The Use of Supplementary Food Sources by Bird Communities and Individuals.
Jack, Shona Lorraine
Thesis or dissertation
University of Exeter
Food availability has a considerable impact on the survival and reproductive output of individuals within a population. In order to support natural populations, supplementary food can be provided to natural populations with the aim of improving reproduction or survival of individuals. In a less scientific way, supplementary food is also provided to garden birds as a leisure pursuit. The provision of a supplementary food source to garden birds is a widespread and popular activity throughout the UK, but the full impact of this still requires extensive research. Relatively little is known about how a wide range of species use garden bird feeders, but there are also some gaps in our understanding of which individuals within a species are utilising a supplementary food source, particularly in relation to varying ambient temperature. In this thesis I explored whether there were differences in feeding behaviour between and within species at a supplementary food source with the overall aim of gaining understanding whether there were particular species or individuals which were more likely to utilise supplementary food, and whether this was influenced by the type of food provided and ambient In order to study behavioural differences between species, European Greenfinch (Chloris chloris) (hereafter Greenfinch), Common Chaffinch (Fringilla coelebs) (hereafter Chaffinch), European Robin (Erithacus rubecula) (hereafter Robin), Great Tit (Parus major), Eurasian Blue Tit (Cyanistes caeruleus) (hereafter Blue Tit) and Coal Tit (Periparus ater) were observed for a period of four months at feeding stations which provided two types of food. There were differences in feeding frequency and duration between species, and this was influenced by both body mass and ambient temperature. Larger species tended to spend longer at the feeders at lower temperatures, whereas smaller species such as Blue Tit and Coal Tit, spent longer at higher temperatures. Additionally, smaller species tended to visit more often. It was also conclusive that a food type with a shorter handling time was preferred overall. This reveals that garden bird feeders are utilised differently by species and therefore the impact of supplementary food may differ between species. Furthermore, ambient temperature should also be considered when exploring supplementary food use. To study within species-differences in feeding behaviour, Blue Tits were studied. Individuals were fitted with Passive Integrated Transponder (PIT) tags which allowed individuals to be logged at bird feeders which were modified to support Radio Frequency Identification (RFID) technology. Data were gathered to inform which individuals were using supplementary food sources, the time of day they visited and how often they visited. This revealed that there were differences in feeding frequency which can be partially explained by body mass, showing that lighter individuals visited more frequently. Despite predictions that individuals with greater access to supplementary food would have brighter feathers due to the increased availability of dietary carotenoids, the yellow chroma of the breast feathers did not reflect the use of a supplementary food source, but this would benefit from further investigation. The time of day also influenced which individuals were likely to be using a supplementary food source; in this study lighter individuals tended to visit more frequently in the early morning and midday than their heavier counterparts. This indicates that conspecifics do not use food sources equally and that lighter individuals are probably being supported by supplementary feeding to a greater extent. In conclusion, the continued study of garden birds and their behaviours at supplementary food sources is necessary to understand how a range of species are using an ever changing environment. Individual-level studies should be considered hand-in-hand with population level studies as both levels of detail are useful and necessary to gain a more comprehensive understanding of the impacts of supplementary feeding. With a more complete idea of how feeding may impact garden birds, it is possible to create more informed guidelines for the public who provide supplementary food. This could be beneficial for maintaining species numbers while continuing to engage the public with nature.
MbyRes in Biological Sciences