There have been no detailed studies of predator or non-predator causes of mortality and failure at nests of the Red-shouldered Hawk (Buteo lineatus), and identification of such causes has been largely speculative. There is ample information about rates of nest success, defined as the fledging of ≥1 nestling from a nest, but this measure of reproductive rate is limited in its scope. Fledging success, measured by quantifying total nestlings lost or fledged is a more informative assessment of reproductive success, but is not often reported. We used video monitoring of suburban Red-shouldered Hawk nests to identify causes of mortality or failure. Eight of 25 nests failed completely (32%), and 17 were successful (68%). However, nine of the 17 successful nests experienced some nestling mortality, and the fledging success of individual nestlings (n = 67) was only 58%, as 28 nestlings (42%) died before fledging. Causes of mortality or nest failure included depredation of an incubating female parent at one nest and of nestlings at multiple nests by Great Horned Owls (Bubo virginianus), depredation of nestlings by raccoons (Procyon lotor), disturbance by eastern gray squirrels (Sciurus carolinensis), unexplained disappearance of female parents, starvation of nestlings, and nestlings falling from the nest. These results provide a thorough and accurate account of reproductive success, and valuable identification of predator and non-predator causes of nestling mortality or nest failure throughout the nesting period.
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Vol. 49 • No. 2