Project House sparrow (Passer domesticus)

The following group(s) participate in this project:

Lorna Shaw

The House Sparrow is a common and widespread species, and is one of the most well known birds to visit gardens in the UK. The species is particularly adapted to living alongside human habitation, and it is estimated that two thirds of the UK house sparrow population is found in urban areas.

However, house Sparrow populations have been declining in many urban areas since the mid 1980’s. In the UK this trend is particularly apparent in the South and East, which holds just over 50% of the UK sparrow population. The overall population of house sparrows is estimated to have declined from approximately 13 million pairs in the early 1970’s to around 6 million pairs by the late 1990’s. This decline is so abrupt that the latest review of birds in the UK placed the house sparrow on the red list reserved for species of special conservation concern.

House sparrows declined in the1920s due to a reduction in the use of horse drawn vehicles, and therefore the amount of spilt grain for the adult birds to feed on. House sparrows in rural areas also declined in the 1970’s as a result of changing farming practices, which again reduced the amount of food available. However, the recent decline of sparrows in urban areas is especially concerning, as there is no obvious reason why such a dramatic reduction should have occurred in such a short space of time.

A number of hypotheses have been suggested to explain the recent decline of urban house sparrows. These include: lack of food, particularly insects, which are fed to chicks in the breeding season; disease or competition; increased pollution; an increase in predation; and reduced availability of nest sites.

Increasing use of bird tables and feeders by homeowners may increase the likelihood of disease transmission between urban birds, particularly house sparrows. However, there have been no reports of diseased individuals in urban areas, as would be expected if an epidemic was causing a significant reduction in house sparrow numbers. Cat ownership has also increased, and cats are capable of having a substantial negative impact on house sparrow populations. However, this does not explain why sparrow populations have been affected in some areas more than others, or the suddenness of the decline. Avian predator numbers have also increased in many urban areas, but there is no reason why sparrows should be affected by predation more than other birds.

During the breeding season, house sparrows also require insect-based food. It has been suggested that components of leadfree petrol, may have a detrimental effect on insect populations. A lack of insects such as aphids could reduce the number of young birds that are produced each year, although again this would be expected to apply to other bird species as well.

The availability of nesting sites in urban areas may also have decreased in recent years. Modern buildings often have flatter, closer fitting roof tiles than older ones, and sofits and fascias on modern houses are now made of plastic rather than wood. As house sparrows often nest in roof cavities and the holes in wooden fascia boards, this change could have led to a substantial reduction in the nest sites available to them. In addition to this, traditional privet hedges and shrubs are being replaced by concrete driveways outside many houses. This not only reduces the potential number of nest sites available, but also the amount of food and cover available to the birds.

I hope to compare data on house sparrow abundances in the city of Bristol, UK, with data on houses and gardens in the area, obtained by surveying Bristol residents. The data will include information on house type and age, the type of roof tiles on the houses, and repairs and alterations made to the houses, and the presence of cats. I am also putting up nestboxes in different areas of the city, to see whether having more nest sites available might make a difference to the number of house sparrows in an area. By using this data, and information gathered from BTO (British Trust for Ornithlogy) bird surveys, I hope to identify factors which might be contributing to the decline of the urban house sparrow, and suggest measures which could reverse the trend.