An evaluation of the temporal changes, distribution and abundance of the UK overwintering population of pink-footed geese (Anser brachyrhynchus) and an assessment of the North Norfolk population wintering foraging ranges

Stone, John Matthew

Abstract

Pink-footed geese (Anser brachyrhynchus) is a high arctic breeder, breeding in Greenland, Iceland and Svalbard. There are two distinct sub-populations, both of which migrate and winter in North West Europe. The largest of these populations’ breeds in Iceland and over- winters in the UK, accounting for c. 85% of the world population. In the UK the species is listed as amber in status in the BOCC, Birds of Conservation Concern 4 list. Since early records began in the middle of the last century their numbers have been shown to increase substantially, with a UK wintering population now in excess of half a million individuals.

This study reviews the latest population data available, based on data collated as part of the annual Icelandic breeding goose census (IGC) surveys, to further review the UK wintering distribution and abundance of pink-footed geese. As a species of conservation concern, pink- footed geese are monitored by statutory conservation bodies, who are required to assess any potential impact on the population size that land-use change may have. Concern exists within Natural England that potential loss of agricultural and foraging areas in proximity to known roosts of pink-footed geese, may result in a reduction of available foraging resources. Quantifying the impacts of any such loss is complex to model and requires an understanding of a number of factors, including the species energetic needs, daily food intake, resource availability, but also a better understanding of the species daily movements in relation to daily energetics and the ranges in which they forage. This study quantified the daily distances pink- footed geese travelled and their home range size during their wintering stay in North Norfolk.

A review of the annual records, supplied by the Wildfowl and Wetlands Trust (WWT), provided evidence of population growth and changes in the UK wintering distribution, with a focus on changes between 1990 and 2018 for which site-specific datum existed and has been analysed. These data provided strong evidence of population growth from an estimated 52,000 individuals in 1951, to an estimated UK wintering population size of 510,000 individuals in 2018. Evidence showed that there had been limited range expansion into new sites with relatively few new sites adopted in place of rising abundances at existing sites, in particular those in England.

Targeted capture and marking of pink-footed geese in North Norfolk, over the winters of 2017- 2018 and 2018-2019, enabled a total of 18 individuals to be fitted with GPS / GSM neck collars. The annual movements of these birds were summarised, along with a detailed examination and presentation of their home ranges and daily distances travelled within North Norfolk over the two winters. The mean daily distance travelled was calculated to be 12 km in year 1 of the study and 20.2 km in year 2 of the study. Correspondingly, the wintering ranges in North Norfolk also varied from 20.4 km2 to 100.8 km2 between years 1 and 2 respectively. The varied results between years demonstrated the species’ ability to be both able and willing to move substantial distances to find suitable food resources.

The complexities of understanding the factors affecting population growth were reviewed, as were the potential pressures arising due to the increased reliance on agricultural crops as a food resource across their range. Analysis of the availability and abundance of the harvested remains of sugar beet, determined by the crop coverage in the study area, provided insight into the number of pink-footed geese that can be sustained by this resource in North Norfolk.

Pink-footed geese populations overwintering in the UK have been shown to increase substantially, between 1990 – 2018, with a 3.1% annual compound growth rate. Tracking recorded the ability of individual pink-footed geese to move over large areas with a maximum range of 795.8 km2 recorded for one individual in the study area. In North Norfolk, given the substantial annual crop cover of sugar beet initial calculations suggest that the carrying capacity of North Norfolk for pink-footed geese has not been reached. The species population size also does not appear highly vulnerable to the loss of functionally linked land. Theoretically it was estimated that the annual crop of sugar beet in North Norfolk could support a wintering population in excess of 200,000 individuals. The geese studied appeared to be adaptable at seeking out and foraging on food resources and were shown to be highly mobile as demonstrated by their wide-ranging movements between North Norfolk and the Norfolk Broads and Hickling Broad.

Estimations of the wintering home range sizes and daily distances travelled by pink-footed geese within North Norfolk contribute valuable new data that can be applied and used in further assessments of the daily energetic requirements of the geese in Individual Based Models (IBM). Studies utilising IBM techniques are on-going and have been commissioned by Natural England, involving the WWT, Bournemouth University and Manchester University, and aim to help build applied tools capable of assisting in the assessment of the vulnerability of a number of swan and geese species in relation to the potential loss of functionally linked land.

Citation

Stone, J. M. (2020). An evaluation of the temporal changes, distribution and abundance of the UK overwintering population of pink-footed geese (Anser brachyrhynchus) and an assessment of the North Norfolk population wintering foraging ranges. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4223332

• Thesis Type: Thesis
• Deposit Date: Aug 10, 2021
• Publicly Available Date: Feb 23, 2023
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4223332
• Additional Information: Department of Biological & Marine Science, The University of Hull
• Award Date: Sep 1, 2020