**3. Results**

In total, 515 deer were observed remotely and 23 deer were tranquilized over three study seasons. In July 2015, 265 deer were observed, in March 2016, 189 deer were observed, and in July 2016, 61 deer were observed remotely, and 23 were tranquilized. At each time point, the samples were slightly more heavily represented by female deer; approximately 60–70% were female. The remote samples were heavily represented by mature deer, and ranged from approximately 75–90% mature deer at each time period.

#### **3.1 Deer health indicators associated with drought conditions**

The data confirm the hypothesis that there is an association between deer health and phase of drought conditions. For all six measures, a relationship between the stage of drought was statistically discernible (significant), which suggests that the onset, peak, and recovery phases were not all equally difficult for the deer. More specifically, a relationship was found between time points relative to drought and average cortisol levels (*F*(2, 63) ≈ 18, *p* < .00001) as well as average T3 levels (*F*(2, 63) ≈ 5.8, *p* ≈ 0.005). Similarly, statistically discernible (significant) associations were found between time point relative to drought and proportion of deer with fair/poor rankings on each of the four measures observed visually (tick level, coat condition, body health, and musculature, with respective *p*-values of .013, .01, .005, and .001, respectively) (**Figures 4**, **5** and **Table 2**).

#### **Figure 4.**

*Percentages of deer with coat condition issue (i.e., categorized as poor or fair condition) at each of the three time points (drought onset, peak, and recovery). This was the only indicator that presented higher prevalence of issues during the peak of the drought, while having lower prevalence both at the drought onset and recovery phases. Chi-square test indicates an association between time and prevalence of coat condition issues (<sup>2</sup> (2 degrees of freedom) = 8.9, p = .01).*

#### **Figure 5.**

*Indicators that presented higher prevalence of issues both at the onset and peak of the drought, while having lower prevalence after drought in a study of white-tailed deer (Odocoileus virginianus) during a 2015–2016 drought on St. John Island. (a) Percentages of deer with body decomposition (i.e., categorized as poor or fair condition) at each of the three time points (onset, peak, and recovery of the drought). Chi-square test indicates an association between time and prevalence of body decomposition (<sup>2</sup> (2) = 15.1, p = .005). (b) Percentages of deer with muscle atrophy observed at each of three time points (onset, peak, and recovery of the drought). Chi-square test indicates an association between time and prevalence of muscle atrophy (<sup>2</sup> (2) = 17.9, p = .0001). (c) Percentages of deer with ticks observed at each of three time points (onset, peak, and recovery of the drought). Chi-square test indicates an association between time and prevalence of ticks (<sup>2</sup> (2) = 8.8, p = .013).*

In summary, all six measures revealed an association between drought conditions and health of the deer, which does not support a hypothesis that the onset, peak, and recovery phases are all equally difficult on the deer.

Post-hoc analyses were conducted to explore various hypotheses about patterns of how each of the six health measures appeared to respond to the different stages of drought (**Table 2**). There are a few similarities; perhaps not surprisingly, all six measures had high levels of poor health at the peak of the drought. Another similarity is that all six measures revealed relatively improved health at the third time point *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*


#### **Table 2.**

*Post-hoc results (two-tailed p-values) of white-tailed deer (Odocoileus virginianus) health indicator comparisons across time points relative to drought (onset, peak, recovery) on St. John Island during a 2015–2016 regional drought. To flag potential effects, no correction for multiple testing was used.*

(during the recovery phase after the drought). This suggests the deer population showed resilience in the recovery phase.

On the other hand, there were differences in the extent to which the health measures appeared to be sensitive to the onset stage of the drought: some measures indicated poorer health even in the onset, whereas other measures were less sensitive. Three patterns of behavior were observed and named according to relative health at each of the onset, peak, and recovery periods of the drought. The patterns are named: "Low-High-Low," "High-High-Low," and "Medium-High-Low" (where "High" indicates high levels of poorer health).

Coat condition displayed the Low-High-Low pattern. This measure had discernibly higher (statistically significant) prevalence of poorer health only at the peak of the drought (**Figure 4** and **Table 2**). In the drought onset and recovery, percentages were significantly lower than the peak. No statistically discernible (significant) differences were observed when comparing onset vs. recovery phases of the drought (*p* > .5). This supports a hypothesis that coat condition is not particularly sensitive to the onset stage of the drought.

In contrast, the T-3 levels, body condition, musculature, and tick indicators displayed the "High-High-Low" pattern. These three measures showed higher prevalence of poorer health both during the drought onset and peak (**Figures 5**, **6** and **Table 2**). To be clear: for these indicators there were no statistically discernible (significant) differences in deer health when comparing the first two time points: onset versus peak of drought (*p* = .2, .3, .6, and .9, respectively, for T-3, musculature, ticks, and body condition measures). The prevalence of poor health on these indicators was only discernibly different (significant) at the third time point, after the drought. This supports the hypothesis that T-3 levels, body condition, musculature, and tick prevalence are sensitive to drought even in the onset stage.

Cortisol was the only measure to display a "Medium-High-Low" pattern. This measure had statistically discernible (significant) differences when comparing each of the three time points with each other (**Figure 6** and **Table 2**), with a mild sensitivity during the onset stage, increased severity at the peak of the drought, and of course the ability to recover in the third stage.

#### **3.2 Relationships between health measures**

Positive relationships were also present between each of the visually observed measures of deer health (**Table 3**). For example, a deer with fair/poor musculature was

#### **Figure 6.**

*Levels of fecal T3 (a) and cortisol (b) in white-tailed deer (Odocoileus virginianus) populations in a study of deer health indicators during the onset, peak, and recovery phases of a 2015–2016 drought on St. John Island. Sample sizes collected indicated below each period.*


#### **Table 3.**

*Correlation (as measured by Phi coefficient) indicating strength of association between health indicators (coat condition, body condition, musculature, and ticks) for white-tailed deer (Odocoileus virginianus) scored as Excellent/Good vs. Fair/Poor on St. John Island during the onset, peak, and recovery phases of a 2015–2016 regional drought. To avoid inflation, no adjustment for binary outcomes was used (e.g., adjusted phi, etc.). Thus, the correlations given here are conservative.*

more likely to also have fair/poor coat condition (φ = .34). Conversely, a deer with good/ excellent musculature was more likely to also have excellent/good coat condition. Overall health/body condition was strongly correlated to musculature (φ = .64) and coat condition (φ = .48). Coat condition and tick infestation were moderately correlated (φ = .31), as were coat condition and musculature (φ = .34). Smaller correlations were observed between tick infestation and musculature (φ = .2), and between tick infestation and health/body condition (φ = .26). The fact that all the pairwise correlation coefficients between health/body condition, musculature, coat condition, and ticks are positive supports the hypothesis that that these four measures of deer health are related, and/or largely dependent on similar underlying reasons. For this work, that reason was thought to be the multifaceted effects of stress associated with prolonged drought on the island.
