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60% winter losses of grey partridges attributed to sparrow hawks

This winter scientists from the Game & Wildlife Conservation Trust are radio-tagging 100 wild grey partridges as well as sparrowhawks to discover the cause of heavy winter losses of this seriously threatened farmland bird on its Grey Partridge Recovery Project on farmland at Royston in Hertfordshire.

We radio-tagged 64 wild partridges located on one of the project’s participating farms in December 2008 and then located them at least once every week. Until the end of January none of the tagged birds had left the area and none of them died

The Game & Wildlife Conservation Trust’s five-year Grey Partridge Recovery Project has achieved an impressive increase in wild grey partridges with grey partridges peaking at 18.4 pairs per sq kilometre, which equates to a 640 per cent rise since intensive management started in 2002. However, despite this impressive result, a worrying issue was the problem of winter losses, which amounted to nearly 60 per cent per year over the duration of the project.

Dr Francis Buner a research scientists with the Game & Wildlife Conservation Trust is radio-tracking grey partridges this winter to investigate huge over-winter losses

To investigate the cause of these high losses and to thus develop an appropriate practical solution the Trust set up an initial study last winter. Dr Francis Buner, the project scientist explains, "We radio-tagged 64 wild partridges located on one of the project’s participating farms in December 2008 and then located them at least once every week. Until the end of January none of the tagged birds had left the area and none of them died, despite the obvious presence of sparrowhawk females hunting in the same area. However, towards the end of January when the coveys started to break up the situation started to change."

Monitoring the radio-tagged birds the research team located 28 radio tagged females, which were seen in pairs while eight of the 36 tagged cocks started to disperse in search of a mate. One moved 6km away but still failed to find a partner to produce a brood. However, all other dispersing male birds were predated, including the only dispersing hen. Apart from these nine birds all other radio-tagged individuals set up their breeding territories within a distance of 1km from where they were captured.

By the end of April, 24 birds (24 per cent) were killed by raptors and nine (15 per cent) were probably scavenged, most likely by foxes. Thus between February and April, 55 per cent of the population was killed by predators. Francis Buner says, "This is quite remarkable considering that none of these birds had died until the end of January and it is apparent that these losses began as soon as the coveys started to break up into pairs and move from the safety of the middle of the stubble fields towards the edges and along the hedges where it might be easier for predators to spot them."

The initial findings of this study confirm the importance of winter stubble and other widely used cover types such as rape and game cover strips. However, the time of year indicates that this cover provides less protection during the pre-laying period between February and May.

Francis Buner explains the importance of this study in helping to conserve vulnerable farmland bird species, "The research, which is continuing this winter, will involve radio-tracking partridges as well as sparrowhawks to monitor their hunting behaviour. This will help us to improve the design of winter escape cover for threatened species such as partridges and other birds during this vulnerable time. Everything we can do to help improve safety for these declining birds is a crucial factor in ensuring their future survival."