Egg Production in a Coastal Seabird, the Glaucous-Winged Gull (Larus glaucescens), Declines during the Last Century

Abstract

Seabirds integrate information about oceanic ecosystems across time and space, and are considered sensitive indicators of marine conditions. To assess whether hypothesized long-term foodweb changes such as forage fish declines may be reflected in a consumer's life history traits over time, I used meta-regression to evaluate multi-decadal changes in aspects of egg production in the glaucous-winged gull (Larus glaucescens), a common coastal bird. Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study. Combined historical and modern data showed that gull egg size declined at an average of 0.04 cc y−1 from 1902 (108 y), equivalent to a decline of 5% of mean egg volume, while clutch size decreased over 48 y from a mean of 2.82 eggs per clutch in 1962 to 2.25 in 2009. There was a negative relationship between lay date and mean clutch size in a given year, with smaller clutches occurring in years where egg laying commenced later. Lay date itself advanced over time, with commencement of laying presently (2008–2010) 7 d later than in previous studies (1959–1986). This study demonstrates that glaucous-winged gull investment in egg production has declined significantly over the past ∼50–100 y, with such changes potentially contributing to recent population declines. Though gulls are generalist feeders that should readily be able to buffer themselves against food web changes, they are likely nutritionally constrained during the early breeding period, when egg production requirements are ideally met by consumption of high-quality prey such as forage fish. This study's results suggest a possible decline in the availability of such prey, and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas.

Effects of Sea-surface Temperature on Egg Size and Clutch Size in the Glaucous-winged Gull

“…This closely matched the extent of variation reported in the same species over a 50-year period at several breeding colonies in the Salish Sea (Blight 2011), and closely matched the between-year difference in clutch size at a single colony in Alaska (Murphy et al 1984). But contrary to prediction, there was no systematic effect of SST on the mean clutch size.…”

“…In mid-June, just prior to the start of hatching, all eggs in ~50 clutches were measured on a single day in a dense colony atop Puffin Rock, a small islet connected to Triangle Island at low tide. At this stage of their breeding season, most pairs will be incubating complete clutches (Blight 2011). Empty but wellformed nests were recorded, but excluded from the tally for clutch size.…”

“…Third, higher sea-surface temperatures in the early spring were linked to reduced clutch size in Black-tailed Gulls (L. crassirostris), because life-cycle events in the euphausiid prey taken by the gulls occurred too early in warm years (Tomita et al 2009). And finally, Blight (2011) proposed that long-term reductions in the forage fish base in the Salish Sea, a body of water shared by British Columbia and Washington State, had caused long-term declines in both egg size and clutch size in Glaucous-winged Gulls (L. glaucescens).…”

A three‐generational study of In ovo exposure to PBDE‐99 in the zebra finch

“…Blight [41] reported a significant decline in clutch size of the glaucous-winged gull (Larus glaucescens) at colonies in the Salish Sea region of the Pacific coast of Canada. Declines in the availability and quality of prey were thought to be the primary cause.…”

Long-term decline in egg size of Atlantic puffins Fratercula arctica is related to changes in forage fish stocks and climate conditions

“…The egg of the Atlantic puffin represents 14 to 16% of the female body mass and is among the largest relative to body mass among seabirds (Harris & Wanless 2011). As with any other income breeders, the female thus needs to allocate substantial resources to egg production, and will depend on sufficient intake of food resources to cover her energy and nutritional requirements during egg production (Nager 2006, Blight 2011. Because the conservation status of the Atlantic puffin is of concern and because there is a positive link between egg size and chick growth and survival (and potentially also future fecundity) (Krist 2011), it is also important to address the factors affecting the birds during their preparation for breeding.…”