Victoria A. Saab

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.

Modeling the effects of environmental disturbance on wildlife communities: avian responses to prescribed fire

Prescribed fire is a management tool used to reduce fuel loads on public lands in forested areas in the western United States. Identifying the impacts of prescribed fire on bird communities in ponderosa pine (Pinus ponderosa) forests is necessary for providing land management agencies with information regarding the effects of fuel reduction on sensitive, threatened, and migratory bird species. Recent developments in occupancy modeling have established a framework for quantifying the impacts of management practices on wildlife community dynamics. We describe a Bayesian hierarchical model of multi-species occupancy accounting for detection probability, and we demonstrate the models usefulness for identifying effects of habitat disturbances on wildlife communities. Advantages to using the model include the ability to estimate the effects of environmental impacts on rare or elusive species, the intuitive nature of the modeling, the incorporation of detection probability, the estimation of parameter uncertainty, the flexibility of the model to suit a variety of experimental designs, and the composite estimate of the response that applies to the collection of observed species as opposed to merely a small subset of common species. Our modeling of the impacts of prescribed fire on avian communities in a ponderosa pine forest in Washington indicate that prescribed fire treatments result in increased occupancy rates for several bark-insectivore, cavity-nesting species including a management species of interest, Black-backed Woodpeckers (Picoides arcticus). Three aerial insectivore species, and the ground insectivore, American Robin (Turdus migratorius), also responded positively to prescribed fire, whereas three foliage insectivores and two seed specialists, Clarks Nutcracker (Nucifraga columbiana) and the Pine Siskin (Carduelis pinus), declined following treatments. Land management agencies interested in determining the effects of habitat manipulations on wildlife communities can use these methods to provide guidance for future management activities.

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.

TESTS OF LANDSCAPE INFLUENCE: NEST PREDATION AND BROOD PARASITISM IN FRAGMENTED ECOSYSTEMS

The effects of landscape fragmentation on nest predation and brood parasitism, the two primary causes of avian reproductive failure, have been difficult to generalize across landscapes, yet few studies have clearly considered the context and spatial scale of fragmentation. Working in two river systems fragmented by agricultural and rural-housing development, we tracked nesting success and brood parasitism in > 2500 bird nests in 38 patches of deciduous riparian woodland. Patches on both river systems were embedded in one of two local contexts (buffered from agriculture by coniferous forest, or adjacent to agriculture), but the abundance of agriculture and human habitation within 1 km of each patch was highly variable. We examined evidence for three models of landscape effects on nest predation based on (1) the relative importance of generalist agricultural nest predators, (2) predators associated with the natural habitats typically removed by agricultural development, or (3) an additive combination of these two predator communities. We found strong support for an additive predation model in which landscape features affect nest predation differently at different spatial scales. Riparian habitat with forest buffers had higher nest predation rates than sites adjacent to agriculture, but nest predation also increased with increasing agriculture in the larger landscape surrounding each site. These results suggest that predators living in remnant woodland buffers, as well as generalist nest predators associated with agriculture, affect nest predation rates, but they appear to respond at different spatial scales. Brood parasitism, in contrast, was unrelated to agricultural abundance on the landscape, but showed a strong nonlinear relationship with farm and house density, indicating a critical point at which increased human habitat causes increased brood parasitism. Accurate predictions regarding landscape effects on nest predation and brood parasitism will require an increased appreciation of the multiple scales at which landscape components influence predator and parasite behavior.

REPRODUCTIVE SUCCESS OF LEWIS'S WOODPECKER IN BURNED PINE AND COTTONWOOD RIPARIAN FORESTS

Abstract Lewiss Woodpecker (Melanerpes lewis) has been characterized as a “burn specialist” because of its preference for nesting within burned pine forests. No prior study, however, has demonstrated the relative importance of crown-burned forests to this woodpecker species by examining its reproductive success in different forest types. We studied breeding Lewiss Woodpeckers in cottonwood (Populus fremontii) riparian forest patches of Colorado and crown-burned ponderosa pine (Pinus ponderosa) forests of Idaho to compare their reproductive success, productivity, and potential source-sink status in the two forest types. Daily nest survival rates were significantly lower in cottonwood compared to burned pine forests. Nesting success was 46% (n = 65) in cottonwood forests and 78% (n = 283) in burned pine forests. Proportion of nests destroyed by predators was significantly higher in cottonwood forests (34%) compared to burned pine forests (16%). We consistently found crown-burned forests to be potential source habitat, whereas cottonwood riparian sites were more often concluded to be potential sink habitat. Cottonwood riparian forests were surrounded primarily by an agricultural landscape where the composition and abundance of nest predators was likely very different than the predator assemblage occupying a large-scale burn in a relatively natural landscape. Conversion of riparian and adjacent grassland landscapes to agriculture and prevention of wildfire in ponderosa pine forests have likely reduced nesting habitat for this species. Prescribed understory fire is the prevailing management tool for restoring ponderosa pine ecosystems. Conditions created by crown fire may be equally important in maintaining ponderosa pine systems and conserving nesting habitat for the Lewiss Woodpecker. Éxito Reproductivo de Melanerpes lewis en Bosques de Pinos Quemados y Bosques Ribereños de Populus fremontii Resumen. Melanerpes lewis ha sido caracterizado como un “especialista de quemas” porque prefiere anidar en áreas de pinos maduros quemados. Sin embargo, ningún estudio anterior ha demostrado la importancia relativa de los bosques de árboles con copas quemadas para este carpintero examinando su éxito reproductivo en diferentes tipos de bosques. Estudiamos M. lewis reproductivos en parches de bosques ribereños de Populus fremontii en Colorado y bosques de Pinus ponderosa con las copas quemadas en Idaho para comparar su éxito reproductivo, productividad y la condición potencial de fuente-sumidero de los dos tipos de bosques. Las tasas diarias de supervivencia de los nidos fueron significativamente más bajas en los bosques de Populus fremontii que en las áreas de pinos maduros quemados. El éxito de los nidos fue de 46% (n = 65) en los bosques de Populus fremontii y 78% (n = 283) en los bosques de pinos quemados. La proporción de nidos destruídos por depredadores fue signicativamente más alta en los bosques de Populus fremontii (34%) que los bosques de pinos quemados (16%). Encontramos consistentemente que las áreas de pinos con las copas quemadas son potencialmente hábitats fuente mientras que los bosques de Populus fremontii fueron considerados como sumideros potenciales con mayor frecuencia. Los bosques de Populus fremontii estaban rodeados principalmente por un paisaje agrícola donde la composición y la abundancia de los depredadores de nidos eran probablemente muy diferentes de las de un área quemada de gran escala en medio de un paisaje natural. La conversión de paisajes ribereños y de pastizales a áreas agrícolas y la prevención de fuegos naturales en los bosques de P. ponderosa probablemente ha reducido el habitat de anidación de esta especie. El manejo de fuegos planificados en el sotobosque es la técnica más utilizada para reestablecer los ecosistemas de P. ponderosa. Las condiciones creadas por el fuego en las copas de los árboles podrían ser igualmente importante para mantener los sistemas de P. ponderosa, incluyendo la conservación de los hábitats de anidación de M. lewis.

Impact of Pasture Development on Winter Bird Communities in Belize, Central America

We studied bird use of actively grazed and abandoned (2-4 years) pastures during February 1990 in Belize, where pastures often are maintained by repeated mowing. A total of 46 species was observed in the two pasture types, with 15 species detected in grazed and 39 in abandoned. Species richness for both migrants and residents was lower by >50% in grazed pastures. Overall abundance of birds was lower by nearly 70% in grazed pastures compared with the more structurally diverse abandoned pastures (P < 0.001). Based on data from a concurrent study on bird use of forest interior habitat in Belize, 2-4 times more resident species would be expected in nearby broadleaved forests compared to an equal census effort in grazed pastures. In contrast, only about 1.5 times more migrant bird species would be predicted in broadleaved forest interior than in grazed pastures. Foraging guilds were not equally represented between pasture treatments; most notable was an absence of frugivores and nectarivores in grazed pastures maintained by mowing. Our results indicate that retention of some shrubs and overstory trees may reduce the negative effects of pasture development of winter bird populations in Central America.

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.

Do male and female black‐backed woodpeckers respond differently to gaps in habitat?

We used population‐ and individual‐based genetic approaches to assess barriers to movement in black‐backed woodpeckers (Picoides arcticus), a fire‐specialist that mainly occupies the boreal forest in North America. We tested if male and female woodpeckers exhibited the same movement patterns using both spatially implicit and explicit genetic analyses to define population structure and movement patterns of both sexes among populations. Three genetic groups were identified, a large, genetically continuous population that spans from the Rocky Mountains to Quebec, a small isolated population in South Dakota and a separate population in the western portion of their distribution (Oregon). Patterns of genetic diversity suggest extensive gene flow mediated by both males and females within the continuous boreal forest. However, male‐mediated gene flow is the main form of connectivity between the continuously distributed group and the smaller populations of South Dakota and Oregon that are separated by large areas of unforested habitat, which apparently serves as a barrier to movement of female woodpeckers.

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.

Habitat Suitability and Nest Survival of White-Headed Woodpeckers in Unburned Forests of Oregon

ABSTRACT We evaluated habitat suitability and nest survival of breeding white-headed woodpeckers (Picoides albolarvatus) in unburned forests of central Oregon, USA. Daily nest-survival rate was positively related to maximum daily temperature during the nest interval and to density of large-diameter trees surrounding the nest tree. We developed a niche-based habitat suitability model (partitioned Mahalanobis distance) for nesting white-headed woodpeckers using remotely sensed data. Along with low elevation, high density of large trees, and low slope, our habitat suitability model suggested that interspersion-juxtaposition of low- and high-canopy cover ponderosa pine (Pinus ponderosa) patches was important for nest-site suitability. Cross-validation suggested the model performed adequately for management planning at a scale >1 ha. Evaluation of mapped habitat suitability index (HSI) suggested that the maximum predictive gain (HSI = 0.36), where the number of nest locations are maximized in the smallest proportion of the modeled landscape, provided an objective initial threshold for identification of suitable habitat. However, managers can choose the threshold HSI most appropriate for their purposes (e.g., locating regions of low-moderate suitability that have potential for habitat restoration). Consequently, our habitat suitability model may be useful for managing dry coniferous forests for white-headed woodpeckers in central Oregon; however, model validation is necessary before our model could be applied to other locations.