How owl siblings hatch hours, days, or even weeks apart!

While going through some photos, I noticed that this photo of Long-Eared Owl nestlings is a great example of the size difference you can see in nestlings that hatch asynchronously. Asynchronous hatching refers to a clutch of eggs that hatches at different time periods, days apart, rather than all of them hatching at roughly the same time or within minutes or hours of each other. This is determined by when the parent bird begins incubating the eggs. For example, with asynchronous hatching the parent will begin incubation after the first egg is laid, rather than after all of the eggs are laid. Because eggs can be laid days apart from each other, this means that they will also hatch days apart from each other since they all require roughly the same amount of time to hatch. Certain species, like these LEOW’s and some other raptor species, are known to asynchronously hatch while others do not.

One thing I like about this photo is that you can notice that these birds were asynchronously hatched. One hint is the size of the nestlings. These nestlings are obviously not the same size, and the size difference is so drastic that it is likely not due solely to differences you would see if one were a male and the other a female. Another difference that is a little bit more subtle is the development of the feathers. You can see that the nestling on the right already has flight feathers and that the patterns and colors on that bird’s face are more like an older LEOW. If you look closely, you can also see that the bird in the middle has a more developed facial pattern than the one on the left. For example, if you look towards both sides of the middle nestling’s face you can see that the characteristic chestnut colored patches are starting to become apparent but they are still mostly absent in the bird on the left. So with one look, you can notice that the birds are lined up oldest to youngest from right to left.

As we were writing this blog post, we got a call from Idaho Department of Fish and Game about a Barn Owl nest in need of relocation. The youngest of the brood is just 10 days old, and the oldest hatched about 4 weeks ago! The nestlings were found in a building during the process of demolition, and they are being moved to a nest box just a few hundred yards away, where their parents will continue to raise them.

Asynchronous hatching doesn't just provide the opportunity for adorable photographs. It allows parents to raise the largest number of offspring that can be supported by unpredictable prey populations. The first siblings to hatch are able to bully and beg their way to more than their share of the food brought to the nest, and the youngest chicks only survive in years of abundant prey supply. While this method may seem cruel to the younger siblings, asynchronous hatching ultimately allows for more chicks to survive to healthy maturity by matching each year's brood size with unpredictable food resources.

For birds like quail, duck, and geese, whose young hatch ready to follow mom in search of food, it is crucial that all of the chicks hatch at roughly the same time. A California Quail lays 12-16 eggs in a clutch, but she cannot possibly lay all of those eggs in one day. To ensure synchronous hatching, she lays about five eggs per week, but does not begin incubation until all eggs are laid. Chicks further synchronize their hatching by making clicking calls from within the eggs to communicate to each other and to their parents when they are ready to hatch.

By Nick Ciaravella and Carrie Ann Adams. See more of Nick's photos at

Learn more about asynchronous hatching at

Photo Credit: Idaho Department of Fish and Game

Photo Credit: Idaho Department of Fish and Game

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