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)

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

Effects of barred owl (\u3ci\u3eStrix varia\u3c/i\u3e) range expansion on \u3ci\u3eHaemoproteus\u3c/i\u3e parasite assemblage dynamics and transmission in barred and northern spotted owls (\u3ci\u3eStrix occidentalis caurina\u3c/i\u3e)

The range of the barred owl (Strix varia) has expanded westward over the past century and now entirely overlaps the range of the federally threatened northern spotted owl (S. occidentalis caurina) in the Pacific Northwest. We compared Haemoproteus blood parasite assemblages among northern spotted owls in their native range and barred owls in both their native and invasive ranges to evaluate predictions of five hypotheses about parasites and biological invasions: (1) Enemy Release, where hosts benefit from a loss of parasites in their invasive range, (2) Enemy of My Enemy, where invasive hosts introduce parasites to naı¨ve native hosts, (3) Parasite Spillback, where invasive hosts act as a new reservoir to native parasites, (4) Increased Susceptibility, where native hosts introduce parasites to naı¨ve invasive hosts, and (5) Dilution Effect, where invasive species act as poor hosts to native parasites and decrease the density of potential hosts in their invasive range. We used haplotype network analyses to identify one haplotype common to both owl species throughout North America, three more haplotypes that appeared to be isolated to the barred owl’s historic range, and a fifth haplotype that was only found in California. Based on infection status and parasite diversity in eastern and western barred owl populations, we found strong support for the Enemy Release Hypothesis. Northern spotted owls had higher parasite diversity and probability of infection than sympatric barred owls, offering some support for the Parasite Spillback and Dilution Effect Hypotheses. Overall, this study demonstrates the complexity of host-parasite relationships and highlights some of the ways in which species’ range expansions may alter such relationships among both invasive and native hosts

Exposure to rodenticides in Northern Spotted and Barred Owls on remote forest lands in northwestern California: evidence of food web contamination

The documentation of anticoagulant rodenticides (AR) in nontarget species has centered around wildlife that inhabit urban or agricultural settings. However, recent studies in California have shown that AR use in remote forest settings has escalated and has exposed and killed forest carnivores. Anticoagulant rodenticides have been documented as physiological stressors for avian species. Northern Spotted Owl (Strix occidentalis caurina) critical and occupied habitat overlaps the areas where these studies occurred, yet no data were previously available to demonstrate whether this species was similarly affected. We investigated whether avian predators are also exposed to these specific pesticides and whether Barred Owls (Strix varia) may be a surrogate to indicate exposure rates in Northern Spotted Owls. We documented that 70% of Northern Spotted Owls and 40% of Barred Owls were exposed to one or more anticoagulant rodenticides. None of the rodent prey species sampled within the study area were positive for ARs. There were no spatial clusters for either low or high rates of exposure, though we detected low temporal trend early on throughout the study area. We hypothesize a recent change in land-use toward marijuana cultivation may have led to the increased use of AR in this area. This study demonstrates environmental contamination within occupied Northern Spotted Owl habitat and that Barred Owls can be used as adequate surrogates for detecting these pollutants in a rare species such as the Northern Spotted Owl. Furthermore, additional studies should focus on whether these pesticides are also affecting prey availability for these forest avian species