Ecology and Breeding Habits of the Savanna Hawk in the Llanos of Venezuela

Abstract

The ecology of the savanna hawk (B. meridionalis) was studied in the palm-savannas of Venezuela in 1978-1980. Pairs produced only 1 egg per clutch (no more than 1 young per calendar year), and had eggs or young in nests from Feb. to Dec., coinciding largely with the wet season. In comparison to North American red-tailed hawks (Buteo jamaicensis), savanna hawks had significantly fewer young per pair per year, lower nest success (47.1% vs. 82.5%) (mainly due to lower hatching success (64.1% vs. 84.4%)), and a lower proportion of pairs laying eggs (73.3% vs. 88.0%). Survival of young savanna hawks from hatching to near fledging was 70.4%, and the adult survival rate, 71.1%; these values are approximately equal to those for red-tailed hawks. The brood size was artificially doubled from 1 to 2 at 10 savanna hawk nests, but the adults could find only enough food to feed and raise 1 chick in most cases. Food appeared to be both the ultimate and approximate factor controlling the timing of breeding. The savanna hawk has evolved interrelated habits that counter its low fecundity: the capability of renesting after the initial eggs or young have perished; a post-fledging dependency period of 4-7 mo. to help insure survival of the single young; and permanent or long-lived pair-bonds. The ability to renest is enhanced by hunting versatility. Long-lived pair bonds may improve intra-pair activities, thereby enhancing the reproductive success of experienced breeders.