Monica L. Bond

Habitat use and selection by California spotted owls in a postfire landscape.

Abstract Forest fire is often considered a primary threat to California spotted owls (Strix occidentalis occidentalis) because fire has the potential to rapidly alter owl habitat. We examined effects of fire on 7 radiomarked California spotted owls from 4 territories by quantifying use of habitat for nesting, roosting, and foraging according to severity of burn in and near a 610-km2 fire in the southern Sierra Nevada, California, USA, 4 years after fire. Three nests were located in mixed-conifer forests, 2 in areas of moderate-severity burn, and one in an area of low-severity burn, and one nest was located in an unburned area of mixed-conifer–hardwood forest. For roosting during the breeding season, spotted owls selected low-severity burned forest and avoided moderate- and high-severity burned areas; unburned forest was used in proportion with availability. Within 1 km of the center of their foraging areas, spotted owls selected all severities of burned forest and avoided unburned forest. Beyond 1.5 km, there were no discernable differences in use patterns among burn severities. Most owls foraged in high-severity burned forest more than in all other burn categories; high-severity burned forests had greater basal area of snags and higher shrub and herbaceous cover, parameters thought to be associated with increased abundance or accessibility of prey. We recommend that burned forests within 1.5 km of nests or roosts of California spotted owls not be salvage-logged until long-term effects of fire on spotted owls and their prey are understood more fully.

Does Access to Females or Competition among Males Limit Male Home-Range Size in a Promiscuous Rodent?

To maximize fitness, female mammals attempt to maximize offspring survival, whereas males attempt to mate with as many females as possible, which results in differential use of space. The relative influence of male competition versus access to females on space use by males has not been addressed theoretically or empirically. We conducted an experiment in which we manipulated total density, density of females, and density of males to determine relative influence of density of each sex on space use and overlap by male gray-tailed voles (Microtus canicaudus). Home-range size was correlated inversely with total density and was influenced separately by each sex. Home-range sizes of males were significantly smaller in high male-low female populations than in low female-high male populations. Males overlapped 4-5 females and 4-5 other males in populations with low densities of both sexes and high densities of both sexes. When sex ratios were skewed toward females, males still overlapped 4-5 females but only one other male. When sex ratios were skewed toward males, males overlapped only two females while overlapping three other males. Home-range size of a male does not appear to expand beyond an overlap with about five members of either sex. Thus, intrasexual competition with five males or overlap with five females appear to set upper limits to home-range size of male gray-tailed voles. We conclude that space use by males is influenced by intrasexual competition and access to females with an upper limit of overlap with either sex.

Complex Early Seral Forests of the Sierra Nevada: What are They and How Can They Be Managed for Ecological Integrity?

ABSTRACT: Complex early seral forests (CESFs) occupy potentially forested sites after a stand-replacement disturbance and before re-establishment of a closed-forest canopy. Such young forests contain numbers and kinds of biological legacies missing from those produced by commercial forestry operations. In the Sierra Nevada of California, CESFs are most often produced by mixed-severity fires, which include landscape patches burned at high severity. These forests support diverse plant and wildlife communities rarely found elsewhere in the Sierra Nevada. Severe fires are, therefore, essential to the regions ecological integrity. Ecologically detrimental management of CESFs, or unburned forests that may become CESFs following fire, is degrading the regions globally outstanding qualities. Unlike old-growth forests. CESFs have received little attention in conservation and reserve management. Thus, we describe important ecological attributes of CESFs and distinguish them from early serai conditions created by logging. We recommend eight best management practices in CESFs for achieving ecological integrity on federal lands in the mixed-conifer region of the Sierra Nevada.

DYNAMICS OF BREEDING-SEASON SITE OCCUPANCY OF THE CALIFORNIA SPOTTED OWL IN BURNED FORESTS

Abstract. Understanding how habitat disturbances such as forest fire affect local extinction and probability of colonization—the processes that determine site occupancy—is critical for developing forest management appropriate to conserving the California Spotted Owl (Strix occidentalis occidentalis), a subspecies of management concern. We used 11 years of breeding-season survey data from 41 California Spotted Owl sites burned in six forest fires and 145 sites in unburned areas throughout the Sierra Nevada, California, to compare probabilities of local extinction and colonization at burned and unburned sites while accounting for annual and site-specific variation in detectability. We found no significant effects of fire on these probabilities, suggesting that fire, even fire that burns on average 32% of suitable habitat at high severity within a California Spotted Owl site, does not threaten the persistence of the subspecies on the landscape. We used simulations to examine how different allocations of survey effort over 3 years affect estimability and bias of parameters and power to detect differences in colonization and local extinction between groups of sites. Simulations suggest that to determine whether and how habitat disturbance affects California Spotted Owl occupancy within 3 years, managers should strive to annually survey ≥200 affected and ≥200 unaffected historical owl sites throughout the Sierra Nevada 5 times per year. Given the low probability of detection in one year, we recommend more than one year of surveys be used to determine site occupancy before management that could be detrimental to the Spotted Owl is undertaken in potentially occupied habitat.

Influence of Pre-Fire Tree Mortality on Fire Severity in Conifer Forests of the San Bernardino Mountains, California

High tree mortality due to drought and insects often is assumed to increase fire severity once ignition occurs. In 2002-2003, coniferous forests in the San Bernardino Mountains, California experienced a significant tree mortality event due to drought and an outbreak of western pine beetles (Dendroctonus brevicomis). In October 2003, fire burned approximately 5,860 ha of conifer forest types in many beetle- and drought-affected stands where most pre-fire dead trees had retained needles. We used pre- and post-fire GIS data to examine how fire severity was affected by pre-fire tree mortality, vegetation characteristics, and topography. We found no evidence that pre-fire tree mortality influenced fire severity. These results indicate that widespread removal of dead trees may not effectively reduce higher-severity fire in southern Californias conifer forests. We found that sample locations dominated by the largest size class of trees (>61 cm diameter at breast height (dbh)) burned at lower severities than locations dominated by trees 28-60 cm dbh. This result suggests that harvesting larger-sized trees for fire-severity reduction purposes is likely to be ineffective and possibly counter-productive.

Occupancy of California Spotted Owl sites following a large fire in the Sierra Nevada, California

ABSTRACT High-severity forest fire often is presumed to adversely affect the occupancy of territories by California Spotted Owls (Strix occidentalis occidentalis) because these owls are associated with mature and old-growth forests. We used single-season, multi-state occupancy statistics to estimate site occupancy probability for Spotted Owls at 45 historically occupied sites during the breeding season immediately following the 2013 Rim Fire, which was one of the largest forest fires on record in California. We quantified how occupancy probability was influenced by the amount of high-severity fire occurring in mature forested habitat within Protected Activity Centers (PACs). The model-averaged estimate of site-occupancy probability for at least a single owl was 0.922 (±SE = 0.073), which was higher than other published occupancy probability estimates for this subspecies in either burned or long-unburned sites in the Sierra Nevada. Mean site-occupancy probability for pairs was 0.866 (±0.093), and most sites (33) were occupied by pairs. The amount of high-severity fire in the PAC did not affect pair occupancy. Occupancy probability by at least a single bird was negatively correlated with the amount of high severity fire in the PAC but remained >0.89 in 100% high-severity burned PACs. These data add to observations that California Spotted Owls continue to use post-fire landscapes, even when the fires were large and where large areas burned at high severity, suggesting that owls are not generally negatively impacted by high-severity fire. Based on this and other studies of Spotted Owls, fire, and logging, we suggest land managers consider burned forest within and surrounding PACs as potentially suitable California Spotted Owl foraging habitat when planning and implementing management activities, and we recommend against logging burned forest within at least 1.5 km of nests or roosts for the conservation and recovery of this declining subspecies.

Variation in home-range size of Black-backed Woodpeckers

ABSTRACT The Black-backed Woodpecker (Picoides arcticus) is a species of conservation concern that is strongly associated with recently burned forests. Black-backed Woodpeckers are known to have variable home-range sizes, yet the ecological factors related to this variation have not been adequately explored and may hold insights into the natural history of the species and the management of its habitat. During 2011 and 2012, we radio-tracked Black-backed Woodpeckers nesting in 3 forested areas of California that burned between 2 and 5 years before the initiation of tracking. Among 15 individuals with robust tracking data, we found that home-range size varied by an order of magnitude, from 24.1 to 304.1 ha, as measured by movement-based kernel estimation. Using an information-theoretic approach, we evaluated the functional relationship between snag basal area—an a priori key resource—and home-range size, additionally controlling for sex, age, and years since fire as covariates. We found that snag basal area alone best predicted home-range size, explaining 54–62% of observed variation. As snag basal area increased, home-range sizes exponentially decreased. This relationship held true both with and without the inclusion of 3 individuals that nested in burned forest yet foraged predominantly outside the fire perimeter in unburned forest. Snag basal area, unlike other potential influences on home-range size, is an attribute that forest managers can directly influence. We describe a quantitative relationship between home-range size and snag basal area that forest managers can use to predict Black-backed Woodpecker pair density in burned forests and assess the likely population consequences of specific harvest treatments. Given that the birds in our study, foraging primarily in burned forest, all had home ranges with an average snag basal area ≥17 m2 ha−1, this may represent a benchmark for minimum habitat needs in postfire stands.

Spatial variation in giraffe demography: a test of 2 paradigms

Examination of spatial variation in demography among or within populations of the same species is a topic of growing interest in ecology. We examined whether spatial variation in demography of a tropical megaherbivore followed the “temporal paradigm” or the “adult survival paradigm” of ungulate population dynamics formulated from temperate-zone studies. We quantified spatial variation in demographic rates for giraffes (Giraffa camelopardalis) at regional and continental scales. Regionally, we used photographic capture-mark-recapture data from 860 adult females and 449 calves to estimate adult female survival, calf survival, and reproduction at 5 sites in the Tarangire ecosystem of Tanzania. We examined potential mechanisms for spatial variation in regional demographic rates. At the continental scale, we synthesized demographic estimates from published studies across the range of the species. We created matrix population models for all sites at both scales and used prospective and retrospective analyses to determine which vital rate was most important to variation in population growth rate. Spatial variability of demographic parameters at the continental scale was in agreement with the temporal paradigm of low variability in adult survival and more highly variable reproduction and calf survival. In contrast, at the regional scale, adult female survival had higher spatial variation, in agreement with the adult survival paradigm. At both scales, variation in adult female survival made the greatest contribution to variation in local population growth rates. Our work documented contrasting patterns of spatial variation in demographic rates of giraffes at 2 spatial scales, but at both scales, we found the same vital rate was most important. We also found anthropogenic impacts on adult females are the most likely mechanism of regional population trajectories.

Previous year's reproductive state affects Spotted Owl site occupancy and reproduction responses to natural and anthropogenic disturbances

ABSTRACT Understanding interactions among site occupancy, reproduction, vegetation, and disturbance for threatened species can improve conservation measures, because important aspects of vegetation and disturbances may be identified and managed. We used 9 yr of survey data collected at 168 sites to investigate dynamic site occupancy and reproduction in a declining population of California Spotted Owls (Strix occidentalis occidentalis) in southern California, USA. We used multistate models to examine the relationship among owl site occupancy, reproduction, high-severity wildland fire, and postfire logging, while accounting for variation in vegetation characteristics and variation in detectability. Both occupancy and reproduction were positively correlated with successful reproduction in the previous year. Tree cover (ha) in a sites 203-ha core area also was positively correlated with both occupancy and reproduction. We detected no effect of disturbance covariates on reproduction, given that a site was occupied. Fire and logging covariates were both negatively correlated with the probability of site occupancy, and the effect sizes of these disturbances were large in sites that were occupied by owls that were nonreproductive the previous year (reduced 0.19 by fire and 0.26 by post-fire logging), but small in sites that were occupied by owls that were reproductive the previous year (reduced 0.02 by fire and 0.03 by postfire logging). This study illustrates the important contribution of consistently occupied and productive breeding sites to this population of Spotted Owls, and demonstrates that both occupancy and reproduction at these productive sites exhibited negligible effects from disturbances. Our results suggest that sites with recent owl reproduction and sites with more tree cover in this study area should receive enhanced protection from management actions that modify vegetation utilized by Spotted Owls.

Growth, Age at Maturity, and Age-Specific Survival of the Arboreal Salamander (Aneides lugubris) on Southeast Farallon Island, California

Abstract Growth, age at maturity, and survival are life-history parameters that provide important information for understanding population dynamics. We modeled growth and age at maturity for an island population of Arboreal Salamanders, Aneides lugubris, using snout–vent length (SVL) growth intervals from a 4-yr capture–mark–recapture study fit to the von Bertalanffy growth interval model. We estimated annual survival as a function of SVL using a multistate open robust design model, and computed age-specific survival using results from the von Bertalanffy growth model. Arboreal Salamanders have indeterminate growth that slows with age from hatchling size (24.4-mm SVL) to the mean adult (asymptotic) size of 66.0-mm SVL. Age at maturity is 2.69 yr, and average adult age is 8–11 yr. Annual survival increased with age from 0.363 in age 0 to 0.783 in ages >4 yr. Our results provide the first estimates of life-history parameters for this species and indicate similarities to other terrestrial salamanders from low-elevation Mediterranean climates.