Action: Use supplementary feeding to reduce predation
- A controlled cross-over experiment from the UK found that there was no difference in grouse adult survival or productivity when supplementary food was provided to hen harrier Circus cyaneus compared to in control areas.
- This study and another from the USA that used artificial nests found that nest predation rates were reduced in areas when supplementary food was provided to predators. A second study from the USA found no such effect.
If predators are dependent on threatened birds then providing supplementary food for the predators may remove some predation pressure whilst also supporting the predator population. However, it is also possible that providing supplementary food will allow an increase in the predator population and therefore increase predation pressure.
Studies describing the effects of supplementary food on fed populations are described in a separate chapter.
Supporting evidence from individual studies
A randomised, replicated and controlled experiment on eight Conservation Reserve Program sites in 1993-94 in Texas, USA (Vander Lee et al. 1999) found that the predation rates on artificial nests (containing three chicken Gallus gallus domesticus eggs with 1 nest/4.3 ha), were 45% lower in plots where supplementary predator food was provided (details of food provided are not given), compared to nests in control plots. A total of 1,735 artificial nests were used.
A controlled cross-over experiment, on moorland in southwest Scotland, UK, in 1998 and 1999 (Redpath et al. 2001) found that adult red grouse Lagopus lagopus scoticus survival was no higher in 13 hen harrier Circus cyaneus territories that were provided with a total of 256 kg of food in spring (over two years), than in control (unfed) territories (78% survival for 94 birds in fed areas vs. 74% of 97 in control areas). Supplementary feeding in the summer (when harriers are provisioning young) reduced the number of grouse chicks being brought to 14 fed broods, compared to ten unfed broods (an average of 0.5 chicks/100 hr, seven in total vs. 3.7 chicks/100 hr, 32 in total). However, there was no corresponding improvement in grouse breeding success in fed areas.
A replicated, randomised and controlled study in May-July 2000 in 28 longleaf pine Pinus palustris forest plots in Georgia, USA (Jones et al. 2002) found no differences in predation rates on artificial nests in areas provided with supplementary food (commercial dry dog food supplied ad libitum from feeders) and control areas (nest predation over one week: 62% for prey-supplemented areas vs. 55% for control plots; 770 nests tested). Birds and small mammals were responsible for more predation events in food-supplemented plots, whilst unknown predators were responsible for more in non-supplemented plots. Nests were placed on the ground and contained two Japanese quail Corturnix japonica eggs and one wax covered wooden egg. This study also evaluated the impact of prescribed burning on nest survival, discussed in ‘Use prescribed burning – pine forests’. There was no interaction between feeding and burning.
- Vander Lee B.A., Lutz R.S., Hansen L.A. & Matthews N.E. (1999) Effects of supplemental prey, vegetation, and time on success of artificial nests. The Journal of Wildlife Management, 63, 1299-1305
- Redpath S.M., Thirgood S.J. & Leckie F.M. (2001) Does supplementary feeding reduce predation of red grouse by hen harriers? Journal of Applied Ecology, 38, 1157-1168
- Jones D.D., Conner L.M., Warren R.J. & Ware G.O. (2002) The effect of supplemental prey and prescribed fire on success of artificial nests. The Journal of Wildlife Management, 66, 1112-1117