House Sparrow, by Edmund Fellowes / BTO

BTO House Sparrow Survey

House Sparrow, by Edmund Fellowes / BTO

House Sparrow Survey

House Sparrow populations have declined by nearly 71% since 1977. Although the reasons for the decline of House Sparrows in farmland habitats are well-understood, we still need to find out more about what has been happening to them in urban and suburban habitats. The BTO House Sparrow Survey provided a focus for this work.

BTO launched a detailed study into urban and suburban populations of House Sparrows in 2002, something made possible because of the generosity of those people contributing to the BTO House Sparrow Appeal. During 2003 and 2004, we carried out an extensive field survey, building upon previous work and examining the relationship between House Sparrow numbers of local habitat factors.

Possible reasons for House Sparrow decline

There are a number of possible reasons for the decline in House Sparrow populations within urbanised landscapes. These include:

  • a reduction in the availability of favoured food, either for adults or chicks or both,
  • increased levels of pollution, impacting productivity and/or survival,
  • the loss of suitable nesting sites,
  • the increased prevalence of disease,
  • increased levels of predation.

Some of these possible reasons have been investigated through other BTO work, most notably that looking at productivity and predation by a recovering Sparrowhawk population.

Methods

The work we carried out through the BTO House Sparrow Survey looked primarily at the question of habitat use, something that may reveal the role of food availability, predation and nesting opportunities. This work had two components: a questionnaire to highlight factors that might be worth more detailed study, and a field survey.

Questionnaire survey

The questionnaire was sent out in 2002 to all BTO Garden BirdWatchers and to any other people interested in contributing their observations on House Sparrows. The results from this questionnaire were useful in guiding the work that we went on to carry out through an extensive field study.

Field survey

The main thrust of the research was a survey of House Sparrow numbers and distribution in urban habitats, using a series of 1,500 survey squares visited by BTO volunteers.

Stratified random sampling techniques were employed to target sufficiently representative 1-km squares of urbanised habitat in the UK. Observers covering these squares were asked to walk along all pavements, paths and roads, into parks and allotments and along field boundaries with the aim of mapping the location of all House Sparrows detected. Chirping males, other males and females were each recorded separately. We were then able to determine and examine House Sparrow densities in each habitat type and to establish if they favoured some habitats over others.

Results – questionnaire survey

Preliminary results from the 11,269 useable returns were published as an insert to Bird Table 36.

The House Sparrow Questionnaire was divided into sections covering the various factors implicated in the decline of House Sparrows within urban and suburban habitats. Analyses carried out on the responses to questions within each of these sections revealed some interesting patterns.

Section One: Buildings

House Sparrows were more likely to occur at sites where there were gaps in the roof tiles. Modern tile designs do not have these gaps and House Sparrow nest sites may be lost where re-roofing takes place. Just over 25% of respondents reported that they had had such gaps blocked, many within the last 10 years, and 7% within the last year. The addition of loft insulation (90% of lofts were known to be insulated) may also influence House Sparrows.

Section Two: Gardens

Features within individual gardens were found to have little effect on whether or not House Sparrows were present in a garden, suggesting perhaps that it is the wider environment that will ultimately determine the presence or absence of House Sparrows. However, House Sparrows were more likely to be reported from suburban and urban gardens than rural ones, something that matches our understanding derived from other BTO surveys. Not surprisingly, House Sparrows were more likely to occur at those sites where food was provided year-round than at those where feeding only took place occasionally or not at all.

Section Three: The wider landscape

Some 16 variables describing the landscape outside a garden (such as the presence of allotments, arable land, schools, parks and waste ground) were significantly associated with the presence of House Sparrows in gardens. In broad terms, these associations suggest that House Sparrows occur with higher frequency where sites are close to farmland or where they are close to suburban features such as schools, parks or waste ground.

Section Four: Predators, competitors and mortality

There were a number of significant associations with other species, most of which were related to the habitat preferences of House Sparrows and the other species with which they were associated. It is interesting to note that House Sparrows were more likely to occur at those sites where Sparrowhawks were present, possibly suggesting that predation by these avian predators may not be as important as some authors have suggested.

Dead or dying House Sparrows were recorded at 6% of sites where this part of the questionnaire had been completed. The likelihood of finding a dead sparrow was similar across rural, suburban and urban gardens but there was an interesting association between dead sparrows and the volume of traffic recorded outside the house, with dead sparrows more likely to be found at sites near busier roads. There may be a reporting bias here, in that dead Sparrows may be easier to find at such sites than in other habitat or vegetation types.

Results – field survey

Residential areas, farm buildings and allotments were found to be key habitats for House Sparrows. The high densities in areas of private housing and the consistent effect of the area of housing confirms earlier studies showing the importance of this habitat. 

House Sparrows occurred at higher densities when gardens were present within residential habitat, something which suggests they may be important in providing feeding opportunities. Allotments were also found to be important foraging areas (being important generally, but less so for chirping males).

A further examination of these data, this time in respect of House Sparrow colonies, also showed a strong preference for houses with gardens. House Sparrow colonies were strongly associated with gardens, although in more rural areas, both allotments and greenspace were found to provide useful alternatives. Predators and roads were not avoided, something that may reflect their ubiquitous nature rather than any lack of a detrimental impact.

Outputs and outcomes

This study demonstrated the importance of the suburban landscape for House Sparrows: houses with gardens supported some of the highest densities, and the area of this habitat was the most consistent predictor of both breeding male House Sparrows and of all House Sparrows. This study is, to our knowledge, the first of its kind to demonstrate the importance of allotments to House Sparrows within urbanised environments. A BTO Research Report and a peer-reviewed paper were published as a result of this research.

Habitat use

Chamberlain et al. 2007. House Sparrow (Passer domesticus) habitat use in urbanised landscapes. Journal of Ornithology 148: 453–462.
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House Sparrow habitat preferences

Shaw et al. 2011. Spatial distribution and habitat preferences of the House Sparrow Passer domesticus in urbanised landscapes. BTO Research Report 599.
Access the report