Aggressive behavior of white-tailed deer at concentrated food sites as affected by population density

Aggressive interactions among white-tailed deer (Artiodactyla: Cervidae) at 4-poster devices for host-targeted tick control

White-tailed deer, Odocoileus virginianus Zimmermann (Artiodactyla: Cervidae), are the primary wildlife host for adult stages of blacklegged ticks (Acari: Ixodidae: Ixodes scapularis Say) and an important host for lone star ticks (Acari: Ixodidae: Amblyomma americanum Linnaeus), both of which are vectors of numerous tick-borne pathogens. The 4-poster passive deer treatment device is a topical, host-targeted method to control free-living tick populations and has been proven to successfully reduce tick abundance in several states. Aggressive behavior of white-tailed deer at concentrated feeding stations is hypothesized to interfere with the effective use of 4-poster devices and deer contact with acaricide applicators. We analyzed images collected by camera traps at 4-poster feeding stations deployed at 3 sites in Maryland and found a negative relationship between some aggressive interactions and contact with applicators. Our results emphasize the need for further investigation into whether deer social dynamics can impact 4-poster efficacy for tick control. This study serves as a reminder that intraspecific interactions are important to consider when using host-targeted acaricide approaches.

White-Tailed Deer Spatial Distribution in Relation to '4-Poster' Tick Control Devices in Suburbia

Deer are keystone hosts for adult ticks and have enabled the spread of tick distributions. The ‘4-Poster’ deer bait station was developed by the United States Department of Agriculture to control ticks feeding on free-ranging deer. Although effective in certain scenarios, ‘4-Poster’ deer treatment stations require the use of bait to attract deer to one location, which may cause increased deer disease transmission rates and habitat damage. To better understand and manage the impact of baited ‘4-Poster’ stations on deer movements, we captured and GPS-monitored 35 deer as part of an integrated pest management project. Fifteen ‘4-Poster’ stations were deployed among three suburban county parks to control ticks. To quantify the effects of ‘4-Poster’ stations, we calculated deer movement metrics before and after feeders were filled with whole kernel corn, and we gathered information on visitation rates to feeders. Overall, 83.3% of collared deer visited a feeder and revisited approximately every 5 days. After feeders were refilled, collared deer were ~5% closer to feeders and conspecifics than before filling. Males used a higher percentage of available feeders and visited them more throughout the deployment periods. Although these nuanced alterations in behavior may not be strong enough to increase local deer abundance, in light of infectious diseases affecting deer populations and effective ‘4-Poster’ densities, the core range shifts and clustering after refilling bait may be a cause for concern. As such, trade-offs between conflicting management goals should be carefully considered when deploying ‘4-Poster’ stations.

Medicated corn feeders to disinfest cattle fever ticks, Boophilus (Boophilus) microplus (Acari: Ixodidae), from a suburban population of white-tailed deer, Odocoileus virginianus (Cervidae)

Following its eradication from the USA, the cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini), a vector of bovine babesiosis, has made episodic incursions into, and sometimes beyond, an established barrier zone separating tick-free from endemic areas. In large part the incursions involve hosting and transport by wild ungulates, particularly deer and antelope. One approach to disinfest ticks from wild hosts is with food baits medicated to stop parasites. The approach has had mixed success due to factors that have been previously identified with supplemental feeding of wildlife especially competition for the bait, social dominance behavior, and the availability of alternative food sources. Given that not all of the target hosts will intake a therapeutic dose of the medication (ivermectin) at all seasons of the year, an open question is whether the approach is efficacious as a stand-alone treatment or even as part of an integrated program. As detailed in the present study an intensive effort was successful in eradicating a local outbreak of fever ticks.

Predation risk increases intraspecific heterogeneity in white-tailed deer diel activity patterns

Prey species often mitigate predation risk through alteration of spatiotemporal diel activity patterns whereby prey access high-quality resources in risky areas during predator downtimes. However, dominance hierarchies exist in some prey species, and temporal partitioning is a mechanism thought to reduce aggressive intraspecific interactions. How demographic-specific responses to predation risk influence intraspecific temporal partitioning in prey are largely unknown and could be key to understanding the effects of predators on intraspecific interactions in prey. To assess the effects of predation risk on intraspecific interactions in white-tailed deer (Odocoileus virginianus), we monitored deer diel activity during the fawning season in four pairs of predator exclusion and control plots (~40 ha) from 2015 to 2018 using 16 camera traps. We examined the effect of predation risk on diel activity of males, females, and nursery groups by comparing the within-group coefficient of activity overlap (d̂) across predator exclusion and control plots. We then examined within-treatment activity overlap between groups in the predator exclosure and control plots. All groups maintained different diel activity patterns in safe and risky areas. Unconstrained by predation risk, all groups behaved more similarly, and interspecific group overlap was greater in the predator exclusion plots than control plots. Male-nursery group overlap exhibited the strongest treatment effect, increasing 24% in predator exclusion plots (d̂ = 0.91, confidence interval [CI]: 0.87–0.95) relative to control plots (d̂ = 0.67, CI: 0.57–0.76). Our results suggest predators increase heterogeneity in prey behavior and may be important drivers of behavioral processes, such as temporal partitioning, that minimize antagonistic intraspecific interactions of prey.

EFFICACY OF WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS) TREATMENT FOR CATTLE FEVER TICKS IN SOUTHERN TEXAS, USA

White-tailed deer (Odocoileus virginianus) serve as a host for cattle fever ticks (Rhipicephalus [Boophilus] microplus and Rhipicephalus [Boophilus] annulatus; CFTs); therefore, deer are a concern for CFT control programs in southern Texas, US. Systemic (oral delivery of ivermectin) and topical (permethrin on pelage) treatment devices have been developed for white-tailed deer; however, the efficacy of these treatment options has not been determined for CFTs in southern Texas. Our objectives were to evaluate the effectiveness of CFT treatment strategies by 1) measuring exposure rates of deer to the acaricides permethrin and ivermectin, 2) determining the relationship between CFTs on deer and exposure to the acaricides, and 3) determining if photos from remote cameras at medicated bait sites can be used as a measure of acaricide treatment. We captured 327 deer at four sites in southern Texas. Deer visitation to medicated bait sites was monitored using remote cameras from March 2010 to February 2012. There was no relationship between the presence of permethrin and the probability of being infested with CFTs (P≥0.336). The probability of infestation with CFTs decreased as serum ivermectin levels increased for male (n=18, P=0.098) and female (n=33, P<0.001) deer. Our results indicate ivermectin may be more effective in treating CFTs than permethrin; thus it would be worthwhile to develop topical acaricides other than permethrin for treating white-tailed deer in southern Texas.

Intraspecific temporal resource partitioning at white-tailed deer feeding sites

Individuals may reduce competition by temporally partitioning their use of a shared resource. Behavioral differences between sexes in ungulates may encourage segregation as individuals attempt to avoid antagonistic interactions. However, dominant sex and age groups may reduce subordinates' access to food resources, regardless of the subordinate's sex. We hypothesized that white-tailed deer Odocoileus virginianus temporally segregated at supplemental feeding sites based on social rank (subordinate: yearling males and adult females; dominant: adult males) and that segregation was affected by phase of the breeding season and diel cycle. If deer temporally segregate according to social rank, we predicted that the resulting activity patterns would manifest in one social class being relatively more susceptible to hunter-induced mortality. We used a multi-state modeling approach to quantify temporal segregation and calculated the probability that a feeding site was in a particular state during diurnal and nocturnal hours for each of the 3 phases of the breeding season. We determined that transition probabilities differed by season and diel cycle and dominant and subordinate social classes clearly avoided each other, with <1% co-occurrence at feeding sites. During the pre-breeding season, the probability of a subordinate being present during diurnal hours was 3.0× more likely than a dominant being present, but did not differ during nocturnal hours. There was no difference for dominants and subordinates during diurnal or nocturnal hours during the breeding season. In the post-breeding season, subordinates were 1.7× more likely to occur at the feeding site than a dominant during diurnal hours but they did not differ during nocturnal hours. Our results indicate that dominance status influences temporal segregation at feeding sites and is affected by the phase of the breeding season. Therefore, the resulting activity patterns may increase subordinates' risk to human predation during the pre-breeding and post-breeding seasons.

Breeding chronology and social interactions affect ungulate foraging behavior at a concentrated food resource

Prey species must balance predator avoidance behavior with other essential activities including foraging, breeding, and social interactions. Anti-predator behaviors such as vigilance can impede resource acquisition rates by altering foraging behavior. However, in addition to predation risk, foraging behavior may also be affected by socio-sexual factors including breeding chronology and social interactions. Therefore, we investigated how time-of-day, distance-to-forest, group size, social interactions (presence of different sex-age class), and breeding chronology (pre-breeding, breeding, post-breeding seasons) affected probability of feeding (hereafter: feeding) for different sex and age-classes (mature males, immature males, adult females, and juveniles) of white-tailed deer at feed sites. We developed a set of candidate models consisting of social, habitat, reproductive, and abiotic factors and combinations of these factors. We then used generalized linear mixed models (GLMMs) to estimate the probability of feeding and used model averaging of competing models for multimodel inference. Each adult sex-age class’ feeding was influenced by breeding chronology. Juveniles were more likely to be feeding than adults in all seasons. Feeding increased with group size for all sex-age classes. The presence of a mature male negatively influenced the feeding of immature males and juveniles were more likely to be feeding when an adult female was present. Feeding decreased with increasing distance-to-forest for mature males but not for other sex-age classes. Our results indicate that each sex-age class modulates vigilance levels in response to socio-sexual factors according to the unique pressures placed upon them by their reproductive status and social rank.

Quantifying dominance of adult female white-tailed deer in the presence of abundant food

Dominance is a behavioural mechanism that allows individuals to access and monopolize resources which should ultimately improve their fitness. Hierarchy strength should be strongest when resources are limited; however, this relationship is not consistent. We provided abundant food to assess whether hierarchy strength was consistent with resource abundance using 9 groups of captive female white-tailed deer (Odocoileus virginianus). We further assessed how body mass, age and testosterone levels were associated with rank position. Deer displayed a weak hierarchy with a mean linearity () of 0.39 (SD = 0.09) and a mean directional consistency index of 0.83 (SD = 0.06). Rank was related to body mass (, slope = 0.011), but not age or testosterone levels (). We demonstrate that hierarchy strength was weak in the presence of abundant food resources and suggest the possibility that dominance is a plastic behaviour that may vary with resource abundance.

Contrasting the Effects of Maternal and Behavioral Characteristics on Fawn Birth Mass in White-Tailed Deer

Maternal care influences offspring quality and can improve a mother's inclusive fitness. However, improved fitness may only occur when offspring quality (i.e., offspring birth mass) persists throughout life and enhances survival and/or reproductive success. Although maternal body mass, age, and social rank have been shown to influence offspring birth mass, the inter-dependence among these variables makes identifying causation problematic. We established that fawn birth mass was related to adult body mass for captive male and female white-tailed deer (Odocoileus virginianus), thus maternal care should improve offspring fitness. We then used path analysis to identify which maternal characteristic(s) most influenced fawn birth mass of captive female white-tailed deer. Maternal age, body mass and social rank had varying effects on fawn birth mass. Maternal body mass displayed the strongest direct effect on fawn birth mass, followed by maternal age and social rank. Maternal body mass had a greater effect on social rank than age. The direct path between social rank and fawn birth mass may indicate dominance as an underlying mechanism. Our results suggest that heavier mothers could use dominance to improve access to resources, resulting in increased fitness through production of heavier offspring.