Age composition of a breeding Ring-billed Gull population

TitleAge composition of a breeding Ring-billed Gull population
Publication TypeJournal Article
Year of Publication1968
AuthorsSouthern WEdward
JournalInland Bird Banding News

In an earlier paper (Bird Banding, 38(1): 52-60. 1967) I briefly presented data regarding the age structure of a Ring-billed Gull (Larus delawarensis) colony located on a man-made peninsula near Rogers City, Presque Isle County, Michigan. At that time my sample consisted of only 77 ring-bills of known ages. Since then, I have continued to trap adults and by the end of the 1968 breeding season 332 gulls ranging between two and twelve years old had been captured. The proportion of the total sample represented by each year class is graphically presented in Figure 1. Banded gulls found dead within or near the colony were not included in these figures. All of the birds were captured by means of cannon nets. The larger sample provides an improved indication of the age composition of this particular Ring-billed Gull breeding population. Ninety-six per cent of the birds were between two and seven years of age and 80.4% of the total capture was between three and six years of age. It is possible that rebanding techniques and future cannon-netting activities will show that a slightly larger proportion of the population is represented by gulls older than seven years. Table 1 includes a list of the numbers of birds representing each age class. The cannon net trap represents an ideal method of sampling gull populations during the breeding season or during migration. Increased use of this technique would greatly enhance our knowledge regarding topics such as population biology, distribution, and migration patterns. However, caution should be exercised when using cannon nets in colonies because improper use can cause increased mortality and nest desertion.