Jonathan G. Dudley

Nest densities of cavity-nesting birds in relation to postfire salvage logging and time since wildfire

Abstract ABSTRACT We monitored the nest densities and nest survival of seven cavity-nesting bird species, including four open-space foragers (American Kestrel [Falco sparverius], Lewiss Woodpecker [Melanerpes lewis], Western Bluebird [Sialia mexicana], and Mountain Bluebird [S. currucoides]) and three wood-foragers (Hairy Woodpecker [Picoides villosus], Black-backed Woodpecker [P. arcticus], and Northern Flicker [Colaptes auratus]), after two wildfires (one partially salvage-logged and one unlogged) in western Idaho from 1994–2004. We estimated the relationship between nest density and time since fire, tested for statistical differences in nest densities and nest survival in the partially salvage-logged vs. unlogged wildfires, and tested for differences in nest survival between early (1–4 years after fire) and late (5–12 years after fire) postfire periods. Nest densities of open-space foragers and Northern Flickers generally increased with time since fire, whereas nest densities of Black-backed and Hairy Woodpeckers peaked 4–5 years postfire. Nest densities of wood-foraging species and Mountain Bluebirds were significantly higher in the unlogged burn, whereas Lewiss Woodpeckers had significantly higher nest densities in the partially logged burn. Kestrels tended to favor the partially logged burn, while Western Bluebird nest densities were nearly equal in both burned areas. For most species, postfire period and treatment (partially logged vs. unlogged) had little influence on nest survival. However, Hairy Woodpecker nest survival was significantly lower in the partially logged burn versus the unlogged wildfire in the early postfire period, and Lewiss Woodpecker nest survival was significantly reduced in the later postfire period versus the early postfire period in the partially logged burn. Importantly, the salvage logging was designed to retain more than half of the snags over 23 cm in diameter, which provided suitable nesting habitat for open-space foragers during the decade following fire.

Factors influencing occupancy of nest cavities in recently burned forests

Abstract Recently burned forests in western North America provide nesting habitat for many species of cavity-nesting birds. However, little is understood about the time frame and the variables affecting occupancy of postfire habitats by these birds. We studied factors influencing the occupancy and reuse of nest cavities from 1–7 years after fire in two burned sites of western Idaho during 1994–1999. Tree cavities were used for nesting by 12 species of cavity nesters that were classified by the original occupant (strong excavator, weak excavator, or nonexcavator) of 385 nest cavities. We used logistic regression to model cavity occupancy by strong excavators (n = 575 trials) and weak excavators (n = 206 trials). Year after fire had the greatest influence on occupancy of nest cavities for both groups, while site of the burn was secondarily important in predicting occupancy by strong excavators and less important for weak excavators. Predicted probability of cavity occupancy was highest during the early years (1–4) after fire, declined over time (5–7 years after fire), and varied by site, with a faster decline in the smaller burned site with a greater mosaic of unburned forest. Closer proximity and greater interspersion of unburned forest (15% unburned) may have allowed a quicker recolonization by nest predators into the smaller burn compared to the larger burn with few patches of unburned forest (4% unburned). In combination with time and space effects, the predicted probability of cavity occupancy was positively affected by tree and nest heights for strong and weak excavators, respectively. Factores que Influencian la Ocupación de Cavidades de Nidificación en Bosques Recientemente Quemados Resumen. Los bosques del oeste de América del Norte que han sido recientemente quemados proveen hábitat de nidificación para muchas especies de aves que nidifican en cavidades. Sin embargo, se sabe poco sobre el marco temporal y las variables que afectan la ocupación por parte de las aves de los hábitats luego del fuego. Entre 1994 y 1999, estudiamos los factores que influencian la ocupación y el uso repetido de las cavidades de nidificación entre 1 y 7 años luego del fuego, en dos sitios quemados en el oeste de Idaho. Las cavidades de los árboles fueron usadas para nidificar por 12 especies de aves, las que fueron clasificadas (385 cavidades) según el ocupante original (excavador fuerte, excavador débil y no excavador). Usamos regresión logística para modelar la ocupación de las cavidades por parte de excavadores fuertes (n = 575 pruebas) y débiles (n = 206 pruebas). El año luego del fuego tuvo la mayor influencia en la ocupación de las cavidades de nidificación para ambos grupos, mientras que el sitio de la quema tuvo una importancia secundaria en predecir la ocupación por parte de excavadores fuertes y menos importancia por parte de excavadores débiles. La probabilidad predicha de ocupación de las cavidades fue mayor durante los primeros años (1–4) luego del fuego, declinó con el tiempo (5–7 años luego del fuego) y varió entre sitios, con una disminución más rápida en el sitio quemado más pequeño que presentó un mayor mosaico de bosque no quemado. La proximidad y la mayor dispersión de bosques no quemados (15% no quemado) puede haber permitido una recolonización más rápida de los depredadores de nidos en el sitio quemado pequeño, comparado con el sitio quemado mayor que presentó pocos parches de bosque no quemado (4% no quemado). En combinación con los efectos de tiempo y espacio, la probabilidad predicha de ocupación de cavidades fue afectada positivamente por la altura de los árboles y de los nidos para los excavadores fuertes y débiles, respectivamente.

Habitat‐Suitability Models for Cavity‐Nesting Birds in a Postfire Landscape

Abstract Models of habitat suitability in postfire landscapes are needed by land managers to make timely decisions regarding postfire timber harvest and other management activities. Many species of cavity-nesting birds are dependent on postfire landscapes for breeding and other aspects of their life history and are responsive to postfire management activities (e.g., timber harvest). In addition, several cavity nesters are designated as species at risk. We compare the ability of 2 types of models to distinguish between nest and non-nest locations of 6 cavity-nesting bird species (Lewiss woodpecker [Melanerpes lewis], black-backed woodpecker [Picoides arcticus], hairy woodpecker [P. villosus], northern flicker [Colaptes auratus], western bluebird [Sialia mexicana], and mountain bluebird [S. currucoides]) in the early postfire years for a ponderosa pine (Pinus ponderosa) forest in Idaho, USA. The 2 model sets consisted of 1) models based on readily available remotely sensed data and 2) models containing field-collected data in addition to remotely sensed data (combination models). We evaluated models of nesting habitat by quantifying the models ability to correctly identify nest and non-nest locations and by determining the percentage of correctly identified nest locations. Additionally, we developed relative habitat-suitability maps for nesting habitat of black-backed and Lewiss woodpeckers from the best models. For all species except Lewiss woodpeckers, model performance improved with the addition of field-collected data. Models containing remotely sensed data adequately distinguished between nest and non-nest locations for black-backed woodpecker and Lewiss woodpecker only, whereas models containing both field-collected and remotely sensed data were adequate for all 6 species. Improvements in the availability of more accurate remote sensing technology would likely lead to improvements in the ability of the models to predict nesting locations. External validation with data from other wildfires is necessary to confirm the general applicability of our habitat-suitability models to other forests. Land managers responsible for maintaining habitat for cavity-nesting birds in postfire landscapes can use these models to identify potential nesting areas for these species and select areas in burned forests where postfire salvage logging is most likely to have minimal impacts on cavity-nesting bird habitats.

Modeling nest survival of cavity-nesting birds in relation to postfire salvage logging

ABSTRACT Salvage logging practices in recently burned forests often have direct effects on species associated with dead trees, particularly cavity-nesting birds. As such, evaluation of postfire management practices on nest survival rates of cavity nesters is necessary for determining conservation strategies. We monitored 1,797 nests of 6 cavity-nesting bird species: Lewiss woodpecker (Melanerpes lewis), hairy woodpecker (Picoides villosus), black-backed woodpecker (P. arcticus), northern flicker (Colaptes auratus), western bluebird (Sialia mexicana), and mountain bluebird (S. currucoides) from 1994 to 2004 in ponderosa pine (Pinus ponderosa), mixed-severity burned forests (partially logged and unlogged) of Idaho, USA. Based on a priori hypotheses, we modeled daily survival rate (DSR) of nests as a function of abiotic (temperature, precipitation), temporal (time since fire, calendar year) and biotic factors (distance to unburned forest, nest height, and tree harvest [partial-salvage logging vs. unlogged]). Multiple abiotic and biotic factors, other than direct effects of salvage logging, affected daily survival rates of breeding cavity-nesting birds. Hairy woodpecker was the only species in which partial-salvage logging had a measurable, negative impact on DSR. Managers implementing carefully planned salvage logging prescriptions that include both unlogged reserves and partially logged areas can expect to maintain habitat for successfully breeding cavity-nesting birds of the interior northwestern United States. Our results also suggest that nest survival for some species of cavitynesting birds could be improved if unlogged reserves are located centrally in postfire forests, distant from unburned habitats that potentially serve as sources of nest predators.

HOME RANGE SIZE OF BLACK-BACKED WOODPECKERS IN BURNED FORESTS OF SOUTHWESTERN IDAHO

Abstract We examined home range size of Black-backed Woodpeckers (Picoides arcticus) in burned ponderosa pine (Pinus ponderosa) / Douglas-fir (Pseudotsuga menziesii) forests of southwestern Idaho during 2000 and 2002 (6 and 8 years following fire). Home range size for 4 adult males during the post-fledging period was 115.6–420.9 ha using the 95% fixed-kernel method, and 150.4–766.1 ha using the 100% minimum convex polygon method. Smoothed bootstrap estimates (95%) were 130.0–521.9 ha. Home range sizes were significantly smaller 6 years after fire than 8 years after fire. Each male had from 2 to 8 areas of concentrated use within his home range. We provide recommendations for estimating area requirements of Black-backed Woodpeckers in post-fire ponderosa pine / Douglas-fir forests.

Ensemble modeling to predict habitat suitability for a large-scale disturbance specialist

To conserve habitat for disturbance specialist species, ecologists must identify where individuals will likely settle in newly disturbed areas. Habitat suitability models can predict which sites at new disturbances will most likely attract specialists. Without validation data from newly disturbed areas, however, the best approach for maximizing predictive accuracy can be unclear (Northwestern U.S.A.). We predicted habitat suitability for nesting Black-backed Woodpeckers (Picoides arcticus; a burned-forest specialist) at 20 recently (≤6 years postwildfire) burned locations in Montana using models calibrated with data from three locations in Washington, Oregon, and Idaho. We developed 8 models using three techniques (weighted logistic regression, Maxent, and Mahalanobis D2 models) and various combinations of four environmental variables describing burn severity, the north–south orientation of topographic slope, and prefire canopy cover. After translating model predictions into binary classifications (0 = low suitability to unsuitable, 1 = high to moderate suitability), we compiled “ensemble predictions,” consisting of the number of models (0–8) predicting any given site as highly suitable. The suitability status for 40% of the area burned by eastside Montana wildfires was consistent across models and therefore robust to uncertainty in the relative accuracy of particular models and in alternative ecological hypotheses they described. Ensemble predictions exhibited two desirable properties: (1) a positive relationship with apparent rates of nest occurrence at calibration locations and (2) declining model agreement outside surveyed environments consistent with our reduced confidence in novel (i.e., “no-analogue”) environments. Areas of disagreement among models suggested where future surveys could help validate and refine models for an improved understanding of Black-backed Woodpecker nesting habitat relationships. Ensemble predictions presented here can help guide managers attempting to balance salvage logging with habitat conservation in burned-forest landscapes where black-backed woodpecker nest location data are not immediately available. Ensemble modeling represents a promising tool for guiding conservation of large-scale disturbance specialists.

Detection probabilities of Woodpecker nests in mixed conifer forests in Oregon.

Abstract Accurate estimates of Black-backed (Picoides arcticus) and Hairy Woodpecker (P. villosus) nests and nest survival rates in post-fire landscapes provide land managers with information on the relative importance of burned forests to nesting woodpeckers. We conducted multiple-observer surveys in burned and unburned mixed coniferous forests in Oregon to identify important factors influencing detection rates of woodpecker nests. We found 21 Black-backed Woodpecker nests and 38 Hairy Woodpecker nests in burned forest, and three Hairy Woodpecker nests in unburned forest. Competing models of detection probability in Program MARK indicated that nest-detection probability differed by nest stage. We found no evidence to indicate that detection rates of nests were associated with survey timing during the nesting season. Raw nest counts in burned coniferous forests may underestimate nest numbers, especially for nests in early stages of development. Black-backed Woodpecker nests were slightly more detectable than those of Hairy Woodpeckers in burned forests, and observers may differ in their abilities to detect nests.

Transferability of habitat suitability models for nesting woodpeckers associated with wildfire

ABSTRACT Following wildfire, forest managers are challenged with meeting both socioeconomic demands (e.g., salvage logging) and mandates requiring habitat conservation for disturbance-associated wildlife (e.g., woodpeckers). Habitat suitability models for nesting woodpeckers can be informative, but tests of model transferability are needed to understand how broadly models developed at one location can be applied to inform post-fire forest management at other locations. We developed habitat suitability models and tested their transferability for 2 disturbance-associated woodpecker species, Black-backed (Picoides arcticus) and Lewiss (Melanerpes lewis) woodpecker. Habitat suitability models consisted of weighted logistic regression models comparing environmental conditions at nest versus non-nest sites. We developed models at each of 3 wildfire locations in Washington, Oregon, and Idaho, and then examined predictive performance for each model at alternate (“application”) locations. Models generally discriminated nest from non-nest sites well at locations where they were developed but performance was variable at application locations, indicating limited transferability. Models for Black-backed Woodpecker and those that included field-collected environmental covariates exhibited greater transferability than models for Lewiss Woodpecker and those that only included remotely sensed covariates. Transferability was also generally poor between Oregon and the other 2 locations. Limitations to model transferability observed in this study suggest models developed at any one wildfire location are unlikely to be generally applicable across the entire range of Black-backed and Lewiss woodpeckers. Generally applicable models to inform post-fire forest management will therefore likely require integration of data from multiple wildfire locations.