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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... As part of the recovery plan for Key Largo woodrat, over 1500 supplemental nests sites have been established throughout the protected hammock (Cove et al., 2019). The food web in Key Largo is fairly depauperate with native rodent predators including colubrid snakes (Pantherophis alleghaniesis and Coluber constrictor), eastern diamondback rattlesnakes (Crotalus adamanteus), eastern screech-owls (Megascops asio), and coyotes (Canis latrans), along with the invasive cats and pythons (Cove et al., 2017). ...
... Camera trap sites were selected out of a grid of 642 supplemental nest sites encompassing the entirety of the Key Largo woodrat's range, all spaced approximately 150 m apart (Fig. S1). Camera traps (Reconyx Hyperfire HC550-800 Infrared/WhiteFlash or Reconyx Hyperfire II 850, RECONYX, Inc., Holmen WI, USA) were deployed at nest structures following established protocols (Cove et al., 2017;Watersmith et al., 2023). Three independent nest site camera surveys were completed over the study period. ...
... ArcGIS 10.0 (Environmental Systems Research Institute [ESRI], Inc., Redlands, CA, USA) was used to derive nest-site specific habitat covariates that might influence rodent occupancy at nest sites based on prior surveys (Cove et al., 2017(Cove et al., , 2019. The effects of covariates on the occurrence of both Key Largo woodrats and black rats were investigated using multi-species occupancy models following the framework outlined by Rota et al. (2016). ...
Negative interactions among invasive predators, competitors and native species can often disrupt ecosystem services, particularly when keystone species are affected. The Key Largo woodrat (Neotoma floridana smalli) is an endangered ecosystem engineer, endemic to protected hammocks on the northern third of the island of Key Largo, FL, USA. Invasive predator control efforts have assisted in woodrat recovery, but less is known about how a potential competitor, the black rat (Rattus rattus), interacts with the woodrat. We conducted camera trap surveys at supplemental nest sites throughout the range of the woodrat and used multi-species occupancy models to investigate factors influencing woodrat and black rat co-occurrence. Supplemental nest sites were surveyed each year over a three-year period, during which the population of black rats within the protected hammock declined precipitously. Woodrats and black rats occurred at similar levels in the first survey with occupancy probabilities of 22.8% and 15.6%, respectively. Both species occurred at fewer sites in the second survey, but while woodrats later rebounded, black rats were only detected twice in the final survey. There was evidence of species avoidance between the rodents based on a species interaction term, and they exhibited opposing J o u r n a l P r e-p r o o f relationships with predictor variables of both detection and occupancy probabilities. As the occupancy of black rats decreased, the relationship between woodrats and distance from developed areas also weakened. Following the black rat decline, woodrats recolonized an area previously dominated by black rats, where they had been presumed extirpated for 2-3 decades. Our results indicate that black rat competition restricted occupancy of Key Largo woodrats, hindering recovery efforts that previously concentrated on invasive predator removal, demonstrating the need to consider influences of both invasive predators and competitors in species recovery programs. Introduction:
... Vertical gray dotted lines denote the years when nest camera trap data were used for dynamic occupancy modeling from Key Largo woodrat (Neotoma floridana smalli) nest monitoring camera traps. Vertical gray dashed lines denote the years when free-ranging cat (Felis catus) monitoring camera trap data were used for the generalized linear models Mammal declines correspond with increasing prevalence of Burmese pythons at their southern… allapaticola; Barbour and Humphrey 1982;Cove et al. 2017). Burmese pythons are known to frequently consume rodents ) and were recently detected using the active nest of a Key Largo woodrat (King et al. 2022), which may be particularly concerning consequences of python establishment in Key Largo. ...
... These independent datasets allowed us to clarify how mammal community occupancy at camera trap sites has changed over time in relation to increasing python prevalence. aimed to photograph nest activity between 1 and 3 m from the nest, and were set to high motion sensitivity and continuous photos in bursts of 10 photos without a quiet period upon sensor activation (sensu Cove et al. 2017). Each nest received an individually numbered forestry tag, and its location was marked with a handheld GPS unit (GPSmap 60CSx, Garmin International, Inc., Olathe, KS, USA; Cove et al. 2017). ...
... aimed to photograph nest activity between 1 and 3 m from the nest, and were set to high motion sensitivity and continuous photos in bursts of 10 photos without a quiet period upon sensor activation (sensu Cove et al. 2017). Each nest received an individually numbered forestry tag, and its location was marked with a handheld GPS unit (GPSmap 60CSx, Garmin International, Inc., Olathe, KS, USA; Cove et al. 2017). While December through January is peak breeding season for Burmese pythons and they do reduce predation rates (McCleery et al. 2015), the original study chose this period because mammals are more active in the hammocks during the cooler winter months (Cove et al. 2017). ...
The negative impacts of invasive Burmese pythons (Python bivittatus) on mammal communities in mainland South Florida are well-documented. However, few studies have examined the ecological effects of Burmese pythons along their southern invasion front in the Florida Keys. The establishment of Burmese pythons in the Keys could be devastating for island mammal communities and their ecosystem functions. We leveraged long-term data from camera trap surveys of endangered Key Largo woodrats (Neotoma floridana smalli) and free-ranging cats (Felis catus), as well as publicly available datasets to create time-dependent occupancy and generalized
linear models to explore potential changes in the mammal community associated with increasing prevalence of Burmese pythons on Key Largo. Top occupancy models indicated that detection probabilities of endangered Key Largo cotton mice (Peromyscus gossypinus allapaticola), Key Largo woodrats, and invasive black rats (Rattus rattus) all decreased since the establishment of Burmese pythons in 2016
on North Key Largo, but the detection probability of Virginia opossums (Didelphis virginiana) might have increased. Additionally, top models indicated that increasing python prevalence was associated with high local extinction probabilities for woodrats and black rats. Generalized linear models indicated raccoon (Procyon lotor) and opossum counts decreased locally over time in areas where pythons were present, despite no broad-scale changes in occupancy. These results reveal a complex dynamic wherein Burmese pythons are likely having a stronger effect on rodent communities over mesopredator communities in North Key Largo—presumably due to demographics of a relatively new established python population. This study indicates that the python invasion in Key Largo has started to have ecological impacts. While these findings are cause for concern, evidence does suggest python removals are mitigating effects on certain mammal populations.
... Recent studies underscore these declines, demonstrating that native mammals, including rodents, lack resilience to Burmese pythons (Taillie et al., 2021). North Key Largo represents the entire global distribution of two federally endangered species of rodents, the Key Largo woodrat and the Key Largo cotton mouse (Peromyscus gossypinus allapaticola, KLCM -Barbour and Barbour and Humphrey, 1982;Cove et al., 2017). Extant native predators of KLWR and KLCM include eastern screech-owls (Megascops asio), eastern diamondback rattlesnakes (Crotalus adamanteus), eastern rat snakes (Pantherophis alleghaniensis), North American racers (Coluber constrictor), and corn snakes (Pantherophis guttatus - Cove et al., 2017). ...
... North Key Largo represents the entire global distribution of two federally endangered species of rodents, the Key Largo woodrat and the Key Largo cotton mouse (Peromyscus gossypinus allapaticola, KLCM -Barbour and Barbour and Humphrey, 1982;Cove et al., 2017). Extant native predators of KLWR and KLCM include eastern screech-owls (Megascops asio), eastern diamondback rattlesnakes (Crotalus adamanteus), eastern rat snakes (Pantherophis alleghaniensis), North American racers (Coluber constrictor), and corn snakes (Pantherophis guttatus - Cove et al., 2017). Taillie et al. (2021) observed that invasive black rats responded positively to increasing python prevalence, likely because of high-fecundity and a broad habitat breadth, suggesting black rats may benefit from pythons consuming their native predators and competitors. ...
... From the python's initial entrance to the pipe network on 26 October 2022 and exit on 5 December 2022, we documented five strikes at KLCM, two of which were successful predation events. We suggest that the restricted space within this pipe system may represent an optimal hunting scenario for a Burmese python because multiple pipes in this subterranean network and other anthropogenic refuse are used by the endangered rodents (Cove et al., 2017). The pipe network can funnel prey items into the confined space, but it is noteworthy that the mice were not trapped in these spaces and could come and go freely. ...
The allometric scaling of predators and their prey is well established within snakes (i.e., gape-width limits
maximum prey sizes). However, while some species exhibit ontogenetic shifts to larger prey as they grow, others
exhibit telescoping prey selection and continue to consume small prey in addition to larger prey. The Burmese
python (Python bivittatus) is a large dietary generalist constrictor native to Southeast Asia that is established in
South Florida (USA). As part of survey efforts at the southern invasion front in the Florida Keys, we used camera
traps to document predation on endangered Key Largo cotton mice (Peromyscus gossypinus allapaticola) by an
adult female Burmese python. These images represent the first photo documentation of predation attempts upon
a federally endangered species in the python’s invasive range, but we note three additional instances of Key
Largo cotton mice in the gut contents of euthanized pythons from Key Largo. These observations suggest Burmese
pythons exhibit telescoping prey selection behavior where even small rodents (<30 g) are viable prey for adult
snakes. However, based on the number of documented strikes with failed predation events and low frequency of
occurrence in gut contents, we suspect mice may be less common prey items for adult (i.e., >185 cm SVL)
pythons relative to cotton mouse abundance in the environment. However, we also documented endangered Key
Largo woodrats (Neotoma floridana smalli) and Key Largo cotton mice collecting and consuming the shed skins of
pythons, which suggests the two rodent species remain naïve to the threat of these invasive predators. Further
understanding of the impact of Burmese pythons on native prey communities can help inform efforts to minimize
biodiversity loss along their invasion fronts.
... Historical Key Largo rodent livetrapping surveys before establishment of cat feeding stations and colonies on the island in the 1990s (Cove et al. 2017) resulted in both similar capture numbers for black rats and Key Largo woodrats (Hersh 1981) and instances where black rat numbers were very low (Barbour and Humphrey 1982), indicating some degree of population fluctuation in the invasive rodents. Modern camera trap surveys at supplemental nest sites constructed as part of the Key Largo woodrat recovery effort have also shown fluctuation in black rat numbers. ...
... Modern camera trap surveys at supplemental nest sites constructed as part of the Key Largo woodrat recovery effort have also shown fluctuation in black rat numbers. Indeed, black rats were only detected at two supplemental nests (,1% naïve occupancy of the 284 nests surveyed) when camera trap surveys started in 2013 (Cove et al. 2017). Subsequently, naïve occupancy of black rats peaked at 37% (172/460 nests) in 2016 following feral and free-ranging cat reduction (Herrera et al. 2022), only to decline rapidly to 18% (140/759 nests) in 2018, and further to approximately 4% naïve occupancy (23/592 nests) in 2020-suggestive of a population collapse (McDonald et al. 2024;Redinger et al. 2024). ...
We collected and screened black rats (Rattus rattus) in Key Largo, Florida, USA, to determine the potential role of disease or parasites in the collapse of the local population. Rats appeared healthy, but 94% (n¼15/16) tested positive for Sarcocystis sp. The partial 18S rRNA gene sequence was 98.7-99.7% similar to a strain of Sarcocystis zuoi that is now considered a strain of the newly described Sarcocystis kani within the larger S. zuoi species complex that contains numerous new species. These Sarcocystis spp. use Asian snakes as definitive hosts and rodents, shrews, or tree shrews as intermediate hosts. Pythons are the definitive host for several Sarcocystis spp. in Asia, including a related parasite (Sarcocystis singaporensis) that has been used as a biologic control agent for Rattus spp. in southeast Asia. It is probable that increasing numbers of invasive Burmese pythons (Python bivittatus) in the Florida Keys are contributing to the spread of this parasite in addition to imposing predation pressure on both rodents and native snakes. As such, further surveillance and molecular and morphologic characterization of parasites from rodents and snakes in south Florida should be prioritized.
... For example, the European Union Habitats Directive defines conservation status as "the sum of the influences acting on the species that may affect the long-term distribution and abundance of its populations," and requires that member states monitor and maintain a number of protected species at favorable conservation status. Abundance estimates have been widely used to establish baseline population sizes (e.g., Araújo-Wang et al., 2022;Henry & Anderson, 2016) and, if clearly linked to policy objectives (Nichols & Williams, 2006), to inform management and conservation decisions, for example, setting annual waterfowl hunting quotas (Nichols et al., 1995), supporting the recovery of endangered rodents (Cove et al., 2017(Cove et al., , 2019, prioritizing species and protected areas for conservation (Johnston et al., 2015;Williams et al., 2014), and selecting windfarm locations to minimize collision risk to birds (Bright et al., 2008;Winiarski et al., 2014). ...
Estimating the size of animal populations plays an important role in evidence‐based conservation and management. Some methods for estimating population size rely on animals being individually identifiable. Traditionally, this has been done by marking physically captured animals, but increasingly, animals with distinctive natural markings are surveyed noninvasively using cameras. Animal reidentification from photographs is usually done manually, which is expensive, laborious, and requires considerable skill. An alternative is to develop computer vision methods that can support or replace the manual identification task. We developed an automated approach using deep learning to identify whether a pair of photographs is of the same individual or not. The core of the approach is a similarity learning network that uses paired convolutional neural networks with a triplet loss function to summarize image pairs and decide whether they are from the same individual. Prior to the main matching step, two additional convolutional neural networks perform image segmentation, cropping the animal object within the image, and orientation prediction, deciding which side of the animal was photographed. We applied the approach to four species, with images of the same individual often spanning several years: systematic surveys of bottlenose dolphins (Tursiops truncatus, 2008–2019) and harbor seals (Phoca vitulina, 2015–2019), a citizen science dataset of western leopard toads (Sclerophrys pantherina, unknown dates), and a publicly available repository of humpback whale images (Megaptera novaeangliae, unknown dates). For these species, our best‐performing models were able to identify whether a pair of images were from the same individual or different individuals in 95.8%, 94.6%, 88.2%, and 83.8% of the cases, respectively. We found that triplet loss functions outperformed binary cross‐entropy loss functions and that data augmentation and additional manual curation of training data provided small but consistent improvements in performance. These results demonstrate the potential of deep learning to replace or, more likely, support and facilitate manual individual identification efforts.
... Between December 21, 2020 and May 6, 2021, we homed in on snakes to locate their exact locations and secured a single camera trap (Reconyx PC800, RECO-NYX Inc.) pointed at the most likely entrance/exit to their exact point location (often subterranean) for 1-9 continuous trap nights, depending on when the snake moved to its next location. The exact deployment of cameras varied and was largely dependent on the access of the snake and local factors like trees or branches that could support camera traps-exact angles or distances were not routinely recorded but cameras were set within 1-2 m and pointed directly at the target entrance/exit and set like camera deployment for concurrent mammal surveys (see Cove et al., 2017). We set each camera with high motion sensitivity and continuous photos when motion-activated (1 s between photos), as well as a time-lapse photo taken every 5 min to capture snake detections that were not triggered by motion. ...
The Burmese python (Python bivittatus) is an invasive predator responsible for broad mammal declines in South Florida, United States. Despite their large size, pythons remain cryptic and require multifaceted approaches for detection. We evaluated a novel technique by deploying camera traps at known locations of radiotagged pythons in the Florida Keys. We estimated daily detection probabilities of snakes and plotted diel activity patterns. Our results suggest camera traps can effectively survey pythons but seasonality and camera trigger mechanisms affect utility. Pythons were most detectable with time‐lapse camera traps and more detectable in winter. The diel activity pattern of pythons peaked midday through early afternoon, indicating an optimal survey time for other search methods. Artificial intelligence can alleviate photo volume, so we recommend a combination of motion detection and time‐lapse with shorter time (1 min) intervals for python‐specific surveys and where camera traps are deployed to monitor mammals to improve passive python detection.
... A network of over 1000 supplemental nest structures has been deployed throughout protected areas in northern Key Largo as part of the Key Largo woodrat recovery effort (Cove et al., 2017). A subset of 197 nest structures were monitored with camera traps for rodent activity. ...
Anthropogenic climate change is contributing to an increase in the frequency of extreme weather events. These extreme events may affect interactions in mutualisms that provide key ecosystem functions, especially when the event is rare for a given system and participants are differentially affected. The tropical hardwood hammocks of Key Largo, Florida, USA are inhabited by a highly specialized endangered rodent, the Key Largo woodrat (Neotoma floridana smalli), which may be an important seed disperser of many native fleshy-fruited plant species. Other potential mammalian dispersers are generalist omnivores, northern raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana), that are less selective. We sought to demonstrate that extreme climate events could alter seed dispersal mutualisms by differentially affecting fruit preference of potential dispersers. We designed a replicated cafeteria-style experiment across the entire range of the Key Largo woodrat with fruit from sixteen native plant species and simulated an extreme climate event by exposing half of the fruits to sub-freezing temperatures. Freezing temperatures are rare in this tropical environment, but increased frequencies of these types of extreme events are predicted with climate change. Using camera traps, we monitored the removal of fruit and seeds by woodrats and the generalist consumers, predicting that changes in fruit quality resulting from exposure to sub-freezing temperatures would reduce preference by the more specialized woodrat relative to its generalist consumers. Indeed, exposure to subfreezing temperatures decreased the probability of fruit and seed removal by woodrats while generalist consumers preferentially removed more of the fruits and seeds exposed to sub-freezing temperatures. These data provide evidence that extreme climate events may affect species preferences for food asymmetrically, which may shift the dynamics of seed dispersal mutualisms. Over time, increasing frequencies of extreme weather events could indirectly affect communities and ecosystem services by shifting interactions between organisms.
... A network of over 1000 supplemental nest structures has been deployed throughout protected areas in northern Key Largo as part of the Key Largo woodrat recovery effort (Cove et al., 2017). A subset of 197 nest structures were monitored with camera traps for rodent activity. ...
The biodiversity crisis is exacerbated by a growing human population modifying nearly three‐quarters of the Earth's land surface area for anthropogenic uses. Habitat loss and modification represent the largest threat to biodiversity and finding ways to offset species decline has been a significant undertaking for conservation. Landscape planning and conservation strategies can enhance habitat suitability for biodiversity in human‐modified landscapes. Artificial habitat structures such as artificial reefs, nest boxes, chainsaw hollows, artificial burrows, and artificial hibernacula have all been successfully implemented to improve species survival in human‐modified and fragmented landscapes. As the global shift towards renewable energy sources continues to rise, the development of photovoltaic systems is growing exponentially. Large‐scale renewable projects, such as photovoltaic solar farms have large space requirements and thus have the potential to displace local wildlife. We discuss the feasibility of ‘conservoltaic systems’ – photovoltaic systems that incorporate elements tailored specifically to enhance wildlife habitat suitability and species conservation. Artificial habitat structures can potentially lessen the impacts of industrial development (e.g., photovoltaic solar farms) through strategic landscape planning and an understanding of local biodiversity requirements to facilitate recolonization.
Ecosystem engineers play a vital role in community assembly by modifying the environment to create novel habitat features. Woodrats (Neotoma sp.) build and maintain intricate stick-nests that stockpile organic materials and create habitat for other small species. The Key Largo woodrat (Neotoma floridana smalli) is an endangered subspecies endemic to Key Largo, Florida, USA, that has undergone substantial declines due to habitat loss and predation by invasive predators. We leveraged data from a camera trap monitoring grid at supplemental woodrat nest structures to survey bird communities to evaluate the role of woodrat nest use and stick-nest building related to bird abundance using generalized linear models. We predicted that woodrat occurrence and stick-nest building would positively correlate with bird species richness and abundance due to the creation of habitat structures that support prey for birds. To test this, we analyzed the relationship that bird abundance and species richness have with several indicators of woodrat activity along with other environmental and predator variables. Bird abundance was positively associated with woodrat supplemental nest use and stick-nest building. However, these positive associations were largely negated by the presence of free-roaming cats (Felis catus), an invasive predator, and dampened by proximity to human development. We provide evidence that woodrats may have cascading effects on their local food webs by creating foraging grounds for birds, but this positive relationship is disrupted by the presence of an introduced predator.
Here we report on several lines of evidence that lead us to suspect the anthropological extinction of the woodrat Neotoma bunkeri Burt from Isla Coronados, Mexico. This species is represented by only six adult specimens housed at the Museum of Systematic Biology, UCLA, and appeared to be unique in that it had attained a very large body size relative to other insular or mainland woodrats. Our analysis suggests that depletion of food resources and/or the presence offeral cats have led to the decline. Similar combinations of habitat destruction and predator introduction on other small islands in the Gulf of California are probably endangering many extant insular populations, and may ultimately lead to the extinction of an array of unique flora and fauna
Remote photography and infrared sensors are widely used in the sampling of wildlife populations worldwide, especially for cryptic or elusive species. Guiding the practitioner through the entire process of using camera traps, this book is the first to compile state-of-the-art sampling techniques for the purpose of conducting high-quality science or effective management. Chapters on the evaluation of equipment, field sampling designs, and data analysis methods provide a coherent framework for making inferences about the abundance, species richness, and occupancy of sampled animals. The volume introduces new models that will revolutionize use of camera data to estimate population density, such as the newly developed spatial capture-recapture models. It also includes richly detailed case studies of camera trap work on some of the world's most charismatic, elusive, and endangered wildlife species. Indispensible to wildlife conservationists, ecologists, biologists, and conservation agencies around the world, the text provides a thorough review of the subject as well as a forecast for the use of remote photography in natural resource conservation over the next few decades.
Southern flying squirrels (Glaucomys volans) and gray squirrels (Sciurus carolinensis) segregated in their use of nest boxes in 70-yr-old mixed pine-hardwoods in the Ouachita National Forest, Arkansas. Of 13 variables associated with nest boxes, entrance diameter was the primary factor separating the two species. Flying squirrels established nests in small-holed boxes, whereas, gray squirrels established nests in large-holed boxes. Feeding stations of flying squirrels were established in boxes on hardwoods significantly more often than those on pines. Other variables were not consistently significant over the 3-yr study, emphasizing the importance of long-term studies.
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.