Thursday, April 5, 2012

Egg Laying at the RMRP

While watching the Kestrel's twitter account (@RaptorProgram), I noticed that he's been posting about the number of eggs being laid by the educational female Common Barn Owl (she's up to four!) and realized you Humans may have some questions about egg-laying. To that end, I've created a list of egg-related questions and answers:

1. When is egg-laying season?
Female Barn Owl in her nest box
Egg-laying season is different for every bird, and a little bit different every year. This winter was warm and mild, with lots of tasty mice running around, so the Owls have been able to start breeding (and therefore laying eggs) earlier than usual. Typically, at least around Fort Collins, the Common Barn Owls lay eggs in mid-April, and the Great Horned Owls in February (although it can be as early as January). This year Barn Owls are sitting on the eggs right now, and Great Horned Owls already have chicks! In fact, a briefly orphaned Great Horned Owl chick was brought in to the RMRP two weeks ago, but was able to be returned to the nest that same day.

Male Barn Owl standing guard over his lady
2. Do captive birds lay eggs?
Yes, we will lay eggs, but only some of us, and only in the right conditions. It takes the perfect combination of conditions (food base, stress, and age key among them) for a raptor to lay eggs, even in the wild. In captivity a raptor has a steady, healthy diet, so that usually isn't a factor, but if the raptor never gets completely comfortable with being in captivity, she simply won't lay eggs. On the other hand, some birds take to egg-laying in captivity like an Owl takes to nighttime. We have numerous educational birds that lay eggs each year, and those birds often lay large clutches since they have the diet and care to support the effort.

3. What does the RMRP do with eggs laid in captivity?
Common Barn Owl eggs
According to the Humans at the RMRP, it takes a lot of work, permitting and money to breed raptors in captivity. They have decided to not follow that path for a number of reasons: they already have enough work and permits to worry about, and none of the species the RMRP cares for have at-risk populations that require captive breeding. So in order for the Humans to not break the law when the educational birds do lay eggs, they have to destroy them. What this usually means is taking the eggs from the nest and replacing them with fake eggs, or taking the eggs from the nest, making them unviable, then returning them.

Young Great Horned Owls with "mom"

Here's the great part of this process: because the parents are allowed to sit on fake eggs and stay "in the zone", they're ready to take on mom-and-dad duty when orphaned raptors are brought in to the center! When it comes down to it, we raptors are only as smart as our instincts. So if one day we wake up and there are baby birds in the nest, even though they seem a little old for new hatchlings, and gee, I never saw them actually hatch...we don't care! We're wired in one way: if it's an egg, sit on it; if it's a baby, feed it. Through this quirky process, the RMRP is able to supply orphaned raptors with real-life role models. The educational birds teach the kids how to eat (and what to eat), how to keep feathers in good condition, how to hiss and strike at Humans, etc. It works out for everyone.

4. Why don't you hand over the orphaned raptors to other birds in rehabilitation, instead of giving them to educational birds?
Young Great Horned Owl reacting appropriately to a Human
 Well, not all raptors are good parents. Add to that the stressors of being new to captivity, and healing from a traumatic event...they certainly don't need to be raising babies, too. The educational birds are tried-and-true parents, and the Humans know the educational birds aren't going to kill the babies, or steal all their food. Here are some amazing numbers to prove it: the Grey Female Great Horned Owl who passed away a month ago raised ~50-75 chicks with her cage-mate during their time at the RMRP, and the pair of Common Barn Owls have raised over fifty babies between them! And don't worry: the Humans are very careful about how they interact with young birds, so all those chicks were released to the wild with a healthy level of Human-hate.

5. How many eggs do captive raptors lay?
Baby American Kestrel eating lunch
It varies from bird to bird, and from year to year. Last year the female Barn Owl laid six eggs and the female Kestrel has laid as many as 10 in one year. The female Swainson's Hawk (at the ripe age of 21) still produces ~2 eggs each year! The normal clutch size for these birds in the wild is typically 4-5 for Common Barn Owls, 4-5 for American Kestrels, and 2-3 for Swainson's Hawks. In a really bumper year for the prey base, some Barn Owls will lay a second clutch to take advantage of the conditions!


Those are all the questions I've come up with today, but if you think of any more, feel free to email me ( or simply post a comment below, and I promise I'll answer! And stay tuned for details and pictures of eggs and, eventually, baby owls.

No comments:

Post a Comment