Impact of helminth parasitism on a snowshoe hare population in central Wisconsin: a field experiment

1995 ◽  
Vol 73 (10) ◽  
pp. 1891-1898 ◽  
Author(s):  
Sara E. M. Bloomer ◽  
Thomas Willebrand ◽  
Ingegerd M. Keith ◽  
Lloyd B. Keith
Keyword(s):  
Survival Rates ◽  
Snowshoe Hare ◽  
Marrow Fat ◽  
Proximate Cause ◽  
Risk Of Death ◽  
Snowshoe Hares ◽  
Condition Indices ◽  
Time Specific ◽  
And Control ◽  
Hare Population

We tested the hypothesis that helminth parasitism is demographically significant to a noncyclic population of snowshoe hares (Lepus americanus) near the species' geographic boundary in central Wisconsin (U.S.A.). During November 1988 to December 1991, we injected 93 individuals (≥760 g, aged ≥2 months) with anthelmintics: Ivermectin for nematode and Droncit for cestode infections. We injected 98 control hares with propylene glycol, the common vehicle for both drugs. All treated and control hares were radio-collared with mortality-sensing transmitters and monitored daily to weekly from the ground or air. Prevalence and intensity of lungworms (Protostrongylus boughtoni), intestinal worms (Nematodirus triangularis), and stomach worms (Obeliscoides cuniculi) were markedly reduced by Ivermectin treatment. No other nematodes were found to be present. Treatment with Droncit to remove intestinal cestodes was apparently unnecessary, as prevalence among necropsied untreated hares and controls was just 10%. We compared body-condition indices (mass changes, response to trap stress, and bone-marrow fat), reproduction (pregnancy rate and litter size), home-range sizes, and time-specific survival rates of anthelmintic-treated versus control hares. None of these demographic variables differed significantly between treated and control cohorts, nor was there any evidence that parasitism increased the risk of death from predation, which was the proximate cause of 96% of all natural mortalities. We conclude that helminth parasitism played no detectable role in the dynamics of this Wisconsin snowshoe hare population.

Survival of juvenile hares during a cyclic population increase

1998 ◽  
Vol 76 (10) ◽  
pp. 1949-1956 ◽  
Author(s):  
Elizabeth A Gillis
Keyword(s):  
Cause Of Death ◽  
Food Availability ◽  
Survival Rates ◽  
Lepus Americanus ◽  
Population Increase ◽  
Differential Survival ◽  
Proximate Cause ◽  
Supplemental Food ◽  
Snowshoe Hares ◽  
And Control

Snowshoe hares (Lepus americanus) are multilittered synchronous breeders that produce up to four distinct litters of young each summer. I used radiotelemetry to determine the effects of juvenile cohort (i.e., litter group) and food availability on postweaning survival of hares in the southwestern Yukon during the increase phase of a hare cycle. During the study, I monitored 86 juvenile hares from control areas and areas in which supplemental food was provided. Twenty-eight-day survival did not differ between food addition and control areas for any juvenile cohort, and survival rates of juveniles (all cohorts combined) did not differ significantly from those of adults (juveniles: 0.91 per 28 days; adults: 0.93 per 28 days). However, when examined by juvenile cohort, survival of third and fourth litters was significantly lower than that of adults and first and second litters. These differences were the result of differential survival among the juvenile cohorts during a 3-month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% of deaths.

Dynamics of a snow shoe hare population in fragmented habitat

1993 ◽  
Vol 71 (7) ◽  
pp. 1385-1392 ◽  
Author(s):  
Lloyd B. Keith ◽  
Sara E. M. Bloomer ◽  
Tomas Willebrand
Keyword(s):  
Patch Size ◽  
Canis Latrans ◽  
Lepus Americanus ◽  
Fragmented Habitat ◽  
Proximate Cause ◽  
Lower Survival ◽  
The Third ◽  
Snowshoe Hares ◽  
Poorly Drained Soils ◽  
Hare Population

During November 1988 – December 1991 we livetrapped, radio-collared, and monitored the survival, reproduction, and movements of snowshoe hares (Lepus americanus) in highly fragmented habitat near the species' geographic limit in central Wisconsin. Our 7 study areas centered on 5- to 28-ha patches of prime habitat: dense stands of willow (Salix), alder (Alnus), and regenerating aspen (Populus) on poorly drained soils. Maximum hare densities averaged 1.6 – 0.8/ha, and were unrelated to patch size. Rapid declines to extinction occurred on 3 of the 5 smallest study areas; on another, where extinction seemed imminent, juvenile ingress restored the population. On the 2 largest areas (23 – 28 ha of prime habitat) hare populations were stationary during the first 2 years, but declined by 50 – 70% in the third as mean annual (September – August) survival of radio-collared hares fell from 0.27 (1988 – 1990) to 0.07 (1990 – 1991). Annual survival on the 3 extinction sites averaged just 0.015 compared with 0.179 elsewhere. Reproduction did not differ between small (5 – 7 ha) vs. larger (23 – 28 ha) patches nor between years. Estimated dispersal of adult and juvenile hares from the 5 small study areas was twice as high as from the 2 larger, viz. 16 vs. 35% annually. Dispersers appeared to have markedly lower survival. Predation, chiefly by coyotes (Canis latrans), was the proximate cause of 96% (117 of 122) of natural deaths among radio-collared hares, and was therefore the overwhelming determinant of survival and thus population trend. Results of this study suggest that probabilities of extinction in such fragmented habitat depend importantly on patch size and attendant hare numbers; i.e., fall populations of < 10 hares frequenting patches of prime habitat ≤ 5 ha are not likely to persist long without ingress.

Reproductive change in the 10-year cycle of snowshoe hares

1979 ◽  
Vol 57 (2) ◽  
pp. 375-390 ◽  
Author(s):  
John R. Cary ◽  
Lloyd B. Keith
Keyword(s):  
Pregnancy Rate ◽  
Litter Size ◽  
Weight Change ◽  
Ovulation Rate ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Cyclic Variation ◽  
Reproductive Parameters ◽  
Snowshoe Hares ◽  
Hare Population

Reproduction was monitored during a 16-year study of snowshoe hare (Lepus americanus) populations near Rochester, Alberta. Pregnancy rate, ovulation rate, and litter size changed markedly between successive litters within the breeding season; these parameters were thus further categorized by litter in our analyses. Most reproductive components varied significantly between years; a significant '10-year' periodicity was the dominant source of this variation. The cyclic fluctuations of reproductive parameters were broadly synchronous and tended to precede the population cycle by about 3 years, thereby producing a range in potential natality annually of 7.5 to 17.9 young per female. The year-to-year variability of pregnancy rate, ovulation rate, and litter size was markedly larger in the later litters than in the early ones. Paunched weight, mean age, incidence of endoparasites, liver and spleen weights, and midwinter-to-spring weight change also possessed significant 10-year cycles; paunched weight cycled directly with the hare population, but the others cycled either directly with or counter to reproduction. We believe that the correspondence between midwinter-to-spring weight change and reproduction implicates winter nutrition as the primary cause of the cyclic variation. Onset of spring accounted for a significant amount of variability in onset of breeding, adding to that due to the periodic change.

Proximate causes of losses in a snowshoe hare population

1986 ◽  
Vol 64 (3) ◽  
pp. 606-610 ◽  
Author(s):  
Stan Boutin ◽  
C. J. Krebs ◽  
A. R. E. Sinclair ◽  
J. N. M. Smith
Keyword(s):  
Population Density ◽  
Population Increase ◽  
Snowshoe Hare ◽  
Snowshoe Hares ◽  
Causes Of Mortality ◽  
Proximate Causes ◽  
Hare Population ◽  
Kluane Lake ◽  
Predation Rates

We used radiotelemetry to monitor proximate causes of mortality of snowshoe hares during a population increase, peak, and decline at Kluane Lake, Yukon. Predation and starvation rates increased 1.6- and 9-fold, respectively, in the winter of peak population density. Predation accounted for 58% of the losses during the winter of peak densities while losses were equally divided between predation and starvation in the winter following the peak. Starvation and predation rates were lower on a food-supplemented grid than on control grids in the peak winter. In the following spring and winter, starvation rates remained low on the food grid while predation rates increased to equal those on control areas. We conclude that both starvation and predation were the proximate causes of mortality during the hare decline at Kluane Lake.

Risk of parasite-induced predation: an experimental field study on Townsend's voles (Microtus townsendii)

2002 ◽  
Vol 80 (7) ◽  
pp. 1286-1292 ◽  
Author(s):  
Harald Steen ◽  
Mary Taitt ◽  
Charles J Krebs
Keyword(s):  
Parasite Prevalence ◽  
Control Groups ◽  
Red Grouse ◽  
Proximate Cause ◽  
Snowshoe Hares ◽  
Causes Of Mortality ◽  
Parasite Infestation ◽  
Breeding Seasons ◽  
And Control ◽  
Microtus Townsendii

Studies of causes of mortality in rodents, snowshoe hares, and red grouse show that many individuals succumb to predation and few die from starvation or parasite infestation. Predation may be the proximate cause of death and factors like parasite infestation and starvation could facilitate predation. Our aim was to test whether Townsend's voles, Microtus townsendii, experimentally rid of parasites are less likely to be killed by predators than are control voles. During two breeding seasons we treated half of the adults caught at Boundary Bay, British Columbia, Canada, with the anthelmintic Ivomec® and left the other half as controls. Voles were randomly assigned to the treatment and control groups. Predators killed 5 of 23 treated voles and 11 of 26 control voles in 1998. In 1997 predators killed 3 of 17 treated voles and 2 of 18 control voles. Vole density was higher in 1998 than in 1997 and predation was the main cause of mortality in both years. Survival of control voles was lower in 1998 than in 1997, indicating lower predation pressure in 1997 than in 1998. Botfly prevalence and intensity were low and similar in both years. We speculate that the lack of treatment effect in 1997 could have been due to lower overall parasite prevalence in that year than in 1998, resulting in relatively higher susceptibility of voles to predation. Parasite-induced predation reduced monthly survival by 17% in 1998.

Snowshoe hare adrenal weights in relation to population density

1977 ◽  
Vol 55 (3) ◽  
pp. 634-637 ◽  
Author(s):  
E. O. Höhn ◽  
J. G. Stelfox
Keyword(s):  
Adrenal Weight ◽  
Gastric Ulcers ◽  
Population Cycle ◽  
Snowshoe Hare ◽  
Lower Body ◽  
Population Densities ◽  
The Third ◽  
Snowshoe Hares ◽  
Body Weights ◽  
Hare Population

Adrenal and body weights of snowshoe hares from three areas in which hare population densities differed markedly were determined in a search for evidence of adrenal enlargement in the course of the population cycle. In the first area hares were in a sudden decline after a peak. Dead hares were found there in some numbers. Hare populations in the other two areas were still rising (population peaks occurred 18 months after sampling), but hare density was considerably greater in the second as compared with the third area. There were no significant differences in absolute adrenal weight between any of the groups. Relative adrenal weights were also similar, except for significantly higher relative adrenal weights in hares found dead as compared with those shot, but this was apparently due merely to the lower body weights of animals found dead compared with those killed. There was no evidence of significant differences in relative adrenal weight according to sex or age. No gastric ulcers were found in 26 hares taken from a population at the peak of the cycle.

Differential mortality of sympatric snowshoe hares and cottontail rabbits in central Wisconsin

1993 ◽  
Vol 71 (8) ◽  
pp. 1694-1697 ◽  
Author(s):  
Lloyd B. Keith ◽  
Sara E. M. Bloomer
Keyword(s):  
Low Temperatures ◽  
Escape Behavior ◽  
Survival Rates ◽  
Differential Mortality ◽  
Interspecific Difference ◽  
High Survival ◽  
Sylvilagus Floridanus ◽  
Proximate Cause ◽  
Snowshoe Hares ◽  
Foot Loading

During 1990 and 1991 we livetrapped and radio-collared cottontail rabbits (Sylvilagus floridanus) and snowshoe hares (Lepus americanus) on five sites (three in lowland deciduous cover, two in conifer bogs) in central Wisconsin. The survival rates of these sympatric cottontails and snowshoes were equally high during snow-free periods from mid-March through October. With the onset of persistent snow cover (mean depth 20 cm) and low temperatures (mean daily minimum −14 °C) in November 1991, the 60-day survival rate of cottontails plummeted from 0.89 to 0.18 (P < 0.01) whereas snowshoe survival declined only moderately from 0.84 to 0.63 (P = 0.19). This interspecific difference reflected continued high survival of snowshoes (0.80), but not of cottontails (0.15), in the conifer bogs. Predation, primarily by coyotes, was the proximate cause of 37 of 39 rabbit and hare deaths, and was thus the overwhelming determinant of survival. We speculate that where persistent snow and low temperatures characterize winter, the cottontail's greater foot loading, brown coloration, and escape behavior markedly increase its vulnerability to predators. This probably explains the absence of cottontails from the forests of northern Wisconsin.

scholarly journals Estimating abundance, temporary emigration and the pattern of density dependence in a cyclic snowshoe hare population in Yukon, Canada

2021 ◽  
Author(s):  
Madan K. Oli ◽  
Alice J. Kenney ◽  
Rudy Boonstra ◽  
Stan Boutin ◽  
Vratika Chaudhary ◽  
...  
Keyword(s):  
Population Density ◽  
Large Scale ◽  
Seasonal Pattern ◽  
Survival Rates ◽  
Population Cycles ◽  
Sampling Period ◽  
Snowshoe Hare ◽  
Temporary Emigration ◽  
Cyclical Fluctuation ◽  
Hare Population

Estimates of demographic parameters based on capture-mark-recapture (CMR) methods may be biased when some individuals in the population are temporarily unavailable for capture (temporary emigration). We estimated snowshoe hare abundance, apparent survival, and probability of temporary emigration in a population of snowshoe hares (Lepus americanus Erxleben 1777) in the Yukon using Pollock’s robust design CMR model, and population density using spatially-explicit CMR models. Survival rates strongly varied among cyclic phases, seasons, and across five population cycles. We found strong evidence that temporary emigration was Markovian (i.e., non-random), suggesting that it varied among individuals that were temporary emigrant in the previous sampling period and those that were present in the sampled area. The probability of temporary emigration for individuals that were in the study area during the previous sampling occasion (γ´´) varied among cycles. Probability that individuals that were temporarily absent from the sampled area would remain temporary emigrants (γ´) showed strongly seasonal pattern, low in winter and high during summers. Snowshoe hare population density ranged from 0.017 (0.015–0.05) hares/ha to 4.43 (3.90–5.00) hares/ha and large-scale cyclical fluctuation. Autocorrelation functions and autoregressive analyses revealed that our study population exhibited statistically significant cyclic fluctuations, with a periodicity of 9-10 years.

scholarly journals Estimating snowshoe hare population density from pellet plots: a further evaluation

2001 ◽  
Vol 79 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Charles J Krebs ◽  
Rudy Boonstra ◽  
Vilis Nams ◽  
Mark O'Donoghue ◽  
Karen E Hodges ◽  
...  
Keyword(s):  
Population Density ◽  
Strong Relationship ◽  
Geographic Range ◽  
Lepus Americanus ◽  
Snowshoe Hare ◽  
Fecal Pellets ◽  
Density Estimates ◽  
Snowshoe Hares ◽  
Pellet Counts ◽  
Hare Population

We counted fecal pellets of snowshoe hares (Lepus americanus) once a year in 10 areas in the southwestern Yukon from 1987 to 1996. Pellets in eighty 0.155-m2 quadrats were counted and cleared each June on all areas, and we correlated these counts with estimates of absolute hare density obtained by intensive mark–recapture methods in the same areas. There is a strong relationship between pellet counts and population density (r = 0.76), and we present a predictive log–log regression to quantify this relationship, which improves on our previously published 1987 regression, particularly at low hare densities. The precision of density estimates can be improved most easily by increasing the number of sets of quadrats in an area (one set = 80 plots), rather than increasing the number of plots counted within one set. The most important question remaining concerns the generality of this relationship for snowshoe hares living in other habitats in the eastern and southern portions of their geographic range.

A demographic analysis of a southern snowshoe hare population in a fragmented habitat: evaluating the refugium model

2002 ◽  
Vol 80 (1) ◽  
pp. 169-177 ◽  
Author(s):  
Aaron J Wirsing ◽  
Todd D Steury ◽  
Dennis L Murray
Keyword(s):  
Survival Rates ◽  
Snowshoe Hare ◽  
Metapopulation Dynamics ◽  
Fragmented Habitat ◽  
Preferred Habitat ◽  
Marked Decline ◽  
Poor Recruitment ◽  
The Stability ◽  
Hare Population ◽  
Site Population

The allegedly noncyclic dynamics of southern snowshoe hare (Lepus americanus) populations may be explained by a model invoking habitat fragmentation and facultative predation (the refugium model) under which animals dispersing from patches of preferred habitat fail to establish themselves because of predation by facultative carnivores. We compared the refugium model with a revised model invoking heavy on-site predation in preferred habitat as the proximal mechanism responsible for the stability of southern snowshoe hare populations. The survival and movements of hares in a fragmented habitat in central Idaho were monitored via radiotelemetry on 6 sites differing in habitat quality (indexed by understory cover) from 1998 to 2000. In support of the revised model, predation rates were high irrespective of cover availability or hare density, and predators did not kill dispersing animals disproportionately. Furthermore, predation was focused on small hares, suggesting that poor recruitment of juveniles may be the mechanism ultimately responsible for the damped dynamics of southern snowshoe hare populations. The low survival rates we measured suggest that the population under study was undergoing a marked decline. However, the observed decline, determined by comparing study-site population estimates, was less severe, implying that the persistence of local snowshoe hare populations in some areas of the species' southern range may be influenced by metapopulation dynamics. Specifically, southern snowshoe hare populations in small patches of usable habitat may be prevented from going extinct by the arrival of immigrants from similar nearby patches.

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