Charlotte L. Roy

Effects of hunting and hunting-hour extension on mourning dove foraging and physiology

During 1993, the Illinois Department of Natural Resources extended mourning dove (Zenaida macroura) hunting hours to increase recreational opportunities. We investigated the physiological response of doves to extended hunting hours through a combination of laboratory and field procedures. We determined that food deprivation causes corticosterone levels to increase in doves, suggesting that if doves were excluded from foraging areas by hunting pressure, a rise in corticosterone levels should be detectable. Field procedures revealed that hunting resulted in a measurable increase in corticosterone levels, although the magnitude of the observed increase probably was not biologically significant (preseason x = 1.35 ng/ml vs. hunting x = 1.87 ng/ml). We did not detect differences in corticosterone levels between traditional and extended hunting hours (P = 0.25), but did find evidence to suggest that dove foraging was affected by hunting and hunting hours. Mourning dove weights were greater preseason (x = 117.4 g) than during hunting season (x = 111.0 g), which may be partially explained by an increase in the number of empty crops during hunting season (54.1% hunting season vs. 25.8% preseason). The absence of food in crops most likely accounted for the observed weight loss. Furthermore, sunflower seeds (the dove attractant) were more frequently found in crops preseason (45.1%) than after the start of hunting (22.1%), suggesting that doves hunted during traditional hunting hours foraged on sunflower seeds more than doves harvested during extended hunting hours. However, the effects of hunting on foraging did not cause rises of corticosterone levels comparable to those observed in food deprivation experiments. We conclude that most doves were not stressed by the hunting-hour change.

Resistance is futile: effects of landscape features on gene flow of the northern bobwhite

Habitat for the northern bobwhite (Colinus virginianus) has declined and changed drastically in spatial structure throughout the last century. Undoubtedly such changes have impacted bobwhite and may have altered their ability to access available habitat. We investigated whether landscape resistance, geographic distance, or interstate highway barriers were related to dispersal and gene flow of bobwhite in central and southern Illinois. Landscape resistance was determined from two empirically informed models depicting habitat suitability for bobwhite. During 2007–2008, hunters submitted bobwhite tissue samples from which we amplified 11 microsatellites. The relationship between individual genetic distances and spatial variables was analyzed with Mantel tests and causal modeling was used to verify the spatial variables influencing gene flow. Genetic distance was correlated with geographic distance but showed no relationship with interstate highway barriers. Habitat suitability did not enhance gene flow, and was inversely related in some partial Mantel tests. We suggest that bobwhite dispersal from suitable habitat patches may be less frequent than from suboptimal habitats. Bobwhite may be able to access suitable habitat across gaps of unsuitable habitat but distance limits their dispersal. Because available habitat for bobwhites may have a greater likelihood of being colonized when closer to occupied habitat, we suggest that lands closer to occupied habitat should be targeted for conservation or habitat improvement efforts.

Comparative Genetic Structure of Sympatric Leporids in Southern Illinois

Many leporid species have overlapping ranges, but ecological differences may make for profoundly different population structure in the same area. In southern Illinois, swamp rabbits (Sylvilagus aquaticus) and eastern cottontails (S. floridanus) co-exist, but swamp rabbits are habitat specialists associated with floodplain forests and eastern cottontails exhibit more general habitat preferences. Additionally, swamp rabbits exist at the northern edge of their range in southern Illinois, whereas eastern cottontails are well within the core of their range. To determine whether these differences resulted in differences in genetic structure, we assessed the population differentiation of these 2 sympatric species in southern Illinois using polymorphic microsatellite markers. We employed a combination of sampling techniques including tissue sampling from trapped rabbits and collection of fecal pellets from swamp rabbit latrine logs. Swamp rabbits appeared to be differentiated within 50 km of Illinois’ Cache River watershed (K = 4 populations) suggesting that local populations are relatively isolated, whereas eastern cottontails exhibited no discernable genetic structure (K = 1). Such a result confirms the expected relationship of greater genetic structure in a habitat specialist (i.e., swamp rabbits) versus a habitat generalist (i.e., eastern cottontails). Unlike eastern cottontails, our results suggest that swamp rabbits experience low genetic connectivity in southern Illinois likely due to restricted dispersal, linear distribution of habitat, and smaller effective population size as mediated by habitat fragmentation.

Hybridization and polymorphic microsatellite markers for two lagomorph species (Genus Sylvilagus): implications for conservation

Eastern cottontails (Sylvilagus floridanus) are a prolific and popular game species in North America but have declined within the core of their range. Swamp rabbits (S. aquaticus) are sympatric with eastern cottontails and are a species of concern at the northern fringe of their range in Illinois. Although hybridization between these species may be a potential factor affecting their declines, no studies have yet been conducted to address this issue. We examined the potential for hybridization between sympatric eastern cottontails and swamp rabbits in Illinois by sequencing a portion of the mitochondrial 12S gene in 17 individuals of each species. Additionally, we developed six microsatellite markers for the eastern cottontail (7–13 alleles/locus) that also amplify in swamp rabbits (3–5 alleles/locus). We found fixed differences between species with haplotypes forming well-differentiated clades indicating a lack of hybridization. Hybridization between eastern cottontails and swamp rabbits does not appear to be affecting their declines. Misidentification due to ambiguous morphological characteristics of the two species occurred in an earlier study and in our own. We suggest the mitochondrial 12S gene may be a convenient molecular marker for the resolution of species identity questions. Information on microsatellites, occurrence of natural hybridization, and a molecular marker for species resolution will be useful for developing management plans for lagomorphs and focusing further research on factors affecting population status.

Change in Density of Duck Nest Cavities at Forests in the North Central United States

Abstract During the past century, clear-cut hardwood forests of the north central United States have regenerated, and trees have matured into size classes increasingly capable of producing cavities...

Spatio-temporal variation in prevalence and intensity of trematodes responsible for waterfowl die-offs in faucet snail-infested waterbodies of Minnesota, USA

Several non-native trematodes hosted by the invasive Eurasian faucet snail, Bithynia tentaculata, have been causing die-offs of waterfowl in the Midwestern United States and Canada for several decades. Because of the potential implications of these die-offs on waterfowl in non-native settings, it is necessary to better understand the trematodes that cause the die-offs. Here, we studied the spatio-temporal dynamics of two trematodes, Cyathocotyle bushiensis and Sphaeridiotrema spp., known to infect waterfowl in northern Minnesota, USA, via their intermediate host, the faucet snail (Bithynia tentaculata). We studied prevalence (% of snails infected within a sample) and intensity (mean number of parasites per infected snail within a sample) of faucet snail infection with these two trematodes in small lakes, large lakes, ponds, and rivers in northern Minnesota in the spring, summer, and fall of 2011–2013. We tested whether parasite prevalence and infection intensity could be explained spatially (as a function of the abundance of faucet snails, average snail size, water depth, and proximity to known waterfowl groups) and temporally (across years and seasons) using generalized estimating equation models. The spatial and temporal patterns we observed varied within and among waterbodies. For both parasite species, parasite prevalence and intensity of infection were consistently higher in samples with larger snails and in deeper portions of the waterbodies. In Lake Winnibigoshish, prevalence was lower farther from the large waterfowl groups we observed, but the abundance of snails in a sample had no effect on prevalence or intensity of infection. Our findings help improve understanding of this multi-species system, but also illustrate the complexity of modeling the spatial and temporal dynamics of infections in waterbodies that are so variable in size, shape, waterfowl use, and function.

Thinking like a duck: fall lake use and movement patterns of juvenile ring-necked ducks before migration.

The post-fledging period is one of the least studied portions of the annual cycle in waterfowl. Yet, recruitment into the breeding population requires that young birds have sufficient resources to survive this period. We used radio-telemetry and generalized estimating equations to examine support for four hypotheses regarding the drivers of landscape scale habitat use and movements made by juvenile ring-necked ducks between the pre-fledging period and departure for migration. Our response variables included the probability of movement, distances moved, and use of different lake types: brood-rearing lakes, staging lakes, and lakes with low potential for disturbance. Birds increased their use of staging areas and lakes with low potential for disturbance (i.e., without houses or boat accesses, >100 m from roads, or big lakes with areas where birds could sit undisturbed) throughout the fall, but these changes began before the start of the hunting season and their trajectory was not changed by the onset of hunting. Males and females moved similar distances and had similar probabilities of movements each week. However, females were more likely than males to use brood-rearing lakes later in the fall. Our findings suggest juvenile ring-necked ducks require different lake types throughout the fall, and managing solely for breeding habitat will be insufficient for meeting needs during the post-fledging period. Maintaining areas with low potential for disturbance and areas suitable for staging will ensure that ring-necked ducks have access to habitat throughout the fall.