W. Matthew Vander Haegen

TEETERING ON THE EDGE OR TOO LATE? CONSERVATION AND RESEARCH ISSUES FOR AVIFAUNA OF SAGEBRUSH HABITATS

Abstract Degradation, fragmentation, and loss of native sagebrush (Artemisia spp.) landscapes have imperiled these habitats and their associated avifauna. Historically, this vast piece of the Western landscape has been undervalued: even though more than 70% of all remaining sagebrush habitat in the United States is publicly owned, <3% of it is protected as federal reserves or national parks. We review the threats facing birds in sagebrush habitats to emphasize the urgency for conservation and research actions, and synthesize existing information that forms the foundation for recommended research directions. Management and conservation of birds in sagebrush habitats will require more research into four major topics: (1) identification of primary land-use practices and their influence on sagebrush habitats and birds, (2) better understanding of bird responses to habitat components and disturbance processes of sagebrush ecosystems, (3) improved hierarchical designs for surveying and monitoring programs, and (4) linking bird movements and population changes during migration and wintering periods to dynamics on the sagebrush breeding grounds. This research is essential because we already have seen that sagebrush habitats can be altered by land use, spread of invasive plants, and disrupted disturbance regimes beyond a threshold at which natural recovery is unlikely. Research on these issues should be instituted on lands managed by state or federal agencies because most lands still dominated by sagebrush are owned publicly. In addition to the challenge of understanding shrubsteppe bird-habitat dynamics, conservation of sagebrush landscapes depends on our ability to recognize and communicate their intrinsic value and on our resolve to conserve them. ¿Tambaleando en el Borde o Demasiado Tarde? Asuntos de Conservación e Investigación para la Avifauna de Ambientes de Matorral de Artemisia spp Resumen. La degradación, fragmentación y pérdida de paisajes nativos de matorrales de Artemisia spp. han puesto en peligro a estos ambientes y su avifauna asociada. Históricamente, esta vasta porción del paisaje occidental ha sido subvalorada: aunque más del 70% de todo el hábitat de matorral de Artemisia de los Estados Unidos es de propiedad pública, <3% de éste es protegido por reservas federales o parques nacionales. En este artículo revisamos las amenazas a las que se enfrentan las aves de los matorrales de Artemisia para enfatizar la urgencia de emprender acciones de conservación e investigación, y sintetizamos la información existente que constituye la base para una serie de directrices de investigación recomendadas. El manejo y conservación de las aves de los matorrales de Artemisia necesitará más investigación en cuatro tópicos principales: (1) la identificación de prácticas primarias de uso del suelo y su influencia sobre los ambientes y las aves de Artemisia, (2) un mejor entendimiento de las respuestas de las aves a componentes del hábitat y a procesos de disturbio de los ecosistemas de Artemisia, (3) el mejoramiento de diseños jerárquicos para programas de censos y monitoreos y (4) la conexión de los movimientos de las aves y los cambios poblacionales durante la migración y en los períodos de invernada con la dinámica en las áreas reproductivas de matorrales de Artemisia. Estas investigaciones son esenciales porque ya hemos visto que los ambientes de Artemisia pueden ser alterados por el uso del suelo, la diseminación de plantas invasoras y la disrupción de los regímenes de disturbio más allá de un umbral en el que la recuperación natural es poco probable. La investigación en estos asuntos debe instituirse en tierras manejadas por agencias estatales o federales porque la mayoría de las tierras aún dominadas por Artemisia son de propiedad pública. Además del desafío de entender la dinámica aves-hábitat en las estepas arbustivas, la conservación de los paisajes de matorral de Artemisia depende de nuestra habilidad de reconocer y comunicar su valor intrínseco y de nuestra decisión para conservarlos.

Predation on artificial nests in forested riparian buffer strips

We used artificial nests to examine predation in riparian buffer strips created by commercial clear-cutting and in unharvested control areas on industrial forestlands in eastern Maine. Nests in riparian buffer strips were depredated more often than those in intact riparian forests. This pattern was similar for both ground and shrub nests and for both trials. Predation rate for nests in control stands was 15%, compared to 31% in 20-40m wide buffer strips along tributary streams (P = 0.016) and 23% in 60-80m wide buffer strips along mainstem streams (P = 0.045). Predation rates were similar (P = 0.41) in mainstem and tributary buffer strips. Greater predation rates documented for nests in riparian buffer strips likely resulted from an elevated number and diversity of predators associated with the narrow, linear forest stands. Remotely-triggered cameras placed on a subset of nests revealed 6 species of nest predators. Predators identified at nests were mostly forest species and not species directly associated with riparian habitats. Red squirrels (Tamiasciurus hudsonicus) and blue jays (Cyanocitta cristata) were responsible for >50% of the identified depredations. Black bears (Ursus americanus) were photographed only in tributary buffer strips and may have been using them to travel between larger forested stands. Increased predation of eggs and young probably reduces the nesting success of birds in riparian buffer strips. Managers should leave wide (≥ 150-m) buffer strips along riparian zones to reduce edge-related nest predation, especially in landscapes where buffer strips are an important component of the existing mature forest.

PREDATION ON REAL AND ARTIFICIAL NESTS IN SHRUBSTEPPE LANDSCAPES FRAGMENTED BY AGRICULTURE

Abstract Clearing of shrubsteppe communities for agriculture has created a highly fragmented landscape in eastern Washington, a condition that has been shown to adversely affect nesting success of birds in some forest and grassland communities. We used artificial nests monitored by cameras to examine relative effects of fragmentation, distance to edge, and vegetation cover on nest predation rates and to identify predators of shrubsteppe-nesting passerines and grouse. Predation rate for artificial nests was 26% (n = 118). Fragmentation had a strong influence on predation rates for artificial nests, with nests in fragmented landscapes about 9 times more likely to be depredated as those in continuous landscapes. Daily survival rate (± SE) for 207 real nests of 4 passerine species also was greater in continuous (0.978 ± 0.004) than in fragmented (0.962 ± 0.006) landscapes, although pattern of predation between real and artificial nests was not consistent among sites. Artificial nests were depredated by Common Ravens (Corvus corax), Black-billed Magpies (Pica hudsonia), Sage Thrashers (Oreoscoptes montanus), least chipmunks (Tamias minimus), and mice. Most nests in fragments were depredated by corvids (58%), whereas only Sage Thrashers and small mammals depredated nests in continuous landscapes. Increased predation by corvids and lower nest success in fragmented landscapes may have played a part in recent declines of some shrubsteppe birds. Future research should measure annual reproductive success of individual females and survival rates of juveniles and adults. Depredación de Nidos Naturales y Artificiales en Paisajes de Estepa Arbustiva Fragmentados por Agricultura Resumen. El reemplazo de estepa arbustiva por campos de cultivo ha creado un paisaje altamente fragmentado en el este de Washington, afectando adversamente el éxito de nidificación de aves en algunas comunidades de bosque y pastizal. Usamos nidos artificiales monitoreados por cámaras para examinar los efectos relativos de la fragmentación, la distancia al borde y la cobertura de la vegetación sobre las tasas de depredación de nidos, y para identificar los depredadores de paserinos y gallinas silvestres (Phasianidae) que nidifican en la estepa arbustiva. La tasa de depredación de los nidos artificiales fue del 26% (n = 118). La fragmentación tuvo una fuerte influencia en las tasas de depredación de nidos artificiales, ya que los nidos en paisajes fragmentados tuvieron una probabilidad de ser depredados 9 veces mayor que aquellos en paisajes continuos. La tasa de supervivencia diaria (± EE) de 207 nidos naturales pertenecientes a 4 especies de paserinos también fue mayor en paisajes continuos (0.978 ± 0.004) que fragmentados (0.962 ± 0.006), aunque el patrón de depredación entre nidos naturales y artificiales no fue consistente entre sitios. Los nidos artificiales fueron depredados por Corvus corax, Pica hudsonia, Oreoscoptes montanus, Tamias minimus y ratones. La mayoría de los nidos en fragmentos fueron depredados por C. corax (58%), mientras que sólo O. montanus y pequeños mamíferos depredaron nidos en paisajes continuos. Un incremento en la depredación por parte de C. corax y un menor éxito de los nidos en paisajes fragmentados puede haber jugado un rol en la disminución de algunas aves de la estepa arbustiva. Futuras investigaciones deberían medir el éxito reproductivo anual de hembras individuales y las tasas de supervivencia de juveniles y adultos.

Predation rates on artificial nests in an industrial forest landscape

Abstract We examined patterns of predation among ground and shrub nests in extensive forests, forest fragments, regenerating clearcuts, and young plantations in a landscape dominated by industrial forest management in north-central Maine, USA. The predation rate in extensive forests (65%) was greater ( P = 0.0001 ) than that in forest fragments (47%). This result contrasts with previous studies from agricultural and developed landscapes and may be due to surrounding land use types and their associated predator communities. In forest fragments, shrub nests within 75 m of the edge were more likely to be depredated than those farther than 75 m ( P = 0.043). Predation in clearcuts (23%) was less than that in forest fragments ( P = 0.0001) or plantations (41%) ( P = 0.0015) and decreased with increasing distance from the edge ( P = 0.001) and increasing vegetation cover at the nest site ( P = 0.006). In contrast, predation rates in plantations increased with increasing vegetation density ( P = 0.0174) and distance to edge ( P = 0.0235). Results from our study suggest that findings documented in other, more developed, landscapes cannot readily be applied to extensive managed forests, and that conversion of naturally regenerating stands to plantations may lower the nesting success of birds that breed in early successional forests.

Survival and Causes of Mortality of Head-Started Western Pond Turtles on Pierce National Wildlife Refuge, Washington

Abstract The western pond turtle (Actinemys marmorata) is a species of conservation concern over much of its range and is listed as endangered in Washington State. From 2000 to 2004, we used radiotelemetry to document survival and mortality factors of head-started western pond turtles (n  =  68) released into Pierce National Wildlife Refuge in southwestern Washington. Survival estimates for first year and older turtles ranged from 86% to 97% and overlapping confidence intervals indicated no detectible differences among age classes or among years. Subadult turtles released at ≥90-mm carapace length apparently avoided capture by most aquatic predators, indicating that terrestrial predators should be the focus of research and management where predation on larger age-classes is a concern. High annual survival combined with the documented nesting by ≥7-year-old female head-started turtles in Washington suggest that recruitment of adults is being achieved; however, head-starting is only practical as an interim solution and strategies for effective removal of aquatic predators must be developed and implemented where natural recruitment is inadequate to maintain populations.

Nest Site Selection by Western Gray Squirrels at Their Northern Range Terminus

Abstract The western gray squirrel (Sciurus griseus) in Washington, USA, is limited to 3 disjunct areas and is a state threatened species. Information is lacking for the North Cascades population, which is the northernmost population for the species. Squirrels in this population exist without oaks (Quercus spp.) that provide forage and cavities for maternal nests elsewhere in their range. During May 2003 to August 2005, we studied selection of nest sites and nest trees by 18 radiocollared squirrels in Okanogan County, Washington. Without oak cavities, females reared their young in dreys. General nest-tree characteristics were similar to characteristics of western gray squirrel nest trees in Southeastern Cascades: relatively tall ponderosa pines (Pinus ponderosa) ≥40 cm diameter at breast height. Results from conditional logistic models determined that the odds of a squirrel selecting a tree for nesting increased with greater diameter at breast height and with infection by dwarf mistletoe (Arceuthobium spp.). Nest sites with high selection probability by squirrels had greater basal area and number of tree species than available unselected sites. Retention of forest patches that include a mix of conifer species or conifer and deciduous trees and moderate to high basal area could promote nesting opportunities, connectivity for arboreal travel, as well as abundance and diversity of hypogeous fungi. Experiments to test the efficacy of retaining untreated patches of varying size (including trees infected with mistletoe) on nesting by western gray squirrels within stands managed for fire suppression and forest health would provide important information about the effects of forest fuel management on arboreal wildlife.

Daily Energy Expenditure of Ovenbirds (Seiurus aurocapillus) Feeding Nestlings

Abstract The doubly labeled water method was used to measure daily energy expenditure of adult Ovenbirds (Seiurus aurocapillus) feeding nestlings in large and small forests in northern New England. Carbon dioxide production for all birds averaged 7.67 ± 1.29 mL g−1 hr−1 (n = 27), equivalent to 90.1 ± 15.0 kJ day−1. Carbon dioxide production did not differ between males and females within the same pair measured over the same period. Ratio of daily energy expenditure to basal metabolic rate (BMR) for Ovenbirds (3.4) was closer to the mean value derived for aerial foragers (3.8) than that for ground foragers (2.3) in a sample of passerines feeding nestlings. High daily energy expenditure for Ovenbirds may be related to their relatively brief breeding season in northern climates and their use of cool, closed-canopy forests. Although daily energy expenditure for Ovenbirds was high when compared to other ground-foraging passerines, most individuals were not working near the hypothetical maximum of 4× BMR (Drent and Daan 1980). Daily energy expenditure for Ovenbirds feeding young was greater in large forests than small forests, although the difference was not statistically significant. We speculate that time used for foraging (and hence energy expenditure) may be lower in small forests as a result of increased prey density, or alternatively, greater risk of nest predation in forest fragments leads to greater vigilance at the nest site and less time available for foraging. Further studies of avian energetics in large and small forests, including detailed time–activity budgets, may reveal hidden costs of forest fragmentation.