Assessing movements of Lesser Black-backed Gulls using GPS tracking devices in relation to the Walney Extension and Burbo Bank Extension Offshore Wind Farms

Abstract

  1. Offshore wind farm developments form a major part of the UK government’s commitment to obtain 15% of the UK’s energy needs from renewable sources by 2020. However, there is concern over the potential detrimental effects that offshore developments may have on bird populations.
  2. Many seabird species included as features of Special Protection Areas (SPAs) might potentially be affected by these developments, as their breeding season foraging ranges and migratory routes may overlap with wind farm sites. Any impacts may also vary between years as well as between construction and operational phases of wind farm developments.

  3. This study investigated the movements of Lesser Black‐backed Gulls (Larus fuscus) using birdborne telemetry devices over four breeding seasons (2016‐2019) and three non‐breeding seasons in relation to the development of the Walney Extension and Burbo Bank Extension offshore wind farms in northwest England. The overall objectives of this study were to assess:

    i. Foraging ranges and foraging distributions during four breeding seasons;

    ii. Connectivity with the Walney Extension and Burbo Bank Extension (and other) offshore wind farms during four breeding seasons;

    iii. The extent of area use of the Walney Extension and Burbo Bank Extension offshore wind farms through construction into operation;

    iv. Movements during three non‐breeding seasons;

    v. Behaviour within offshore wind farms and avoidance.

    This report covers objectives i‐iv, with additional outputs provided as scientific papers.

  4. Breeding individuals were tracked from two colonies in Cumbria, UK: South Walney, a large but declining coastal colony within the Morecambe Bay and Duddon Estuary SPA, and adjacent urban areas in Barrow‐in‐Furness. During 2016, 20 high temporal resolution University of Amsterdam (UvA) GPS devices were attached using permanent harnesses to adults trapped at the nest at South Walney. Data were also available for an additional 17 individuals (12 UvA devices and 5 Movetech Telemetry GPS‐GSM devices) tagged under a previous project at South Walney funded by the Department for Business, Energy and Industrial Strategy (BEIS) between 2014‐2016. A total of 32 Movetech devices were fitted to individuals at Barrow‐in‐Furness (2016 ‐ 10, 2017 ‐ 13, 2018 ‐ 9), those in 2017 and 2018 using temporary harnesses, designed to fall off birds after a period of time. The return rates and productivity of tagged individuals were compared with those of an untagged control group to assess potential detrimental effects of the devices.
  5. Over the 2016‐2019 breeding seasons, a total of 8,128 and 3,445 complete foraging trips were recorded for 36 and 29 of the individuals tracked from the South Walney and Barrow‐in‐ Furness colonies respectively. At South Walney, trip duration increased significantly from a mean (± SD) of 5 ± 4.9 to 7 ± 5.8 hours between the 2016 and 2019 seasons and correspondingly the mean foraging range per trip also increased significantly over time from 9.3 ± 10.2 to 14.2 ± 18.4 km. Similarly, data from Barrow‐in‐Furness indicated that foraging trip duration increased from 5.5 ± 5 to 7.8 ± 5.9 hours between 2016 and 2019, although this increase was not significant. Foraging ranges were also more similarly across years for birds tagged in Barrow and no significant changes over time were detected. However, significant increases in foraging range were only observed at the individual level for two of 13 individuals from South Walney tracked for at least three years.
  6. The telemetry data revealed predominantly terrestrial space use, including use of landfill, agricultural and urban habitats. The maximum time spent offshore across individuals in any given year was <5% for birds from South Walney and <3% for birds from Barrow‐in‐Furness. Overall, 20 individuals from South Walney and 12 individuals from Barrow showed connectivity with offshore wind farms, just six (five from South Walney and one from Barrowin‐ Furness) with the Walney Extension offshore wind farm and three (from South Walney) with the Burbo Bank Extension offshore wind farm. There was no significant change in the proportion of individuals showing connectivity with the offshore wind farms through the construction period.
  7. Utilisation distributions were calculated using a Time‐in‐Area approach and identified individual and colony scale core and total home ranges. Core home ranges were significantly larger for birds from the South Walney colony than for birds from Barrow‐in‐Furness. At the colony scale, the core home range also increased over time for birds from South Walney, with novel locations visited during 2019; however, no significant changes to the size of the core home range were detected at the individual scale. The core home ranges of only two individuals (from South Walney) overlapped with any offshore wind farms, while across birds, total home ranges showed less than 2% overlap. Across all years, for all birds pooled together, the time spent inside offshore wind farms was <1% of the overall time budget. The maximum spatial overlap with Walney Extension in any year was 0.22% of the total home range and there was no overlap with the Burbo Bank Extension site.
  8. Data were also available to assess non‐breeding season movements in 2016/17, 2017/18 and 2018/19. There was considerable variation in wintering locations between individuals. All individuals (except one wintering in Morocco during the 2016/17 period) from the South Walney colony remained in Europe with a tendency to winter in Northern Europe (such as UK and France) over the course of the study. One individual was recorded travelling to Denmark during the post‐breeding period but subsequently returned to the UK to winter. Although the sample size was smaller, individuals tracked from the Barrow colony were apparently more evenly spread across the various wintering destinations selected and travelled a greater maximum distance from the colony compared with birds from South Walney. There was a large amount of individual variation however, with the range for maximum distance travelled away from the colony during the non‐breeding season ranging from 85 to 2370 km for birds from South Walney and from 188 to—2473 km for birds from Barrow. Individual birds tended to be consistent between years in their selected wintering site.
  9. Conclusions: The majority of individuals tracked from both the South Walney and Barrow colonies made relatively limited use of the marine environment through the 2016‐19 breeding seasons and less than seen during the 2014‐2016 BEIS‐funded study at South Walney. Birds spent less than 1% of their time within offshore wind farms, with very limited connectivity with the Walney Extension and Burbo Bank Extension sites. Given this, it was not possible to formally assess changes in the use of these areas between the pre‐construction, construction and operational phases and it is difficult to infer whether their development had any detrimental effect to the colonies studied, but it is unlikely. Further, there was no evidence of broad scale changes in area use associated with the construction of these new wind farms. Nevertheless, while use of the Walney Extension and Burbo Bank Extension sites was limited, the study has provided valuable data, building on the previous BEIS project that has furthered understanding of birds’ use of offshore wind farms and their potential effects on birds providing benefit to the wider offshore wind industry.