Lower Keys Marsh Rabbit
Post-Hurricane Irma Report 2017
Texas A&M Natural Resources Institute
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LOWER KEYS MARSH RABBITS POST-HURRICANE IRMA
I.D. PARKER, A.E. MONTALVO, A.A. LUND, N.J. SILVY, M. GRASSI, AND R.R. LOPEZ
Distribution authorized to U.S. Government Agencies only.
Florida Keys National Wildlife Refuge Complex 28950 Watson Boulevard Big Pine Key, FL 33043 305-872-2239 ext. 209
Under Grant Agreement Award F17AP00039 Modification No. 4 Monitored by U.S. Fish and Wildlife Service Artela Jacobs, Contracting Officer Division of Contracting and Grant Services 1875 Century Boulevard Atlanta, GA 30345 404-679-7197
Prepared by:
578 John Kimbrough Blvd. College Station, TX 77843 Phone: 979-845-1851 Fax: 979-845-0662
Report Contact: Israel Parker [email protected]
On the cover: Adult Lower Keys marsh rabbit; courtesy of Tom Dixon
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LOWER KEYS MARSH RABBIT POST-HURRICANE IRMA ASSESSMENT
OVERVIEW & BACKGROUND
Report provides U.S. Fish and Wildlife Service (USFWS) with an evaluation of spatial distribution of the Lower Keys marsh rabbit (Sylvilagus palustris hefneri; LKMR) following the landing of Hurricane Irma in the Lower Florida Keys. Hurricane Irma was a Category 4 storm when the eye passed through the center of the LKMR’s range (Figure 1) on 10 September 2017. The storm significantly impacted the vegetation structure and hydrology of the Lower Keys, potentially affecting numerous patches of LKMR habitat. The focus of report is to compare LKMR patch occupancy and vegetative composition pre- and post- Hurricane Irma.
Patch-level presence- absence surveys for LKMRs have been conducted sporadically since the 1980s, with official survey protocols established in 2009 (Faulhaber et al. 2007, Figure 1. Hurricane Irma prior to the arrival in the Lower Hughes 2014). These Florida Keys (black box), September 2017. methodologies monitored LKMR patch occupancy dynamics using pellet counts and habitat attributes to guide management strategies and future recovery actions.
METHODS Following Hurricane Irma, Texas A&M University Natural Resources Institute (NRI) personnel conducted a rapid occupancy assessment (December 2017) using USFWS survey methods in a subset of USFWS managed patches, including only those patches which contained pellets during any of the previous 3 surveys (i.e., 2014, 2015, 2017 pre-hurricane [no survey was performed in 2016]). As a result, a total of 128 circular plots (12-m radius) was sampled within the 30 selected patches, assessing habitat across Big Pine, Little Pine, No Name, Sugarloaf, Cudjoe, Little Torch, Middle Torch, and Big Torch keys. Patches varied in size from 0.1 to 27 ha and contained between 2 and 9 plots depending on patch size. At each plot, we recorded data on patch occupation, cover and vegetation, and predator or Key deer (Odocoileus virginianus clavium) occurrence (Table 1, Figure 2, Appendix A).
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Figure 2. Patches sampled on Sugarloaf, Cudjoe, Big Torch, Middle Torch, Lower Torch, Big Pine, No Name, and Little Pine keys, December 2017.
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Table 1. Patches sampled and their locations (key), area (ha), number of sampling plots, past survey detections of pellets, pellet counts (pre- and post-hurricane), juvenile pellet counts (pre- and post-hurricane), mean number of pellets per plot (pre- and post-hurricane), and pellet density (pellets/m2; pre- and post-hurricane).
Past Detections 2017 Pellet Counts 2017 Juvenile Pellets 2017 Pellet Means 2017 Pellet Density # of Patch Key Area Pre- Post- Pre- Post- Pre- Post- Pre- Post- Plots 2014 2015 2017 Hurricane Hurricane Hurricane Hurricane Hurricane Hurricane Hurricane Hurricane 1200 Big Pine 4.3 2 X 40 0 0 0 20 0 0.09 0.00 2002 Big Pine 19.6 6 X X X 1661 96 151 0 277 16 0.41 0.14 2003 Big Pine 15.6 6 X X * 195 * 0 * 32.5 * 0.29 2004 Big Pine 7.8 3 X 1878 66 78 0 626 22 1.85 0.19 2005 Big Pine 10.6 4 X X * 216 * 0 * 54 * 0.48 2011 Big Pine 6.0 3 X * 38 * 0 * 12.7 * 0.11 2108 Big Pine 0.3 2 X 858 0 280 0 429 0 1.90 0.00 2109 Big Pine 18.7 8 X X * 32 * 0 * 4 * 0.04 2110 Big Pine 18.5 8 X X * 552 * 0 * 69 * 0.61 2113 Big Pine 17.8 5 X X X 23 0 0 0 4.6 0 0.01 0.00 2906 Big Pine 12.0 5 X * 134† * 9 * 26.8 * 0.24 3102 Big Pine 27.0 9 X X * 0 * 0 * 0 * 0.00 3103 Big Pine 20.0 7 X 255 0 0 0 36.4 0 0.05 0.00 3105 Big Pine 22.7 8 X X * 0 * 0 * 0 * 0.00 3501 Big Pine 13.6 4 X X 28 0 0 0 7 0 0.02 0.00 3607 Big Pine 15.2 6 X X * 85 * 4 * 14.2 * 0.13 3610 Big Pine 10.4 3 X X X 223 14 7 0 74.3 4.67 0.22 0.04 3612 Big Pine 0.5 2 X X * 0† * 0 * 0 * 0.00 3613 Big Pine 1.0 2 X X * 0 * 0 * 0 * 0.00 3614 Big Pine 7.5 3 X * 6 * 0 * 2 * 0.02 3615 Big Pine 0.1 2 X 135 0 0 0 67.5 0 0.30 0.00 3704 Big Pine 0.1 2 X 46 0 7 0 23 0 0.10 0.00 5200 No Name 0.8 2 X 658 0 202 0 329 0 1.46 0.00 13108 Little Pine 25.3 8 X X 199 0 16 0 24.9 0 0.03 0.00 13109 Little Pine 6.5 3 X 97 0 0 0 32.3 0 0.10 0.00 31211 Middle Torch 8.8 3 X 249 0 0 0 83 0 0.24 0.00 34402 Big Torch 0.3 2 X 15 0 0 0 7.5 0 0.03 0.00 33403 Little Torch 0.2 2 X 10 0 0 0 5 0 0.02 0.00 44530 Cudjoe 0.9 2 X 800 0 0 0 400 0 1.77 0.00 57402 Sugarloaf 16.4 6 X * 0 * 0 * 0 * 0.00 * Missing data † Incidental pellets
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Patch Occupation At each plot, the number of pellets were counted and classified by age class (i.e., juvenile, adult) and condition (i.e., fresh, old). Pellets with a diameter of 6.7 mm or larger were classified as ‘adult’ whereas smaller pellet diameters were considered ‘juvenile’ (Forys 1995). Pellets classified as ‘fresh’ were shiny, consolidated, and dark brown in coloration. Pellets classified as ‘old’ were a dull and light brown in coloration. Pellets were classified as ‘indeterminable’ when decomposition made aging and condition classification unreliable (Hughes 2014). Finally, incidental LKMR pellet sightings between plots also were recorded. These data are used to monitor patch occupancy rates and population trends because LKMR density estimates are strongly correlated with LKMR fecal pellets per square meter (Schmidt et al. 2011).
Cover and Vegetation Cover was visually estimated for open substrate (e.g., bare ground, organic matter, marl, muck, debris, fill), herbaceous species (e.g., seashore dropseed [Sporobolus virginicus], bushy bluestem [Andropogon glomeratus], cattail [Typha spp.], glasswort [Salicornia spp.], sea oxeye daisy [Borrichia frutescens], saw palmetto [Serenoa repens]), and woody species (e.g., buttonwood [Conocarpus erectus], mangrove, pine [Pinus spp.]) to the nearest 5%. Independent of the above cover estimates, percent standing water was estimated to the nearest 5% and depth at the plot center was estimated to the nearest whole number (cm; Hughes 2014). Pines were counted and classified by maturity (i.e., seedling, sapling, mature) and status (alive or dead). Seedlings were those pines with a diameter at breast height (dbh) less than 2 cm. Samplings were those pines with a dbh between 2–5 cm. Mature pines were those with a dbh greater than 5 cm or whose stem or stump was greater than 1.22 m (4 ft; Hughes 2014). Thatch palms (e.g., Key thatch palm [Thrinax radiata], silver thatch palm [Thrinax morrisii]) greater than 1.22 m (4 ft) were counted and classified as dead or alive (Hughes 2014). These data are used to monitor changes in LKMR habitat and judge the need for further management actions including control of hardwood cover, removal of exotic invasive species, and indications of anthropogenic damage (e.g., dumping, camping, vehicle damage).
Key Deer and Predators Tracks, scat, or direct sightings were recorded for raccoons (Procyon lotor), Virginia opossum (Didelphis virginiana), fire ants (Solenopsis invicta), and Key deer (Hughes 2014). Incidental sightings between plots also were recorded. These data are used to monitor Key deer as well as predator patch occupancy which can be a significant limiting factor for LKMR populations (Forys and Humphrey 1999, Schmidt et al. 2010).
Data Analysis Data were averaged and, when possible, were statistically compared to data collected by USFWS in Spring 2017 pre-Hurricane Irma. Analyses with earlier survey data (i.e., 2014, 2015) were not calculated because of inconsistencies in data and changes in patch delineation.
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RESULTS AND DISCUSSION Patch Occupation Pellets were observed in the sampling plots of 11 patches, averaging 8.60 pellets/plot and at a density of 0.08 pellets/m2. Incidental pellets also were observed between plots within patch 3612 and 2906. The number of juvenile pellets decreased 98% (741 pellets to 13 pellets). Looking only at patches with data from 2017 both before and after the hurricane (n = 17), 82% of patches were abandoned (n = 14), the average number of pellets per sampling plot decreased 98% (43.91 pellets/plot to 2.51 pellets/plot), and the average pellet density decreased 96% (0.50 pellets/m2 to 0.02 pellets/m2; Table 1).
The decrease in rabbit pellet detection after Hurricane Irma is likely attributed to both direct mortality from the storm and flooding, as well as indirect mortality from the loss of critical, salt- sensitive herbaceous cover (Ross et al. 2008). Studies after the Category 1 impact of Hurricane Wilma in 2005 showed 38% patch abandonment (Schmidt et al. 2011) 6 months after landfall, with 71% of radio-collared rabbits being killed (N.D. Perry, unpublished data). Data from this survey is consistent with previous studies, though the magnitude of the loss post-Hurricane Irma appears more severe.
Cover and Vegetation Overall, Hurricane Irma visibly damaged vegetative cover with many plots showing an increase in debris, mud, and replacement of herbaceous LKMR habitat with bare ground (Figure 3). For cover data, we compared all plots with pellets sampled before (n = 41) and after Hurricane Irma (n = 24). Our data shows that after Hurricane Irma, on average, pellets were found at plots with a greater amount of open cover, a more intermediate amount of herbaceous cover and woody cover, and areas with slightly more standing water (Figure 4). These changes in percent open cover (Fisher’s exact: P < 0.001), herbaceous cover (Fisher’s exact: P < 0.001), woody cover (Fisher’s exact: P < 0.001), and standing water (Fisher’s exact: P < 0.001) were all found to be significant. Figure 3. Little Pine Key damage after Hurricane Irma including loss of herbaceous cover (foreground) and accumulation of woody debris (background).
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Figure 4. Percent of plots with LKMR pellets according to percent open cover (A), percent herbaceous cover (B), percent woody cover (C), and percent standing water (D) both before (blue bars; n = 41) and after Hurricane Irma (red bars; n = 24) with accompanying moving averages (dotted lines).
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Looking at all patches (n = 30), average pine density (pine/m2) was greatest for dead mature pines (0.046/m2), followed by live sapling pines (0.018/m2), live mature pines (0.016/m2), dead sapling pines (0.006/m2), live seedling pines (0.001/m2), and dead seedling pines (<0.001/m2; Table 2). For thatch palms, average patch density (palm/m2) was greater for live thatch palms (0.13/m2) than dead thatch palms (0.01/m2; Table 2). Comparison of pine and thatch palm data with pre- hurricane data was not possible due to missing records.
Key Deer and Predators Predator signs at plots indicated an increase in the occurrence of raccoons (+3 patches) with post- hurricane surveys now showing evidence of Virginia opossum (2 patches). Fire ants were seen in a single patch both before and after Hurricane Irma. Key deer were seen in 100% (17/17 patches) of pre-Hurricane Irma survey patches and 77% (23/30 patches) of post-Hurricane survey patches (Table 3). Difference in predator and Key deer patch occupancy are likely a result of both changes in vegetative cover and direct mortality post-Hurricane Irma.
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Table 2. Patches sampled and their associated count (n) and density (D; plant/m2) for live seedling pine, live sapling pine, live mature pine, dead seedling pine, dead sapling pine, dead mature pine, live thatch plam, and dead thatch palm Live Seedling Live Sapling Live Mature Dead Seedling Dead Sapling Dead Mature Live Thatch Dead Thatch
Patch Pine Pine Pine Pine Pine Pine Palm Palm n D n D n D n D n D n D n D n D 1200 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2002 0 0 11 0.016 34 0.050 0 0 0 0 0 0 124 0.183 0 0 2003 0 0 0 0 52 0.077 0 0 6 0.009 37 0.055 121 0.179 0 0 2004 0 0 0 0 37 0.109 0 0 0 0 34 0.1 184 0.543 0 0 2005 0 0 0 0 0 0 0 0 0 0 43 0.095 90 0.199 0 0 2011 0 0 46 0.136 0 0 0 0 0 0 77 0.227 128 0.378 0 0 2108 0 0 0 0 0 0 0 0 0 0 32 0.142 80 0.354 14 0.062 2109 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2110 0 0 13 0.014 12 0.013 0 0 0 0 101 0.112 106 0.117 43 0.048 2113 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2906 0 0 0 0 0 0 0 0 0 0 8 0.014 79 0.14 21 0.037 3102 4 0.004 49 0.048 4 0.004 3 0.003 9 0.009 22 0.022 112 0.11 0 0 3103 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3105 0 0 0 0 0 0 0 0 0 0 40 0.044 32 0.035 0 0 3501 0 0 0 0 5 0.011 0 0 0 0 1 0.002 40 0.089 0 0 3607 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3610 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3612 0 0 13 0.058 25 0.111 0 0 31 0.137 11 0.049 74 0.327 0 0 3613 0 0 0 0 22 0.097 0 0 0 0 64 0.283 84 0.372 0 0 3614 0 0 0 0 0 0 3 0.009 10 0.03 18 0.053 45 0.133 1 0.003 3615 7 0.031 60 0.266 1 0.004 0 0 0 0 44 0.195 135 0.597 0 0 3704 0 0 0 0 0 0 0 0 0 0 0 0 14 0.062 0 0 5200 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 13108 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 13109 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 31211 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 34402 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 33403 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 44530 0 0 0 0 0 0 0 0 0 0 0 0 22 0.097 34 0.150 57402 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Sum 11 0.035 192 0.537 192 0.477 6 0.012 56 0.184 532 1.392 1470 3.914 113 0.3 Average 0.367 0.001 6.4 0.018 6.4 0.016 0.2 <0.001 1.867 0.006 17.73 0.046 49 0.13 3.767 0.01
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Table 3. Patches sampled and the associated detection of predators (R = raccoon, O = Virginia opossum, and F = fire ants) and Key deer (K) both pre- and post-Hurricane Irma.
2017 Predators and Key Deer Patches Pre-Hurricane Post-Hurricane
1200 K K
2002 K & R K 2003 * K 2004 K K 2005 * K
2011 * K 2108 K 2109 * K & R 2110 * K
2113 K K & O
2906 * K 3102 * K 3103 K 3105 * K & R
3501 K & R K, F, & R 3607 * K & R 3610 K K, O, & R 3612 *
3613 *
3614 * K 3615 K & R 3704 K K 5200 K K
13108 F, K, & R K & R
13109 K & R K 31211 K & R R 34402 K K 33403 K
44530 K K & R 57402 * K & R * Missing data
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POPULATION STATUS At this time, it is recommended that USFWS continue to monitor the status of LKMR populations. Specifically, the following actions are recommended for consideration:
Continue annual fecal pellet counts as an index of distribution and presence/absence ― to monitor post-hurricane recovery. Continue vegetation maintenance (i.e., control of invasive exotic and native hardwood species) and consider enhancement of habitat patches ― to maintain or enhance patches to optimal habitat conditions. Predator control of feral and free-ranging house cats and raccoons in and around habitat patches ― to reduce potential LKMR mortalities. Consider translocation of LKMR – to repopulate unoccupied patches
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LITERATURE CITED Faulhaber, C. A., N. D. Perry, N. J. Silvy, R. R. Lopez, P. A. Frank, P. T. Hughes, and M. J. Peterson. 2007. Updated distribution of the Lower Keys marsh rabbit. Journal of Wildlife Management 71:208–212. Forys, E. A. 1995. Metapopulations of marsh rabbits: a population viability analysis of the Lower Keys marsh rabbit (Sylvilagus palustris hefneri). Dissertation, University of Florida, Gainesville, USA. Forys, E., and S. R. Humphrey. 1999. The importance of patch attributes and context to the management and recovery of an endangered lagomorph. Landscape Ecology 14:177–185. Hughes, P. 2014. Initial survey instructions: Lower Keys marsh rabbit occupancy and habitat monitoring for adaptive resource management, Florida Keys National Wildlife Refuge Complex. Big Pine Key, Florida, USA. Ross, M. S., J. J. O'Brien, R. G. Ford, K. Zhang, and A. Morkill. 2009. Disturbance and the rising tide: the challenge of biodiversity management on low-island ecosystems. Frontiers in Ecology and the Environment 7:471–478. Schmidt, P. M., R. A. McCleery, R. R. Lopez, N. J. Silvy, and J. A. Schmidt. 2010. Habitat succession, hardwood encroachment and raccoons as limiting factors for Lower Keys marsh rabbits. Biological Conservation 143:2703–2710. Schmidt, P. M., R. A. McCleery, R. R. Lopez, N. J. Silvy, J. A. Schmidt, and N. D. Perry. 2011. Influence of patch, habitat, and landscape characteristics on patterns of Lower Keys marsh rabbit occurrence following Hurricane Wilma. Landscape Ecology 26:1419–1431.
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APPENDIX A. Survey patches and plots for the 2017 Post-Hurricane Irma Lower Keys Marsh Rabbit Survey
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