Ecological Significance of the Early Breeding in White-backed Woodpeckers Dendrocopos leucotos

Abstract

The breeding ecology of five sympatric species of woodpeckers (Dendrocopos kizuki, Dendrocopos major, Dendrocopos leucotos, Picus canus, and Dryocopus martius) was studied from 1974 to 1976 in the broad-leaved forest of the Tomakomai Experiment Forest of Hokkaido University.(1) In the Experiment Forest all of the five species of woodpeckers showed preference for the broad-leaved forest than for the coniferous plantation. All nest trees found were in broadleaved and second-growth forests.(2) Among the five species, the breeding of White-backed Woodpeckers (D. leucotos) was earliest and their nestlings fledged in early June. The breeding of Black Woodpeckers (D. martius) was next and their nestlings fledged about the middle of June. Lastly, nestlings of Japanese Pygmy (D. kizuki), Great Spotted (D. major), and Grey-headed Green (P. canus) woodpeckers fledged in late June, about one month later than that of D. leucotos.(3) All of the nests found were in broad-leaved trees. The nests of D. leucotos were relatively and absolutely higher than those of the other species. Seven out of 11 nests (63.6 %) of D. leucotos were found above the tree crown layer, whereas the nests of the other species were normally belowthat layer.(4) In D. kizuki and D. major the main food of nestlings was lepidopterous larvae taken from the surface of leaves by gleaning. The food of nestlings of D. leucotos consisted mainly of coleopterous larvae taken from fallen logs and stumps by hammering and pecking. P. canus fed the nestlings with lepidopterous larvae and ants, whereas D. martius raised the nestlings chiefly with ants.(5) The biomass of lepidopterous larvae reached to a peak from early to mid June at Tomakomai. The nestling periods of D. kizuki, D. major, and P. canus, which mainly depend on lepidopterous larvae to raise their nestlings, coincided with the peak of the biomass.(6) The early breeding of D. leucotos was discussed from the points of view that breeding seasons in birds are timed in relation to the availability of food for their nestlings. It is suggested that the larger body size of D. leucotos caused the early breeding which was related to the effective utilization of coleopterous larvae. Further, some behavioral modification of D. leucotos associated with their early breeding were noted.