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March 19, 2010--How to tell the adults apart

by Bob Sallinger


Posted on March 19, 2010 at 7:26 AM

Updated Wednesday, Oct 30 at 7:46 AM

Adult, female, Raptor Cam Red-tail in flight 2009 by Bob Sallinger

Dear Westridge Elementary School 3rd and 4th Graders,

Thanks for your question  regarding telling the two parents apart. It can be pretty difficult as they look somewhat similar. However there are some tricks. The mom at this nest does most of the incubating of the eggs--most of the time when you see a bird sitting on the eggs it will be mom. The easiest way to tell one adult from another is that the male is significantly smaller. Red-tailed hawks, like many birds of prey have something called "reverse sexual dimorphism." That is a really fancy way of saying that the males are smaller than the females. In fact the males can sometimes be as much as a third smaller than the females! There are a lot of theories as to why this is the case. One theory is that the female lays the eggs and does most of the incubating and brooding and therefore it helps her to be larger. Another theory is that by having the males and females be different sizes, it allows them to go after different types of prey with the male hunting smaller faster animals and female hunting slower, bigger animals. My favorite theory is that the male typically courts the female and if she doesn't like a male who is seeking her as a mate she is bigger and can chase him off. Most likely is is a combination of factors that caused this size difference between males and females. Watch for times when both birds are at the nest--the male will be noticeably smaller. Also note the size of the birds relative to their surroundings--the male tends to fill a much smaller area when he is on the eggs.

Red-tails actually have a great variety of coloration patterns ranging from  light phase birds whose body feathers appear almost  white or beige from a distance to dark phase birds whose body feathers appear almost completey chocolate brown. These two birds however both show the most common red-tail coloration patters with dark heads, light chests and a dark belly band. The  female in my opinion has a larger whitish area on the back of her head. Keep watching and see if you can identify other markings to tell them apart.

All red tails regardless of feather patterns on their bodies have red tails when they are adults. However for the first year of their life, their tails are brown. The begin to get their red tail feathers during their second year. However, it takes a while so you can often tell a red-tail is in its second year by the fact that it has a mix of red and brown tail feathers.

When the chicks hatch, they will be fed the same things as their parents eat. Red-tails have a pretty diverse diet which includes small mammals, birds and reptiles. In the city, the majority of their diet is made up of pigeons and rats. The parents will rip the prey into very small pieces and feed the chicks early on. However by their third week after hatch the nestlings will be starting to rip and tear food that is delivered by their parents by themselves.

Thanks for your questions!