Changes in resource utilisation in declining gull populations

Nager & Rona McGill (SUREC)

NERC 'Grant-in-Kind'

The project's objective is to investigate whether observed changes in abundance of gull population are associated with temporal changes in the birds' resource utilization, possibly brought about by changes in the marine environment.
Working hypotheses to be addressed by the stable isotope analysis:
(1) Do changes in population abundance coincide with changes of the birds' resource utilisation?
(2) Is the variation in patterns in populations change between regions and species associated with variation in resource utilisation between regions and species?
(3) Is there intra-annual variation in resource utilisation and is this associated with changes in population abundance?

The stable isotope analysis of gull feathers of historic museum specimens as well as contemporary birds in the field can provide valuable information on the variation in foraging ecology and resource utilization of the gulls within a year as well as between years: stable carbon isotopes can provide information on benthic vs. pelagic and (or) marine vs. terrestrial feeding location and stable nitrogen isotopes information on trophic level. Additional stable isotope data from different potential prey items collected in the same region as the gulls will allow us to gain a better understanding of the birds' diet.

Finally, analysis of stable isotopes of feathers of historic and contemporary Common Eiders, a specialized mussel forager in coastal marine habitat will allow as to track changes in the forage base in some of the regions where we assessed the gulls’ resource utilisation. Together, this will provide us a better understanding of the gulls foraging ecology and pattern of resource utilisation reflecting changes in the coastal habitat in which the gulls live.