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

Reproduction of the herons Cochlearius cochlear-ills (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 II 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 cm(3)) was larger than the volume at site B (16.95 +/- 0.30 cm(3)). The eggs of C. cochlearius (35.01 +/- 7.04 cm(3)) 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 homogeneous, 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.