Is the last egg going to hatch?

The last egg in the Original Decorah nest

As of this morning, the unhatched egg in Decorah is somewhere between 49 and 42 days old. Can it still hatch? Eagle eggs have hatched as late as 44 days after they were laid. If this is the last egg, we still have roughly two days in which hatch could occur. However, eggs have never hatched this far apart in Decorah before. Given the dates, it is possible that we've seen the hatch of eggs number two and three instead of eggs number one and two as we initially assumed. Roughly 3% to 12% of bald eagle eggs fail to hatch based on the studies I read, although some sources put the number a little higher, at 10% to 25%.

So why wouldn't the egg hatch? Eggs fail to hatch because they are either infertile or nonviable. Infertile eggs occur when the ovum is not fertilized before it begins its journey down the female's oviduct. We know that bald eagles copulate frequently before and during egg laying, which helps assure that sperm is present in the right place (the infundibulum) at the right time (when the ovum arrives).  Since female birds don't have a way to reject or stop the egg-laying process once it begins, incomplete, poorly timed, or insufficient copulation can result in unfertilized eggs.

A nonviable egg occurs when an embryo fails to develop properly and dies. This is mostly likely to happen within the first three days of incubation (embryonic organs fail to develop) or the last three days immediately prior to hatch (major organ failure becomes apparent or hatch starts but cannot be completed). Non-viability can happen for a number of reasons, including:

• Insufficient incubation. Incubation is fairly complex! Eggs must be kept at the proper temperature and humidity and turned regularly. Freshly laid eggs can spend time in the zone of suspended development (roughly 28.4 to 80.6°F) with no harm to the egg or embryo, but eggs must remain between about 99 and 104°F once development starts. Time off the eggs regulates humidity and helps keep pores from clogging. Turning or rolling the eggs prevents the developing embryo from sticking to the side of the egg, brings it into contact with fresh 'food' and important nutrients supplied by the yolk and white, and assures proper development of the membranes that exchange gas and protect the embryo from contaminants. 
• Piercing or cracking of the shell. If the egg shell is pierced or cracked before the embryo is fully developed, it will die. This can happen if the egg is jostled too vigorously, stepped on, or damaged or destroyed by an intruder - something that has been documented in many species of birds. 
• Insufficient nutrition. Given all that we've seen the eagles eat, this doesn't seem to be especially likely in Decorah. But if a female bird is insufficiently nourished before she begins laying eggs, her eggs won't have the nutrients needed to nourish the developing embryo. 
• Bacterial or chemical contamination. Although the embryo is protected by a shell and layers of membrane, contaminants can sometimes make their way into an egg and impede or kill the embryo inside it. 

We aren't going to attempt to retrieve the egg if it doesn't hatch - at least not while the birds are in the nest. Without opening the egg, we have no way of knowing why it failed. On one hand, the eagles spent a surprising amount of time off the first two eggs. On the other, studies in some species of birds indicate that infertility is more common than non-viability. Infertility is also more likely to prevail in first and last-laid eggs, which is unsurprising given the importance that timing plays in fertilization. 

What will happen to the egg? Different species do different things, but bald eagle eggs are commonly buried under layers in the nest, where they presumably break and decompose. Eggs may also be pierced or trampled as siblings grow and become more active. We will look for the egg if we go into the nest this fall. If we find it intact, we will turn it over to the USFWS for study. 

Will the next eaglet to hatch be called D26 or D27? This is confusing to followers who have seen nothing but production success. However, peregrine falcons aren't always successful and we don't count production until after banding. A falcon that makes it to fledge but dies soon after is still considered in production counts, but a falcon that dies before banding is not. If this egg doesn't hatch, the next living eaglet will be called D26. 

It's hard to believe that we could have an unhatched egg after so many years of success. How many times have we been worried about something only to have it all turn out right? But eggs don't always hatch and even excellent parents like our Mom and Dad experience failure. I'm glad we have D24 and D25 to watch this year and I look forward to studying the dynamics and rearing of two siblings, even though I wish there were three.  If we have a chance, we'll retrieve the egg for inspection and we will also review the video record to determine how much time was spent off the first egg.

Note: While I included contaminants on the list of things that can cause eggs to fail, my guess would be that this egg failed due to infertility (statistically more likely according to what I could find) or incubatory failure due to cold exposure.

Do bald eagles delay incubation?

2014, Egg #2. Temp with windchill: -40F.

Do bald eagles delay incubation? It wasn't an a question we've thought about much, since bald eagles in Iowa usually lay eggs in temperatures under - sometimes well under - freezing! However, this year was quite a bit warmer, and the eagles in Decorah and Fort St. Vrain seemed to spend more time off the first two eggs than we are used to.

The question seems pretty cut and dried. After all, peregrine falcons delay full incubation very consistently until the third egg in a four-egg clutch, and the fourth egg in a five-egg clutch. In cold years (2013, 2014), we tend to experience higher losses than in warm years, since eggs one and two can freeze and die prior to the beginning of full incubation. However, it isn't that simple with bald eagles and many other birds.

2016, Egg#2: Temp no windchill: between 25-40F.

According to Professor Jim Grier, birds often start incubation slowly or gradually when temperatures aren't in the freezing range. Freshly laid eggs can spend a lot of time in the zone of suspended development (roughly 28.4 to 80.6°F or -2°C to 27°C) with no harm to the egg or embryo. While I don't have storage times for bald eagle eggs, Wikipedia tells me that the freshly laid eggs of domestic fowl, ostrich, and several other species can be stored for about two weeks when maintained under 5 C. That is quite a bit longer than the time between eggs one and two in a bald eagle nest!

Temperature aside, why do some birds begin incubating immediately? In a blog on the subject, David Hancock discussed two theories of immediate incubation: one, to protect eggs from marauding ravens and other predators, and two, to assure the survival of at least some young during periods of food scarcity. In the last case, the 'strategy' assumes that it is better to have one or two surviving children than no surviving children at all.

However, there are more benefits to delaying incubation so eggs hatch closer together: indeed, the survival of many waterfowl depends on it since adults leave the nest 24-48 hours after hatch begins, whether all of the eggs are hatched or not. Perhaps most importantly, delaying incubation helps assure that rapidly growing young are in the same stages of development. In the presence of an abundant food supply, more young will likely survive when incubation is delayed, since there will be less variation in size and ability between older and younger siblings, and food should be shared more equitably as a result.

Professor Grier pointed out that the nature (if not essence!) of biology is variation. This caused me to think back on eagles and monogamy. When we first started this adventure, everyone 'knew' that eagles were monogamous and mated for life. A new mate would be taken only if the old mate died. Remember when that was true? But once we really started looking, eagle relationships turned out to be more complicated. While many eagle couples appear to be monogamous, we've also documented extra-pair copulations, eagle 'divorce', polygyny, and polyandry.

The same is undoubtedly true for incubation. Professor Grier wrote that he would expect variation among different pairs of bald (and other eagles) in how much time they spent off the egg(s) both at the start and as incubation proceeded, as well as under different conditions such as temperature, humidity, and precipitation. We've certainly seen that in Decorah. In 2014, February's mean temperature was 9.4F - the coldest in 20 years of recording! Under those conditions, Mom and Dad incubated almost constantly. But in 2012, February's mean temperature was 27.8F - not the warmest ever recorded, but quite close to it. As indicated by video footage and all of the blogs and posts we did on the subject, Mom and Dad spent much more time off the eggs in 2012 than they did in 2014. While weather is clearly a factor, David Hancock noted timing variability between rural and urban bald eagles, and speculated that the presence of predators might make a difference in whether incubation was delayed.

The world is not a static place. Animal populations fluctuate as food supply, weather, and disease cause cycles of booms and busts. High populations and/or low food supplies can result in massive dispersals or irruptions as birds compete for territory and food. Populations may adopt different behaviors at different levels of density and food abundance, perhaps becoming less aggressive in a situation where neighbors and food are both in high supply. Everything changes over time: given a large enough timescale, the continents themselves flow like water. In that light, it is no surprise that eagle incubatory behavior might vary, or that eagles might adopt different behaviors as their population and/or the world around them changes.

So philosophy aside, can we really answer the question of delayed incubation in bald eagles and other birds? That's a tough one. The onset of incubation doesn't seem to involve timing in most species of birds, since they appear to be responding more to external factors than to an internal clock. This makes it hard to define what exactly 'delay' is for most birds. If I'm staying off my eggs because it is warm out, am I really a delayed incubator? If I almost always incubate right away because I lay eggs in sub-zero temperatures, am I really an immediate incubator?

Short answers are often necessary in our instantaneous and highly-connected world, so here is mine: "Bald eagles may or may not begin incubation immediately after the first egg is laid, depending at least in part on local factors that include temperature, humidity, precipitation, and predators. Apart from that, bald eagles exhibit variability: that is, not all pairs act the same way, even given the same or similar situations. There is more to learn, so keep watching, keep documenting, and trust the eagles!"

I'm going to close by quoting Professor Grier again: "The nature (if not essence!) of biology is variation." In my experience, almost every time we say a species always does this, or never does that, the species proves us wrong! Onset of incubation and mating systems are just two more examples of that.

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Our ideas about birds have been shaped by how we observe them. Professor Grier pointed out that in the past, normal incubation details for various birds were studied from blinds, long-term and time-lapse photography, and with electronically telemetered artificial eggs, nest thermometers, treadles or scales to measure adult presence on the eggs. He wrote: "Eagle cams provide a whole new opportunity to observe and study traits such as incubation behavior (by individual parent, gender, total time, and under various environmental conditions) on increasing sample sizes of birds under undisturbed conditions." In other words, nest cams give us an unparalleled opportunity to observe large populations of birds in the wild, relatively free from human interference. Who knows what we will find, or what theories and beliefs will be challenged? We've got the cameras in the field. The next step is to develop appropriate methodologies and tools to enable large scale data collection across species and populations.

Thanks to the following for helping me learn about this subject.

• Personal communication, Professor James Grier. Any mistakes I made in interpreting his email are my own. 
• Personal communication, Bob Anderson. Bob used to tell us that eagles were pretty smart, but peregrine falcons were only about as smart as garter snakes. Even though he loved falcons, he believed that their lower intelligence made them less variable in their response to external stimuli. While that was outside the scope of this blog, I will return it later on.
• David Hancock's blog on Bald Eagle Laying and Hatching Sequences

What Makes Birds Incubate?

Red-tailed hawk Stitch incubating eggs

Looking out my window this morning, it seems unlikely that spring will ever arrive. But most of the birds we watch are incubating eggs or, in the case of bald eagles, feeding young. Clearly, they aren't waiting for the ice and snow to melt.

Daylight length has a profound effect on the physiology of birds. As the length of daylight increases, light receptors deep in the brains of birds detect the changing day length and trigger the seasonal development of the reproductive system. Hormones flow and reproductive organs increase in size. Courtship begins and pair-bonds are formed or re-established between male and female birds. Nest work kicks into overdrive: eagles and hawks fetch in sticks and greenery, while falcons create a scape, digging into gravel or substrate with their breast and pushing with their legs to create a depression for the eggs.

So what makes active birds like hawks, falcons, and eagles spend so much time sitting on eggs? Like the rest of bird reproductive behavior, egg-sitting is triggered by hormones. Initially, luteinizing hormones trigger the production of testosterone in males and progesterone in females. Testosterone triggers sexual behavior and aggression in male birds, while progesterone induces egg production in female birds. Birds are really louder and brighter in the spring, when bird song, plumage, and courting behavior are in full swing. However, shortly before incubation, female birds (and male birds that share incubation duties) experience another big hormonal change. Prolactin, a hormone which promotes incubation in birds, rises sharply while other hormones decrease. Opioid peptides stimulate prolactin secretion, which may explain why even active birds become lethargic while incubating their eggs.

The eagles have young and Stitch and Spot's eggs are ready to hatch. Over the next 30-40 days, the peregrine falcons will enter what Bob calls the incubation doldrums. We'll watch them sit, and fritter with gravel, and sit, and sit some more. The induced lethargy will end quickly once eggs begin hatching, and prolactin (and presumably opioid peptides) begin declining.

Prolactin plays an interesting role in bird parenting behavior. We'll return to it a little later in the season. See the bottom of the page for my links.

This chart shows the relationship between testosterone and prolactin in a male emu. Note the sharpness of the curves.

Things that helped me learn and write about this subject:

• Bob Anderson. He could write a book on the subject and his personal experience breeding falcons.
• This really excellent blog: http://www.wqed.org/birdblog/page/2/. I read a fair amount on the topic, but this blog made it very clear. 
• This article about endocrine and testicular changes: http://www.sciencedirect.com/science/article/pii/S0378432098001109
• Photoperiodic Regulation of Seasonal Breeding in Birds: http://onlinelibrary.wiley.com/doi/10.1196/annals.1327.024/abstract
• Prolactin Secretion: http://www.ncbi.nlm.nih.gov/pubmed/6840521
• Opioid Pathways in the Hypothalamus of a Turkey: http://www.ncbi.nlm.nih.gov/pubmed/10567857
• Prolactin and Starlings: http://www.ncbi.nlm.nih.gov/pubmed/6693831

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.