Factors affecting offspring growth and daily nest survival rates in the coastal breeding Western Reef Heron ('Egretta gularis') in the Persian Gulf

Abstract

Offspring growth and nest survival of waterbirds are important and prominent characteristics of their life history. Nestling growth and daily survival rates of the Western Reef Heron 'Egretta gularis' were studied in Hara Biosphere Reserve, Persian Gulf, Iran. Growth parameters were determined in relation to both age ranking of each nestling within a brood and the brood size using data from known-age nestlings. Nesting success was modeled based on the information-theoretic approach implemented by the program MARK to assess the effects of clutch initiation date, nest size and location on daily survival rates of nests. Mean daily growth rate of body mass was 18.06±6.22 g during the first 2 weeks of age and was independent of brood size but was greater in nestlings hatching earlier within the brood. Wing and tarsus growth rate was influenced by both brood size and nestling rank within the brood, but culmen growth was independent of both factors. Earlier hatched nestlings grew faster than those hatched later. Growth of all morphometric parameters followed the Logistic growth curve model except for wing chord, which fitted the Gompertz growth model. Nest size and nest height above the ground were the most important predictors of nest survival (ω = 0.79 and ω = 0.69, respectively), with survival among Western Reef Heron nests improving as the nest size and nest height increased. This study shows the importance of temporal and spatial variables for breeding ecology of a common but little-known breeding heron in coastal areas of Persian Gulf.