Ageing American Kestrel Chicks

It has been a busy month! About half the boxes that I have been monitoring in Levy and Marion counties are being used by breeding Southeastern American Kestrels (a hand full have been taken over by Eastern Screech-Owls, Tufted Titmice, Great Crested Flycatchers, Eastern Bluebirds, and Flying Squirrels). Over half of the boxes that had eggs have hatched, and we have banded 3 nests so far at, at 25 days old! Over the past week, 2 new nests have been initiated, but it is getting too late in the season to expect more. Surprisingly, there are a number of kestrel pairs on territories near boxes that don’t show interest in them. Over the next few weeks I hope to find where they are nesting, likely in natural cavities (accessing private land is the issue here). Nests that are not in nest boxes will be easier to find once the eggs hatch, as the parents start making more frequent trips with food for their babies. I have found a few nests in cavities in utility poles, but they aren’t exactly natural!



Back to the boxes. As with most baby birds, kestrel babies seem to grow amazingly fast. On day 0 (hatching day!) chicks appear “wet” for under an hour (looking more like pink aliens than birds), and then turn into small puffy white babies as their downy feathers dry out. For the most part, they are still about the size of an egg for most of the day, but parents are quick to feed them, making their small bellies grow to almost twice their size by the day’s end. Also on hatch day, chicks still tend to appear “egg-shaped” as they strengthen their necks and legs that have been tucked inside a small egg for about 30 days! For most five egg clutches, 4 eggs hatch on day 0, followed by the remaining egg on day 1. However, sometimes 3 chicks hatch one day, and 2 the next. There have also been a few cases where hatching of all chicks is spread out over a three-day period, but this is uncommon.





On day 1 (their first full day of life!), chicks don’t appear as feeble as the previous day, but are still quite small. On this day, it is hard to imagine that the chick came out of a small egg, as it now appears slightly larger than the egg. There are usually a few wet or recently hatched chicks present for comparison between the day 0 chicks and the recent hatched chicks. Unfortunately, the recently hatched chicks often get sat on for most of the next few days of their life, and are easily over-powered by the chicks that are stronger and more able to beg for food quickly. Throughout the first 2 weeks, one or two chicks of each nest appear much smaller than the others (keep this in mind as you view the remaining photos in this post; the age listed will be of the oldest chick in the box). Unfortunately, it is these smaller chicks that usually get eaten by fire ants at a young age; larger/older chicks can usually fend them off, and if chicks have made it past their first week, they can usually fend the ants off by preening (unless there is an overwhelming number of ants). In addition, chicks usually open their eyes by day 1 (sometimes on day 0!), but some won’t open their eyes for a few days.




From about day 3 through day 8 of life, kestrel chicks are notoriously hard to age. No feather “sheaths” develop at this time, and what chicks look like can really depend on how much they are getting fed individually. This is why it is important to know hatch date, which is how I have aged all of these chicks. During this time, chicks are still naive and don’t really look at humans as a threat, and “beg” for food at the site of a human hand. In my opinion they look quite “dopey” during this time; their legs seem to grow very fast, while their wings still look like tiny featherless chicken wings.






From day 9 onwards, feather sheaths start to appear as feathers begin to develop, starting with the primaries. At this age and onward, chicks can start becoming aggressive (in a cute way), rolling onto their backs and trying to “foot” you with their talons. More aggressive individuals usually turn out to be females. They may also try to bite. Usually though, in the heat of the day, they aren’t very concerned with you unless they are really hungry (and cranky). At this stage in the game, kestrel chicks are starting to act and look more like adults and less like babies. They have also done a really great job of plastering the walls with a thick coat of whitewash.








Between days 11 and 20, the rate of feather development is unbelievable. Some smaller chicks within a nest can look completely different than their older siblings if they are just 1 or 2 days younger. By day 13 or so, tail feathers start to develop, and primary feathers should be developed enough to have coloring to them. Because of this, it is possible to determine sex over the latter part of the next few days.



The next three photos were taken in the same box.





By day 17 or a bit earlier, flank spots (for males) and breast streaks (for females) are obvious. Their bodies can still have a fair amount of “fluff” on them , though, especially their heads.


The next three photos were taken in the same box. Note the young age of the bird on the left, and note that you can sex the other two by the color of their primary feathers.





From day 19 onward, you really have to be careful when opening a nest box. Kestrel chicks fledge around day 27, but a disturbance a few days before this can cause them to “force fledge.” For this reason, I usually only check on chicks once from day 10 onwards until we band them at 25 days of age. Kestrels look very much like miniature adults at this point.


The next three photos were taken in the same box. Note that there are 4 males and one female. The female’s back is heavily barred, and as to be expected, she is the largest. Southeastern males have much less barring on their backs than migrant male kestrels. Note the varying amount of white “fluff” on heads, the youngest chicks having the most.






Day 20 should really be the last day you visit a nest box, as chicks are becoming very large and space is limited in the box. The next box was like a bomb waiting to go off. At this point you want to be as quiet as possible when putting up the ladder, and block the entrance hole just in case a chick goes bonkers. All it takes is one chick to get the others riled up. The next 2 photos were taken at the same box, at 20 days old. Note that the box contains 4 females and one male, and one female has that crazy look in her eye. She ended up standing up and getting the male to go into defense mode as well, but the other females remained calm, as it was really hot and humid.






Over the next few weeks, we will be banding all of these kestrels at 25 days of age. Look for more photos to come of the banding process when I return from the Biggest Week in American Birding (Alex will be returning with me to help out for a month).