A nuisance to commercial property owners, house sparrow populations thankfully seem to be on the decline. But why?
Historically, the house sparrow (Passer domesticus) would be named as one of the main pest birds in Australia and indeed globally. However, although it may still be one of the top five bird pests, its prevalence in Australia seems to be decreasing, a trend seen worldwide. And experts aren’t sure why…
The house sparrow is a small finch around 14-16 cm from head to tail. It is a sexually dimorphic grey-brown bird: the male has a black bib on its grey chest (dominant males have the largest bibs), whereas females have a uniform, grey chest.
The importation of English birds was a common practice of the first settlers, one of the activities of the Acclimatisation Society. They thought the sparrow would be an ideal candidate to help with insect control, even though they knew it would cause some crop damage. The house sparrow first arrived in Australia in 1862, but not from England as is generally believed. Whilst there were undoubtably arrivals from the UK, the documentation and genetic analysis actually confirm the first sparrow arrivals came from India.
Sparrows are commensal with humans. Their spread across Australia followed the spread of human dwellings and cropping areas and they quickly became common across much of the eastern seaboard. However, even now they haven’t become established in Western Australia – the Nullarbor has proved to be a significant barrier. In addition, the WA Government is taking preventative measures and eliminating start-up populations when they occur.
The efforts to keep the house sparrow out of Western Australia have certainly helped protect the agricultural industry. Sparrows are predominantly seed feeders, but will also consume flowers, buds, fruits and insects. With their long breeding season (July to April), pairs can raise up to three broods of between two and six chicks, meaning numbers can increase rapidly. In rural areas at the end of the breeding season they can congregate in flocks of several thousands. They commonly cause damage to fruit, vegetable, grain and oilseed crops in Australia and can consume stored grain and feed at piggeries and poultry farms.
In urban areas they have adapted their diet and have become quite adept scavengers. They are a nuisance in commercial buildings and homes with their nesting habits. They produce small, untidy nests under eaves and in gaps in roofing. Gutters and drains often get blocked from their nesting material. Their droppings are unsightly and can cause food contamination issues at commercial sites. But it’s their nesting habits that might give us a clue as to their decline.
House sparrow numbers have been in decline since the 1970s, not just in Australia but around the world. For example, the Garden Bird Survey in Canberra has recorded a reduction in abundance of 75% since the mid 1980s and its ranking has dropped from the second most abundance species to position 41 by 2015. In the 2018 Aussie Backyard Bird Count, the house sparrow only featured in the top three counted birds in Victoria, South Australia and Tasmania.
In Europe the decline has been attributed to changes in farming practices (less food available) and the urban decline attributed to a change in available nesting sites in buildings. This later point could be a contributing factor in Australia. Over the last few decades architecture has changed – corrugated roofing has become less popular, the size of eaves has decreased and air conditioning rather than natural ventilation has been the way to go. All of these architectural changes has meant there are fewer nesting places available. Coupled with the reducing size of the urban backyard, food availability has also decreased. Cities have become increasingly noisy, which birds don’t like, so the impact of stress cannot be excluded either. Although the house sparrow can be quite aggressive itself, increasing competition from the Indian myna, which nests in similar locations, may also be impacting numbers.
Maybe we have a case of unintentional integrated pest management here? By reducing nesting sites and food sources through changes in building design and modi cations in the urban environment, we have successfully ‘modified the pest environment’ making it more difficult for house sparrows to breed and survive.