SIBLICIDE IN SWALLOW-TAILED KITES

We Studied the reproductive behavior of Swallow-tailed Kites (Elanoide s forficatus) in northern Guatemala. Modal clutch size was two (range 1-2), but no nests succeeded in fledging more than one young. Eggs wer e laid at intervals of three to four days and hatched at intervals of three to Ave days. Second eggs weighed significantly less than first e ggs. Second chicks either received no fond or obtained so little that they did not grow. First chicks vigorously attacked their nestmates, a nd all second chicks died within five days of hatching. Food stress wa s not found to be a proximate cause of this behavior. Siblicide appear s to be innate in this population of Swallow-tailed Kites, even though the northern subspecies does not exhibit this behavior. Swallow-taile d Kites are, in certain aspects, an anomaly among species within the o rder Falconiformes that exhibit obligate siblicide.