Woodpecker legacies: cavity production, and the effects on cavity occupancy, and abundance and diversity of the secondary cavity nesting community

TRZCINSKI, M. KURTIS; WIEBE, KAREN L.; EDWORTHY, AMANDA B.; MARTIN, KATHY; COCKLE, KRISTINA L

Congreso; 8th International Woodpecker Conference; 2019

Tree cavities are a critical reusable nesting resource for cavity-nesting birds and mammals globally, however, tree cavities may decline in occupancy and quality as they age. Although we know that trees and their cavities change as they age, with trees becoming softer and cavities becoming larger, we do not know how their value as nesting resources varies with age. In the context of wildlife and forest management, we investigated the relative value of generating a supply of fresh tree cavities?which are thought to be of high quality?versus protecting cavities as they age and expand in interior volume. For 21 years (1995?2016), we monitored the formation and occupancy of tree cavities used by more than 30 species of birds and mammals in British Columbia, Canada. Cavity occupancy by secondary users was highest 1 year post-excavation (53%), declined to 40% after 2 years, remained at 33 % between 3 and 16 years of age, and increased to 50% use from 17?20 years post-excavation. Woodpeckers that reused cavities strongly selected 1 and 2 yr old cavities; large-bodied nonexcavators (ducks, raptors, squirrels) selected mid-aged cavities; and mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) selected most strongly for the oldest cavities. Cavities created in living aspen trees, especially those excavated by northern flickers (Colaptes auratus), maintained high occupancy by secondary users across cavity age. Altogether, our results show that a diverse woodpecker community is needed to generate a supply of fresh cavities in the ecosystem, and the retention of the mid-aged and older cavities helps support larger-bodied species. Understanding the value of old cavities which are available across many years, versus fresh cavities, which may provide high quality, preferred nest sites helps to inform better forest management for cavitynesting vertebrate communities.