Seasonal Population Fluctuations of Herring Gulls in Central Maine

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Abstract
The gull population in the region of Bangor, Maine was studied from 1 Dec. 1964 through 15 Feb. 1966. With a cannon net 810 gulls were caught and then banded with Fish and Wildlife Service bands and also with a numbered, plastic leg tag. The methods of using the cannon net, the making of the tags, and their usefulness is discussed. The fluctuations in the age-class percentages and the central numbers of the gulls present in the area are discussed with an explanation for these fuctuations during the seasons. During the winter 1964-65 the population varied between 150 and 500 birds. In late April the numbers peaked to approximately 900 birds. June through Aug. the population was consistently 200 to 300 birds. From Sept. into Nov. the population peaked to about 1600 to 1700 birds. In Dec. and into Feb. 1966 the population averaged near 750 gulls. During the winter 1964-1965 the adults made up 87% to 95% of the population but in May they dropped to 13%; throughout the summer a gradual rise occurred until late Dec. when the number of adults built back up to near 90%. The percentages of intermediate gulls and 6-to 10 month old birds during the winter 1964-65 were low (1% to 10%) but both increased to near 40 to 50% during May. Through the summer and into Oct. these groups slowly dropped off in numbers, and in Nov. they were back to near 5 to 10% of the population. Chicks 1st appeared in this region during the 1st week of Aug. and reached 65% of the population by the first of Sept. After the date there was a steady rapid drop to 1% to 3% of the population Dec. through Feb. 1965-1966. The fluctuations noted above are explained in relation to the breeding season and the migratory tendencies of the spp. A daily fluctuation in the numbers of birds in the area is correlated with weather changes. Clear days invariably had a lower population than the preceding cloudy day. Evidence is presented that during the summer the gulls found near Bangor were staying within a funnel shaped area in the Eastern Penobscot Bay from Schoodic Point to Belfast, Maine. During the fall, as migration begins, this demarcation is less rigid as displacement southward occurs. Through reading band and tag numbers of free gulls with a telescope, the wandering dispersal of the young as they leave the nesting colonies and the daily movements of individual gulls are obtainable. Gulls banded in the summer of 1965 throughout most of the range of the herring gull from the Sister Islands, Wisconsin to Sandy Point, Rhode Island, were seen in Bangor during the summer and fall of the same year. With a cannon net 343 adults were caught and banded and 94 (27%) were sighted again. During the summer these adults were rarely seen but during Sept. and Oct. many of these adults reappeared and were seen consistently until Dec, After the 1st week of Dec. few marked adults were seen. Adults were rarely seen 3 to 6 days immediately following banding. Out of the 190 intermediates banded 90, or 47% were sighted again. These intermediates were seen consistently throughout the summer. During the fall, however, fewer intermediates were sighted. During the 3 to 6 days after banding the intermediates were seen more than the banded adults. Of 135 chicks banded 69 (52%) were sighted again. The chicks showed a decided persistence in this area for several weeks after banding, but after the middle of Nov. none were seen. This information along with the age-class numbers and composition of the population gives a good idea of the migratory tendencies of the herring gull.

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