Notes on Hurricane Irma-related Key Deer mortality estimates:
The Refuge stated that they know of 21 Irma-related deer deaths. These represent ONLY deaths known to Refuge staff through directly finding the carcass or getting a report from a resident. Surely, the Refuge would not be so naïve as to proclaim they know the fate of every Key deer and 21 is the total mortality number – however, their announcement has been lately misinterpreted by the press and there are now some people believing Irma caused a mere 21 deer deaths. This is ridiculous for three primary reasons: 1) No one even attempted to do an actual sweep through the mostly impassable post-Irma woods. Also, many deer on the outer islands (e.g. Long Beach Rd.) were swept into the surrounding waters by the surge. So most carcasses both on land and water were never discovered; 2) numerous carcasses were found by residents but not reported to the Refuge (e.g. 5 from one individual and 6 from another that I know of); 3) if 21 deaths was the true number, then all survey results conducted by Texas A & M University (TAMU) would be completely, utterly wrong and off-base (see below).
The only scientific-based estimate of Irma-related Key deer mortalities comes from pre and post-hurricane survey data analyses by TAMU scientists. Their report (https://www.fws.gov/uploadedFiles/Key%20Deer%20Hurricane%20Irma%20Report%20October%202017(1).pdf ) utilizes deer sighting data from the traditional road drive-by surveys conducted in the months before Irma and 13 surveys done in late-September to early-October after the storm. The authors caution that interpretation of the survey results is difficult and subject to very large error margins, partly and importantly due to the differences in road-side conditions and potential deer behavior changes affecting the post-storm surveys. Indeed, from a strict statistical perspective, results of such significance tests as ANOVA and t-test show the differences between the post-Irma survey group and survey groups done in January and February 2017 to be insignificant. Those that still remember their Statistics 101 realize that the lack of significant differences between the groups does not mean no deer died during Irma, but rather that the error confidence intervals between the survey groups are too large for firm, statistically strong conclusions. Nevertheless with only those data being available, TAMU attempted to use the mean, and upper and lower 95% confidence interval boundaries to essentially provide theoretical “best case” and “worst case” scenarios.
Simply comparing the means of survey groups done in Nov ’16, Dec ’16, Jan ’17 and Feb ’17 to the lower 95% CI boundary of the post-Irma survey group (i.e. worst likely post-Irma survey sighting numbers) yielded a 23% mortality loss. That is the number TAMU now generally accepts as most likely, considering again, the huge margins of error. (Note that this is more than 10x the death count if truly only 21 deer had died as discussed in #1 above). If the same analysis is done using the upper 95% CI boundaries from the pre-Irma survey groups, the results are non-sensical, since comparisons with the Nov ’16 and Dec ’16 surveys suggest that Irma actually had no impact and the deer population actually INCREASEED, up to 8% (!!!) So the final possible combination is comparing the upper pre-Irma limits (i.e. best case before the storm) to the lower post-Irma limit (i.e. worst case after the storm). This comparison yields a loss range over the 4 pre-Irma survey groups of -28% to -68%, with an average of -49.5%.
Based on the TAMU data and interpretation, it is most reasonable to conclude – bearing in mind all the problems inherent in the survey methodology and changes in conditions affecting the surveys due to the storm – that the total Key deer loss was somewhere between 23% and 50%. What has so-far not been brought forth, however, is that, based on many physical and biological signs, the deer mortality rate was likely highly variable regionally. Based on residents’ direct observations of deer in their neighborhoods before and after the storm, as well as physical evidence of storm surge height, force and wreckage, the heaviest deer losses likely occurred on the Long Beach Rd. peninsula and neighboring islands that experienced (as per NOAA reports) as much as 18’ combined storm surge and wave height onslaught that went completely over the land and into Coupon Bight, obliterating numerous houses, most large trees and parts of the road itself. (In that devastation, imagine the survival chances that a 50-80lb deer had…) On the other hand, areas such as Port Pine Heights on Big Pine Key suffered much less force and damage, and deer mortality there can be expected to have been much, much lower. TAMU is planning additional surveys in the future to better define the deer population trends and storm after-effects.
The only other veritable source of information on Key deer Irma-related mortality is from residents within their habitat. As we are all aware of, many (let’s be honest – the majority) of Key deer live close to humans and many residents are well aware of deer that repeatedly use their back yards as part of their individual forage range. Save Our Key Deer organization (SOKD – http://saveourkeydeer.org/) utilized the internet and social media to conduct a deer poll starting immediately after Irma’s passage. While the objective of the survey was not to estimate the remaining population but rather to compile immediate information in what areas deer actually survived and what condition they were in, the responses from 70+ participants from various locations indicated that while some deer obviously survived in the various locations, the post-hurricane counts were down (and continue to be down to this day) by around 40% average – although the great spatial mortality variability mentioned above is very much reflected in the resident reports. What makes this data set important is that while a few residents reported post-Irma counts as high as 87% of pre-storm counts, NOT A SINGLE REPORT posted a gain of deer. So if everybody had a decline, averaging @40%…where are these deer now?? All hiding in some uninhabited-by-humans secret enclave of BPK, NNK or are they all partying on uninhabited LPK?? Although anecdotal, the residents’ observations have a striking consistency which should not be ignored.
As a final note, no one has so far made a very important distinction in why each Irma-related deer death occurred: there were by far two primary causes for deer casualties: 1) Immediate death due to the force of the storm’s winds and water surge by crushing and drowning; 2) Post-storm effects caused by dehydration. Number 1 should be obvious to all. Number 2 is less so: all Key deer can drink water somewhat contaminated by salt (that’s one of their adaptations to the Keys!) but only up to about 1/3rd salt water contamination (BTW – if a human drank that for just one week…he’d die!- they don’t). The Irma storm pretty much destroyed all drinking holes for the deer within their range. So forage ended up NOT being the problem – drinking water did! Through the efforts of SOKD, TAMU and ultimately the Refuges management, a program to provide the deer with palatable water began @ 2 weeks after Irma hit. But these were few and far in between considering the breath of the area affected. A good number of deer likely survived the initial Irma onslaught, only to succumb to dehydration in the following weeks. For proof of the seriousness of the situation, see the many videos on the internet with the first aid workers allowed in giving absolutely desperate deer their water-bottles to drink from. As far as scientific data , TAMU had 8 female deer with radio collars still unremoved before the storm (the whole purpose was to monitor does during the screwworm fiasco). One of them died 14 days after Irma “likely to dehydration” as per TAMU, and she was living in mainland Big Pine. In the extreme, think of the deer on the outer islands that received no rain for several weeks after the storm until SOKD began delivering water buckets there. Did they find them in time???
The bottom line is that the Planet Earth likely had somewhere between 600-800 Odocoileus virginianus clavium left living after the screwworm onslaught in mid-2016-17. Through the 2017 birthing season, the deer tried to up their numbers, but at least in the areas SOKD members live in and/or patrol, and the TAMU scientists, many babies, does and bucks succumbed to Irma’s wrath – to the tune of SEVERAL HUNDRED (not the absurd 21!!!). We should all be grateful that indeed these creatures are as resilient to bless us with their continued presence, yet with their future in human hands…