ECOLOGY
OF
STEPPE BIRDS
WHITE STORK (Ciconia ciconia)
FORAGING BEHAVIOUR
Impacts of landfill use on the movement and behaviour of resident white storks: are white storks addicted to junk food?
The migratory patterns of animals are changing in response to global environmental change. Many previously wholly migratory bird species that used to winter in sub-Saharan Africa are forming resident populations in their southern European breeding grounds. Artificial food available from landfill sites may have facilitated the recent establishment (since the 1980s) of resident white storks populations in Iberia. Foraging on landfill is undoubtedly a major influence as 80 % of overwintering white storks in Iberia congregate near landfill sites and landfill forms 68.8 % of local diets in both adults and juveniles throughout the year. White storks also preferentially nest near landfill sites which has consequences for population distribution and range expansion patterns.
Main goals: we quantify the extent and consistency of landfill use by resident individuals during the breeding and non-breeding seasons and assess its influence on nest use, daily travel, foraging and non-landfill foraging ranges.
Resident white storks used landfill more during non-breeding (20.1 % ± 2.3 of foraging GPS fixes) than during breeding (14.9 % ± 2.2). During non-breeding a large percentage of GPS fixes occurred on the nest throughout the day (27 % ± 3.0 of fixes) in the majority of tagged storks. This study provides first confirmation of year-round nest use by resident white storks. The percentage of GPS fixes on the nest was not influenced by the distance between nest and the landfill site.
Left: White-storks feeding in a Portuguese landfill during the winter season.
Right: White-stork habitat and nest use during the non-breeding season (filled bars) and breeding (open bars) seasons. Asterisks indicate statistically significant differences.
Landfill attendance declined with increasing distance between nest and landfill in both seasons. Storks travelled up to 48.2 km to visit landfills during non-breeding and a maximum of 28.1 km during breeding, notably further than previous estimates. Storks nesting close to landfill sites used landfill more and had smaller foraging ranges in non-landfill habitat indicating higher reliance on landfill. The majority of non-landfill foraging occurred around the nest and long distance trips were made specifically to visit landfill.
Percentage of GPS fixes on landfill (excluding fixes in flight and within 20 m of the nest) in relation to distance from nest to the landfill site during (a) non-breeding and (b) breeding seasons. Total daily distance moved (derived from all available fixes, including flight and nest) in relation to distance between the nest and the landfill site during (c) non-breeding and (b) the breeding season. One individual was considered an outlier (unfilled square) and was excluded from the linear regressions.
More info:
Gilbert NI, Correia RA, Silva JP, Pacheco C, Catry I, Atkinson PW, Gill JA, Franco AMA (2016). Are white storks addicted to junk food? Impacts of landfill use on the movement and behaviour of resident white storks (Ciconia ciconia) from a partially migratory population. Movement Ecology 4: 7.