DOI: 10.5061/dryad.v8j1144
title: Data from: Assessing factors associated with changes in the numbers of birds visiting gardens in winter: are predators partly to blame?

description: The factors governing the recent declines observed in many songbirds have
 received much research interest, in particular whether increases of avian
 predators have had a negative effect on any of their prey species. In
 addition, further discussion has centred on whether or not the choice of
 model formulation has an effect on model inference. The study goal was to
 evaluate changes in the number of 10 songbird species in relation to a
 suite of environmental covariates, testing for any evidence in support of
 a predator effect using multiple model formulations to check for
 consistency in the results. We compare two different approaches to the
 analysis of long-term garden bird monitoring data. The first approach
 models change in the prey species between 1970 and 2005 as a function of
 environmental covariates, including the abundance of an avian predator,
 whilst the second uses a change-change approach. Significant negative
 relationships were found between Eurasian sparrowhawk Accipiter nisus and
 three of the 10 species analysed, namely house sparrow Passer domesticus,
 starling Sturnus vulgaris and blue tit Cyanistes caeruleus. The results
 were consistent under both modelling approaches. It is not clear if this
 is a direct negative impact on the overall populations of these species or
 a behavioural response of the prey species to avoid feeding stations
 frequented by sparrowhawks (which may in turn have population
 consequences, by reducing available resources). The species showing
 evidence of negative effects of sparrowhawks were three of the four
 species most at risk to sparrowhawk predation according to their
 prevalence in the predator's diet. The associations could be causal
 in nature, although in practical terms the reduction in the rate of change
 in numbers visiting gardens accredited to sparrowhawks is relatively
 small, and so unlikely to be the main driver of observed population
 declines.
description: GBFS_cleaned_70_06Cleaned data from the British Trust for Ornithology's Garden Bird Feeding Survey from 1970/71 to 2005/06 on ten species of potential avian prey and Sparrowhawks. These data are the basis for all analyses in the accompanying manuscript. In addition to mean weekly maxima for each site, year and species, the dataset also includes the following variables: site reference number; year of observation (1=1970/71, 36=2005/06); whether site is rural or urban (rural = −1 and suburban/urban = +1); northing and easting of site; minimum temperature over observation months (not used in manuscript); and normalised number of days of ground frost over observation months. Variable 'ransite' determines the unique site numbers, accounting for sites that drop out and rejoin the survey in a later year. These are used in the specification of the random effect terms in the model. Species are: SPARR: Eurasian Sparrowhawk (Accipiter nisus); BLABI: Eurasian Blackbird (Turdus merula); BLUTI: Eurasian Blue Tit (Cyanistes caeruleus); COLDO: Eurasian collared dove (Streptopelia decaocto); CHAFF: Common chaffinch (Fringilla coelebs); COATI: Coal Tit (Periparus ater); GREFI: European greenfinch (Chloris chloris); GRETI: Great tit (Parus major); HOUSP: House sparrow (Passer domesticus); ROBIN: European robin (Erithacus rubecula); STARL: Common starling (Sturnus vulgaris).