**Abstract**

Resident white-tailed deer (*Odocoileus virginianus*) on St. John, US Virgin Islands offer a unique case study for understanding a population under pressure from climate change. During a 2015–2016 regional drought, deer health parameters including body condition, coat condition, tick prevalence, musculature, and stress hormones were tracked over three field seasons representing the onset, peak, and recovery phases of the drought. All health indicators showed significant change over the course of the drought, and post-hoc tests suggest some indicators (body condition, musculature, and ticks) were more sensitive during drought onset. High levels of cortisol during the peak period indicated substantial stress to the population, which normalized during recovery. The strongest correlations were between overall health/body condition and musculature and overall health/body condition and coat condition. The weakest correlations were between ticks and the remaining three variables. These results support the hypothesis that various measures of deer health are related. The frequency and intensity of droughts and environmental stressors are predicted to increase in the future due to climate change, which will further challenge this island deer population.

**Keywords:** stress hormones, climate change, body condition, musculature, coat condition, ticks

### **1. Introduction**

Historically, the Caribbean region has been characterized by relatively predictable seasonal rainfall patterns and moderate fluctuations in annual temperatures. However, this stability is changing rapidly with climate change, and is projected to be highly variable as levels of greenhouse gases in the atmosphere continue to increase [1, 2]. The most recent climate change data predicts that climate change will bring extreme heat waves at greater frequency, droughts that will occur 2–3 times more often, stronger hurricanes with the trend toward hotter temperatures, and wet and dry extremes in local areas [2, 3]. The Caribbean is considered particularly vulnerable to the effects of climate change as weather events that occur in the region increase in both frequency and duration (www.drought.gov). As a result, this area will experience increasing

weather variability and extremes, which will manifest as hotter temperatures, shifting rainfall patterns, more frequent water shortages following decreased annual rainfall, and longer dry seasons. The Virgin Islands have already experienced a series of droughts in recent years, the most severe of which occurred in 2015–2016.

Changing landscape conditions, including more frequent drought, can exert stressors on wildlife populations that have the potential to be detrimental to the health and fitness of individuals [4, 5] and populations over time [6]. For wildlife populations, drought presents multiple simultaneous environmental challenges such as high temperatures, low food availability, and low water availability [1]. Water shortages associated with drought can bring about reduced plant primary productivity and seed survivability, which causes food reduction and changes in water quantity and quality. As a result, suboptimal consumption of protein, vitamins, minerals, and other essential nutrients can lead to malnutrition. Subsequently, malnutrition, prolonged dehydration from heat stress, and parasitism can lead to the depletion of fat reserves, anemia, and poor body condition, and has the potential to result in immunocompromised individuals [7, 8]. These individuals are even more at risk for malnutrition, parasitism, or starvation [9]. Wildlife adapt to drought using physiological and behavioral adaptations, but the stress from prolonged drought can eventually overwhelm their resiliency [10].

Several studies have evaluated deer survival during drought events and demonstrated a clear connection between a weather event and population effects. During drought years, deer often overgrazed available flora and harmed plant species due to intense herbivory [11]. In addition, deer consumed fewer plants, and plants of lower forage quality, and often did not meet their nutritional requirements, which had the potential to limit lactation [12]. Reduced lactation can decrease deer numbers either because of neonate starvation or result in smaller and weaker fawns [13]. Bucks responded to reduced food quantity and quality by displaying smaller body size and antler growth, particularly in young males that were still growing [12]. Therefore, a single year of drought might have lifetime consequences for a cohort of both female and male deer [14]. Overall, the effects of climate change are multidimensional, and exacerbated by the stress of prolonged drought, and can be largely deleterious to the health of wildlife.

The goal of this study was to assess the resilience of a population of whitetailed deer on St. John, US Virgin Islands as they responded to a severe drought in 2015–2016. Health observations were collected through three successive field seasons representing drought onset, peak, and recovery. This work is the first to document the physiological changes observed during drought for a population of isolated residential island deer in the Caribbean region, and as a result, this work was largely exploratory. We hypothesized the lack of food and water resources associated with prolonged drought would have a negative effect on deer on St. John and we predicted that there would be an adverse change to their physiological condition as a result. However, there is little prior research alluding to chronic, pre-existing stress factors or the time points at which the changes would be demonstrated in the deer, including if and when they would resolve. We hypothesized that there would be strong associations between drought and musculature, coat condition, and body condition, due to limited island resources, and that these parameters might decrease due to direct and indirect effects of the drought. Similarly, we hypothesized that there might be an association between the values for cortisol, T-3 levels, and tick presence, and they might increase with drought-associated stress. However, we did not know the strength of the relationship between these different parameters, or which parameters would show differences within the three evaluation periods of this study. Our goal was to provide quantitative evidence for these changes for a protected island population at three distinct time

*Changes to Health Parameters of White-Tailed Deer during a Drought in the US Virgin Islands DOI: http://dx.doi.org/10.5772/intechopen.108270*

periods of a drought. The monitoring of stress and nutrition in wildlife populations can provide researchers with valuable insight into the baseline stability and physiological impacts of environmental change on wildlife populations [6]. The deer of St. John represent a unique and intriguing case study for understanding a population facing highly altered future conditions due to climate change.
