DISSERTATION:
Predictors of foraging behaviour in a small colony of Common Terns (Sterna hirundo) in Chichester Harbour 

By Holly Marshgreen
Project Supervisor Dr Bryony Tolhurst

in part fulfilment of requirements for the degree of

BSc (Hons) Ecology and Conservation

of the

University of Brighton 

ABSTRACT

Common terns (Sterna hirundo) are amber listed as species of conservation concern with the breeding population in Chichester Harbour having declined in sightings by the Chichester Conservancy. The current research project looks to utilise the context of the small breeding colony under conservation management to study aspects of foraging strategy by nesting terns as central place foragers. Field-based continuous scan sampling methods were used to assess the following hypotheses: 1) There is no significant effect of tide (high vs low) on foraging success (measured as returning to nest with food: yes or no). 2) There is so significant effect of direction of return from foraging trips on foraging success. 3) There is no significant effect of tide on direction of return from foraging trips on foraging success. 4) There is no significant interactive effect of tide and direction of return from foraging trips on foraging success. The results show that terns had preferences for foraging in southerly directions of Chichester Harbour and during low tide. Foraging success was predicted by tide, with foraging trips more successful during low tide. Tide also predicted direction of foraging trips. Results associated with tide should be taken with caution as they may be reflective of uneven sampling effort in the study. Direction had no effect on foraging success, nor did the interaction between tide and direction, suggesting that the terns in Chichester make optimal foraging choices with regard to site-specific optimality associated with tide. Wind was also a significant predictor or foraging success and was associated with optimal choices by terns for foraging closer to the nesting site during high wind conditions. Overall, the study agrees with the literature that the foraging behaviour of common terns is strongly associated with the tidal cycle and indicates that the foraging behaviour of the terns follows predictions of optimal foraging theory. The study is indicative of but limited in understanding exact patch choices and their use by terns, discriminating between self and offspring feeding, and variations in prey choices associated with the relationships found.

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