I’d hate to be the youngest: factors affecting fledging success in herring gulls on Mount Desert Rock

Chater, Rosie; Schnell, Marina

From the abstract: "Mount Desert Rock ( Lat: 43.97 Lon: -68.13) is a 1.2 hectare island 40 km off the Maine coast, home to a nesting colony of 290 breeding pairs of Herring Gulls (Larus argentatus). These seabirds have declined rapidly throughout the western North Atlantic. Historically, this colony was actively culled, but it has since re-established and and is one of two increasing colonies in the region. Our study at the Edward McC Blair Research Station focuses on the effect of clutch size and hatch sequence on fledging success. Our study focused on 40 of the island’s nests, with an average clutch size of 2.7. Once chicks hatched, we weighed them and monitored for mortality each day. We banded chicks throughout our study to keep track of individual development. Chicks were considered fledged at 700 grams (about 20 days old), after which we saw little to no mortality. Clutch size among our sample had a similar distribution to that of the entire colony. We found that three-egg nests fledged 61% of their chicks (n=25), two-egg nests fledged 59% (n=11), and one-egg nests fledged 25% (n=4). In terms of hatch sequence, first- and second-hatched chicks fledged at a higher rate. 87% of first-hatched chicks fledged (n=32), 83% of second-hatched chicks fledged (n=31), and 66% of third-hatched chicks fledged (n=18). It is possible that the greater success of three egg nests might be associated with older and more experienced breeders. In order to facilitate long term assessment of age and breeding success we color-banded a large sample of our chicks. Our results suggest a productive year in terms of fledging success for the colony on Mount Desert Rock as a whole, and continuing this study would contribute to a greater understanding of the population dynamics of Herring Gulls in the Gulf of Maine."