Coming upon a large colony can give the impression that house sparrows are very common birds, doing well in the city, with a strong presence. Unfortunately, this is not the case. Because of their gregarious and vocal nature, a colony will readily make its presence known, but as they shrink and disappear, whole neighbourhoods lose that familiar chirrup.
House sparrow decline
House sparrows are one of the most widely distributed birds in the world, but they have been disappearing across their natural range. In the UK, this has meant losing about 70% of our house sparrows across the country, though there is a great deal of variation in where and how this is happening. For instance, there have been multiple studies that have shown that rural, suburban, and urban populations have declined at different rates and face different challenges.
Rural and suburban populations
Rural populations of house sparrows have shown declines of about 47%. Several studies have shown that declines can be linked to changes is farming practices, including sealing grain silos and switching to more intensive agricultural practices. More recently, pesticides have been implicated in population declines: the loss of the invertebrate community has removed a valuable food source for chick-rearing birds.
Another practice that is thought to have affected house sparrows in rural communities is a change from autumn harvesting of cereal crops to spring harvesting. When the cereal crops are harvested in the autumn, the leftover stubble provides a valuable resource that the birds are able to exploit over the winter.
Suburban populations have been studied, as well, to understand what has caused declines. One study found low chick survival and low fledgling body mass when looking at nesting success along an urbanization gradient in England. The researchers attributed this to lack of invertebrates, which are essential to the chicks’ dietary needs, and high concentrations of pollution.
Urban populations
Puzzling out the factors behind urban house sparrow decline has proven more complicated. There are many factors that have been hypothesised to contribute to declines in urban areas, including pollution, increased predation, loss of habitat, and a lack of food availability for both adults and chicks. There is no definitive conclusion as to what the key issues are yet.
Several cities have seen drastic declines, including local extinctions in cities like London. While the Glasgow House Sparrow Project focuses on house sparrows in Glasgow, these declines have been recorded in cities including Brighton, London, Leicester, Edinburgh, and Glasgow. From 1969 to 1998, the Glaswegian population dropped 98%. Scottish numbers have seemed to stabilised, but with such sharp decreases—especially when concentrated in urban centres—the sparrows have a long way to go for recovery.
Official status
Although house sparrows have not been listed as a species of concern by the IUCN, there is a clear declining trend across their range. These declines in Europe have led to the sparrows being listed as Near-threatened in Germany and being Red-listed in the UK since 2002. Species are assessed for the UK Red List for birds through a combination of international conservation status, population trends, historical and current ranges, and localisation using data collected from surveys and national monitoring schemes (such as the Breeding Bird Survey).
Current research
The Glasgow House Sparrow Project aims to understand what the limiting factors of this urban species are and to test theoretical models that predict how changes in garden structure can support and boost sparrow populations.
From the surveys conducted by our volunteers, we have been able to look at trends in breeding success for our 121 known colonies. To do this, we analyse the average number of house sparrows per garden over the breeding season. What we expect to find is that the average number of birds increases from the first survey in April/May to the last survey in August/September, when all the chicks should have fledged and become independent.
During the 2014 breeding season, this is exactly what the data showed—an average garden number increasing from 2.7 birds to 4.2: overall, chicks were successfully reared and joined the flocks. However, in 2015, the average number of birds recorded dropped from 2.5 to 2.1 birds per garden. Conditions in 2015 were not conducive to rearing young, so we can start to investigate what affected the birds during this period. In 2017, we found an average colony size of seven pairs that produced an average of 9.5 fledglings.
