Jeffrey R. Dunk

Using Forest Inventory Data To Assess Fisher Resting Habitat Suitability In California

The fisher (Martes pennanti) is a forest-dwelling carnivore whose current distribution and association with late-seral forest conditions make it vulnerable to stand-altering human activities or natural disturbances. Fishers select a variety of structures for daily resting bouts. These habitat elements, together with foraging and reproductive (denning) habitat, constitute the habitat requirements of fishers. We develop a model capable of predicting the suitability of fisher resting habitat using standard forest vegetation inventory data. The inventory data were derived from Forest Inventory and Analysis (FIA), a nationwide probability-based sample used to estimate forest characteristics. We developed the model by comparing vegetation and topographic data at 75 randomly selected fisher resting structures in the southern Sierra Nevada with 232 forest inventory plots. We collected vegetation data at fisher resting locations using the FIA vegetation sampling protocol and centering the 1-ha FIA plot on the resting structure. To distinguish used and available inventory plots, we used nonparametric logistic regression to evaluate a set of a priori biological models. The top model represented a dominant portion of the Akaike weights (0.87), explained 31.5% of the deviance, and included the following variables: average canopy closure, basal area of trees <51 cm diameter breast height (dbh), average hardwood dbh, maximum tree dbh, percentage slope, and the dbh of the largest conifer snag. Our use of routinely collected forest inventory data allows the assessment and monitoring of change in fisher resting habitat suitability over large regions with no additional sampling effort. Although models were constrained to include only variables available from the list of those measured using the FIA protocol, we did not find this to be a shortcoming. The model makes it possible to compare average resting habitat suitability values before and after forest management treatments, among administrative units, across regions and over time. Considering hundreds of plot estimates as a sample of habitat conditions over large spatial scales can bring a broad perspective, at high resolution, and efficiency to the assessment and monitoring of wildlife habitat.

Natal Dispersal of the Spotted Owl in Southern California: Dispersal Profile of an Insular Population

Abstract We studied the dispersal patterns of an insular population of California Spotted Owls (Strix occidentalis occidentalis) in southern California from 1987–1998. The study area encompassed the entire San Bernardino Mountains and included a nested, 535-km2 study area which we used to evaluate the effects of study area size on dispersal parameter estimation. One hundred and twenty-nine of the 478 banded juvenile owls (27%) had entered the territorial population by 1998. Over half of the successful dispersers became territorial within one year. Additionally, all females and 95% of the males occupied territories within three years. Twenty-three sibling pairs and one set of triplets dispersed successfully. Sibling dispersal distances were not correlated. Sixty-seven males and 62 females dispersed 2.3–36.4 km (mean ± SD = 10.1 ± 7.6 km) and 0.4–35.7 km (mean ± SD = 11.7 ± 8.1 km), respectively. The difference between male and female mean dispersal distances was not significant. Dispersal distance and first-year survival were underestimated when using data collected within the smaller, nested study area. The presence of conspecifics may play a key role in the settling process. Seventy-eight percent of the dispersers settled in territories that were occupied by either pairs or single owls the previous year, 16% settled in vacant territories next to occupied sites, and 6% settled at sites of unknown occupancy. No owls settled at unoccupied sites that were not adjacent to occupied sites. Dispersión Natal de Strix occidentalis occidentalis: Descripción de la Dispersión de una Población Insular Resumen.  Estudiamos los patrones de dispersión de una población insular de lechuza moteada californiana (Strix occidentalis occidentalis) en el sur de California, desde 1987–1998. El área de estudio comprendió las montañas de San Bernardino e incluyó un sito de estudio de 535 km2 incluído en esta zona el cual usamos para evaluar el efecto del tamaño del área de estudio para la estimación de los parámetros de dispersión. Hasta 1998, 129 de las 478 lechuzas juveniles marcadas (27%) habían entrado a la población territorial. Más la mitad de los dispersores exitosos se hicieron territoriales al cabo de un año. Adicionalmente, todas las hembras y el 95% de los machos ocuparon territorios al cabo de tres años. Veintitrés pares de hermanos y un triplete se dispersaron exitosamente. La distancia de dispersión entre hermanos no se correlacionó. Sesenta y siete machos y 62 hembras se dispersaron 2.3–36.4 km (media = 10.1 ± 7.6 km) y 0.4–35.7 km (media = 11.7 ± 8.1 km), respectivamente. La diferencia entre la media de la distancia de dispersión entre hembras y machos no fue significativa. La distancia de dispersión y supervivencia del primer año fueron subestimadas cuando se utilizaron los datos colectados en la sub-área de estudio de menor tamaño. La presencia de conespecíficos puede representar un factor clave en el proceso de asentamiento. Setenta y ocho por ciento de los dispersores se asentaron en territorios que habían estado ocupados por parejas o lechuzas no emparejadas el año anterior, el 16% en territorios no ocupados próximos a sitios ocupados, y el 6% se asentó en sitios con ocupación desconocida. Ninguna lechuza se asentó en sitios desocupados que no estuvieran adyacentes a un sitio ocupado.

Blackfly-induced mortality of nestling red-tailed Hawks

--We documented blackfly infestations (Simulium canonicolum) at 42 Red-tailed Hawk (Buteo jamaicensis) nests in Wyoming. Blackflies caused mortality at 6 of 42 (14%) nests where young hatched (13 of 87 nestlings) and were the only known cause of nestling mortality. The onset of infestations occurred when nestlings were 3 to 20 days old and usually lasted until nestlings died or fledged. Age of nestlings at mortality ranged from 9 to 43 days. Levels of blackfly infestation were highly variable among nests and were affected by weather The cumulative effects of infestations on nestlings, including physical harassment, Leucocytozoon (a blood protozoan transmitted by blackflies) infection, and direct loss of blood and body fluids from biting flies, apparently resulted in mortalities through sustained physiological damage, trauma associated with early nest departure, or both. Because blackfly infestations can be detected only at close range, are ephemeral at nests, and can cause mortality of nestlings over a wide range of ages, the presence of blackflies and their influence on reproduction probably are undetected during most raptor productivity surveys. Received 23 January 1997, accepted 26 August 1997. A VARIETY OF PARASITES has been found in raptors (Trainer 1969, Keymer 1972, Greenwood 1977, Guti6rrez 1989, Philips 1990, Forrester et al. 1994). Although the literature describing parasites in raptors is fairly extensive, few researchers have described the effects of these parasites on their raptor hosts. Blackflies (Simulium spp.) and the parasites they transmit have been associated with at least four species of raptors (Greiner and Kocan 1977, Jolly 1982, Hunter et al. 1997), but their effect on the health of these species is largely unknown. Fitch et al. (1946) reported that 7 of 11 mortalities of nestling Red-tailed Hawk (Buteo jamaicensis) were due to blackflies (Eusimulium clarum). Similarly, Brown and Amadon (1968) reported that during wet years, biting flies (Prosimulium spp.) were a principal cause of mortality of nestling Red-tailed Hawks in Cal4 Present address: Teton Science School, P.O. Box 68, Kelly, Wyoming 83011, USA. E-mail: roger@tetonscience. org s Present address: Department of Wildlife, Humboldt State University, Arcata, California 95521, USA. ifornia. However, they did not suggest possible mechanisms of mortality and gave no source for the information. Stabler and Holt (1965) reported a prevalence of blood protozoa in a number of different hawks, and Forrester et al. (1994) documented the relative occurrence of blood parasites in raptors in Florida but made no mention of the potential effects of these parasites on raptor productivity. Hunter et al. (1997) attributed mortality of Great Horned Owls (Bubo virginianus) to feeding blackflies (Simulidae), anemia, and blood parasite (Leucocytozoon spp.) infection. However, all of the mortality they observed occurred in owls tethered to platforms for experimental purposes. In a portion of our study area in Grand Teton National Park (GTNP), northwestern Wyoming, the number of young Red-tailed Hawks fledged per nest declined from 1.4 to 0.7 between 1947 and 1975 (Craighead and Mindell 1981). More recent monitoring of productivity (1990 to 1991) indicated a high proportion of nesting failures, and dead young were found in and beneath some nests (S. Cain unpubl. data). In all cases where dead nestlings were found, prey items were in the nests, and adults were

PREDICTING THE OCCURRENCE OF RARE MOLLUSKS IN NORTHERN CALIFORNIA FORESTS

Terrestrial mollusks are important components of forest ecosystems, yet we know very little about the distribution and habitat of many of these species. We sampled for terrestrial mollusks in northern California with the goal of estimating the geographic ranges and developing predictive habitat models for five species that were assumed to be sensitive to land management activities. The species of interest were Ancotrema voyanum, Helminthoglypta talmadgei, Monadenia churchi, Monadenia fidelis klamathica, and M. f. ochromphalus. We randomly selected 308 plots for sampling from a grid of points across a 2.2 million-ha study area. We used Generalized Additive Models to estimate each mollusks geographic range and to develop predictive habitat models within their ranges. Models were developed at one microscale (1 ha) and six mesoscales (ranging from 12.5 to 1250 ha) using vegetation, physical, climatic, and spatial location covariates. Estimated geographic ranges varied from 4770 to 15 795 km2. Predictive habi...

Mapping sources, sinks, and connectivity using a simulation model of northern spotted owls

Source-sink dynamics are an emergent property of complex species–landscape interactions. A better understanding of how human activities affect source-sink dynamics has the potential to inform and improve the management of species of conservation concern. Here we use a study of the northern spotted owl (Strix occidentalis caurina) to introduce new methods for quantifying source-sink dynamics that simultaneously describe the population-wide consequences of changes to landscape connectivity. Our spotted owl model is mechanistic, spatially-explicit, individual-based, and incorporates competition with barred owls (Strix varia). Our observations of spotted owl source-sink dynamics could not have been inferred solely from habitat quality, and were sensitive to landscape connectivity and the spatial sampling schemes employed by the model. We conclude that a clear understanding of source-sink dynamics can best be obtained from sampling simultaneously at multiple spatial scales. Our methodology is general, can be readily adapted to other systems, and will work with population models ranging from simple and low-parameter to complex and data-intensive.

Hierarchical Bayesian spatial models for multispecies conservation planning and monitoring

Biologists who develop and apply habitat models are often familiar with the statistical challenges posed by their datas spatial structure but are unsure of whether the use of complex spatial models will increase the utility of model results in planning. We compared the relative performance of nonspatial and hierarchical Bayesian spatial models for three vertebrate and invertebrate taxa of conservation concern (Churchs sideband snails [Monadenia churchi], red tree voles [Arborimus longicaudus], and Pacific fishers [Martes pennanti pacifica]) that provide examples of a range of distributional extents and dispersal abilities. We used presence-absence data derived from regional monitoring programs to develop models with both landscape and site-level environmental covariates. We used Markov chain Monte Carlo algorithms and a conditional autoregressive or intrinsic conditional autoregressive model framework to fit spatial models. The fit of Bayesian spatial models was between 35 and 55% better than the fit of nonspatial analogue models. Bayesian spatial models outperformed analogous models developed with maximum entropy (Maxent) methods. Although the best spatial and nonspatial models included similar environmental variables, spatial models provided estimates of residual spatial effects that suggested how ecological processes might structure distribution patterns. Spatial models built from presence-absence data improved fit most for localized endemic species with ranges constrained by poorly known biogeographic factors and for widely distributed species suspected to be strongly affected by unmeasured environmental variables or population processes. By treating spatial effects as a variable of interest rather than a nuisance, hierarchical Bayesian spatial models, especially when they are based on a common broad-scale spatial lattice (here the national Forest Inventory and Analysis grid of 24 km(2) hexagons), can increase the relevance of habitat models to multispecies conservation planning.

Nest-site selection and reproductive success in common ravens

Studies of habitat selection by animals can be categorized in two ways: behavioral and evolutionary (Krebs 1994). Most studies of habitat selection consider the behavioral perspective whereby biotic and/ or abiotic components of the environment that appear to influence habitat use are identified, generally by comparing used sites with random or available sites (e.g. Mosher et al. 1986, Seamans and Gutierrez 1995). The evolutionary approach examines the effects of selecting particular habitats on an index of fitness, e.g. survivorship or reproduction (see Martin and Roper 1988, Petit and Petit 1996). If nest-site selection is a heritable trait, then natural selection should favor individuals that choose nest sites that confer greater reproductive success. Common Ravens (Corvus corax) are suitable subjects for examination of reproduction in relation to habitat characteristics owing to their variable clutch size, which ranges from three to seven eggs (Dunk et al. unpubl. data). Thus, in any one year, a relatively large range in number of young fledged is possible within a population, and it may be possible to detect a cline in reproductive success relative to nest-site characteristics. Common Ravens are widely distributed throughout North America and Europe. In western North America, ravens have been characterized as pests that easily adapt to human-modified landscapes (Butchko 1990, Boarman 1993, Marzluff et al. 1994). During the past 25 years, raven numbers have increased in many areas of the western United States (Boarman 1993, Dunk et al. 1994, Marzluff et al. 1994). Despite their ubiquitous nature, large numbers, and broad geographic range, little is known about many aspects of the breeding biology of ravens. In particular, very little has been published on raven nest-site selection. Ravens nest on many substrates, including cliffs (Ratcliffe 1962, White and Cade 1971, Hooper 1977, Skarphedinsson et al. 1990), highway overpasses and billboards (White and Tanner-White 1988), churches (Heinrich 1989), power poles (Knight and Kawashima 1993), and trees (Dorn 1972, this study), but nest-site characteristics have been quantified only for cliff nests (White and Cade 1971, Hooper 1977).

A range-wide occupancy estimate and habitat model for the endangered Point Arena mountain beaver (Aplodontia rufa nigra)

The mountain beaver (Aplodontia rufa) is notably the most primitive North American rodent with a restricted distribution in the Pacific Northwest based on its physiological limits to heat stress and water needs. The Point Arena subspecies (A. r. nigra) is federally listed as endangered and is 1 of 2 subspecies that have extremely small and disjunct distributions, putting the taxon at risk from habitat loss and warming global temperatures. We sought to understand their range-wide distribution, to predict the environmental features that best describe their occurrence, and to establish a foundation for monitoring their distribution. We randomly sampled the occurrence of Point Arena mountain beavers (PAMB) from the portion of their geographic range that was accessible (public lands plus private lands where permission was granted). We surveyed 127, 25-ha sample units for their distinctive burrows and estimated the probability of detecting burrows, if they were present, at > 90% per visit. Using this information, we estimated occupancy across the accessible portion of the range to be 26.2%. Range-wide estimates of occupancy, combined with strategically selected locations where abundance and survival can be estimated noninvasively, may comprise a realistic monitoring program for this taxon. We also used the detection and nondetection locations to develop a habitat suitability model by relating these locations to remotely sensed predictors. We evaluated 53 a priori candidate habitat suitability models and the bestfitting model included gentle slopes, low terrain roughness indices, and the high density of rivers and streams. Selecting the probability value that best separated the sample units into suitable and nonsuitable habitat, we estimated a total of 70.5 km2 of suitable habit, or approximately 40.4% of the original geographic range. New detections significantly expanded the known geographic range, moderating concerns about habitat loss, including that predicted by climate change. A substantial number of suitable areas were predicted to occur outside the current range. The identification of high suitability areas allows management agencies to prioritize areas for PAMB conservation planning, evaluate human impacts on habitat, and evaluate how a changing climate may affect distribution.