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

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 Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study.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

Evaluating UAV-based techniques to census an urban-nesting gull population on Canada's Pacific coast

The use of unmanned aerial vehicles, or drones, in wildlife monitoring has increased in recent years, particularly in hard-to-access habitats. We used fixed-wing and quadcopter drones to census an urban-nesting population of Glaucous-winged Gulls in Victoria, Canada. We conducted our study over 2 years and asked whether (i) drones represent a suitable survey method for rooftop-nesting gulls in our study region; and (ii) Victoria’s urban gull population had increased since the last survey >30 years earlier. Using orthomosaic imagery derived from drone overflights, we estimated at least a threefold increase over the 1986 count reported for the entire city (from 114 to 346 pairs), and an approximate tenfold increase in the number of gulls nesting in the downtown core. Drones proved to be an excellent platform from which to census rooftop-nesting birds: occupied nests were readily discernible in our digital imagery, and incubating birds were undisturbed by drones. This lack of disturbance may be due to Victoria’s location in an aerodrome; gulls experience dozens of floatplane and helicopter flights per day and are likely habituated to air traffic. Glaucous-winged Gulls have declined considerably at their natural island colonies in the region since the 1980s. Our results indicate that although urban roofs provide replacement nesting habitat for this species, local gull populations have not simply relocated en masse from islands to rooftops in the region.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Visual surveys provide baseline data on small vessel traffic and waterbirds in a coastal protected area

The coastal waters of southern British Columbia, Canada, encompass habitat of international conservation significance to coastal and marine birds, including sizeable areas designated in the early 1900s as Migratory Bird Sanctuaries (MBS) to protect overwintering waterfowl from hunting near urban centres. Two of these, Shoal Harbour (SHMBS) and Victoria Harbour (VHMBS), have seen significant marine infrastructure development in recent decades and experience considerable vessel traffic. Vessel-related stressors are known to affect waterbirds, but traffic characteristics in coastal urban areas are poorly understood for the smaller vessels not tracked by Automatic Identification Systems (AIS). We conducted a pilot study using shore-based observers to develop small-vessel baselines for the winter months, when regional waterbird numbers are highest. During our surveys we recorded considerable inter-site variability in vessel traffic characteristics, with one site (SHMBS) a source of nearly twice as many vessel transits as the other (VHMBS). Most recorded vessels were small watercraft (mean length 26 ± 17′, mode 18′), and vessels at the high-traffic site were both shorter and faster on average. One in six vessels were classified as ‘noisy’, of interest given that noise is an important component of vessel disturbance of waterbirds and other marine animals. Few vessels (7% of all recorded) were of the type required to carry AIS transponders, which highlights the monitoring gap created by using AIS-based approaches alone in nearshore waters, and allows for correction of AIS-derived vessel counts. Waterbird community composition also varied by locality, with one site dominated by gulls (Laridae), cormorants (Phalacrocoracidae), and seaducks (Tribe Mergini), and the other by gulls, cormorants, and alcids (Alcidae). Our results demonstrate that fine-scale local variability must be taken into account when managing for vessel traffic disturbance of waterbirds, particularly at sites of high human population density and increasing coastal development

A comparison of historical and contemporary reproductive traits in a declining population of Glaucous-winged Gulls (Larus glaucescens)

Understanding how organisms manage life history trade-offs under variable environmental conditions is an aim that is central to ecology. Comparing modern reproductive data with those from historical studies can increase understanding of the range of historical conditions that have acted on a given species over time. We use recent (2008-2010) and historical (1960s-1980s) reproductive data from a single study colony, Mandarte Island, Canada, to help understand the recent population declines experienced by the Glaucous-winged Gull (Larus glaucescens) in North America's Salish Sea, a highly urbanized area. Because this long-lived species has also undergone regional long-term declines in reproductive investment via decreasing egg and clutch size, we assessed whether modern reproductive outcomes were similarly affected. Although our statistical power was hampered by small sample sizes, it appears that hatching success declined over time, from 0.83 (1960s) and 0.76 (1970s-1980s) to 0.60 (2008-2010). An apparent decline in nesting success, from 0.63 (1962) to 0.52 (this study), was not statistically significant. Recent clutch sizes showed intra-seasonal declines, a pattern unchanged from historical trends. In contrast, egg mass historically was constant within a given nesting season, but recent egg-mass data show intra-seasonal declines. We conclude that most gulls currently breeding on Mandarte Island cannot attain historical levels of reproductive success — perhaps because of declining environmental quality in the form of reduced availability of high-quality fish prey — although some high-quality pairs in this population are still able to maximize reproductive output. Our study highlights the importance of long-term study systems for identifying consequences of large-scale ecosystem changes; however, methodological clarity is essential to ensure data comparability through time. Ultimately, further study is needed to identify the drivers of reproductive changes in this population, something that could be used to inform future management decisions

Boxplot summarizing daily counts of vessels (A) and raw daily count data (B) per survey site, Ogden Point (VHMBS), and Roberts Point (SHMBS), Greater Victoria, Canada.

Boxplot summarizing daily counts of vessels (A) and raw daily count data (B) per survey site, Ogden Point (VHMBS), and Roberts Point (SHMBS), Greater Victoria, Canada.</p

Distribution of daily vessel counts by day of week (weekend vs. weekday) and location, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Distribution of daily vessel counts by day of week (weekend vs. weekday) and location, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.</p

Frequency distribution of estimated maximum vessel speeds, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.

Frequency distribution of estimated maximum vessel speeds, Ogden Point (VHMBS) and Roberts Point (SHMBS), Greater Victoria, Canada.</p