Yellowhammer Emberzia citronella breeding distribution in relation to field boundary habitat and summer foraging resources

Background/Question/Methods

A reduction in the availability of suitable breeding and foraging habitats, such as field boundary hedges and invertebrate-rich field margins, are major overarching mechanisms driving farmland bird population declines in the UK.  Habitat diversity can be increased at both a field and farm scale via the design and management of appropriate Environmental Stewardship (ES) options. This study aims to determine the relative importance of both ES summer foraging habitats and hedge features in territory selection. The Yellowhammer Emberzia citronella is the focal species; it represents a priority species for conservation, having experienced rapid population declines due to the impacts of agricultural intensification. Within 10 sites, territory density was monitored along 4km of continuous hedgerow during the peak breeding season (May to July). Buffer zones (300m) were placed around each hedge replicate to account for yellowhammer foraging ranges. Permanent hedge features were used to assess the quality of field boundary vegetation at the end of the breeding season. A generalised linear mixed-effect (GLMM) model with binomial error distributions was considered to be the most appropriate modeling technique. It was constructed in order to determine whether features of territory sites differed from features of randomly selected sites.

Results/Conclusions

Over the 40 km of field boundary habitat surveyed a total of 75 yellowhammer territories were located. Preliminary data analysis has indicated that a number of variables are potentially influential in determining yellowhammer territory establishment: the presence of a song post within a territory, presence of an ideal hedge type, hedge being cut prior to the breeding season and the absence of grass as a habitat. Although the final model does not include the presence of an ES summer foraging habitat adjacent to the field boundary hedge or within their foraging range, this does not disprove the value of such habitat to this species. During territory selection, yellowhammer are unlikely to select a location based upon its potential as an invertebrate food source. Careful management and placement of foraging habitat is essential both at the farm and landscape level to ensure they are located adjacent to appropriate field boundary features. This would increase food provision for nestlings, addressing an underlying issue of the farmland bird decline, namely a reduction in food resources. Such considerations entail minimal cost at the planning stage, but will be highly valuable in the reversal of the decline of this species.