Deferred Maturity

by Dave Hanks

Young song birds hatch, fledge, and are ready for migration. The young birds usually resemble the female parent. However, by the following spring the males acquire their adult breeding plumage and assume parenthood. Their development is relative simple and quick. However, most raptors and gulls go through several stages before reaching sexual maturity. Large birds like eagles or buzzards have 4 to 5 stages of development. Hawks usually have two stages to go through over a two year period to reach maturity.

Buteos are large hawks with broad wings. The FERRUGINOUS HAWK (pictured) is the largest American Buteo. Only the Bald Eagle, Golden Eagle, and female Snowy Owl weigh more than this hawk. Ferruginous Hawks go through three stages after the nestling stage: juvenile, sub-adult, and finally adult – three years from hatching to adulthood. This species has been known to live for 20 years (determined by re-catching banded birds), although the majority die within a 5 year period –which allows a five year old bird two opportunities to nest.

Ferruginous Hawk’s first year mortality is estimated at around 66% and adult mortality at about 25% per year thereafter. This ground nesting bird is preyed upon by Coyotes, Golden eagles, and Great horned Owls. Jackrabbits rank high on this species food list. When prey sources are at a low, many hatchlings will die of starvation. Illegal shooting of adult birds has also caused a problem to this not-so-common species.

This magnificent hawk has been used as a falconry bird in its native range.

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A young Ferruginous in the sub-adult phase

 

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