Recent nest tree use by the critically endangered Okinawa woodpecker in relation to forest age and two exotic forest pests.
Nest tree availability is a critical reproductive requirement for woodpeckers. To inform off-reserve management strategies for Okinawa woodpecker (OW) Dendrocopos noguchii (Syn. Sapheopipo noguchii) nest trees, we assessed the characteristics of 213 nest trees as well as the detailed forest age of the nest sites by using aerial photographs and the local forest registers. The woodpecker used 17 tree species and one tree fern. The dominant tree species used were Castanopsis sieboldii (34% of total nest trees), Melia azedarach (11%), Alnus japonica (24%), and Pinus luchuensis (8%). Castanopsis sieboldii were used most often in the forests ≥ 60 years old, while A. japonica, P. luchuensis, and M. azedarach were used most often in the younger forests. The relatively high frequency of nests in A. japonica and P. luchuensis snags was likely affected by tree die-offs due to outbreaks of the introduced leaf beetle Plagiosterna formosana and pine wilt disease caused by the introduced Pine wood nematode Bursaphelenchus xylophilus, respectively. However, these die-offs were temporary, and snags created by exotic pest outbreaks may not be long-lasting resources in the warm, humid climate. To ensure the stable supply of available nest trees for the OW, we recommend preserving areas of forest ≥ 60 years old, retaining a few C. sieboldii trees when logging, and also retaining most regenerating M. azedarach trees during thinning operations in young forests.