Southeastern American Kestrel Egg Color Variation

Over the past 2 weeks I’ve been spending a lot of time checking Southeastern American Kestrel nest boxes for eggs in Marion and Levy counties in north central Florida. I had two boxes with early eggs laid before March, but most others were laid in the latter part of the first week of March and during the second week of March. Checking boxes for eggs can be extremely addictive!  It is hard to stop looking when you know there could be an egg that wasn’t there yesterday. Typical clutch size for kestrels is 5 eggs, of which they lay every other day (some will only lay 4, and a few will lay 6).  They start incubating after the 4th or 5th egg is laid for about 30 days, when the eggs will hatch. Knowing this, you can figure out when eggs will hatch to just about 2 days if you find the nest in mid-clutch, and even 1 day if you check it twice…which is great information to have, especially on a declining species.  Unfortunately, kestrels aren’t always happy to give up this information to a biologist on a noisy ladder.

Female American Kestrel guarding her nest box

South Eastern American Kestrel - female: note larger more substantial body than male

Southeastern American Kestrel - female: note larger more substantial body than male

Southeastern American Kestrel - male: note smaller size/thinner profile in comparison to larger female

Unfortunately I still battle with Gray Squirrels and Flying Squirrels on a daily basis, but I am happy to report that I am finding kestrels in boxes that squirrels have used and move on from, sometimes in places that I had not yet seen kestrels.  It is still quite frustrating, though, to find a box jammed full of Flying Squirrels, when a kestrel pair is nearby.  You can make the squirrels leave, but they only come right back.

Ten Flying Squirrels packed in!

Here is a look at a variety of kestrel eggs I’ve found that range in color from light pink to dark red, but always with a varying amount of speckling on them. Egg color variation in birds is most often tied to the condition of a female at egg laying, based on what she has eaten, and also genetics.  The amount of variation in these eggs is most intriguing but probably quite normal when looking at eggs over such a large study area.  In some photos, you’ll see some “snacks” left in boxes by adults.

Single heavily mottled kestrel egg: we often add wood shavings/pine bark as nest material, as kestrels do not add nest material on their own

Two egg kestrel egg destroyed, potentially by a squirrel, as this box was formerly occupied by Gray Squirrels: note pale pink coloration of egg and lack of dark mottling

Three egg kestrel nest with eggs appearing uniform in color

Three egg kestrel nest with a green anole "snack"; note varying amount of speckling on eggs and single pale egg

Four egg kestrel nest: note variation in amount of speckling and color and "two-toned" appearance of eggs

Four egg kestrel nest: note lack of dark speckling

Five egg kestrel nest (full clutch): note two-toned/half colored appearance of eggs

Five egg kestrel nest (full clutch): note uniform light color/speckling of 4 eggs and one unique "half-colored" egg

Dead Six-lined Racerunner found in kestrel nest box