Kathryn L. Purcell

DESIGN CONSIDERATIONS FOR EXAMINING TRENDS IN AVIAN ABUNDANCE USING POINT COUNTS: EXAMPLES FROM OAK WOODLANDS

Abstract We used data from two oak-woodland sites in California to develop guidelines for the design of bird monitoring programs using point counts. We used power analysis to determine sample size adequacy when varying the number of visits, count stations, and years for examining trends in abundance. We assumed an overdispersed Poisson distribution for count data, with overdispersion attributed to observer variability, and used Poisson regression for analysis of population trends. Overdispersion had a large, negative effect on power. The number of sampling years also had an especially large effect on power. In all cases, 10 years of sampling were insufficient to detect a decline in abundance of 30% over 10 years. Increasing the sampling period to 20 years provided adequate power for 56% of breeding species at one site. The number of count stations needed for detecting trends for a given species depended primarily on observer variability. If observer variability was high, increasing the number of years and visits was a better approach than increasing the number of stations. Increasing the number of stations was most beneficial for species with low abundance or low observer variability. When the number of stations is limited by the size of the area, we recommend multiple visits to stations. For most species, multiple visits per year (six or more) for 15–20 years were needed to detect a 30% decreasing trend in 10 years with adequate power. We suggest potentially useful focal species for monitoring, such as keystone species like the Acorn Woodpecker (Melanerpes formicivorus). Consideraciones de Diseño para Examinar las Tendencias en la Abundancia de Aves Usando Conteos Puntuales: Ejemplos con Datos de Bosques de Encino en California Resumen. Usamos datos de dos sitios ubicados en bosques de encino en California, con el fin de desarrollar una guía para diseñar programas de monitoreo usando conteos puntuales. Usamos un análisis del poder de la prueba para determinar el tamaño adecuado de la muestra al cambiar el número de visitas, el número de estaciones de conteo y los años de conteo con el fin de examinar las tendencias en la abundancia. Supusimos la distribución de Poisson para el conteo, con sobredispersión atribuida a la variabilidad del observador. La sobredispersión tuvo un efecto fuerte y negativo en el poder de la prueba. El efecto del número de años de muestreo fue especialmente grande sobre el poder. En cada caso, 10 años de muestreo fueron insuficientes para detectar una disminución de la abundancia del 30% en 10 años. Al aumentar el período de muestreo a 20 años, el análisis proporcionó un poder adecuado para 56% de las especies reproductivas en uno de los sitios. El número de estaciones de conteo requeridos para una especie dada dependió principalmente de la variabilidad del observador. Si la variabilidad del observador era alta, aumentar el número de años de observación y visitas fue una estrategia mejor que aumentar el número de estaciones. Aumentar el número de estaciones fue más benéfico para especies poco abundantes o con baja variabilidad del observador. Cuando el número de estaciones es limitado por el tamaño del área, recomendamos visitas múltiples a las estaciones. Para la mayoría de las especies se requieren visitas anuales múltiples (6 o más) durante 15–20 años para detectar una tendencia de decrecimiento a una razón del 30% en 10 años con un poder adecuado. Sugerimos especies focales potencialmente útiles para monitoreo tales como la especie clave Melanerpes formicivorus.

Evaluating management risks using landscape trajectory analysis: a case study of California fisher

ABSTRACT Ecosystem management requires an understanding of how landscapes vary in space and time, how this variation can be affected by management decisions or stochastic events, and the potential consequences for species. Landscape trajectory analysis, coupled with a basic knowledge of species habitat selection, offers a straightforward approach to ecological risk analysis and can be used to project the effects of management decisions on species of concern. The fisher (Martes pennanti) occurs primarily in late-successional forests which, in the Sierra Nevada mountains, are susceptible to high-intensity wildfire. Understanding the effects of fuels treatments and fire on the distribution of fisher habitat is a critical conservation concern. We assumed that the more a treated landscape resembled occupied female fisher home ranges, the more likely it was to be occupied by a female and therefore the lower the risk to the population. Thus, we characterized important vegetation attributes within the home ranges of 16 female fishers and used the distribution of these attributes as a baseline against which the effects of forest management options could be compared. We used principal components analysis to identify the major axes defining occupied female fisher home ranges and these, in addition to select univariate metrics, became our reference for evaluating the effects of landscape change. We demonstrated the approach at two management units on the Sierra National Forest by simulating the effects of both no action and forest thinning, with and without an unplanned fire, on vegetation characteristics over a 45-yr period. Under the no action scenario, landscapes remained similar to reference conditions for approximately 30-yr until forest succession resulted in a loss of landscape heterogeneity. Comparatively, fuel treatment resulted in the reduction of certain forest elements below those found in female fisher home ranges yet little overall change in habitat suitability. Adding a wildfire to both scenarios resulted in divergence from reference conditions, though in the no action scenario the divergence was 4 × greater and the landscape did not recover within the 45-yr timeframe. These examples demonstrate that combining the results of forest growth and disturbance modeling with habitat selection data may be used to quantify the potential effects of vegetation management activities on wildlife habitat.

Canine Distemper in an Isolated Population of Fishers (Martes pennanti) from California

Four fishers (Martes pennanti) from an insular population in the southern Sierra Nevada Mountains, California, USA died as a consequence of an infection with canine distemper virus (CDV) in 2009. Three fishers were found in close temporal and spatial relationship; the fourth fisher died 4 mo later at a 70 km distance from the initial group. Gross lesions were restricted to hyperkeratosis of periocular skin and ulcera-tion of footpads. All animals had necrotizing bronchitis and bronchiolitis with syncytia and intracytoplasmic inclusion bodies. Inclusion bodies were abundant in the epithelia of urinary bladder and epididymis but were infrequent in the renal pelvis and the female genital epithelia. No histopathologic or immu-nohistochemical evidence for virus spread to the central nervous system was found. One fisher had encephalitis caused by Sarcocystis neurona and another had severe head trauma as a consequence of predation. The H gene nucleo-tide sequence of the virus isolates from the first three fishers was identical and was 99.6% identical to the isolate from the fourth fisher. Phylogenetically, the isolates clustered with other North American isolates separate from classical European wildlife lineage strains. These data suggest that the European wildlife lineage might consist of two separate subgroups that are genetically distinct and endemic in different geographic regions. The source of infection as well as pertinent transmission routes remained unclear. This is the first report of CDV in fishers and underscores the significance of CDV as a pathogen of management concern.

Fluctuating populations of house wrens and Bewick's wrens in foothills of the Western Sierra Nevada of California

In foothills of the western Sierra Nevada, 31 km east of Madera, California, we studied whether Bewicks Wrens (Thryomanes bewickii) tend to be excluded from an area occupied by House Wrens (Troglodytes aedon) as reported in several studies in the eastern United States. Neither point counts from 1985 to 1997 nor spot mapping from 1989 to 1993 suggests any interaction between these species. The study period included the most prolonged drought and the most severe period of winter weather in the 64-year climatological record from the study site. House Wren abundance was significantly related to the 4-year running average of annual precipitation and to the lowest temperature recorded in the winter months preceding survey counts. We speculate that House Wrens cannot maintain their numbers by local recruitment during droughts in the oak-pine woodlands that dominate our study area and that recovery of their population following droughts involves recruitment from other areas, probably riparian zones and other mesic habitats elsewhere in the Sierra foothills and Central Valley of California. There was no influence of precipitation on abundance of Bewicks Wrens and, although they apparently sustained heavy mortality during a period of extreme winter weather, their numbers otherwise were not related to the lowest temperature during the winter preceding counts.

Camera trapping estimates of density and survival of fishers Martes pennanti

Abstract Developing efficient monitoring strategies for species of conservation concern is critical to ensuring their persistence. We have developed a method using camera traps to estimate density and survival in mesocarnivores and tested it on a population of fishers Martes pennanti in an area of approximately 300 km2 of the southern Sierra Nevada mountains in California. Fishers in this region are isolated from other populations by a gap of approximately 400 km, and the status of individual populations in the southern Sierra Nevada is poorly understood, making management decisions difficult. We caught fishers in live traps, marked them with ear tags, and resighted them with camera traps. We measured latency to first detection and detection rate to compare our results to previous camera trapping studies of fishers. We used the robust design Poisson log-normal mixed-effects mark-resight model to obtain annual estimates of density and apparent survival. Our values for latency to first detection and detection rate were slightly lower than those obtained by previous studies. Fishers in this isolated region occur at lower densities than at other locations across their range with only approximately 6-11 animals/100 km2. Their average annual, adult survival rate (0.94) was comparable to that found in other studies, though this parameter had very low precision. We experienced relatively high levels of tag loss in our study, suggesting our estimates of abundance are biased upward. We provide recommendations for improving the precision and accuracy of results obtained from this type of study. Our results demonstrate a novel application of mark-resight methods to estimate density and survival for mesocarnivores. These estimates provide timely information to managers about fishers at the local population level in the southern Sierra Nevada mountains.

Patterns of Natural and Human-Caused Mortality Factors of a Rare Forest Carnivore, the Fisher (Pekania pennanti) in California

Wildlife populations of conservation concern are limited in distribution, population size and persistence by various factors, including mortality. The fisher (Pekania pennanti), a North American mid-sized carnivore whose range in the western Pacific United States has retracted considerably in the past century, was proposed for threatened status protection in late 2014 under the United States Endangered Species Act by the United States Fish and Wildlife Service in its West Coast Distinct Population Segment. We investigated mortality in 167 fishers from two genetically and geographically distinct sub-populations in California within this West Coast Distinct Population Segment using a combination of gross necropsy, histology, toxicology and molecular methods. Overall, predation (70%), natural disease (16%), toxicant poisoning (10%) and, less commonly, vehicular strike (2%) and other anthropogenic causes (2%) were causes of mortality observed. We documented both an increase in mortality to (57% increase) and exposure (6%) from pesticides in fishers in just the past three years, highlighting further that toxicants from marijuana cultivation still pose a threat. Additionally, exposure to multiple rodenticides significantly increased the likelihood of mortality from rodenticide poisoning. Poisoning was significantly more common in male than female fishers and was 7 times more likely than disease to kill males. Based on necropsy findings, suspected causes of mortality based on field evidence alone tended to underestimate the frequency of disease-related mortalities. This study is the first comprehensive investigation of mortality causes of fishers and provides essential information to assist in the conservation of this species.

Reproduction, abundance, and population growth for a fisher (Pekania pennanti) population in the Sierra National Forest, California

In the west coast region of the United States, fishers (Pekania pennanti) exist in 2 remnant populations—1 in northern California and 1 in the southern Sierra Nevada, California—and 3 reintroduced populations (western Washington, southern Oregon, and northeastern California). The West Coast Distinct Population Segment of fishers encompassing all of these populations was proposed for listing as threatened by the U.S. Fish and Wildlife Service in October 2014. There are likely fewer than 500 total fishers in the southern Sierra Nevada population isolate, but empirical data on demographic rates, population size, and population growth are almost entirely lacking. Our goal was to estimate demographic parameters and current abundance of a fisher population at the north margin of the southern Sierra Nevada region. Radiocollared fishers were monitored from 2007 to 2013 to estimate survival and demographic rates, and camera traps were used to estimate population size based on detections of individual animals in a capture—mark—resight (CMR) framework. A Leslie matrix model was used to estimate a deterministic population growth rate (&lgr;). Fisher abundance ranged from 48 animals in 2010 to 62 animals in 2012, whereas mean population density varied from 0.075 to 0.096 fishers/km2. Reproductive status was determined for 89 of 93 total denning opportunities; denning and weaning rates were estimated at 84% and 70%, and litter size was 1.6 kits. We documented 8 den failures, mostly associated with predator attacks. Demographic rates in the study population were comparable to reports from elsewhere in California or Oregon, but the CMR-based population density was the lowest reported in the United States. The estimated &lgr; for the population was 0.966 (range 0.786–1.155), which was in agreement with no indication of a positive or negative trend in population density. An encouraging result from sensitivity analyses was that minor improvements in fisher survival and fecundity, facilitated by proposed mitigation or management to reduce exposure to several agents of mortality, could improve &lgr; to 1.06–1.09 over the longer term. We believe that the combination of a population growth rate slightly below 1.0, small population size and low density, multiple challenges to survival and reproduction, and damage to habitat from wildfires warrants concern for the viability of the fisher population in our study area, which may extend to the overall southern Sierra Nevada population if &lgr; trends below 1.0 in other parts of the region. There is a need for continued monitoring and potential mitigation for threats to survival to assure continued presence of fishers in the southern Sierra Nevada, California.

ABUNDANCE AND PRODUCTIVITY OF WARBLING VIREOS ACROSS AN ELEVATIONAL GRADIENT IN THE SIERRA NEVADA

Abstract Recent studies have shown that Warbling Vireos (Vireo gilvus) are declining in California and that these trends are due to low reproductive success. Brood parasitism by Brown-headed Cowbirds (Molothrus ater) has been implicated in the low productivity. I explored two hypotheses related to population dynamics of Warbling Vireos along an elevational gradient: (1) potential source populations exist at high elevations where cowbirds are rare, and (2) potential source populations occur in the center of the elevational distribution with less productive populations at upper and lower elevations. From 1985 through 2002 I studied the abundance and productivity of Warbling Vireos over an elevational gradient in the southern Sierra Nevada. Warbling Vireos were most abundant in mid elevation mixed conifer sites, less abundant in lower elevation ponderosa pine sites and upper elevation true fir sites, and rare in upper elevation lodgepole pine sites. Likewise, daily survival rates of nests were highest at mid elevations (1800 m) and gradually decreased at both higher and lower elevations. Compared to other populations studied in California, nest success in mixed conifer habitat was high (60%, n  =  58). Although rates of brood parasitism were high enough to be of concern in low-elevation ponderosa pine forests, cowbird parasitism was not observed in mid- to upper-elevation forests. Warbling Vireos were most productive where they were most abundant. The hypothesis that potential source populations exist at upper elevations did not appear to hold at the upper bounds of the elevational distribution. The results of this study provide support for the hypothesis that potential source populations occur in the center of the elevational distribution, with less productive populations at both lower and higher elevations.

An evaluation of a weaning index for wild fishers (Pekania [Martes] pennanti) in California

Abstract Conservation concern for fishers (Pekania [Martes] pennanti) in the Pacific states has highlighted a need to develop cost-effective methods of monitoring reproduction in extant and reintroduced fisher populations. We evaluated the efficacy of nipple size as a predictive index of weaning success for females with known reproductive histories from 3 study areas in California. We captured and radiocollared 91 female fishers on 146 occasions between 2004 and 2011 and measured the width and height of all 4 nipples and quantified reproductive status via radiotelemetry. We classified each radiomarked female into 1 of 3 reproductive classes (nonbreeders, attempted breeders, and current breeders) based on our telemetry observations during the den season prior to capture. We used a modified random forests (RF) procedure to account for repeated measures of individual females sampled in multiple years. Our modified RF procedure correctly classified reproductive class for 130 (89%) and 131 (90%) of our 146 observations using raw and weighted vote totals, respectively. We calculated Cohens kappa of 0.80 and 0.81 using raw and weighted vote totals, respectively, indicating strong model performance. We conclude that nipple sizes of female fishers measured during a livetrapping effort can be used as a cost-effective index of the weaning rates of adult female fishers.

RETURN RATES OF BANDED GRANIVORES IN RELATION TO BAND COLOR AND NUMBER OF BANDS WORN

Abstract We tested the null hypotheses of (1) no effect of band color and (2) no effect of number of bands worn on annual recapture rates of birds on their winter range. Results are reported from four species of granivores—Spotted Towhee (Pipilo maculatus), Golden-crowned Sparrow (Zonotrichia atricapilla), White-crowned Sparrow (Z. leucophrys), and Dark-eyed Junco (Junco hyemalis). We found no effect of the number of bands worn on return rates of these species, nor did we detect an effect of band color on return rates. In the latter case, however, the power of our tests was low, and some results hinted at possible effects of color, especially yellow bands on Golden-crowned Sparrows.