Derek E. Lee

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.

Entanglements of marine mammals and seabirds in central California and the north-west coast of the United States 2001–2005

Entanglement records for seabirds and marine mammals were investigated for the period 2001-2005. The entanglement records were extracted from databases maintained by seven organizations operating along the west coast of the United States of America. Their programmes included beach monitoring surveys, rescue and rehabilitation and regional pinniped censuses. Records of 454 entanglements were documented in live animals and in carcasses for 31 bird species and nine marine mammal species. The most frequently entangled species were Common Murres, Western Gulls and California sea lions. The entanglement materials identified were primarily fishing related. Entanglements were recorded every year suggesting that although the incidence level differs annually, entanglement is a persistent problem. It is recommended that each programme records details in standardized categories to determine entanglement material sources. Numbers of entanglements observed during these surveys are likely to be a conservative view of the actual entanglement rate taking place at sea.

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.

DUSKY-FOOTED WOODRAT DEMOGRAPHY AND PRESCRIBED FIRE IN A CALIFORNIA OAK WOODLAND

Abstract We investigated the effects of prescribed understory fire and shrub density on a population of dusky-footed woodrats (Neotoma fuscipes) live-trapped each spring and fall from October 1993 to 2001. We performed model selection with program MARK on capture–recapture data using Pollocks robust design to estimate survival and temporary emigration. Abundance increased from 1993 to a peak in 1997 and then decreased steadily from 1997 to 2001, accompanied by reduced reproduction. Survival was age- and time-dependent. Differential temporary emigration probabilities were explained by home-range size differences. Survival and abundance were higher in plots with high shrub cover vs. plots with low shrub cover. A low-medium intensity, prescribed understory fire in the fall of 1997 had no negative effect on survival or temporary emigration. The only fire-related negative demographic effect was a reduction in the number of juveniles per adult female on burned plots in the spring immediately after the fire. Prescribed understory fire in oak woodland is unlikely to alter woodrat populations significantly if patches of well-structured habitat are maintained.

AGE-SPECIFIC STOPOVER ECOLOGY OF BLACK BRANT AT HUMBOLDT BAY, CALIFORNIA

Abstract We analyzed capture-mark-recapture (CMR) data from 1,061 Black Brant (Branta bernicla nigricans) using Humboldt Bay, California, during northward migration (Jan–May), 2000–2001. We estimated immigration and emigration rates, and calculated stopover duration (length of stay), volume (total number of birds using the Bay), and chronology (time frame of the migration at this site). Migration of Brant through Humboldt Bay began in late December and ended in mid-May with peak numbers occurring in mid-March (i.e., 13% of the entire flyway population). Median age of newly arrived birds was highest in the first half of February. Immigration probability was nearly constant, but emigration probability increased through time, indicating a seasonally progressive migratory state. Mean (±SE) stopover duration from all birds for January–April at Humboldt Bay was 26 ± 2 days. Stopover duration was inversely related to bird age due to age-specific emigration probabilities; older birds arrived sooner and stayed for less time than younger birds. Estimates of stopover duration from concurrent radiotelemetry of 12 birds were consistent with CMR model selection-derived estimates. Humboldt Bay was visited by approximately 28% of the Pacific Flyway Black Brant population in 2000 and 58% in 2001. Estimates derived from this technique offer statutory authorities improved information upon which to base management action along migratory pathways.

GRIT-SITE SELECTION OF BLACK BRANT: PARTICLE SIZE OR CALCIUM CONTENT?

Abstract We examined selection of grit-ingestion sites by Black Brant (Branta bernicla nigricans) on South Humboldt Bay, California in relation to particle size and calcium content. We hypothesized that Brant site selection was dependent primarily upon calcium content and secondarily upon distribution of substrate particle size. We (1) mapped grit-ingestion sites, (2) ranked their importance by Brant abundance and individual movement probabilities between sites, (3) characterized Brant gizzard grit and compared it with grit available at ingestion sites, and (4) compared calcium content and particle-size distribution between ingestion sites and unused sites, and between primary and secondary ingestion sites. Brant repeatedly congregated at specific, discrete sites during the 2 years of observation. The distribution of gizzard-grit particle size was right-skewed toward larger particles (>0.5 mm) relative to the proportional availability of particle sizes in the substrate. We found no significant differences in calcium content or particle size between sites where grit was ingested and unused sites. Within used sites, the calcium content of substrates at the primary ingestion site was significantly higher than at the secondary ingestion sites, as ranked by Brant abundance and between-site movement probabilities. Our findings from the field corroborate previous laboratory results, and confirm that calcium is a significant ecological factor for this species.

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.

SURVIVAL AND ABUNDANCE OF THREE SPECIES OF MICE IN RELATION TO DENSITY OF SHRUBS AND PRESCRIBED FIRE IN UNDERSTORY OF AN OAK WOODLAND IN CALIFORNIA

Abstract We investigated effects of prescribed understory fire and shrub density on the pinyon deermouse (Peromyscus truei), brush deermouse (P. boylii), and California pocket mouse (Chaetodipus californicus) in a mixed blue oak-coast live oak (Quercus douglasii-Q. agrifolia) woodland of coastal-central California. We simultaneously estimated survival and abundance of all species during pre-burn and post-burn. Abundance of pinyon deermice and California pocket mice was significantly higher in plots with high (>25%) shrub cover compared to plots with low (<10%) shrub cover. A light-to-moderate intensity, prescribed, understory fire had no significant effect on survival for any of the three species we investigated. The fire significantly reduced abundance of pinyon deermice in the trapping session immediately after the fire, but abundance increased in subsequent trapping sessions relative to controls. Low intensity, prescribed, understory fire in oak woodland is unlikely to significantly alter populations of rodents if patches of well-structured habitat are maintained. Benefits of prescribed fire for oak woodlands in reduction of the risk of wildfire and rejuvenation of vegetation likely outweigh any short-term negative effects on populations of mice.

NORTH PACIFIC CLIMATE MEDIATES OFFSPRING SEX RATIO IN NORTHERN ELEPHANT SEALS

Abstract Determinants of sex ratios in animal populations have been of general interest to ecologists for decades. We tested the hypothesis that offspring sex ratio in a population of northern elephant seals (Mirounga angustirostris) was related to large-scale environmental indices reflecting ocean climate and productivity that affected the condition of reproductive females over 31 years (1976–2006). More males were produced during years of weaker pressure differences and warmer sea surface temperature anomalies in the northeastern Pacific, conditions that reduce or disperse prey resources for gestating females in the North Pacific Ocean. For this species, sexually distinct forage resources exist, so competition for food resources occurs predominately within sex. These results are consistent with the resource competition model for facultative adjustments of offspring sex ratio. Anthropogenic global warming is predicted to warm the North Pacific. This could result in altered basin-scale ocean productivity, increased nutritional stress, and an overabundance of males that may adversely affect this and other similarly regulated mammalian populations.