Sibling rivalry (??)

As I’m writing this post, I’m still not sure if there’s only one chick or more than one chick in the Peregrine Falcon nest at One Well Fargo in uptown.  Haven’t heard about it, yet?  Check out the FalCam at the Carolina Raptor Center.

The question, though, is whether or not to be worried if the other egg hasn’t hatched, yet. Well?  Worry?  Nah.  Save your energy.  Like many birds, the Peregrine Falcons don’t lay all their eggs at the same time.  A female that had all those eggs inside her would have a very hard time flying.  As a result, they prepare eggs for laying in sequence.  A typical laying interval for the these birds might be 2 or 3 days.  Since the first chick was hatched either Saturday night or Sunday morning, we’d expect the second to hatch VERY soon (if it’s going to hatch).

Herbert, R.A. and K.G.S. Herbert.  1965. Behavior of Peregrine Falcons in the New York City region.  Auk 82:  62-94.

Now if you go back on the FalCam’s DVR and check out any pictures of the chick from Sunday, you can see just how much it has grown in just a few days.  These birds grow very fast.  It has (by my totally and completely unofficial estimates) more than doubled in size since Sunday.  Now imagine what that means when the second chick does hatch.  That size difference can result in some serious sibling rivalry- at least in the first few days after hatching.  In some species, that size difference can result in siblicide (Black Eagles and  Great Egrets are famous for this kind of behavior).  Siblicide?   It’s what happens when two siblings just don’t get along.  If the smaller one can’t escape (or get enough food), well, the bigger chick takes it beyond just name calling.  In a quick search that I made this morning, there is only one anecdotal reference to siblicide in Peregrines, so we won’t likely see any of that sort of behavior, here.

If that second egg hatches, we will see some big size differences.  What will become interesting (and please, if you’re tracking what the parents feed, keep track of which chick they feed, too) is to see who gets fed (and how much they get fed).  There are some data out there on sex ratios and feeding rates.

One study notes that first chicks are often females.

Olsent, P.D. and A. Cockburn.  1991.  Female-biased sex allocation in Peregrine Falcons and other raptors.  Behavioral Ecology and Sociobiology 28: 417-423.  

Raptors are a group of birds that show a pattern sexual size dimorphism where the females are larger than the males.  If that first chick is a female, then she may retain that size advantage throughout her entire life.  If the chicks are the same sex, then we would expect that size advantage to disappear quickly.  Partly, that change may occur after about 3 weeks in the nest, when growth rates of those kids will probably start to change.  All chicks go through VERY rapid growth in the first 3 weeks.  After that time, though, things start to change.  Male growth rates actually begin to slow down while female growth rates remain high.  That size dimorphism really takes shape early in life.

Boulet, M.; P. Olsen; A. Cockburn; and K. Newgrain.  2001. Parental investment in male and female offspring by the Peregrine Falcon, Falco peregrinus.  Emu 101:  95-103.

So, your continuing job:

1.  What are the parents feeding the chick (or chicks)?

2.  Which chick is getting fed more frequently?

3.  Can you identify the band numbers on the legs of the parents? (more on banding in another post)



About thomasbiology

I'm an Associate Professor of Biology at Queens University of Charlotte with a background in animal behavior with an emphasis in bird song. I've got two secret goals with this blog (well, since I'm sharing them, they're not so secret): 1. To encourage people to look at the natural world around them- not just as a hiking destination, but to notice all the little things moving around them all the time; and 2. To show some of the science that relates to these little things moving around. There's some really fascinating research out there that so few people get to see.
This entry was posted in ecology, falcons, foraging, mating, raptors, reproduction. Bookmark the permalink.

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