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Year-round foraging strategies of far-ranging marine predators: flexibility, consistency and constraint

Prof Keith Hamer (SoB), Dr Chris Hassall (SoB)

Contact email: k.c.hamer@leeds.ac.uk

Recent studies of a wide range of species have revealed that during the breeding season, individual predators may employ consistent and distinctive strategies to locate and capture prey. For instance, during the chick-rearing period each year, individual gannets have marked and consistent differences in their foraging distances, locations, movement patterns at sea and marine habitat associations, all reflecting qualitative differences in the types of food resources that birds exploit when providing food  for their chicks (small planktivorous fish such as sandeels, fast mid-water predatory fish such mackerel and herring or material discarded from fishing vessels; Patrick et al. 2015; Wakefield et al. 2015). The constraints on parents with offspring to feed are, however, very different to those operating at other times of year, and it is not known how the foraging strategies of individuals vary across the annual cycle. Yet the degree of within- and between-season flexibility in foraging strategies has important implications both for understanding how such individual specializations are developed and maintained, and for predicting the likely population-level consequences of fisheries and climate related changes to marine ecosystems.

The development of miniaturised electronic logging and tracking devices now enables the detailed study of wide-scale movements of free-ranging wild animals, at costs compatible with obtaining appropriate sample sizes for statistical analysis. In particular, the use of GPS tags and time-depth recorders enables the study of individual movements and behaviour, including diving behaviour, with great precision and at high spatial and temporal resolution, while the use of miniature geolocators allows individuals to be tracked at lower resolution across the entire year. Over the past seven years (since 2010) we have established a study group of >300 breeding adult gannets, each individually colour-ringed for ease of identification, at the world’s largest gannet colony at Bass Rock, SE Scotland (Plate 1). Many of these birds are of known sex and have a known foraging strategy during chick-rearing, identified through analysis of both tracking and physiologically-derived dietary information (Wakefield et al. 2015). Crucially, we are also able to capture and track these birds almost as soon as they return to the colony each spring, providing the exciting prospect of tracking individual birds from pre-laying onwards each year. This project will now take advantage of this near-unique opportunity to examine the variation in individual foraging strategies and specialization across the entire annual cycle.

 

Figure 1: Colour-ringed gannet equipped with a tail-mounted GPS logger and attending its chick

Objectives

In this project, you will join a growing team of researchers at Leeds using tracking data to study the foraging and breeding behaviour of a wide range of taxa including dragonflies, birds and marine mammals (currently three PhD students studying gannets). In particular, this studentship will include:

  1. Quantifying how the foraging strategies of individual birds vary across the annual cycle in consecutive years;
  2. Examining the flexibility in foraging strategies at different times of year in the face of environmental change;
  3. Analysing the links between seasonal foraging strategies and key life-table variables including timing of breeding and reproductive success;;
  4. Assessing the benefits and importance of flexibility vs consistency in year-round foraging strategies.

Potential for high impact outcome

Impacts of anthropogenic changes to marine ecosystems on higher predators are an issue of pressing concern (e.g. Cleasby et al 2015a) and we are strongly placed to answer important unresolved questions about how individual foraging strategies are likely to drive population-level responses. This research thus has very strong potential to yield high-impact outputs, building on recent work within this research group (e.g. Wakefield et al 2013).

Training

You will work under the supervision of Professor Keith Hamer and Dr Chris Hassall within the wildlife telemetry group in the School of Biology.  This project provides a high level of specialist scientific training in: (i) capturing, handling and deploying a wide range of trackers and loggers on free-living wild birds; (ii) analysis and presentation of tracking data using a wide range of advanced geostatistical and related methods. You will also have access to a broad spectrum of training courses and workshops provided by the School of Biology and the NERC DTP, from numerical modelling and data analysis using R, through to effective use of social media, managing your degree and preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

References

Cleasby IR, Wakefield ED, Bearhop S, Bodey TW, Votier SC, Hamer KC (2015a) Three dimensional tracking of a wide-ranging marine predator: flight heights and vulnerability to offshore wind farms. Journal of Applied Ecology: in press

Cleasby I, Wakefield ED, Bodey TW, Davies RD, Partick S, Miller P, Newton J, Votier S, Bearhop S, Hamer KC (2015b) Sexual segregation in a wide-ranging marine predator is a consequence of habitat selection. Marine Ecology Progress Series 518: 1-12 (featured article)

Patrick SC, Bearhop S, Bodey TW, Grecian WJ, Hamer KC, Lee J, Votier SC (2015) Individual seabirds show consistent foraging strategies in response to predictable fisheries discards. Journal of Avian Biology 46: doi: 10.1111/jav.00660

Wakefield ED, Cleasby IR, Bearhop S, Bodey TW, Davies R, Miller PI, Newton J, Votier SC, Hamer KC (2015) Long-term individual foraging site fidelity – why some gannets don’t change their spots. Ecology 96: in press

Wakefield ED, Bodey TW, Bearhop S, Blackburn J, Davies R, Dwyer RG,  Green J, Grémillet D, Jackson AL, Jessopp MJ, Kane A, Langston RHW, Lescroël A, Murray S, Le Nuz M, Patrick SC, Péron C, Soanes L, Wanless S, Votier SC, Hamer KC (2013) Space partitioning without territoriality in gannets. Science 341: 68-70

Related undergraduate subjects:

  • Biology
  • Conservation biology
  • Ecology
  • Evolution
  • Natural sciences
  • Spatial ecology
  • Zoology