Structure of the New England herring gull population
Dataset Identification:
Resource Abstract:
Measurements of the rates of population increase, reproduction, and mortality together with an observed age ratio, were used
to analyze the population of the Herring Gull in New England. Data from sporadic censuses prior to this study, aerial censuses
by the authors, and National Audubon Society Christmas Bird Count indicated that the New England breeding population has been
doubling every 12 to 15 years since the early 1900's. This increase has involved founding new colonies and expanding the breeding
range There is evidence that 15 to 30% of the adults do not breed in any given year. Sixty-one productivity measurements on
43 islands from 1963 through 1966, involving almost 13,000 nests, showed that from 0.8 to 1.4 young/breeding pair/year is
the usual range of rate of production. The age distribution in the population was determined by classifying Herring Gulls
by plumage category on an aerial census of the coast from Tampico, Mexico, to Cape Sable, Nova Scotia. Of the 622,000 gulls
observed, 68% were adults, 17% were second- and third-year birds, and 15% were first-year birds. Mortality rates derived from
band recovery data were too high to be consistent with the observed rate of population growth, productivity, and age structure.
Loss of bands increasing to the rate of about 20%/year 5 years after banding eliminates most of the discrepancy. The age structure
and rate of population increase indicate a mortality rate of 4 to 9% for gulls 2 years old or older, compared with the 25
to 30% indicated by band recoveries. The population structure we have developed fits everything we have observed about Herring
Gull population dynamics, except mortality based on band recoveries.
Citation
Title Structure of the New England herring gull population