Red-cockaded Woodpecker Nest-cavity Selection: Relationships with Cavity Age and Resin Production

-We evaluated selection of nest sites by male Red-cockaded Woodpeckers (Picoides borealis) in Texas relative to the age of the cavity when only cavities excavated by the woodpeckers were available and when both naturally excavated cavities and artificial cavities were available. We also evaluated nest-cavity selection relative to the ability of naturally excavated cavity trees to produce resin, which is used by the woodpeckers to maintain a barrier against predation by rat snakes (Elaphe spp.). Longleaf pines (Pinus palustris) selected by breeding males as nest trees produced significantly greater resin yields at 2, 8, and 24 h post-wounding than cavity trees used for roosting by other group members. This preference was observed in loblolly pine (I! taeda) and shortleaf pine (I? echinata) cavity trees only at the 2-h resin-sampling period. When only naturally excavated cavities were available, Red-cockaded Woodpeckers in both longleaf pine and loblolly-shortleaf pine habitat selected thenewest cavities available for their nest sites, possibly as a means to reduce parasite loads. When both naturally excavated and artificial cavity inserts were available, Red-cockaded Woodpeckers continued to select the newest cavity for nesting in loblolly-shortleaf pine habitat but not in longleaf pine habitat. Resin production in existing longleaf pine nest trees remained sufficient for continued use, whereas resin production in loblolly pine and shortleaf pine nest trees decreased through time, probably because of woodpecker activity at resin wells. For these latter tree species, breeding males switched to newer cavities and/or cavity trees with higher resin yields. Received 7 ]uly 1997, accepted 11 November 1997. T HE R E DCOCKADED W OODPECKER ( P i c o i d e s borealis) is a cooperatively breeding species that lives in groups of two to seven members (Ligon 1970, Lennartz et al. 1987, Walters et al. 1988). Groups usually are composed of a single breeding pair and one to several adult helpers, typically males, from previous nestings. Each group member usually roosts singly at night in its own cavity (Ligon 1970). Group members occasionally roost in the open, in the fork of a tree or other natural tree crevice, when roost cavities are in limited supply or in late summer prior to acquisition of roost cavities by fledglings (Hooper and Lennartz 1983, Conner et al. 1996). The breeding male typically is the dominant individual of the group (Walters 1990) and likely would have first choice when selecting a roost cavity. The quality of the cavity selected by the breeding male is important to all group members because the breeding male’s roost 3 E-mail: [email protected] cavity is used as the nest cavity during the breeding season. Breeding males often select the newest cavity in the cavity-tree cluster (Conner and Rudolph pers. obs.). A possible benefit of this behavior is a decreased parasite load for nestlings and incubating adults. Since 1990, artificial cavities (Allen 1991) have been used to provide roosting and nesting sites. The effect of the addition of artificial cavities on nest-site selection is unknown. Roosting and nesting Red-cockaded Woodpeckers make daily excavations at small wounds, termed resin wells, around their cavity entrance, from which resin flows down the tree (Ligon 1970). The breeding male may select cavity trees with greater resin flow than other active cavity trees within the cluster. Such cavity trees would enhance the quality of the resin barrier against rat snakes (E&he spp.), thereby increasing the probability of nestling survival and the safety of the dominant, breeding male (Jackson 1974, Rudolph et al. 1990). Rat snakes regularly attempt to climb active