UPLANDS - GREY PARTRIDGES |
13%
4%
4%
Figure 2 Diet of grey partridge chicks on upland farms in northern England from 14 broods Spiders and harvestmen 23% Bugs and leaf hoppers Sawfly larvae
31% Parasitic wasps
6%
Ants
Beetles 19%
rushes. Overall breeding productivity differed between years, with hens rearing 6.3 chicks per hen in 2010, 2.5 in 2011, but none in 2012. Breeding failure in 2012 was caused by a cold, wet June, which was the second wettest on record with more than double the average rainfall falling in the dale. The prolonged wet weather affected grey partridges throughout the breeding period. Nesting success was only 20% compared with 50% in 2010 and 45% in 2011. Similarly, hatching success was only 34% compared with 100% and 76% in the previous two years. The preferred nest sites of radio-tagged hens were in rushes. However, rushes flourish in the wetter areas leaving nest sites vulnerable to waterlogging. This was a particular problem in 2012 (n=10 hens) when three hens abandoned flooded clutches mid-way through incubation. Two hens were also found dead, one mid-incubation and the other shortly after hatching. Post-mortem examination showed no clear signs of worms or disease in either bird. Possibly the increased effort invested in incubation, having to spend longer on the nest and less time away feeding, may have resulted in poor condition and ultimately death. This was despite supplementary food made available from wheat-filled hoppers until mid-March. Only two hens hatched a clutch and both lost their chicks within the first week after hatching. The poor breeding observed in the small sample of radio-tagged hens was widespread in the study area, with our summer counts finding no chicks from 53 adult birds. Annual breeding productivity of grey partridges on upland farms in northern England has been monitored since 1989. On average the young-to-old ratio was 2.1 (range 0-4.6). Breeding productivity in 2012 was the lowest recorded during this period (see Figure 1). We collected chick droppings from eight pairs where we had the hen tagged and six where we had only the cock tagged. In 2010, we sampled broods every four days until they were four weeks old, collecting droppings from 15 brood roosts from the four pairs. In the following years, this was reduced to a minimum of one brood roost from each pair within two weeks of hatching, with 11 roosts from seven pairs collected in 2011 and three roosts from three pairs in 2012. For analysis, we pooled samples from each brood. Overall, beetles (31%), sawfly larvae (23%) and ants (19%) were the main chick prey items (see Figure 2). Only sawfly larvae in the diet varied between years, comprising 32% in 2010, 16% in 2011 and 9% in 2012. Sawfly larvae are a rich source of protein for growing chicks, and the low proportion in chick diet in 2012 suggests that the availability of this chick prey item was also affected by the inclement weather. In the uplands, grey partridge breeding productivity is strongly weather-dependent. On upland farms, rushes provide nesting cover but are vulnerable to waterlogging in wet summers. To maintain partridge numbers, it is important to pursue extensive management of grassland habitats, combined with predator control, so that when weather conditions are good, birds breed well.
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Supplementary food was provided for the grey partridges using feeders. Š Tom Hornby/GWCT
GAME & WILDLIFE REVIEW 2013 | 41