Friday, 5 October 2012

Lesser Black-backed Gull Census 2012

Thanks to a hard working group of volunteers the Lesser Black Backed Gulls are surveyed each year. The results show that there are only 8643 Apparently Occupied Nests (AONs) this season (2012) - Which has followed a decline since the 1990s (20200 AONs). This may reflect a reduction in food source available from mainland sources (rubbish tips are now under stricter regulations to cover up exposed rubbish - a food source for Gulls and some rubbish tips have also employed scaring tactics to reduce "pests"). There has also been a reduction in the availability of fishing discards.
LBBG numbers on Skomer 1960-2012 (Source: Skomer Seabird Report)

Comparing this with the national trends we see that this is not a localised trend: The current UK estimate for Lesser Black-backed Gulls is 112,000 AONs It could be a case that the UK population is returning to more "normal" levels after an artificially high food availability (rubbish/fishery discards)

 Trend in UK abundance index (solid line) of lesser black-backed gull 1986-2011 with 95% confidence limits (dotted lines). Based on SMP data;
Source: JNCC "Latest Population trends"

Skomer has seen adult survival (number of adults returning year after year) reduce between 1993 and 2002 matching a decline in population - suggesting that the energy cost of reproduction is causing adults to not return to the colony. Skomer is the only location in the UK where adult survival rates are monitored so to what extent the changes in adult survival have effected the UK population as a whole is unknown. 
 Adult Survival of LBBGs on Skomer (Source: Skomer Seabird Report)

Lesser Black-backed Gulls are an interesting species and one which Skomer Island is providing a safe breeding habitat.

Thanks for all the volunteers (over all the years) who help with the Gull counts - without whom the task would be impossible. 

Chris Taylor
Skomer Warden.

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