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.