Year-round use of anthropogenic food sources in human modified landscapes by adult and young Kelp Gulls

FRIXIONE, MARTÍN G.; LISNIZER, NORA; YORIO, PABLO

Food Webs

Elsevier

Año: 2023 vol. 35

2352-2496

Predictable anthropogenic food subsidies attract species with generalist andopportunistic feeding habits, often resulting in conflicts with human populations. Weassessed the spatio-temporal distribution and abundance of Kelp Gulls (Larusdominicanus) during the annual cycle at anthropogenic food sources located along 70km of urban and agricultural-livestock landscapes in the lower Chubut River valley,Argentina. We quantified the seasonal abundance of adult and young Kelp Gullsthrough monthly counts from July 2021 to June 2022 at six identified anthropogenicfood sources, complemented with strip transect sampling along cultivated land andcattle grazing areas. In addition, we analysed the differential use of waste types by adultand young Kelp Gulls at a mixed livestock waste dump where different food remains(cattle remains, poultry remains and urban waste) are disposed in independent pits. Thetotal number of Kelp Gulls counted each month along the river valley was variable, witha mean number of 2,585 ± 822.7 individuals (range = 276 in December and 8,958 inJune). The highest gull abundance was recorded at a pig farm (mean = 1784.5 ± 640.1individuals). The transect survey showed a relatively low use by gulls of the cultivatedland and cattle grazing areas, with a mean of 29.7 ± 11.2 individuals recorded persurvey (range = 0-96). Kelp Gull abundance patterns recorded in the river valleythroughout the annual cycle evidenced a contrasting seasonal use of anthropogenic foodsources between the breeding and non-breeding seasons, being clearly less abundantduring the former, when gulls move to their main breeding grounds and adjacent marinehabitats in coastal Chubut. At the mixed livestock waste dump, Kelp Gull numbersvaried among the three waste patches, with higher numbers and a significantly higherproportion of adults at the cattle remains pit. This study shows the high trophicplasticity of Kelp Gulls and their use of alternative foraging habitats. Further monitoringand evaluations of the use by Kelp Gulls of predictable anthropogenic food sourcesalong the Chubut River valley, particularly those related to the growing livestockproduction, are needed to support management decisions.