Does the abundance and timing of defoliating caterpillars influence the nest survival and productivity of the Great Spotted Woodpecker Dendrocopos major?

Abstract

ABSTRACTCapsule: Nest survival of Great Spotted Woodpeckers Dendrocopos major was not related to the abundance or timing of their caterpillar prey, whereas the number of young fledged per nest was higher in years with high numbers of defoliating caterpillars and when there was a good temporal match between food demand and the peak caterpillar abundance.Aims: To test whether the breeding parameters of Great Spotted Woodpeckers were affected by the abundance and timing of their caterpillar prey.Methods: The breeding parameters of Great Spotted Woodpeckers were monitored in four woods in Hertfordshire, UK, from 2001 to 2016. All nests and their outcomes were followed by regular observations and inspection using nest video cameras; 836 nests were found. The timing and abundance of defoliating caterpillars were monitored using frass trays and damage assessments of oak leaves.Results: The caterpillar abundance rose to a peak and fell again towards the end of the 16-year study. The date of the maximum frass fall was best predicted by the mean April–May temperature. On average, the date of peak food demand of the young woodpeckers was mismatched with the peak prey by four days. The mean number of young fledged per nest was higher in years with high numbers of defoliating caterpillars and in years when the greatest food demand of the chicks coincided with the peak caterpillar abundance. Nest survival was high and was unrelated to caterpillar abundance or timing.Conclusion: A high abundance of defoliating caterpillars and good synchronization of timing of breeding with the peak availability of the caterpillars can increase brood productivity of the generalist Great Spotted Woodpecker. A combination of low caterpillar abundance and a warm spring is predicted to reduce productivity considerably.