This time of year is a great time to observe Osprey pairs (male and female together) as they are spending much of their time within a specific territory. However, try to observe raptors from a distance of course so as to not disrupt their nesting behavior or habits. Anyway, I have gotten several recent emails in regards to the reliability of sexing Ospreys based on the amount of streaking on their chest (often referred to as a "bib"). It was thought long ago that adults with a black-streaked chest were females, and adults that lacked the chest streaking were males, but I wrote in 1998 that this trait is variable on both sexes and not 100% reliable. Also, young birds of both sexes typically have a “bib” (that is of course variable), so don’t try to sex juveniles by this trait. It is true though that if you observe a mated pair of Ospreys and one of the birds has a bib and one does not that the one with the bib will likely be the female and the one with the clean breast will likely be the male. So, in a nutshell, the rule of averages play in favor of sexing Ospreys by their bib or lack of, but be careful!
Check out this photograph of a mated pair of Ospreys in Yellowstone, WY by my buddy Scott Edmisten (thanks Scott). This is a great example of both sexes lacking a bib...if the female (on the right, possibly the larger bird?) were to be seen alone, I bet most people would call the bird a male and never think twice about it. Well, now we can all think twice! Hope this post helps, and always feel free to comment and share your thoughts.