Citation
Clewley, G.D., Scragg, E.S., Thaxter, C.B. & Burton, N.H.K. 2017. Assessing the habitat use of Lesser Black-backed Gulls (Larus fuscus) From the Bowland Fells SPA. BTO Research Report 694: British Trust for Ornithology, Thetford
Overview
This report investigates the habitat use of Lesser Black-backed Gulls Larus fuscus breeding within the Bowland Fells SPA.
In more detail
- Findings from a GPS tracking study of Lesser Black-backed Gulls breeding in the Bowland Fells Special Protection Area (SPA) are presented in this report. The aims were to i) describe the home range of Lesser Black-backed Gulls during the breeding season and the spatial overlap with the SPA; ii) quantify the maximum foraging distances; and iii) assess the time spent by individual birds inside the SPA.
- Twelve GPS-GSM tags (Movetech Telemetry) were deployed during 2015 but unfortunately subsequent performance was not as expected and the work was repeated in 2016, with an additional sample of tags also deployed, resulting in 22 deployments across two sites (Tarnbrook Fell and Langden Head). In total, data from 20 individuals were considered suitable for analysis (one individual from both years). Data were only analysed up until the last date that each individual was present in the SPA.
- Home range analyses were carried out using time invariant kernel density estimate methods and were performed separately for day and night periods due to different GPS sampling rates. GPS fixes obtained from inside the colony boundary were excluded from home range analyses to give a more accurate reflection of foraging space use. Foraging distance was the maximum distance away from the nest and was calculated for each discrete trip away from the colony.
- Tracked Lesser Black-backed Gulls from the Bowland Fells SPA likely foraged almost exclusively in terrestrial habitats. There was some individual variation in the extent and pattern of their foraging ranges, but generally the degree of overlap with the SPA was low for most birds and in total was <10%. The most frequently visited habitats tended to be urban areas and landfill sites to the south and southwest of the SPA but regular use of nearby agricultural land was also seen. Unfortunately it was not possible to tag an equal sample from each colony, and the sample from Tarnbrook was much smaller, but it appears that birds from each colony are highly segregated inside the SPA and may even have different foraging site preferences outside the SPA boundary.
- Birds spent only a small proportion of their time - on average 12% - within the SPA during the periods that they were away from the colony. Total time within the SPA was closer to 50% when GPS data recorded from inside the colony boundary were also included, as would be expected from sharing of nest attendance by pairs during incubation and chick rearing. It was not possible to precisely know the behaviour of the Lesser Black-backed Gulls from the tracking data; however, data on estimated ground speed suggest that most fixes within the SPA but outside the colony were obtained during active flight. However, there is low certainty around this without further analyses.
- While the SPA provides an important breeding site for the Lesser Black-backed Gulls, the tracking data indicate that it does not currently provide important foraging sites and that the gulls travel daily to other sites outside the SPA. It is likely that a small proportion of individuals spent relatively more time within the SPA and make greater use of nearby agricultural land but at present it seems profitable for most birds to continue to travel relatively long distances to forage around human occupied environments, predominantly urban areas, but also farmland.
