We’re getting a lot of questions about eagles and what might be called menopause this week. Many of you want to know if female bald eagles stop laying eggs due to age-related changes in their bodies – the avian version of menopause. Is Mom disinterested in DM2 because she’s done with eggs? The short answer is ‘No’, but I want to unpack the question a little further.
Human menopause is very unusual. Unlike the vast majority of animals, human women can live decades after no longer being able to give birth. We share this trait with a handful of toothed whales, elephants, and fellow primates. Like us, they are social and have long childhoods and long lives. Groups benefit from matriarchs who don’t compete with their daughters, help care for young, and bring their experience to bear on problems that threaten the group such as food shortages. But very few animals live like humans, toothed whales, and primates.
Fertility and Age in Peregrine Falcons
We don’t have a lot of data about age and fertility in wild bald eagles, but we’ve collected a lot of data about peregrine falcons. We know that female peregrines often start experiencing declines in fertility at around fourteen years of age. We’ve seen them lay white eggs (peregrine falcons normally lay reddish brown eggs), ‘squishy’ or oddly shaped eggs, and clutches with a higher percentage of eggs that don’t hatch. In short, they experience a decline in fertility, although they don’t stop laying eggs altogether and don’t experience menopause as we know it. But very few female peregrines reach 14 years of age. If wild peregrines can live to 16 years old, these falcons are about 87% of the way through their possible life span – ancient matriarchs and real outliers based on everything we know about them.
Without band numbers and longitudinal studies, it would be easy to conclude that wild female falcons don’t experience a diminishment in fertility because very few of them live long enough to do so. Perhaps the same is true of bald eagles.
But What About Mom?
If fertility starts declining late in an eagle’s lifetime, where is Mom relative to any potential fertility declines? The oldest known free-living bald eagle died at 38 years of age, after he was struck by a car. If we do a rough back-of-the-envelope calculation and use a conservative figure of 80%, we might expect female bald eagle fertility to begin declining at 30 years old. We celebrated Mom’s 17th birthday this year, so she should have a long way to go before her fertility declines. We don’t know why the Decorah eagles seem to be off to a late start, but we were happy to see both of them at N2B this morning! Eagle on, everybody!
Things that helped me learn and write about this topic
- Data from our longitudinal research program. We’ve been collecting data on falcons since 1987 and we share it with other groups who do what we do. It is an invaluable source of potential research and information.
- https://qz.com/1372767/twice-as-many-animals-go-through-menopause-as-scientists-previously-thought/. This is a really interesting article that made me wonder about elephants. Elephants share some traits with humans and toothed whales, but don’t experience declines in fertility that I know. I hope to do more reading on the topic.
The Raptor Resource Project