Demographic response of northern spotted owls to barred owl removal

Federally listed as threatened in 1990 primarily because of habitat loss, the northern spotted owl (Strix occidentalis caurina) has continued to decline despite conservation efforts resulting in forested habitat being reserved throughout its range. Recently, there is growing evidence the congeneric invasive barred owl (Strix varia) may be responsible for the continued decline primarily by excluding spotted owls from their preferred habitat. We used a long-term demographic study for spotted owls in coastal northern California as the basis for a pilot barred owl removal experiment. Our demography study used capture–recapture, reproductive output, and territory occupancy data collected from 1990 to 2013 to evaluate trends in vital rates and populations. We used a classic before-after-control-impact (BACI) experimental design to investigate the demographic response of northern spotted owls to the lethal removal of barred owls. According to the best 2-species dynamic occupancy model, there was no evidence of differences in barred or northern spotted owl occupancy prior to the initiation of the treatment (barred owl removal). After treatment, barred owl occupancy was lower in the treated relative to the untreated areas and spotted owl occupancy was higher relative to the untreated areas. Barred owl removal decreased spotted owl territory extinction rates but did not affect territory colonization rates. As a result, spotted owl occupancy increased in the treated area and continued to decline in the untreated areas. Prior to and after barred owl removal, there was no evidence that average fecundity differed on the 2 study areas. However, the greater number of occupied spotted owl sites on the treated areas resulted in greater productivity in the treated areas based on empirical counts of fledged young. Prior to removal, survival was declining at a rate of approximately 0.2% per year for treated and untreated areas. Following treatment, estimated survival was 0.859 for the treated areas and 0.822 for the untreated areas. Derived estimates of population change on both study areas showed the same general decline before removal with an estimated slope of –0.0036 per year. Following removal, the rate of population change on the treated areas increased to an average of 1.029 but decreased to an average of 0.870 on the untreated areas. The results from this first experiment demonstrated that lethal removal of barred owls allowed the recovery of northern spotted owl populations in the treated portions of our study area. If additional federally funded barred owl removal experiments provide similar results, this could be the foundation for development of a long-term conservation strategy for northern spotted owls.This is the publisher’s final pdf. The article is copyrighted by the Wildlife Society and published by John Wiley & Sons, Inc. It can be found at: http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291937-2817Keywords: barred owl, removal experiment, northern spotted owl, demography, competitio

The past and future roles of competition and habitat in the range-wide occupancy dynamics of Northern Spotted Owls

Slow ecological processes challenge conservation. Short-term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession)

The effects of habitat, climate, and Barred Owls on long-term demography of Northern Spotted Owls

Estimates of species' vital rates and an understanding of the factors affecting those parameters over time and space can provide crucial information for management and conservation. We used mark–recapture, reproductive output, and territory occupancy data collected during 1985–2013 to evaluate population processes of Northern Spotted Owls (Strix occidentalis caurina) in 11 study areas in Washington, Oregon, and northern California, USA. We estimated apparent survival, fecundity, recruitment, rate of population change, and local extinction and colonization rates, and investigated relationships between these parameters and the amount of suitable habitat, local and regional variation in meteorological conditions, and competition with Barred Owls (Strix varia). Data were analyzed for each area separately and in a meta-analysis of all areas combined, following a strict protocol for data collection, preparation, and analysis. We used mixed effects linear models for analyses of fecundity, Cormack-Jolly-Seber open population models for analyses of apparent annual survival (ϕ), and a reparameterization of the Jolly-Seber capture–recapture model (i.e. reverse Jolly-Seber; RJS) to estimate annual rates of population change (λ[subscript]RJS) and recruitment. We also modeled territory occupancy dynamics of Northern Spotted Owls and Barred Owls in each study area using 2-species occupancy models. Estimated mean annual rates of population change (λ) suggested that Spotted Owl populations declined from 1.2% to 8.4% per year depending on the study area. The weighted mean estimate of λ for all study areas was 0.962 (± 0.019 SE; 95% CI: 0.925–0.999), indicating an estimated range-wide decline of 3.8% per year from 1985 to 2013. Variation in recruitment rates across the range of the Spotted Owl was best explained by an interaction between total winter precipitation and mean minimum winter temperature. Thus, recruitment rates were highest when both total precipitation (29 cm) and minimum winter temperature (−9.5°C) were lowest. Barred Owl presence was associated with increased local extinction rates of Spotted Owl pairs for all 11 study areas. Habitat covariates were related to extinction rates for Spotted Owl pairs in 8 of 11 study areas, and a greater amount of suitable owl habitat was generally associated with decreased extinction rates. We observed negative effects of Barred Owl presence on colonization rates of Spotted Owl pairs in 5 of 11 study areas. The total amount of suitable Spotted Owl habitat was positively associated with colonization rates in 5 areas, and more habitat disturbance was associated with lower colonization rates in 2 areas. We observed strong declines in derived estimates of occupancy in all study areas. Mean fecundity of females was highest for adults (0.309 ± 0.027 SE), intermediate for 2-yr-olds (0.179 ± 0.040 SE), and lowest for 1-yr-olds (0.065 ± 0.022 SE). The presence of Barred Owls and habitat covariates explained little of the temporal variation in fecundity in most study areas. Climate covariates occurred in competitive fecundity models in 8 of 11 study areas, but support for these relationships was generally weak. The fecundity meta-analysis resulted in 6 competitive models, all of which included the additive effects of geographic region and annual time variation. The 2 top-ranked models also weakly supported the additive negative effects of the amount of suitable core area habitat, Barred Owl presence, and the amount of edge habitat on fecundity. We found strong support for a negative effect of Barred Owl presence on apparent survival of Spotted Owls in 10 of 11 study areas, but found few strong effects of habitat on survival at the study area scale. Climate covariates occurred in top or competitive survival models for 10 of 11 study areas, and in most cases the relationships were as predicted; however, there was little consistency among areas regarding the relative importance of specific climate covariates. In contrast, meta-analysis results suggested that Spotted Owl survival was higher across all study areas when the Pacific Decadal Oscillation (PDO) was in a warming phase and the Southern Oscillation Index (SOI) was negative, with a strongly negative SOI indicative of El Niño events. The best model that included the Barred Owl covariate (BO) was ranked 4th and also included the PDO covariate, but the BO effect was strongly negative. Our results indicated that Northern Spotted Owl populations were declining throughout the range of the subspecies and that annual rates of decline were accelerating in many areas. We observed strong evidence that Barred Owls negatively affected Spotted Owl populations, primarily by decreasing apparent survival and increasing local territory extinction rates. However, the amount of suitable owl habitat, local weather, and regional climatic patterns also were related to survival, occupancy (via colonization rate), recruitment, and, to a lesser extent, fecundity, although there was inconsistency in regard to which covariates were important for particular demographic parameters or across study areas. In the study areas where habitat was an important source of variation for Spotted Owl demographics, vital rates were generally positively associated with a greater amount of suitable owl habitat. However, Barred Owl densities may now be high enough across the range of the Northern Spotted Owl that, despite the continued management and conservation of suitable owl habitat on federal lands, the long-term prognosis for the persistence of Northern Spotted Owls may be in question without additional management intervention. Based on our study, the removal of Barred Owls from the Green Diamond Resources (GDR) study area had rapid, positive effects on Northern Spotted Owl survival and the rate of population change, supporting the hypothesis that, along with habitat conservation and management, Barred Owl removal may be able to slow or reverse Northern Spotted Owl population declines on at least a localized scale.Keywords: Northern Spotted Owl, occupancy, population change, Strix varia, Strix occidentalis caurina, fecundity, Barred Owl, surviva

A Field Observation on the Feeding Behavior of \u3cem\u3eCrotalus viridis lutosus\u3c/em\u3e

Rattlesnakes (Crotalus spp.) are generally considered to be sit-and-wait predators that strike and envenomate, release and then search for their envenomated prey (Fitch and Twining, 1946; Klauber, 1956; Reinert et al., 1984). This behavior by rattlesnakes and other pit vipers has led to laboratory studies on the searching behaivor following envenomation and the role of strike-induced chemosensory searching (Chiszar et al., 1977; Duvall et al., 1980; Chiszar et al., 1981; Gillingham and Clark, 1981; Golan et al., 1982; Scudder et al., 1983). This feeding technique results in the loss of some fatally-envenomated prey (Fitch and Twining, 1946), and may result in rattlesnakes being predisposed to feed on carrion (Klauber, 1956; Patten and Banta, 1980; Gillingham and Baker, 1981; Lillywhite, 1982), but its importance in the feeding ecology of rattlesnakes is unknown. A fortuitous set of field observations on a single rattlesnake reported here provide a type of information on the feeding behavior of snakes that is difficult to obtain (Fitch 1987). In addition, these observations may also stimulate testing some new questions on the feeding behavior of rattlesnakes

Comparative Ecology of Great Basin Rattlesnakes (Crotalus viridis lutosus) and Great Basin Gopher Snakes (Pituophis melanoleucus deserticola) and Their Impact on Small Mammal Populations in the Snake River Birds of Prey Natural Area

Capture data from southwestern Idaho indicate that P. melanoleucus disperse shortly after spring emergence in mid-April, while C. viridis, which emerge in late April, remain near hibernacula for several weeks. Both species reach a peak of activity in late May to early June with activity gradually diminishing throughout summer and early fall. Most daily activity of C. virdis occurs between 1000 and 1300 hours with little evidence of nocturnal activity. Daily activity of P. melanoleucus is strongly bimodal during summer with peaks in mid-morning and earlu evening. At the time of capture, most snakes for both species had a cloacal temperature of about 30° C when the air temperature was about 22° C and the subrstrate temperature was about 33° C. However, C. virdis had a narrower range of eccritic cloacal temperatures. Based on recapture data, 40% of all recaptures of C. viridid occured within 5 m of the originaal capture point. Of movements over 5 m, 70% were between 30 to 150 m. Limited recapture data on P. melanoleucus indicate they are more vagile. Both species appear to fit the concept of a total range . Male C. viridis are significantly larger than femaes, while both sexes of P. melanoleucus are essentially equal in size. The sex ratio is nearly equal for C. viridis, but male P. melanoleucus clearly outnumber females due to a supposed increaes mortalit in females. Female C. viridis grow more slowly than makes. Two-year-old P. melanoleucus show a spurt in grwoth which is believed to be associated with a change in prey utilized. Females for both species reproduce for the first time in their fourth year. Male C. viridis had sperm present in the vas deferens by the fall of their second year, while male P. melanoleucus reached this condition by late summer of their third year. Ovulation occurred in early June for both species. Limited observations indicate that young C. viridis are born from mid-September to October, while P. melanoleucus hatch in October indicating a shorter developmental period for the live-bearing C. viridis. Mean clutch sizes were 8.3 and 6.9, respectively, for C. viridis and P. melanoleucus. Annual reproductive effort for P. melanoleucus. Both species show a strong correlation between clutch size and female size (r = 0.78 C. viridis; r = 0.86 P. melanoleucus). Fat bodies as a percent of body weight are larger in C. viridis than P. melanoleucus. Also, females of both species tend to have larger fat bodies than males. Nonreproductive mature female C. viridis have larger fat bodies than gravid or pregnant females. Males of both species tend to have excess fat reserves, so that seasonal fat body cycles can not be identified. Fat bodies were used primarily for reproduction in both specis [sic.]. Based on drift fence captures, mean densities were 0.6 snakes/ha for C. viridis and 1.3 snakes/ha for P. melanoleucus. C. viridis occurred at a high density (6.9 snakes/ha) in rocky habitats such as the canyon rim and basalt outcrops, but were rare in all other habitats. The density of P. melanoleucus was between about 1 and 2 snakes/ha throughout most of the study area. More than 80% of the adult C. viridis diet was composed of Spermophilus townsendi, while P. melanoleucus took a variety of small mammals. In general, C. viridis was seen as an ecological specialist and P. melanoleucus an ecological generalist. Feeding studies with captive snakes indicated annual consumption rates of 300% body weight (3.0%/day) for young C. viridis and 160% (1.6%/day) for adult C. viridis. P. melanoleucus had corresponding annual consumption rates of 220% (2.2%/day) for young and 150% (1.5%/day) for adults. Production efficiency (total production of body tissues/total weight of ingested prey) was 30% and 28%, respectively, for young and adult P. melanoleucus. C. viridis annually take an estimated 25% of the Spermophilus townsendi, while P. melanoleucus take 10% of the S. townsendi, 20% of the Sylvilagus nuttalli and 10% of the Permomyscus maniculatus. The patchy distribution of C. viridis suggests that they would have a high impact on S. townsendi only in localized areas of high snake density, but little impact elsewhere

Aspects of the Life History and Ecology of the Desert Night Snake, \u3cem\u3eHypsiglena torquata deserticola\u3c/em\u3e: Colubridae, in Southwestern Idaho

Seventy-seven desert night snakes (Hypsiglena torquata deserticola) were collected from 1975-1983 in southwest Idaho and analyzed for life history features. Females were nearly 50% longer and three times greater in body mass than males. The sex ratio favored males 2.5 to 1. Mature males captured from April to September had spermatozoa in the ductus deferens but spermatogenesis probably occurred during midsummer. The sexual segment of the kidney tubules was largest in males collected during spring with regression occurring through the summer. Only three clutches of three, four and seven eggs were counted in six sexually mature females. Ovulation and oviposition probably occurred during June, but the possibility of a wider range of ovulation times was not excluded. Males reached sexual maturity at about 29 cm SVL, whereas females were about 40 cm SVL at sexual maturity. Major surface activity began in mid-May and reached a peak in early July. Most captures occurred in rocky habitats and H. torquata deserticola was locally abundant. Lizards (primarily Uta stansburiana) and their eggs were the most common food items, but anurans may also be important prey