Provide supplementary food for woodpeckers to increase adult survival
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 3
Background information and definitions
Well-fed animals are likely to be in better physical condition than those with too little food: having greater muscle mass and larger fat supplies to help them survive lean periods. However, it is worth noting that species that forage in groups can have dominance hierarchies, which alter the relationship between weight and fitness. For example Gentle and Gosler (2001) found that, amongst great tits Parus major in Oxfordshire, England, more dominant birds had a lower mass than subdominants, particularly when perceived predation risk was high. Birds with lower masses are better able to take off and therefore escape predators than heavier birds (Krams 2002). However, because of their dominance, they were able to usurp other birds from food resources when hungry. Care should therefore be taken when interpreting results which do not directly examine survival.
Krams, I. (2002) Mass-dependent take-off ability in wintering great tits (Parus major): comparison of top-ranked adult males and subordinate juvenile females. Behavioral Ecology and Sociobiology, 51, 345–349.
Gentle, L.K. & Gosler, A.G. (2001) Fat reserves and perceived predation risk in the great tit, Parus major. Proceedings of the Royal Society of London. Series B: Biological Sciences, 268, 487.
Supporting evidence from individual studies
A replicated, controlled study in deciduous forests in Ohio, USA, in the winter of 1988-9 (Grubb & Cimprich 1990) found that 12 female downy woodpeckers Picoides pubescens grew longer feathers and grew them faster (a proxy for nutritional condition) when supplied with sunflower seeds and suet in excess, compared to six unfed control females. There were no such differences in eight fed and nine control male woodpeckers. The impact on three songbird species is discussed in ‘Provide supplementary food to increase adult survival – Songbirds’.Study and other actions tested
A replicated, controlled study in 54 woodlots and riparian corridors in an agricultural landscape in Ohio, USA, in the winters of 1995-9 (Doherty & Grubb 2002) found that 378 downy woodpeckers Picoides pubescens did not have higher survival rates in either woodlots or riparian strips provided with supplementary food, compared with unfed, control sites. The impact on three songbird species is discussed in ‘Provide supplementary food to increase adult survival – Songbirds’. Supplementary food consisted of sunflower seeds and suet provided in excess throughout winter.Study and other actions tested
Another analysis (Doherty & Grubb 2003) of the same data as Doherty & Grubb 2002 found that downy woodpeckers Picoides pubescens did not have higher nutritional statuses (judged by the size of feather growth bars) than woodpeckers in unfed control woodlots. The impact on three songbird species is discussed in ‘Provide supplementary food to increase adult survival – Songbirds’.Study and other actions tested