Kestrel Eggs Appearing in Ulster County


Yesterday was my day to make the rounds of the nest boxes and check for eggs. Since rain was forecasted for today (correctly) and I hadn't checked most boxes for about 10 days, I needed to see nest contents before clutches were complete, which typically takes 9 days. I was really hoping for eggs and was not disappointed. Five of the boxes had either one or two eggs. Here's what the inside of three boxes looked like yesterday: 









The female from the box with two eggs likely began laying, at the earliest, on 20 April. An average clutch is 5 eggs, so if she lays one egg every other day, her clutch should be complete around 29 April and her eggs should hatch sometime around 1 June (incubation takes about a month). Box checks with incomplete clutches are ideal, because now I know roughly when incubation will start and the eggs will hatch. If my first look at eggs was of a complete clutch, the female could have completed yesterday or a week ago...not ideal. I will estimate clutch completion dates for these boxes, and check again a few days later to confirm the final clutch size. All of this allows for a fairly precise estimate of hatching date. I will then check the boxes again about a week later to get a count of nestlings and estimate their age to determine when to return for banding...the really fun part. 

The news yesterday wasn't all rosy, as I found a couple of starling nests, with eggs, in boxes where kestrels were in residence only a few days prior. Starlings...grrrrrrr. These persistent, non-native birds are a serious competitor with kestrels for nest sites here in the northeastern US where open habitat and cavities are at a premium. 

But the kestrels are breeding, which is great news. There are pairs occupying a few of the new boxes I installed this year, which is encouraging. Hopefully these birds will establish breeding territories that will be occupied for years to come.  ¡Viva cernicalos!

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