Time to Fly
July 19, 2018
By Farallon Island seabird intern Sophie Bennett
As mid-July comes to Southeast Farallon Island, the chicks of the Island’s most dominant breeding seabird species, the Western Gull, are beginning to fledge. Over 8,500 pairs of Western Gulls breed across the island, which equates to >30% of the global population, making Southeast Farallon the most important site in the world for this species. While Western Gulls are considered ‘least concern’ by the IUCN (International Union for the Conservation of Nature), like many gull species they are threatened by overfishing, disease, increasing pressure from climate change, and oil spills. Hence, regular monitoring of this species is crucial in ensuring that we identify any fluctuations or declines in the population at an early stage.
Researchers from Point Blue have been monitoring the breeding biology and life history traits of this species since 1972. In particular, productivity data has facilitated Point Blue’s studies on how the breeding success of these gulls changes over time, and combined with climate data, can allow us to examine how the success of the birds may be affected by climate change. To determine this, intense observations are carried out in three monitoring plots from early April when breeding adults first began to establish their nesting territories, until mid-July when chicks begin to fledge.
Observations are made every three days to determine the band number of each bird in each pair, and to follow their progress through nest building, egg laying, and chick hatching. Then, when the chicks are roughly 20 days old they are fitted with leg bands to identify each individual. Gull chicks, however, also have the perfect camouflage for hiding among the boulders and scree in the colonies (some better than others).
This can mean that a proportion of chicks are not banded until the end of the breeding season, when a group effort is made by the Island’s research team to systematically work through each plot and ensure that each chick is entered into the study. Over the course of four afternoons this past week, over 300 chicks were carefully removed from their hiding places and fitted with one color and one metal band bearing a unique ID number, bringing the 2018 sample size to 500 chicks from 212 nests. The simple plastic color ring and leg combo identifies the year cohort of that bird (e.g. in 2018 all chicks were given a red color band over a metal band on the left leg). Using a different color band and leg combo each year allows researchers to quickly determine the age of each bird breeding in one of the monitoring plots. So, hopefully we’ll be seeing our 2018 chicks again in three years time when they return to breed as adults, adding to the depth of Point Blue’s longitudinal study on this impressive species.