What is the most reliable criterion to predict the sex of Red-tailed Hawks?

The most reliable criterion to predict the sex of Red-tailed Hawks is based on weight and size. In general, female raptors, including Red-tailed Hawks, are larger than their male counterparts. This size dimorphism is quite pronounced; females tend to weigh significantly more and have a larger wingspan. This difference is a common trait observed in many bird species where females have evolved to be larger, often to aid in incubation and protecting their young.

While other factors like eye color, plumage coloration, and behavioral traits can show some variation between male and female hawks, they are not as consistent or reliable in determining sex. Eye color varies due to age and individual differences rather than strictly by sex. Coloration of plumage remains similar in both sexes among Red-tailed Hawks, making it an unreliable criterion for sexing them. Behavioral traits can offer clues, particularly during breeding seasons, but these observations can be less straightforward and may not apply universally. Thus, reliance on weight and size provides a clear and dependable method for distinguishing between male and female Red-tailed Hawks.