July 24, 2005
Chicks and Gender
Nest Update: Some interesting things to highlight. The ospreys watched a big set of clouds go over the Refuge the other day -- it almost looked like the Refuge was being invaded by a spaceship. :-)
Also, today we saw the oldest chick get his talons off the nest in a flapping exercise. The oldest is probably about a week away from flying, although it could be sooner. He might make some short hover flights over the nest before he actually strikes out.
And the mother osprey has been doing a good job of occasionally positioning herself between the two chicks during feeding time to ensure both get fed. Sometimes she even flies over to the youngest with her food so that he is sure to get some. A good mom.
We’ll update the Gallery on Tuesday. And now onto the topic of gender…
One topic that is always interesting is the possible gender of the chicks. As we said in our posting for the Chick-Naming Contest (don't forget the contest ends on 7/31), we don't know the gender of the cam chicks. But of course that doesn't mean we wouldn't like to know.
Naturally we look for clues. The first reliable sign of gender in ospreys is the “necklace” -- the coloring that an osprey has across their white chest. In adults, this is normally a rather reliable indication of sex (not 100%, but pretty darn good). If the adult osprey has coloring across its chest -- a "necklace" -- then it’s usually female. If the adult osprey has a completely white chest, then it’s usually male.
Of the two pairs we've had on the cam platform, both females had necklaces and both males had white chests (2004 couple, 2005 couple). The one noticeable difference between the two couples was that the two females had different looking necklaces -- one had a very dark necklace and the other had a very light necklace.
In the chicks, necklaces can be deceiving. Many chicks start out with a necklace and then lose it as they mature, so normally necklaces in young ospreys are not very reliable indicators of gender. If the young osprey comes back from South America in a few years when it has matured and it still has the necklace, then that would be an excellent sign that it was a female.
Body size is another indicator of gender in grown ospreys, but again it can be deceiving in chicks. With adult birds, the female is always bigger -- as much as 1/3 bigger. But with chicks, so many things influence their size at this stage, that it's hard to use it as a tool for determining their sex.
A good example of this difficulty can be seen in a batch of osprey chicks that were recently banded in southern Michigan. The website for the Osprey Watch of Southeast Michigan mentions that last month they went up to band five chicks, and they put female bands on all the chicks based on how big their feet were. While they were there, they also took DNA samples, and when the DNA tests came back, they found out that three of the birds had turned out to be male.
Putting the bigger bands on the chicks didn’t cause any problems, but based solely on size, the banders thought they looked female. So size at that stage (4-5 weeks old) was not a great indicator. Order of birth, amount of food received, and other issues can affect the size of a chick, and those factors can make it hard to determine the correct gender just by looking at the bird’s size. Of course, once the birds are fully grown (around the time they’re ready to migrate), size becomes a better indicator.
But for now, it appears that DNA tests are the most reliable way to find out the sex of the chicks, and since we aren't going to climb the platform to take blood samples from the birds, we won't know for sure what sex they are; but of course it's fun to guess. Once the chicks are close to migration, they will be almost fully grown, so maybe then we can look at both their size and their necklaces and make a good educated guess as to what their gender is.
Until next time,
Lisa - webmaster