Seabird eggshell colouration analysed by digital photography: toward a new bioindicator

Supervisor: Ruedi Nager (University of Glasgow)
Environmental changes has great implication on population dynamic and organisms fitness. Nowadays anthropogenic actions lead to great variation affecting Earth climate and causing global, regional or local environmental perturbations. Anthropogenic influence on environment and ecosystems degradation urgently need to be assessed if we want to meliorate the situation. One way to do so is to use biomonitoring tools, which are organisms or groups that show measurable changes in consequence of an environmental shift. We can scale those changes to define a quality state for a chosen environment. Birds are great biomonitoring tools as they are heavily affected by changes of the environment conditions, pollution or dysfunctions coming from the lower level of their food web. Here we investigate the relationship between environmental factors, demographic trait or eggs pollution and eggshell colouration to determine whether egg coloration could be use as a bioindicator of environmental change, Across 9 different Herring Gull (Larus argentatus) colonies we used digital photography to capture and analyse eggshell colouration. Then we first correlated it to environmental factors (winter and pre laying temperature and precipitation) We tested if eggshell colouration would influence bird behaviour using demographic traits as variables (population growth, provisioning rate, chick weigh and colony productivity) and finally we tried to link on pollution content of great skua (Stercorarius skua) eggs and the colouration of their eggshell. We found a correlation between Herring Gull eggshell colouration and winter precipitation, population growth and provisioning rate, whereas we didn’t find a correlation between any of the pollutant tested. Regarding the results, in the case of Herring Gull we are certain that Eggshell colour variation could now be assessed in order to be used as a biomonitoring tool and that digital photography should be more used in this kind of work as its reliable, easy, accurate and a non destructive way of analyzing data.

Key words: Environmental changes, seabirds, eggshell colour, digital photography, biomonitoring