The role of local cavity tree density in the selection of den sites by female fishers (Pekania pennanti) in northern Minnesota

Although several studies have evaluated fisher (Pekania pennanti (Erxleben, 1777)) selection of den structures across their natural range, the role of other nearby trees with suitable cavities that can be used by female fishers for subsequent maternal dens has not been explored. We used conditional logistic regression to describe selection of natal and maternal dens by female fishers in northern Minnesota, United States, and to determine if the density of other cavity trees surrounding a specific tree influences this selection. Our results indicate that cavity density was an important predictor of whether a tree was used as a den site by female fishers. The apparent condition (i.e., live, declining, or dead) and diameter at breast height of the cavity tree itself were also important for selection. These results affirm the need to retain large-diameter cavity trees, illustrate the potential benefits of retaining them in high-density patches, and caution against creating a landscape with highly dispersed denning options.

Cavity-tree use and frequency of response to playback by the Tropical Screech-Owl in northwestern Argentina

The Tropical Screech-Owl (Megascops choliba) is a nocturnal raptor with a wide distribution across the Neotropics, which uses cavity trees as nesting and roosting sites. Our objectives were to address cavity use by the Tropical Screech-Owl in the piedmont forest of Argentina and to evaluate if logging affects the availability of suitable cavities for nesting and roosting and the frequency of response of the species to playback. The Tropical Screech-Owl used trees with DBH values > 46 cm of three tree species (69% Calycophyllum multiflorum, 15% Phyllostylon rhamnoides, and 8% Cedrela angustifolia), besides standing dead trees (8%). The density of suitable cavities was significantly lower in logged forests than in the control site. The frequency of response of the species to playback was significantly lower at one logged site. Our results can contribute to delineate sustainable forest management to ensure the conservation of this owl in logged forest.

Black Woodpecker Dryocopus martius habitat selection in the Italian Alps: implications for conservation in Natura 2000 network

SummaryThe Black Woodpecker Dryocopus martius is the largest woodpecker of the Palearctic Region and it has been recognised as a keystone species whose presence provides critical resources to secondary cavity-users in European forest ecosystems. Here we investigate cavity tree and foraging-habitat selection of Black Woodpecker in three natural parks located in the central and eastern Italian Alps and included in the Natura 2000 network. A total of 94 cavity trees were identified, showing a minimum diameter of 35 cm and a mean diameter of 51 cm. We counted 30 active nests, but only 40% were newly excavated. Silver fir Abies alba and larch Larix decidua were preferred as cavity trees, with silver fir also associated with habitat surrounding the cavity trees. Norway spruce Picea abies and Silver fir were found to be positively associated with the surroundings of feeding sites. Logistic regression models identified the average diameter at breast height and the average tree crown height as significant predictors, positively associated with both cavity trees (AUC: 0.988) and cavity tree plots (AUC: 0.866). Also, the total volume of dead logs and the percentage of understorey cover turned out to be significant predictors of feeding sites, showing a positive and a negative association, respectively (AUC: 0.708). Cross validation of logistic regression models indicated that only cavity tree models can be considered useful tools in conservation practice. Overall, our results indicated that the Black Woodpecker behaves like an opportunist when choosing feeding sites. On the other hand, our results also indicate that the Black Woodpecker clearly behaves as a demanding species when it selects cavity trees, showing a hierarchical pattern in habitat selection and a marked preference for large trees with high crown height. We discuss the implications of our results for the conservation of the Black Woodpecker in Natura 2000 alpine sites.

Cavity Trees, Snags, and Overstory Density in a Riparian Forest in Northeastern Missouri

Snags and cavity trees are important for wildlife habitat, yet knowledge about their abundance and effects of forest management on these components is lacking for riparian forests. We evaluated the effects of clearcutting with reserves, basal area retention, and no harvest on snags and cavity trees in a riparian forest in northeastern Missouri. We also determined whether the established guidelines for snags and cavity trees in Missouri are being met. Preharvest results indicated that 11.3% of standing trees were snags, and 7% of live standing trees were cavity trees at this site. The proportion of snags was greater in small-diameter trees; however, the proportion of live trees with cavities increased as dbh increased. Preharvest snag density (20.6 trees/ac) and cavity trees (21.2 trees/ac) were well above the current minimum recommendations for wildlife tree retention on bottomland forests in Missouri. Following the harvest and girdling of residual trees >8 in. dbh, the abundance of snags increased, whereas cavity tree densities decreased. If the bottomland hardwood forest is going to contribute habitat of cavity tree-using wildlife, greater attention is needed to retaining cavity trees when harvesting.

Reproductive success of cavity-nesting birds in partially harvested woodlots

Cavity-nesting birds are dependent on large declining and dead trees that are frequently removed during partial harvesting. We compared breeding densities, nest survival, nest site characteristics, food abundance, and reproductive parameters of six species of cavity-nesting birds in partially harvested and reference woodlots in southwestern Ontario, Canada. Silvicultural practices significantly altered woodlot structure, with treatment-specific effects on bark arthropod biomass, fledging dates for the Red-bellied Woodpecker ( Melanerpes carolinus (Linnaeus, 1758)), and site suitability for the Yellow-bellied Sapsucker ( Sphyrapicus varius (Linnaeus, 1766)). Red-bellied Woodpecker, Downy Woodpecker ( Picoides pubescens (Linnaeus, 1766)), and Hairy Woodpecker ( Picoides villosus (Linnaeus, 1766)) experienced lower breeding densities in recently cut sites. Daily survival rates were generally greater for nests positioned higher up in large trees and for Northern Flicker ( Colaptes auratus (Linnaeus, 1758)) nests excavated in healthy and hard wood. Conversely, the Black-capped Chickadee ( Poecile atricapillus (Linnaeus, 1766)) had higher daily survival rates in low, small trees (<10 cm diameter at breast height) and sites with lower arthropod abundance. We conclude that although partial harvesting has the potential to decrease cavity-nesting bird breeding densities, conscientious cavity tree retention during harvest may provide suitable nesting sites that maintain high rates of nest success, regardless of the silvicultural treatments that we examined. However, further research is required to monitor these trends beyond a single harvesting rotation.