Sparrowhawk

Sparrowhawk winter distribution between 2007/8 and 2010/11
(Click to enlarge)

Predators have been the focus of a lot of comment and Sparrowhawks, which visit many garden feeding stations, come in for a lot of blame, especially when the recolonisation of areas coincides with the declines we have seen in some passerine populations.

Sparrowhawks can now be seen in almost every part of Britain & Ireland , as shown in the winter map alongside. Most birds are sedentary but there is a relatively small influx of birds from Scandinavia, as shown in the recovery map within the on-line ringing report. There are gaps only in the most mountainous of areas, although the species is quite thinly distributed throughout much of upland Scotland and Wales and the northern hills of England.

Sparrowhawk winter distribution change btween 1981-84 and 2007-11
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The changes since the 1980s are obvious. The second map illustrates this clearly, with gaps being filled in eastern England in particular. The arrival of Sparrowhawks in some of the most densely-populated areas around London may well have contributed to the worry that the species could in part be responsible for the declines in some species of passerine. There is evidence to suggest that the rate of decline of Bullfinch, Tree Sparrow and Reed Bunting have been greatest at sites where Sparrowhawks have increased. However, a number of other factors have been implicated in the declines of these species, particularly relating to changes in farmland, suggesting that a single driver of population decline is unlikely. Locally, Sparrowhawks home in on concentrations of birds, as seen at feeding stations, but there has been little change in the encounter rate in gardens over the period of Garden Bird Watch (1995-present), even in eastern England. 

Distribution changes between the two winter atlases (to left): blue upward-pointing triangles indicate gains and black downward-pointing triangles are losses.

Sparrowhawk breeding distribution change
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As winter turns to spring, male Sparrowhawks become more obvious, as they declare their ownership of territories in gliding, looping aerial display flights. It’s always worth scanning the sky on sunny, still March afternoons. By May, Sparrowhawks are much more secretive, as can be seen from the BirdTrack reporting rate.

The breeding distribution change map, showing changes over the course of the three breeding-season atlases, confirms that recent increases in the east are just the final phase of a recovery that was clearly under way at the time of the publication of the New Atlas of Breeding Birds, in 1993. (Someone should have realised that this would not be ‘new’ for ever and thought of a better title!)

The change in breeding distribution (to right): red upward-pointing triangles are new gains, open triangles are gains between the first two breeding atlases and solid salmon areas have been occupied since at least 1968-72. There have been some losses, indicated by downward-pointing triangles.

Sparrowhawk relative abundance change
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As well as changes in distribution, this time we can also look at changes in relative abundance, using breeding-season information collected during timed counts. For some species, this sort of story can already be told using information from the annual BTO/JNCC/RSPB Breeding Bird Survey but atlas data are more robust for a larger set of species, simply because more squares are visited. For Sparrowhawk , BBS change figures are only published for a small number of regions. In the latest report, covering the period 1995-2010, a decline of 40% is reported for NW England and of 13% for SE England, with increases of 9% and 1% for East and SW England, respectively. No figures can be provided for Wales, Scotland or Northern Ireland, simply because too few Sparrowhawks are encountered on the squares currently surveyed.

Unsurprisingly, when one looks at the latest atlas maps for the east – the area that has most recently been recolonised – there are plenty of warm pink squares, indicating increases relative to low starting points. More interestingly, there are also some clear areas of decline, particularly in SW Wales and NW England. It will be fascinating to look at the distribution of Goshawk when the book appears, bearing in mind the competition between the two species. See VAN BEUSEKOM, C.F. 1972. Ecological isolation with respect to food between sparrowhawk and goshawk. Ardea 60: 72—96.

Change in abundance (above) has been calculated using the timed counts from the breeding seasons of 1988-91 and 2008-11. Deeper pinks show increases and darker browns show decreases. Gaps indicate areas where change was minimal, or the species does not occur in sufficient numbers.

by Graham Appleton

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