females inherit an X chromosome from each parent, while males inherit an X-chromosome from their mothers and a Y-chromosome from their fathers. Since homogametic XX females produce only X chromosomes, heterogametic XY males dictate the sex of their offspring.

Human watchers (including myself) often apply sex-based characteristics to our beloved eagles. Mom and Dad appear to have many of the same housekeeping arrangements and arguments that we do, so it might be surprising to learn that they turn our XY sex-determination system on its head!

Introducing...the ZW sex-determination system!
Birds, some reptiles, some amphibians, and some fish replace our X and Y with the ZW system. Let's look at a few differences:
  • I'm a female homogametic XX and my husband is a male heterogametic XY, but female birds are heterogametic ZW and male birds are homogametic ZZ. Among other things, this means that Mom's ova determines the sex of the little E's (or D's) we coo over in Decorah and elsewhere. 
  • XY and ZW chromosomes come from different areas of the genome. That means that our system for genetically determining sex is not very closely related to a ZW'er's system for determining sex, even though they both work roughly the same way. 
  • ZW sex determination is dose-dependent, at least in birds. Z doesn't create a male in and of itself. Two Z's (ZZ) are required to make enough male-determining product. Females may be female not because of the W, but because they lack two Z's.
Having said that, ZW females still produce eggs and ZZ males still produce sperm. There are some other similarities between us and them:
  • The non-recombining Y and W chromosomes have both degenerated over time. Today, the mammalian X carries over three times more genes than the Y does, whereas the chicken Z carries over ten times more than the W. Like our Y-chromosome, the W doesn't combine well with its opposite. Deletion, degradation, and mutations occur more quickly on the Y and W than on the X and Z. 
  • Y and W resemble X and Z more closely in 'primitive' animals and plants than in those that have evolved more recently, and both Y and W continue to shrink. Will human maleness and bird femaleness disappear? I don't think it's likely, but some people believe that new forms of sex determination might arise from somewhere else in the genome.  
How does the ZW system affect birds?
We know birds aren't human, even though we might call them Mom and Dad, think of them as friends, and invest them with human-like feelings, duties, and housekeeping systems. Still, it seems odd that they have a system of genetically-determined sex that is so different than ours. How does the ZW system affect them? 
  • Z chromosomes contain more genetic information than W chromosomes. Since ZZ male birds have two Z chromosomes, they are more likely to pass on sex-linked traits than ZW female birds. For example, Decorah daughter (ZW) Four got a Z from Dad and a W from Mom, while son (ZZ) Decorah got a Z from each parent. A male bird contributes a Z to sons and daughters, while a female passes a Z to sons only. Since Dad's Z contains a lot more information than Mom's W, Dad contributes more genetic information on that particular chromosome, especially when it comes to daughters. In humans, females conserve more sex-linked traits than males, and pass them on to male and female children. The opposite is true in birds. 
  • What about that flashy male plumage? We know that male birds conserve more sex-linked traits and pass them on to sons and daughters, but male plumage is more complicated than it appears.  Recent work published in the journal Evolution indicates that female birds were once as flashy as males. We think that sexual selection drove male color evolution (females prefer colorful males), and natural selection drove female loss of color (brighter females and young were more likely to be spotted by predators and competitors). 
  • So what role did the ZW system play? A couple of ideas. W has degraded over millions of years and carries much less information than it did previously. If the gene for female color was located on W, it may have been lost somewhere in the past. Alternatively, Z is more highly expressed than W. The resulting imbalance in hormonal secretions between lower ZW females and higher ZZ males drives fundamental sex differences in phenotype, development, and physiology. A ZW chromosome may not provide enough oomph to turn bright plumage on elsewhere in the genome, assuming it exists in female birds.
  • What about birds of prey? Unlike most birds, female raptors or birds of prey are larger than male birds of prey. And unlike most birds, male and female raptors sport the same plumage. With the exception of kestrels, we can't use plumage color to tell males and females apart. What happened to de-link plumage color with sex and why is size, which is still linked to sex, inverse almost uniquely among birds of prey? Is it expressed in the Z or W chromosomes (W chromosomes are 'large in many raptors'), or elsewhere in the genome? Curious minds want to know!  
Why do we have XY and ZW?
No one knows for sure. All snakes and all birds use ZW determination, and all mammals use XY determination (even when it gets weird, as it does with platypus and voles, X is always present). But fish, amphibians, turtles, and lizards might use XY, ZW, or temperature-dependent selection (TDS) depending on the species. The switch from a variety of systems (ZW, TDS, XY) appears to have occurred around the time the ancestor of all reptiles split from the ancestor of all mammals, but it's not yet clear whether there was an intermediate stage between ZW and XY systems, or whether the transitions occurred directly.  

Is the ZW system really that different? I don't think so. While lovely heterogametic ZW Mom determines sex and handsome homogametic ZZ Dad passes more genetic material to his offspring, males still produce sperm, females still produce eggs, and genetically determined sexes are still differentiated by phenotype, development, and physiology. Whatever the reason for XY and ZW, us XY'ers at the Raptor Resource Project wish all birds the best of luck this spring!

A list of resources that helped me learn about this topic:
Did you know?