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The decline and fall of urban birds

Updated: Dec 4, 2023

Over the years we've seen a number of potential explanations for the decline in numbers of urban nesting bird species such as house sparrow, starling and, of course, the Swift. In this blog Tim Norriss of Hampshire Swifts asks why there is not a greater emphasis on looking at the availability of nest sites as a major factor behind these declines.

I was interested recently to read Daria Dadam’s article about House Sparrow decline (BTO Bird Table 99, Autumn 2019) and its potential link to the parasite Plasmodium relictum which causes avian malaria, but I was surprised that no mention was made of loss of nesting sites as being a major factor in that decline in the last 25 years. Back in 2004 the BTO House Sparrow Project reported on the findings of their survey from 11,269 useable returns that “House Sparrows were more likely to occur at sites where there were gaps in the roof tiles ….”. The report continues; “What is of concern is that just over a quarter of respondents reported that they had had such gaps blocked, many within the last ten years, and 7% within the last year.”

House Sparrow Wikimedia Commons, Photo: Mathias Appel

House Sparrow, Common Swift and Starling have all suffered major declines in urban areas. All have a strong association with nesting in man-made structures especially houses in urban and suburban settings. Surely the cause of their decline in these areas is written in plain sight in the final few words of the previous paragraph. Why would reading that not be a ‘light switch moment’ to any researcher on the subject? This loss of potential nesting sites caused by re-roofing and the removal of timber soffits and fascias with plastic (which does not move or rot and is often sealed with mastic) is inevitably having a major impact on these three species. This combined with the fact that modern construction methods, with the wholly desirable aim of reducing heat loss and carbon emissions during the cooler months, means that new-build homes provide few or no nesting opportunities.

The link between loss of nesting sites and the decline of Swifts has been known for many years to those increasing number of Swift groups and individuals around the country that are working hard to reverse their decline. Unfortunately, except in a small number of instances there has been no long- term monitoring of these projects with published data and this is a failing that is only just starting to be addressed. Winchester City Council (WCC) have been re-roofing their ageing housing stock in Hampshire. Some of the areas where these works are being carried out are areas with high populations of these three species and, working with Hampshire Swifts and local residents, WCC are now erecting one swift/sparrow box on each house that is being reroofed. Four out of 21 installed by spring 2019 have already been used by Swifts and most of the others were occupied by House Sparrows in 2019.

Two Zeist swift/house sparrow boxes Model 30 fitted under the eaves of a two-storey house

These birds would have been lost to the area had it not been for putting up nesting boxes. And as an aside, why do so many companies still promote and sell sparrow terraces? They are not cost effective for sparrows as only one chamber is used at a time, although the same pair usually fill the adjacent ones with nest material. Simply put, House Sparrows prefer Swift boxes.

In Southampton in the 1970’s and 1980’s Ron Cooke used to watch feeding flocks and movements of up to 500 Swifts in his area but these days a count of just 40 is notable. He used to see low screaming parties of up to 50 birds in his street where there were many breeding pairs. The decline continued here until there was just one pair left, on his neighbour’s house, in 2002. He started that year putting up nest boxes for them. Initial take-up was slow and it wasn’t until 2006 before a Swift took up residency. Fifteen years later in 2019 he now has 24 out of 29 boxes occupied and many chicks are being fledged. Once again there are large low- flying screaming parties and local residents stop open- mouthed to watch the amazing spectacle.

Ron Cooke with two swift boxes with ends removed to show swift nests inside.

Breeding Starlings have declined 87% between 1967 and 2015. Last year I read an article on Starlings (Birdwatch January 2019) and the research that was being done to investigate the causes of the decline. The author stated that at Hope farm RSPB he had “seen first-hand that Starlings are producing plenty of chicks. This means that the problem is occurring away from the species’ breeding grounds.” Now I’m no scientist or statistician but it seems odd to me to conclude that, based on evidence that they are producing lots of chicks at one place owned and managed by the RSPB, that there isn’t a problem at other breeding sites. The whole thrust of the research seems to be on studying where they go when not breeding. “As we think that the issues are occurring away from the breeding grounds, we first need to find out where starlings head to once the chicks have fledged and breeding is over. We believe that this is the key to understanding the decline.” No mention is made in the article of loss of breeding sites in buildings.

I’m not saying that there aren’t other factors involved in the decline of these three species as there undoubtedly are. But just possibly the more ‘techy’ aspects of such research are more appealing to researchers, or perhaps grant aid for them is easier to obtain, I don’t know. Don’t get me wrong, I don’t underestimate the value of technology for one moment. We learnt far more in one year from Swift A320 fitted with a geolocator in 2010 than we had discovered in many decades of ringing recoveries.

Research on other aspects must continue but are we failing to research the most obvious cause in the urban/suburban setting, namely loss of nesting sites in dwellings, and we are therefore doing these birds a huge disservice.

I believe that what is desperately needed is:

a) More research to quantify the huge scale of loss of nesting sites caused by reroofing and fascia/soffit replacement, and the effect that that has had and is having on the breeding populations of these three species.

b) More documented research on what successes can be achieved in countering these losses by putting up suitable boxes on existing homes and by building in suitable nest bricks into the structure of new homes.

c) More detailed research to show which boxes/bricks, and what entrance hole sizes work best for each species and in which situations.

d) Pressure on government to rapidly introduce legislation for swift/sparrow/starling boxes to be built into all new-build homes at an average of one per dwelling (as recommended by the RIBA).

So I appeal to all scientists working on these species – please give us the science that will do most to help their conservation in the urban setting.

Tim Norriss

Hampshire Swifts

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