Figure 1.
Land cover types include water (blue), urban areas (gray), intensive cultures (mango), extensive cultures (purple), unidentified cultures (rose), lawns (olive green), and woodlots (dark green). Numbers in squares indicate landfill locations (1- Lachute, 2- Ste-Sophie, 3- Terrebonne, 4- St-Thomas), red triangles indicate transhipment site locations, and the bird pictogram indicates the location of the Deslauriers Island Ring-billed gull colony.
Table 1.
Cover percentage of eight habitat types available in the foraging range of 109 Ring-billed gulls breeding on Deslauriers Island established as the minimum convex polygon calculated with all gull locations and mean cover percentage (±1 SD) in movement (residence time <100 s) and foraging (residence time ≥100 s) patches (200-m radius), 2009–2010.
Table 2.
Summary of a priori models based on resource selection functions that predict the probability that a breeding Ring-billed gull will forage in a patch (200-m radius) for a 100-s residence time threshold.
Figure 2.
The effect of distance on habitat selection by foraging Ring-billed gulls.
Number of foraging patches within 1-km concentric bands from the colony (a). Mean (±1 SD) proportion of urban areas (b), waterbodies (c), lawns (d), intensive cultures (e), and extensive cultures (f) in foraging (blue) and movement patches (red) in relation with the distance from the colony.
Table 3.
Mixed-effects averaged logit resource selection functions quantifying the probability that a breeding Ring-billed gull forage in a patch.
Figure 3.
Use of agricultural lands by breeding Ring-billed gulls.
Number of gulls and of tractors observed during surveys on the North and South shores of the St. Lawrence River, 2010.
Figure 4.
Use of landfills and transhipment sites by Ring-billed gulls.
Mean (±1 SD) proportion of Ring-billed gull locations at landfills and transhipment sites in foraging patches within 1-km concentric bands located at different distances from the colony. All landfills and open transhipment sites were visited by at least one tagged individual. Some sites encompassed more than one band.
Figure 5.
Diet of chicks and breeding adults of Ring-billed gulls.
Diet of Ring-billed gull chicks (boli) and breeding adults (boli and stomach contents) at the Deslauriers Island colony, 2009–2010, expressed as the percentage of occurrence of each food category (a) and the proportion based on dry mass of each food category when present (b). Boxplots provide the first (bottom line), second (black midline) and third (top line) quartiles; whiskers extend to observations found up to 1.5 times the interquartile range; observations outside this range are indicated by empty dots.
Table 4.
Mean dry mass (g ± SD) and mean energy value (kJ) of nine food items gathered by sub-adult and adult Ring-billed Gulls in three habitat types (N = number of birds with food items present in their stomach).