Population Viability Analysis for Red-Cockaded Woodpeckers Using an Individual-Based Model

Abstract

Red-cockaded Woodpeckers (Picoides borealis) are distributed in the southeastern United States among closed populations whose maximum size is limited. Previous population viability analyses for this species have been confined to examination of threats posed by catastrophes and loss of genetic variability, because of the lack of demographic models that incorporate the extreme spatial constraints on dispersal that characterize this species. We used a spatially explicit, individual-based simulation model to assess the vulnerability of Red-cockaded Woodpecker populations to demographic and environmental stochasticity. Vulnerability to these threats was relatively low, because the presence of a substantial nonbreeding class (i.e., helpers) ameliorated the impact of stochastic variation in mortality and reproduction on the size of the breeding population. Because dispersal of helpers is spatially restricted, this effect was most pronounced when territories were aggregated or at high densities. Populations of 250 and 500 territories were stable regardless of the level of territory aggregation at the densities examined, whereas populations of 25, 49, and 100 territories ranged from rapidly declining to stable, depending on territory density and level of aggregation. Techniques that enable managers to maintain existing territories and create new ones are well established for this species. Thus managers may reasonably expect to maintain even small populations of Red-cockaded Woodpeckers by increasing the density, level of aggregation, and number of territories.

Weighing the relative potential impacts of climate change and land‐use change on an endangered bird

“…The results suggest that RCW may be less vulnerable to climate change than other species because of the floater class, which also buffers RCW populations against demographic stochasticity (Walters et al. ). Furthermore, evidence suggests that RCW may respond to changes in climate by laying eggs earlier (Schiegg et al.…”

Importance of Buffer Mechanisms for Population Viability Analysis

“…Group living can buffer environmental noise in social species (e.g., in the alpine marmot [ Marmota marmota ]; Grimm et al 2003) because subdominant individuals (helpers) that do not reproduce usually contribute to the survival of the alpha individuals and their offspring. Nonbreeding individuals (floaters) can buffer environmental noise in territorial species because they rapidly occupy territories that have become vacant because of the death of a breeder. This effect is described for Red‐cockaded Woodpeckers ( Picoides borealis ; Walters et al 2002) for which the previous use of simple genetic models led to incorrect management decisions (Lande 1988). An overshooting of the long‐term average population size of the habitat in good years can buffer environmental noise because in the following years, extinction risk resulting from demographic noise will be reduced.…”

“…Nonbreeding individuals (floaters) can buffer environmental noise in territorial species because they rapidly occupy territories that have become vacant because of the death of a breeder. This effect is described for Red‐cockaded Woodpeckers ( Picoides borealis ; Walters et al 2002) for which the previous use of simple genetic models led to incorrect management decisions (Lande 1988).…”

New insights from an attempt to reintroduce Red-cockaded Woodpeckers in northern Florida

“…Population viability models suggest highly aggregated PBGs containing 20–30 adults have a good chance of persisting for 25 yr (Walters et al. ). The recurring management we proposed should enhance chances of population persistence.…”