Combined usage of stable isotopes and GPS-based telemetry to understand the feeding ecology of an omnivorous bird, the Ring-billed Gull (Larus delawarensis)

Abstract

The aim of the present study was to investigate the feeding ecology of an omnivorous bird, the Ring-billed Gull (Larus delawarensis Ord, 1815), breeding in a highly urbanized and heterogeneous landscape (Montréal area, Quebec, Canada). We used gastrointestinal (G.I.) tract content analysis, GPS-based tracking information, and stable isotope profiles of carbon (δ13C) and nitrogen (δ15N) in selected tissues and major food items. Based on GPS tracking data (1–3 days), Ring-billed Gulls were categorized according to their use of three main foraging habitats: agricultural, St. Lawrence River, and anthropogenic (comprising urban areas, landfills, and wastewater treatment plant basins). Ring-billed Gulls that foraged predominantly in anthropogenic habitats exhibited significantly lower δ15N in blood cells and higher total C to N ratios (C:N) in liver. These lower δ15N and higher C:N ratios were characteristic of profiles determined in food items consumed by Ring-billed Gulls at these urbanized sites (e.g., processed foods). The strong positive correlations between δ13C and δ15N in Ring-billed Gull tissues (plasma, blood cells, and liver) that differed in isotopic turnover times, as well as the strong positive correlations in both δ13C and δ15N between tissue pairs, indicated that Ring-billed Gulls exhibited conserved dietary habits throughout the nesting period. This study demonstrates that combining conventional dietary examination, tissue stable isotope analysis, and fine-scale GPS tracking information may improve our understanding of the large intrapopulation variations in foraging behaviour (and isotopic profiles) commonly observed in omnivorous birds.

Effect of habitat use and diet on the gastrointestinal parasite community of an avian omnivore from an urbanized environment

“…Carbon and nitrogen stable isotope analysis in Ring-billed Gull liver was performed at the Centre de recherche en géochimie et géodynamique (GEOTOP), Université du Québec à Montréal (Montréal, Quebec, Canada) following methods described by Caron-Beaudoin et al (2013). Isotopic measurements were obtained using a continuous-flow isotope-ratio mass spectrometer (Micromass Isoprime, Cheadle, UK) and an elementary analyzer (NC1500; Carlo Erba, Milan, Italy).…”

“…However, these biochemical tracers rarely provide information on the biological origin of food and prey items. Recently, Caron-Beaudoin et al (2013) used a combination of stable isotopes and high-resolution global positioning system (GPS) based tracking to investigate habitat use and foraging behavior of Ring-billed Gulls (Larus delawarensis Ord, 1815) breeding in the greater Montréal area (Quebec, Canada), which has a population of over 3.6 million inhabitants. In this study, ␦ 15 N was found to be lower in tissues of individual gulls that foraged predominantly in anthropogenic-related areas (city, landfills, and wastewater treatment ponds).…”

Stable isotopes reveal links between human food inputs and urban ant diets

“…13 C values can serve as a metric to indicate how animals are using human food sources in cities and to what extent they rely on these resources across their range [9,20].…”

Landfill Use by Bald Eagles in the Chesapeake Bay Region

“…They may also prey upon smaller avian species, particularly Larus spp. (e.g., Murie 1940, Todd et al 1982, Buchanan and Watson 2010, Hayward et al 2010) that frequent these sites (Burger and Gochfeld 1983, Belant et al 1995, Caron-Beaudoin et al 2013.…”