Reproduction of Cochlearius cochlearius (boat-billed heron) and Butorides virescens (green-backed heron) in La Manzanilla, Jalisco, Mexico

Abstract

Reproduction of the herons Cochlearius cochlearius (boat-billed heron) and Butorides virescens (green-backed heron) was recorded for La Manzanilla estuary, Jalisco, Mexico, from April to August 1997. Two breeding sites were studied: site A presented 11 nests of C. cochlearius (54.5% were reused) and 16 nests of B. virescens (6.2% were reused); site B exhibited 8 nests of C. cochlearius and 22 nests of B. virescens (13.6% were reused). Mean height of nests of C. cochlearius was higher (308.42 ± 23.81 cm) than that of B. virescens (115.13 ± 4.73 cm). Clutch size of B. virescens (2.71 ± 0.08) was significantly larger than that of C. cochlearius (1.88 ± 0.12). Mean egg volume of B. virescens at site A (18.02 ± 0.19 cm3) was larger than the volume at site B (16.95 ± 0.30 cm3). The eggs of C. cochlearius (35.01 ± 1.04 cm3) were almost twice the size of those of B. virescens. The first nesting species was C. cochlearius, which exhibited a breeding period from April to August and an incubation period of 20 days. The breeding period of B. virescens was shorter and more homogenous, from May to July, with a mean incubation period of 19.4 days. The breeding success estimated for both species fluctuated between 50 and 87%; the highest values were associated with viability and the lowest with flying success.