LOWLAND GAME - MAGPIE PREDATION ON SONGBIRDS |
TABLE 1
Predators identified predating artificial nests using either trail cameras at the nest or marks left on wax eggs Predator identified (%)
Year 2015 2016 Total Source of evidence (n)
Camera (5) Wax (28)
Camera (32) Wax (101) (166)
0.00 0.00 0.60 0.00 0.6
0.00 0.00 0.60 0.00 0.6
3.01 0.00 8.43 0.00 11.4
0.00 0.00 0.60 0.00 0.6
0.00 0.60 3.01 7.83 11.4
0.00 0.00 1.20 1.81 3
Jackdaw Jay Magpie Mammal Rodent Small bird
Unknown Medium bird
0.00 8.43 3.61
27.71 39.8
0.00 7.83 1.20
23.49 32.5
In total, 30% of nests were predated. We looked at the marks made on the
wax-filled eggs and at the photos from the trail cameras to identify the predators. Medium-sized birds were identified as predators of 45% of predated nests, small mammals of 11%, and in 39% of nests predators were unidentifiable. Corvids were the only medium-sized birds seen predating nests on camera (90% of these were magpies). We therefore believe that magpies were the most frequent predators of our artificial nests. There was a difference in corvid predation between magpie nest present (corvids suspected in 50% of cases) and magpie nest absent transects (corvids suspected in 39% of cases). We found that slightly more nests were predated in magpie nest present sites (32% of all nests) than in magpie nest absent sites (25%). This may indicate that terri- torial magpies are more likely to predate nests. As individual magpies were colour- ringed as part of this project, we could identify which magpies were predating nests. We found that the territory holders took the nests inside their territories. This difference in predation between magpie nest present and nest absent sites was greatest in July (just after the magpie young had fledged). In 2016 more nests were predated in open hedgerows compared with hedges with a denser structure. In denser hedges the nests may have been better concealed and harder to find. However, the biggest factor explaining difference in predation between nests was
the specific location of transects. Transects placed in some magpie territories suffered significantly heavier predation. This happened each time nests were placed in those territories. It may be that there was unexplained habitat variation which made some locations more susceptible to predation, but it seems possible that some individual magpies predate nests much more than others. This type of research may help inform more effective, better targeted, management
of corvid numbers, potentially benefiting Britain’s threatened songbirds. It may also show how management for game species can help prevent declines of other species.
BACKGROUND
The numbers of many farmland songbirds continue to fall, despite widespread conservation efforts. This decline has coincided with the growth in numbers of many songbird predators, including corvids such as magpies and crows. However, it is unclear whether or not predation by these greater numbers of corvids has contributed to the decline in songbird numbers. One reason for this unclear picture is the sugges- tion that some individual corvids take many eggs and nestlings from songbird nests whereas other individ- uals take very few or none. This project aimed to investigate whether individual corvids differ in the extent to which they predate songbirds.
Some individual magpies seem to predate nests much more than others. © Peter Thompson/GWCT
ACKNOWLEDGEMENTS
This work has been funded jointly by Songbird Survival and the University of Exeter, in collabora- tion with the GWCT. We would like to thank the Phillips and Glover families for allowing field work on their farms.
www.gwct.org.uk GAME & WILDLIFE REVIEW 2016 | 21
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