Growth and Development of Nestling Brown Pelicans

Growth in birds has recently received considerable attention.Numerous one-year studies of various species exist, and their ecological implications relative to clutch size and growth rate have been thoroughly reviewed by Ricklefs (1968Ricklefs ( , 1972Ricklefs ( , 1974)).Because of the wealth of weight data available, Ricklefs used weight as his standard for analysis.LeCroy and LeCroy (1974) present a detailed study of four years of growth in Common Terns (Sterna hitundo) and elucidate the complicated interactions of different growth parameters, especially in regarding weight and wing length as means for aging nestlings.In the present study I analyze growth data of four nesting seasons for the Brown Pelican (Pelecanus occidentalis), attempting to elucidate the following points: (1) determine the age and growth parameters for this species; (2) examine weight, and other characters such as bill, wing, and tarsus lengths as a measure of growth in this species; (3) to determine if external measurements demonstrate the physical condition of the individual bird, and (4) to use these external measurements as an indication of the age of the nestlings, and thus be able to determine the seasonality of breeding b.y sampling once or twice during the season.This is important since access to breeding colonies is often difiicult, either because of time constraints or the inaccessibility of the colony, and because disturbance of the colony causes undue mortality (Schreiber and Risebrough, 1972).METHODS I measured growth parameters of nestling Brown Pelicans in 1969, 1970, 1971, and 1972.The pelicans nest in discrete units on Tarpon Key, Pinelias County, Florida.I selected one of these units for my growth studies, and measured nestlings in the same area each year, marking a total of over 250 nests for individual study.After noting the presence of the first nest at the beginning of each year, I visited the colony unit at approximately weekly intervals, from early March through July.In all nests included in this analysis the hatching day for one chick in each nest was known precisely.The hatching day of the remaining chicks was known within one or two days.Another criterion for including a nest in this analysis was a minimum of five weekly sets of measurements for one or more nestlings.For most nestlings that fledged, I obtained seven to 11 weekly sets of measurements.Sample size for the later nestling period is smaller because of the difiiculty in capturing large nestlings in the mangrove (Avicennia gerr•inans) without undue disturbance.Measurements were taken of the length of the exposed culmen, wing (unflattened manus and manus plus longest primary feather), 19