Breeding success of a colony of Boat-billed Herons Cochlearius cochlearius (Ciconiiformes: Ardeidae) in pasturelands of Costa Rica

Abstract

Abstract:The breeding success of a double-brooding colony of Boat-billed Herons Cochlearius cochlearius was studied in pasturelands of Costa Rica. Mean clutch size in the first clutches (2.9 eggs/nest) was higher than in second and repeat clutches (2.3 eggs/nest). Breeding success was similar in the first attempt and second attempts (20.7 % and 21.7 %, respectively). In both attempts earlier nests enjoyed a higher breeding success. Starvation of the youngest chicks within the nest and destruction of nests by bad weather conditions were the main factors related to nestling death. No effects of human activity on the reproduction of the breeding colony were observed. Rev. Biol. Trop. 54 (4) This species breeds solitarily or in colonies (Carbonell 1993), and two peaks of activity have been observed during the nesting season of some colonies (Dickerman and Juárez 1971, Carbonell 1993). Similar results were recorded by Gómez et al. (2001), who assessed the second peak of activity to the occurrence of second and repeat clutches.Previous studies of some Boat-billed colonies pointed out that human presence appeared to affect breeding success. In fact, Juarez (1967) reported the occurrence of nest desertion and predation when humans came close to the colony and also reported on the effects of mangrove pruning and egg robbery on the breeding success of these herons. Further, Wetmore (1965) pointed out that this species disappears from areas occupied by humans. The capacity of a species to tolerate the effects of habitat transformation can be an important factor to consider in their conservation. Information on the status of the populations in transformed areas and the factors related to their survival can help us to determine conservation guidelines. This paper presents some data on the breeding of a colony of Boat-billed Herons in pasturelands of Costa Rica and compares the breeding success of the first and second attempts. We do a comparison of the results of other studies that have been done and discuss whether or not human presence is compatible with the conservation of this species. MATERIALS AND METHODSThe study was conducted in Santa Clara de San Carlos (Province of Alajuela, 10°21' N, 84°30' W, 150 masl) located on the northern Caribbean Slope of Costa Rica. In this area pastures prevail, since stockbreeding is the which nest they belonged (Hernández-Vázquez and Fernández-Aceves 1999).A logistic regression model to examine the dependency of nesting success on laying date and clutch type (first versus second and repeat clutches) was used. Logistic regression models have been used to analyze factors affecting nesting success (Staus and Mayer 1999) and are appropriate when response variables are binary (eg. nest success or failure). Analyses were conducted with SPSS for Windows 8.0. RESULTSClutch size ranged from two to three eggs, but clutches of three eggs were more common in first clutches (90 %, N= 10), while clutches of two eggs predominated in second attempts (73 %, N= 15). In fact, first clutches were signific...