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Evaluating nest supplementation as a recovery strategy for the endangered rodents of the Florida Keys: Rodent distribution at supplemental nests

Authors:
  • NOAA - Southwest Fisheries Science Center

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The Key Largo woodrat (Neotoma floridana smalli) and Key Largo cotton mouse (Peromyscus gossypinus allapaticola) are federally endangered subspecies endemic to the tropical hardwood hammocks of Key Largo, Florida. Woodrats are considered generalists in habitat and diet, yet a steady decline in natural stick nests and capture rates over the past several decades suggests that they are limited by the availability of nesting habitat due to habitat loss and fragmentation. The more specialized Key Largo cotton mouse appears to rely on old growth hammock, a habitat type that is rare following past land clearing. In 2004, the U.S. Fish and Wildlife Service started building supplemental nest structures to restore habitat quality and connectivity for these endangered rodents, but nest use requires evaluation. We used camera traps and occupancy models to evaluate the factors influencing woodrat and cotton mouse use of the supplemental nests. We detected woodrats at 65 and cotton mice at 175 of 284 sampled nest structures, with co-occurrence at 38 nests. Woodrat nest use followed a gradient from low nest use in the north to high nest use in the south, which might relate to the proximity of free-ranging domestic cat (Felis catus) colonies in residential developments. Cotton mouse nest use, however, was related positively to mature hammock and related negatively to disturbed areas (e.g. scarified lands). The two species occurred independently of each other. Stick-stacking behavior was observed at supplemental nests and, although it was correlated with detection of woodrats, it was not a strong predictor of their occurrence. We suggest that nest supplementation can be an important tool for species recovery as habitat quality continues to improve with succession.
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... The Key Largo woodrat is a federally endangered subspecies endemic to Key Largo, Florida (US Department of the Interior 1984). Once ranging throughout the tropical hardwood hammock, historical habitat loss and land alterations during the agricultural era have limited their distribution to North Key Largo and reduced the availability of natural nesting substrate in the environment (Winchester et al. 2009, Cove et al. 2017. This loss of habitat and nesting sites has been detrimental to the survival of these v www.esajournals.org 2 September 2020 v Volume 11(9) v Article e03239 ecosystem engineers, as they build substantial stick-nests by layering forest debris at the bases of trees (Fig. 1a), in fallen tree throws, or in solution holes (Cove and Maurer 2019). ...
... Additionally, recent evidence suggests that woodrat distributions have been further limited by the presence of feral and free-ranging cats (Felis catus)-resulting in a shift away from their natural stick-nest building behavior . Once estimated to number fewer than 100 individuals (McCleery et al. 2005), Key Largo woodrats have benefitted greatly from conservation management practices, including nest supplementation and exotic predator removal , and there are now more than 2000 supplemental Key Largo woodrat nests located in their protected habitats (Cove et al. 2017). These nests are constructed from large plastic culvert pipes and covered with rocks or chunks of fossilized coral (Cove et al. 2017). ...
... Once estimated to number fewer than 100 individuals (McCleery et al. 2005), Key Largo woodrats have benefitted greatly from conservation management practices, including nest supplementation and exotic predator removal , and there are now more than 2000 supplemental Key Largo woodrat nests located in their protected habitats (Cove et al. 2017). These nests are constructed from large plastic culvert pipes and covered with rocks or chunks of fossilized coral (Cove et al. 2017). On the exterior, Key Largo woodrats maintain supplemental and natural nests in the same way (i.e., stick-stacking behavior; Cove et al. 2017), but supplemental nest interiors are more enclosed with comparatively little air flow and moisture penetration (Barth 2014). ...
Article
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Supplemental nests are often used to restore habitats for a variety of rare and endangered taxa. However, though they mimic the function of natural nests, they vary in design and construction material. We know from previous research on human buildings that these differences in architecture can alter the types of microbes to which inhabitants are exposed, and these shifts in microbial interactions can be detrimental for individual health and well-being. Yet, no one has tested whether bacterial communities in supplemental structures are distinct from those found in natural nests. Here, we sampled the bacteria from inside supplemental nests of the endangered Key Largo woodrat (Neotoma floridana smalli). We then compared the diversity and composition of those bacteria to the bacteria collected from natural stick-nests and the surrounding forest environment in Key Largo, Florida. In addition, we sampled woodrat bodies to assess the microbiota of nest inhabitants. We observed distinct bacterial communities in Key Largo woo-drat nests, relative to the forest environment; however, we could not differentiate between the bacterial communities collected from supplemental and natural nests. Furthermore, when we considered the potential accumulation of rodent-associated bacterial pathogens, we found no evidence of their presence in supplemental nests, in natural nests, or on the forest floor. Where we expected to see an accumulation of pathogens, we instead observed high relative abundances of bacteria from antimicrobial-producing groups (i.e., Pseudonocardiaceae and Streptomycetaceae). The bacteria on Key Largo woodrat individuals resembled those of their nests, with a low relative abundance of potential pathogens (0.3% of sequence reads) and a high relative abundance of bacteria from antimicrobial-producing groups. Our results suggest that, although there is some microbial interaction between nests and nest inhabitants, there are no detectable differences in the types of bacteria to which Key Largo woodrats are exposed in supplemental and natural nest structures.
... Less than 100 individuals were estimated to remain in their highly-restricted habitat in 2002(McCleery et al., 2006; however, estimates based on trapping conducted between 2007 and 2011 revealed high uncertainty fluctuating between 78 and 696 individuals (Potts et al., 2012(Potts et al., , 2016. The causes of woodrat population declines on Key Largo are still under debate, but nesting habitat loss from historical development and exotic predators are generally accepted as the key factors (Cove et al., 2017;Winchester et al., 2009). ...
... Key Largo woodrat recovery strategies include both habitat and predator management. The U.S. Fish and Wildlife Service (hereafter: USFWS) has built supplemental nest structures to help restore woodrat nesting habitat in forests that are undergoing natural succession (Cove et al., 2017). In 2013, the USFWS implemented an integrated pest management plan to remove exotic predators (including free-ranging cats and Burmese pythons) to restore endangered island endemics including the woodrat (USFWS, 2013). ...
... Supplemental nest structures had a variety of historical forms, but the majority of contemporary structures are composed of 1.5-2 m of corrugated plastic culvert covered in coral, branches, and capped with coral boulders. They occur throughout the tropical hardwood hammocks, successional, and historically disturbed habitats of the refuge (Cove et al., 2017). At the time of the surveys, there were > 1000 supplemental nests in North Key Largo that were established by volunteers to create nest corridors to connect suspected subpopulations and restore scarified and disturbed areas. ...
Article
Exotic predators create novel ecological contexts for native species, particularly when prey exhibit predator naïve behaviors. Population recovery of island endemic species following predator eradication has been documented broadly, but studies examining mammalian prey behavioral responses to exotic predator removal are less common. The Key Largo woodrat (Neotoma floridana smalli) is an endangered Florida endemic species that exhibited drastic declines, signified by the loss of natural stick-nests, over the past three decades due to habitat loss and effects from exotic predators. We conducted camera trap surveys of woodrats at supplemental nests and used dynamic multistate occupancy models to evaluate changes in woodrat distribution and stick-nest building behavior over a two-year period of exotic predator (domestic cats [Felis catus] and Burmese pythons [Python bivittatus]) removal. The distribution of woodrats using supplemental nests increased from 27% to 39% in the two-year period, while the proportion of occupied supplemental nests with stick-nests increased from 37% in 2013 to 54% in 2015. The probabilities of supplemental nest use and stick-nest building behavior increased over time following a gradient away from the northern extent of Key Largo, an area associated with high cat activity and the only sites of python captures during the surveys. Woodrats that built stick-nests were more detectable than those that did not, which suggests that stick-nest building could make woodrats more susceptible to pre-dation from novel predators when performing the behavior. We documented increasing woodrat occurrence, along with increasing stick-nest building behavior, which supports recovery and management objectives focused on exotic predator removal.
... Woodrats are ecosystem engineers that serve a role in forest function by increasing decomposition and dispersing seeds (Barbour andHumphrey 1982, Whitford andSteinberger 2010). Their stick-nests are used by the federally listed Peromyscus gossypinus allapaticola (Schwartz) (Key Largo Cotton Mouse; hereinafter, Cotton Mouse; Cove et al. 2017). Stick-nests might be important refugia for other taxa because they host stable microclimatic environments and unique microbial communities (Thoemmes and Cove 2020). ...
... As part of a long-term survey project, we monitored supplemental and natural Woodrat nests annually for occupancy trends to inform adaptive habitat and exotic predator management (sensu Cove et al. 2017Cove et al. , 2019. Previous surveys revealed that the monitoring and removal of invasive predators including Burmese Pythons and Felis catus L. (Domestic Cat) led to increasing distributions and apparent abundance of Woodrats (Cove et al. 2019). ...
Article
Florida is renowned for its non-native reptile communities, with 2 such pervasive non-native species including the apex predator Python bivittatus (Burmese Python) and the herbivorous Iguana iguana (Green Iguana) that showcase the spectrum of their ecological impacts. Both species have recently expanded into the Florida Keys. We used a camera trap to survey a radio-tagged Burmese Python and documented both non-native reptiles cohabitating in the active, natural stick-nest of an endangered rodent, Neotoma floridana smalli (Key Largo Woodrat), in Dagny Johnson Botanical State Park, Key Largo, FL. An additional nest visitor included Peromyscus gossypinus allapaticola (Key Largo Cotton Mouse), another endangered rodent and potential prey for the python. Camera placement allowed us to detect both rodents on the exterior of the stick-nest. The presence of the Key Largo Woodrat and Key Largo Cotton Mouse at the nest warrant continued monitoring of the 2 reptile species and their interactions with the endangered small mammals as their presence becomes more common in the Florida Keys.
... This proposed response is further supported by the negative effect imposed by distance from development, and positive effect of percent impervious surface. Likewise, cat detections had a positive relationship with non-legacy forests, which tend to be more disturbed patches associated with human development (Cove et al., 2017;Diamond and Ross, 2020). Together, these variables collectively reduce cat detections within the refuge, and make seasonal changes in detection evident. ...
Article
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Free-roaming domestic cats (Felis catus) pose numerous risks to biodiversity conservation, especially in island ecosystems. However, the removal of cats is costly, labor-intensive, and often demands more resources than land managers have at their disposal. These costs might be reduced, however, if trapping effort is regularly scaled to match the prevalence of cats on the landscape rather than consistently exhausting trapping resources even when cats are scarce. Here we analyze the efficacy of a long-term (2014 – 2021) cat removal program which uses motion-activated camera traps to determine monthly trapping effort in the Florida Keys. Furthermore, we compare the trapping effort required for this program against that of a hypothetical removal program with the same resources which does not use surveillance-informed trapping. We hypothesized that cat detections would decline over the study period as a result of the removal program, and that the surveillance-informed approach would require less trapping effort than uninformed trapping would. Our analyses reveal that the sustained, year-round trapping program has reduced the volume and geographic extent of cat detections within the study area. Furthermore, the use of camera traps to inform removal efforts has reduced the number of trap nights required to achieve these goals compared to the hypothetical removal program that did not use surveillance-informed trapping. While climatic and landscape variables also contribute to monthly cat detections, our study reveals that long-term surveillance-informed trapping reduces cat detections without exhausting resources. Such an approach may aid other land managers in their efforts to conserve biodiversity by removing invasive predators.
... As a result of human modifications of ecosystems, many rodent species, particularly in Australia, have experienced population declines or extinctions (Smith and Quin 1996;Firth et al. 2010;Cove et al. 2017;Waller et al. 2017;Roycroft et al. 2021;Vernes et al. 2021). In some cases, introduced rodents have been shown to perform some of the fungal dispersal ecosystem services that were once provided by lost species (Vernes and McGrath 2009). ...
Article
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Context. Rodents in many parts of the world perform an important ecosystem function as dispersers of mycorrhizal fungal spores. These fungi are vital to nutrient uptake in plant communities, but many of the fungal taxa that form these associations have fruiting bodies that are reliant on animals for their spore dispersal. Aims. Numerous studies have focused on the ecological importance of Australian marsupials (especially members of the Potoroidae) for the dispersal of these ecologically important fungi. We chose to focus this study on the role of murid rodents in the dispersal of these fungi in eastern Australia. Methods. To compare fungal taxa in murid diets, we trapped rodents in three regions of eastern Australia; our study sites spanned over 2000 km from temperate eucalypt forests to tropical eucalypt and tropical rainforest habitats. We performed microanalysis on all scats to determine whether fungi were consumed and which taxa were being eaten. Statistical analysis was conducted to investigate trends in levels of mycophagy among species and habitats. Key results. We examined 10 rodent species, and all were shown to ingest mycorrhizal fungi to varying degrees. The diversity, abundance and specific fungal taxa consumed varied depending on the site and forest type. In drier forests dominated by Eucalyptus spp., the fungal taxa consumed and dispersed were primarily ectomycorrhizal; in wetter rainforest habitats, the fungal diversity consumed was far lower and included primarily vesicular arbuscular fungi. We provide the first evidence of mycophagy by grassland melomys (Melomys burtoni) and Cape York melomys (Melomys capensis). Conclusions. Our findings highlight the importance of rodents as dispersers of mycorrhizal fungi across a variety of habitats from temperate to tropical forests of eastern Australia. Implications. This study increases the existing knowledge of rodent diets and habitat requirements. It also provides a new angle for mammal conservation efforts, given the vital nature of the ecosystem service provided by these small and frequently overlooked mammals.
... Increased downed woody structure in the landscape and denser understory because of greater light penetration also may have given foraging woodrats cover from owls and increased the availability of soft mast. Creating additional nesting structure along outcrops, through forestry practices (e.g., creating woody debris piles, releasing the understory) or the creation of artificial nesting structures, could be a useful tool for managers wanting to increase woodrat abundance (Cove et al. 2017;Gooley and Schauber 2018). ...
Article
Hypothesized reasons for the decline of many woodrat populations in the eastern United States include parasitism by raccoon roundworm (Baylisascaris procyonis; Ascaridida: Ascarididae), hard mast shortages, owl predation, and reductions in suitable structures (e.g., rock crevices) for nest construction. We investigated whether abundance and apparent survival of eastern woodrats (Neotoma floridana) within a successfully reintroduced metapopulation in southern Illinois could be predicted by factors underlying these hypothesized reasons for woodrat declines. We analyzed capture histories of 205 eastern woodrats from eight rock outcrop sites in summers of 2013 and 2014 to estimate local population size and apparent survival. We then used repeated-measures models to test how woodrat abundance and apparent survival were associated with availability of mast trees, owl abundance, risk of raccoon roundworm infection, and crevice availability. Mean monthly estimated woodrat abundance at sites ranged from 0.78 to 21.58 in 2013 and 0.48 to 18.08 in 2014, while monthly apparent survival ranged from 0.00 to 0.76 during the summers and 0.05 to 0.90 during the trapping intersession. Crevice availability was positively associated both with abundance and apparent survival of woodrats. Our results did not support the hypothesis that owls reduce woodrat populations because woodrat abundance was positively associated with owl abundance across sites. No raccoon roundworm eggs were found at any site. We conclude that crevice availability was the best predictor of woodrat population success in our study area, while owl abundance may be a proxy for other habitat variables or a response to woodrat abundance. Our findings suggest measures that could be taken to benefit woodrat survival and abundance.
... The mature hardwood hammock is important to locally imperiled fauna. The Key Largo cotton mouse is nearly restricted to old growth hammock (Cove et al. 2017). The Schaus' swallowtail butterfly depends on torchwood as a larval food source, which optimally grows in the oldest hammocks (Ross et al. 2001, Francis 2004. ...
... Both methods have the advantage of directly confirming presence without having to restrain animals. Cameras have been used to investigate woodrat behavior in natural settings(Morton and Pereyra 2008, Stovall and Hayslette 2013, Smyser et al. 2015, Cove et al. 2017.Castleberry et al. (2014) demonstrated that cameras were effective to detect Allegheny woodrats over bait at locations with Allegheny woodrat sign, immediately following Allegheny woodrat captures at the location.The effectiveness of baited track plates for detecting woodrat presence has not yet been investigated. Several studies have compared camera traps with track plates for monitoring medium-to small-bodied mammals, with results varying between species and locations ...
Thesis
Woodrats (Neotoma spp.) are imperiled in the north-central and north eastern United States. In Illinois, eastern woodrats (N. floridana) experienced range reductions and population bottlenecks over the past century. Hypothesized reasons for the decline of many woodrat populations that inhabit rock outcrops in the eastern United States include parasitism by raccoon roundworms (Baylisascaris procyonis), hard mast shortages, owl predation, and reductions in crevice availability for nest construction. During 2004-2005, the isolated remnant populations along the Mississippi bluffs in southwestern Illinois were genetically augmented with 47 eastern woodrats from Arkansas and Missouri resulting in 40% admixture within the largest population. In 2009, a strong windstorm created canopy gaps and woody debris throughout this area, potentially improving habitat for eastern woodrats. During 2003–2009, 422 eastern woodrats were reintroduced to 5 sites in the southeastern Illinois, and 172 eastern woodrats to 2 southern Illinois state parks during 2013–2014. These reintroductions are the only woodrat reintroductions to date with >50 individuals released per site. Most previous woodrat reintroduction attempts have released small numbers of individuals (10–15 per site and 10–54 total) and either failed to establish populations or required frequent management for populations to persist. My objectives were to (1) investigate the status of augmented eastern woodrat populations in southwestern Illinois, (2) evaluate the success of the southern Illinois reintroductions, (3) investigate whether eastern woodrats demographics within a reintroduced metapopulation could be predicted by factors underlying hypothesized reasons for woodrat declines, and (4) develop and evaluate noninvasive alternatives to live-trapping and sign surveys for monitoring woodrat populations. To address my first objective (Chapter 2), I live-trapped remnant eastern woodrat populations in southwestern Illinois and conducted sign surveys during 2011-2015. I captured 263 eastern woodrats with mean trapping success 62.5% higher than trapping during the 1990s and number of individuals captured per trap-night 3-6 times higher than trapping events during the previous 18 years (all P <0.001). I also located eastern woodrat sign 8.9 km east of the remnant populations. I recommended further genetic monitoring to evaluate if population increases are coupled with increased admixture. I also recommend forest management actions that result in periodic habitat disturbance and piles of woody debris to increase eastern woodrat habitat quality. To address my second objective (Chapter 3), I compared eastern woodrat abundance and distribution to published performance indicators. During 2012–2014, I captured 436 individual eastern woodrats from the southeastern Illinois and located eastern woodrats nearly 9 km from release sites. In 2017, I captured 52 eastern woodrats at the state parks. My findings indicated that these eastern woodrat reintroductions could be considered successful and potentially successful. My results added to the sparse information on successful rodent reintroductions. Managers can use this information to inform structured decision making for future conservation and management actions. To address my third objective (Chapter 4), I tested whether abundance and apparent survival of eastern woodrats within the reintroduced metapopulation in southern Illinois could be predicted by availability of hard-mast-producing trees, great horned (Bubo virginianus) and barred (Strix varia) owl abundance, prevalence of raccoon roundworm infected northern raccoon latrines, and crevice availability. To do so, I analyzed capture histories of 205 eastern woodrats in summer 2013 and 2014 from 8 rock outcrop sites to estimate local population size and apparent survival. Mean monthly estimated eastern woodrat abundance at sites ranged from 0.78 to 21.58 in 2013 and 0.48 to 18.08 in 2014, while monthly apparent survival ranged from 0.00 to 0.76 during the summers and 0.05 to 0.90 during the trapping intersession. Crevice availability (P = 0.019) and owl abundance (P = 0.019) both were positively associated with eastern woodrat abundance, and crevice availability (P = 0.023) was also positively associated with apparent survival of eastern woodrats. I concluded that crevice availability was the best predictor of eastern woodrat population success, while owl abundance may be a proxy for other habitat variables or a response to eastern woodrat abundance. Nesting structure is likely the primary limiting factor for eastern woodrat abundance in Illinois when populations are not limited by food, raccoon roundworm, or excessive predation. Creating additional nesting structure along outcrops, through forestry practices or the creation of artificial nesting structures, could be useful for increasing woodrat abundance. I suggested a larger-scale multi-state study to identify common habitat factors that are predictive of local woodrat survival and abundance. This would add greatly to the understanding of woodrat populations and aid both management of imperiled populations and future reintroductions. To address my fourth objective (Chapter 5), I deployed baited camera traps and baited track plates to monitor eastern woodrat presence along rocky outcrops at 4 of the eastern woodrat reintroduction sites in southeastern Illinois, during May 2013 (5 camera and track-plate stations/site) and May and September 2014 (4 camera and track-plate stations/site) to compare their effectiveness. During each deployment, camera traps detected eastern woodrat presence at all 4 sites while track plates only detected presence at 2–3 sites. A greater proportion of camera traps than track plates recorded detections during each deployment. Camera traps required more person-hours to deploy and retrieve, but resulted in more detections per hour effort than track plates. I concluded that baited camera traps are superior to baited track plates for detecting and monitoring woodrat presence.
... Thus in 1995, when water levels were highest (Fig. 3), the greatest mammal diversity was observed. These detection biases showcase that future surveys would benefit from explicitly accounting for detection probability in small-mammal surveys via capture-recapture or occupancy analyses (sensu Cove et al. 2017, Greene et al. 2013. ...
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The Key Largo cotton mouse (Peromyscus gossypinus allapaticola) was federally listed as Endangered in 1984 due to habitat loss and subsequent population decline, but because of infrequent monitoring, the extent of decline and long-term population trends are unknown. We modeled population abundance under a variety of trapping scenarios to develop a monitoring protocol that would provide accurate population estimates and could be conducted more frequently under current personnel and budget constraints. We captured cotton mice on 33 trapping grids in Key Largo, Florida, USA, during 3 trapping sessions (1 Mar–11 May, 4 Jul–7 Sep, and 29 Oct–31 Dec) in 2007. We compared demographic parameter estimates from subsets of trapping grids with estimates from all grids to identify a subset of grids that would produce population estimates within 10% and remain within the 95% confidence intervals of estimates using all grids when both methods were extrapolated to total available habitat. There were insufficient captures in session 1 to produce a reliable population estimate. We found that 13 and 12 trapping grids, respectively, produced abundance estimates meeting our criteria in sessions 2 and 3. We conclude that the subset of 12 grids trapped during November and December will allow a 64% reduction in number of trapping grids necessary to provide a reliable population estimate. Employed annually, our recommended trapping protocol provides state and federal agencies an efficient method for monitoring trends in the Key Largo cotton mouse population. © 2013 The Wildlife Society.
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1. Obtaining robust abundance or density estimates is problematic for many rare or cryptic species. We combine elements of capture–recapture and distance sampling, to develop a method called trapping point transects (TPT), and we applied this method to estimate the abundance of the endangered Key Largo woodrat (Neotoma floridana smalli). 2. Trapping point transects requires two separate surveys to be held concurrently in space and time. In the main survey, the encounter rate (number of animals caught per trap per session) is measured. In the trial survey, animals whose locations are known prior to opening traps are used to estimate the detection function g(r) (the probability of capturing an animal given it is distance r from a trap when it is set), so the effective trapping area in the main survey can be estimated. It is assumed animals in the trial survey are a representative sample of all animals in the population. Individual heterogeneity in trappability is accommodated using random effects in g(r). 3. Performance of two TPT estimators was assessed by simulation. Generally, when underlying capture probabilities were high [g(0) = 0·8] and between-individual variation was small, modest survey effort (360 trap nights in the trial survey) generated little bias in estimated abundance (c. 5%). Uncertainty and relative bias in population estimates increased with decreasing capture probabilities and increasing between-individual variation. Survey effort required to obtain unbiased estimates was also investigated. 4. Given the challenges of working with cryptic, sparse or nocturnal species, we tested the validity of this method to estimate the abundance of the Key Largo woodrats between 2008 and 2011. 5. Trapping point transects was found to be an effective monitoring method yielding annual estimates of the extant wild population of 693, 248, 78 and 256 animals, with CVs of 0·45, 0·55, 0·82 and 0·43, respectively. The TPT method could be adapted to a range of species that are otherwise very difficult to monitor.