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Amy A. Yackel Adams

Publications and source records attributed to Amy A. Yackel Adams.

At least 73 records · Page 4Linked to original sources
USGS2020

Behavior, size, and body condition predict susceptibility to management and reflect post-treatment frequency shifts in an invasive snake

Foraging behavior can have population-level effects that are of interest for wildlife management. For invasive species, foraging behavior has been tied to establishment ability and rate of spread and is generally of import in understanding invasion biology. A major method for controlling invasive vertebrates is using food-based baits as attractants. Tool efficacy is therefore partially driven by individual decision-making during foraging, which may also affect population response to control. We used three studies on the invasive, arboreal brown treesnake ( Boiga irregularis ) on Guam to measure 1) size, body condition, and behavioral correlates with mortality in response to control using toxic baits, 2) shifts in prevalence of those traits after control treatments occurred and, based on the prior two findings, 3) interactive relationships between size, body condition, and behavioral traits at the landscape scale for untreated populations. Each trait was selected due to a potential relationship with foraging behavior or energetic state of an arboreal snake, as a method to estimate how foraging behavior can inform control tool efficacy. We found that snakes were more likely to be killed by toxiic baits if they had a lower body weight, were more active leading up to a bait application, and encountered on the ground more frequently. Across two treated populations, both body size and condition of sampled snakes increased after treatment, while the incidence of ground encounters decreased. Throughout forested habitat on Guam, ground encounter probability was positively correlated with snake size and inversely correlated to body condition. Additionally, size and condition had interactive effects such that snakes in good condition were more arboreal. Thus, body size and behavior (ground encounters) correlated with control-tool susceptibility and frequency shifts occurred in those traits within sampled post-treatment populations. Individual decision-making during foraging may thus inform population responses to bait-based control tools. Management decisions such as prey suppression are likely to directly influence removal efficacy through altered foraging behavior in snakes.

Global Ecology and Conservatuin↗
USGS2020

Landscape dominance of introduced herpetofauna on an oceanic island

Habitat loss and fragmentation can negatively impact native wildlife and facilitate establishment of introduced species. On islands, introduced species are a primary cause of extinction and can alter community membership through predation or competition for resources. Consequently, elucidating the distribution of introduced and native species can improve understanding of the potential synergistic effects of land use and introduced species on native island species. The island of Saipan in the Commonwealth of the Northern Mariana Islands has a long history of herpetofaunal introductions. However, the distribution of native and introduced herpetofauna on Saipan is poorly understood, and the effects of land use and introduced species on the native herpetofauna are largely unknown. In 2018, we randomly selected sites on Saipan from established island-wide transects and used multiple detection methods, repeated surveys, and single-season occupancy models to account for imperfect detection and construct species distribution models. We investigated the role of biotic and abiotic factors in explaining occupancy and detection of Saipan’s native and introduced herpetofauna. We recorded 2568 observations representing 1 amphibian and 11 reptile species. Introduced species were encountered 3.8 times more frequently and were 33% more broadly distributed than native species. Occupancy for the native forest dwelling species Emoia caeruleocauda and Perochirus ateles was positively associated with elevation and enhanced vegetation index, suggesting that human habitat modification at lower elevations may be reducing their suitable habitat.We found evidence of a range contraction for the imperiled P. ateles and suggest potential avenues for implementing targeted conservation of native herpetofauna.

Global Ecology and Conservation↗
USGS2020

Evidence for an established population of tegu lizards Salvator merianae in southeastern Georgia, USA

Documenting emergence of invasive species in new areas is vital to understanding spatiotemporal patterns of invasions, propagule pressure, and the risk of establishment. Salvator merianae (Argentine Giant Tegu) has established multiple unconnected populations in southern and Central Florida, and additional sightings have been reported elsewhere in the state. In 2018, land managers in Georgia received >20 reports of this species in the wild. To evaluate the probability of establishment, we assembled verified records of the non-native Argentine Giant Tegu in Georgia over the past nine years. We report on 47 tegu observations throughout Georgia, with a concentration of sightings (n = 38) in Toombs and Tattnall counties. In 2019, we used modified Havahart traps and captured adult male and female tegus at one of our three locations during 3085 corrected trap nights. While we did not find evidence of a well-established population (i.e., varied size structure of tegus captured) with our limited trapping effort, we suspect tegus are breeding in Toombs and Tattnall counties due to the concentration of captures and reports of adult males and females, the consistent reports of adults across years, the confirmed presence of tegus in 2018, 2019 and 2020, and the reproductive capacity (i.e., turgid testes and secondary follicles) of tegus captured. Ongoing tegu introductions from captivity are likely to maintain high propagule pressure in the southeastern United States. Effective early detection, funded rapid response networks, and public outreach to solicit reports of tegu sightings are critical to prevent establishment and associated ecological impacts of this invasive species elsewhere in the southeastern US.

Southeastern Naturalist↗
USGS2019

Genomic pedigree reconstruction identifies predictors of mating and reproductive success in an invasive vertebrate

The persistence of an invasive species is influenced by its reproductive ecology, and a successful control program must operate on this premise. However, the reproductive ecology of invasive species may be enigmatic due to factors that also limit their management, such as cryptic coloration and behavior. We explored the mating and reproductive ecology of the invasive Brown Treesnake (BTS : Boiga irregularis ) by reconstructing a multigenerational genomic pedigree based on 654 single nucleotide polymorphisms for a geographically closed population established in 2004 on Guam ( N = 426). The pedigree allowed annual estimates of individual mating and reproductive success to be inferred for snakes in the study population over a 14‐year period. We then employed generalized linear mixed models to gauge how well phenotypic and genomic data could predict sex‐specific annual mating and reproductive success. Average snout–vent length (SVL), average body condition index (BCI), and trappability were significantly related to annual mating success for males, with average SVL also related to annual mating success for females. Male and female annual reproductive success was positively affected by SVL, BCI, and trappability. Surprisingly, the degree to which individuals were inbred had no effect on annual mating or reproductive success. When juxtaposed with current control methods, these results indicate that baited traps, a common interdiction tool, may target fecund BTS in some regards but not others. Our study emphasizes the importance of reproductive ecology as a focus for improving BTS control and promotes genomic pedigree reconstruction for such an endeavor in this invasive species and others.

Ecology and Evolution↗
USGS2019

Contact rates with nesting birds before and after invasive snake removal: Estimating the effects of trap-based control

Invasive predators are responsible for almost 60% of all vertebrate extinctions worldwide with the most vulnerable faunas occurring on islands. The brown treesnake ( Boiga irregularis ) is a notorious invasive predator that caused the extirpation or extinction of most native forest birds on Guam. The success of avian reintroduction efforts on Guam will depend on whether snake-control techniques sufficiently reduce contact rates between brown treesnakes and reintroduced birds. Mouse-lure traps can successfully reduce brown treesnake populations at local scales. Over a 22-week period both with and without active snake removal, we evaluated snake-trap contact rates for mouse- and bird-lure traps. Bird-lure traps served as a proxy for reintroduced nesting birds. Overall, mouse-lure traps caught more snakes per trap night than did bird-lure traps. However, cameras revealed that bird-lure traps had a snake contact rate almost 15 times greater than the number of successfully captured snakes. Snakes that entered bird-lure traps tended to be larger and in better body condition and were mostly captured in bird-lure traps, despite numerous adjacent mouse-lure traps. Traps placed along grid edges caught more snakes than interior traps, suggesting continuous immigration into the trapping grid within which bird-lure traps were located. Contact between snakes and bird-lure traps was equivalent before and after snake removal, suggesting mouse-lure traps did not adequately reduce the density of snakes that posed a risk to birds, at least at the timescale of this project. This study provides evidence that some snakes exhibit prey selectivity for live birds over live mouse lures. Reliance on a single control tool and lure may be inadequate for support of avian reintroductions and could lead to unintended harvest-driven trait changes of this invasive predator.

NeoBiota↗
USGS2019

Do observer fatigue and taxon-bias compromise visual encounter surveys for small vertebrates?

Context. Visual encounter surveying is a standard animal inventory method, modifications of which (e.g. distance sampling and repeated count surveys) are used for modelling population density. However, a variety of factors may bias visual survey counts. Aims. The aim of the present study was to evaluate three observer-related biases: (1) whether fatigue compromises detection rate as a survey occasion progresses; (2) whether long-term fatigue or boredom compromise detection rates over the course of a survey period; and (3) whether observers exhibit biases in detection rates of different animal taxa. Methods. We analysed >2.3 × 10 4 observations of lizards and small mammals from nocturnal pedestrian visual encounter surveys, each 4 h in duration, conducted by a pool of 29 observers, each of whom surveyed for up to 31 nights. Key results. Detections of sleeping (diurnal) emerald tree skinks ( Lamprolepis smaragdina ) exhibited a small but statistically verified decline as the evening progressed, whereas detections of sleeping (diurnal) green anoles ( Anolis carolinensis ) increased as the evening progressed. Detections of nocturnal geckos (several species pooled) showed a weak and non-significant declining trend. Small mammal sightings (rats, shrews and mice pooled) declined strongly over the course of an evening. The participants saw greater or equal numbers of animals the more nights they surveyed. Most participants exhibited statistically significant, and often strong, taxonomic detection bias compared with the pool of peer observers. The skills of some observers appeared to be consistently above average; others consistently below average. Conclusions. Data on sleeping lizards suggest that neither short-term nor long-term observer fatigue is of much concern for 4-h visual searches. On the contrary, differences among observers in taxonomic bias and overall detection skills pose a problem for data interpretation. Implications. By comparing temporal detection patterns of immobile (e.g. sleeping) with actively moving animal taxa, sampling biases attributable to searcher fatigue versus the animals’ circadian rhythm can be disentangled and, if need be, statistically corrected for. Observer skill differences and observer-specific taxonomic biases may hamper efforts to statistically evaluate survey results, unless explicitly included as covariates in population models.

Wildlife Research↗
USGS2019

Optimizing walking pace to maximize snake detection rate: A visual encounter survey experiment

Visual encounter survey efforts can be defined and constrained by duration, distance, or both duration and distance simultaneously. This study examines the optimal walking pace that will maximize the number of animal detections within a limited time frame. We predicted that animal sighting rate per unit of distance would decline with increasing pace, but that maximal sighting rate per unit of time would occur at some intermediate pace because walking faster means covering more ground and passing more animals that could potentially be detected. We conducted a controlled experiment during which we searched for Brown Treesnakes ( Boiga irregularis ) while walking 220-m-long transects at three different speeds. For transects inside the forest, detection rate per unit distance decreased (nonlinearly) with increasing pace. When considering catch per unit time, however, we found 5% more snakes at the medium pace compared with the slow pace, and 63% more snakes at the fast pace compared with the slow pace. The pattern appeared different for surveys along forest edges with higher vegetation density, in which snakes might be more difficult to spot. Surprisingly, pace had no detectable effect on the body sizes or perch heights of snakes successfully detected. Finding the optimal search pace for a particular study organism in a focal habitat has the potential to substantially increase survey cost-efficacy.

Herpetologica↗
USGS2018

Analysis of population change and movement using robust design removal data

In capture-mark-reencounter studies, Pollock’s robust design combines methods for open populations with methods for closed populations. Open population features of the robust design allow for estimation of rates of death or permanent emigration, and closed population features enhance estimation of population sizes. We describe a similar design, but for use with removal data. Data collection occurs on secondary sampling occasions clustered within primary sampling periods. Primary sampling periods are intervals of brief enough duration that it can be safely assumed that the population is unchanged by births, deaths, immigration or emigration during them; all population change and movement occurs between primary sampling periods. Our model provides a basis for inference about population size, changes in population size, and movement rates among sample locations between primary sampling periods. Movement rates are modeled as functions of distance and time. Capture probabilities are modeled as a function of effort. We apply the model to data obtained in attempting to eradicate an introduced population of veiled chameleons ( Chamaeleo calyptratus ) on the island of Maui in Hawaii.

Journal of Agricultural, Biological, and Environme↗
USGS2018

Inferring the absence of an incipient population during a rapid response for an invasive species

Successful eradication of invasives is facilitated by early detection and prompt onset of control. However, realizing or verifying that a colonization has occurred is difficult for cryptic species especially at low population densities. Responding to the capture or unconfirmed sighting of a cryptic invasive species, and the associated effort to determine if it indicates an incipient (small, localized) population or merely a lone colonizer, is costly and cannot continue indefinitely. However, insufficient detection effort risks erroneously concluding the species is not present, allowing the population to increase in size and expand its range. Evidence for an incipient population requires detection of ≥1 individual; its absence, on the other hand, must be inferred probabilistically. We use an actual rapid response incident and species-specific detection estimates tied to a known density to calculate the amount of effort (with non-sequential detections) necessary to assert, with a pre-defined confidence, that invasive brown treesnakes are absent from the search area under a wide range of hypothetical population densities. We illustrate that the amount of effort necessary to declare that a species is absent is substantial and increases with decreased individual detection probability, decreased density, and increased level of desired confidence about its absence. Such survey investment would be justified where the cost savings due to early detection are large. Our Poisson-based model application will allow managers to make informed decisions about how long to continue detection efforts, should no additional detections occur, and suggests that effort to do so is significantly higher than previously thought. While our model application informs how long to search to infer absence of an incipient population of brown treesnakes, the approach is sufficiently general to apply to other invasive species if density-dependent detection estimates are known or reliable surrogate estimates are available.

PLoS ONE↗
USGS2018

Behavioral differences following ingestion of large meals and consequences for management of a harmful invasive snake: A field experiment

Many snakes are uniquely adapted to ingest large prey at infrequent intervals. Digestion of large prey is metabolically and aerobically costly, and large prey boluses can impair snake locomotion, increasing vulnerability to predation. Cessation of foraging and use of refugia with microclimates facilitating digestion are expected to be strategies employed by free‐ranging snakes to cope with the demands of digestion while minimizing risk of predation. However, empirical observations of such submergent behavior from field experiments are limited. The brown treesnake (Serpentes: Colubridae: Boiga irregularis ) is a nocturnal, arboreal, colubrid snake that was accidentally introduced to the island of Guam, with ecologically and economically costly consequences. Because tools for brown treesnake damage prevention generally rely on snakes being visible or responding to lures or baits while foraging, cessation of foraging activities after feeding would complicate management. We sought to characterize differences in brown treesnake activity, movement, habitat use, and detectability following feeding of large meals (rodents 33% of the snake's unfed body mass) via radio telemetry, trapping, and visual surveys. Compared to unfed snakes, snakes in the feeding treatment group showed drastic decreases in hourly and nightly activity rates, differences in refuge height and microhabitat type, and a marked decrease in detectability by trapping and visual surveys. Depression of activity lasted approximately 5–7 days, a period that corresponds to previous studies of brown treesnake digestion and cycles of detectability. Our results indicate that management strategies for invasive brown treesnakes need to account for cycles of unavailability and underscore the importance of preventing spread of brown treesnakes to new environments where large prey are abundant and periods of cryptic behavior are likely to be frequent. Characterization of postfeeding behavior changes provides a richer understanding of snake ecology and foraging models for species that consume large prey.

Ecology and Evolution↗
USGS2018

Habitat type and structure affect trap capture success of an invasive snake across variable densities

Detection represents an important limitation of accurately estimating population size, abundance, and habitat suitability for wildlife, which can be especially true for cryptic animals. Moreover, for reptiles, juveniles are often less likely to be detected than later life stages. In the case of invasive species, preventing false negatives early in the invasion process can be critical for improving outcomes of control measures. We evaluated habitat structure in relation to catch per unit effort (CPUE) and mean size of trapped invasive brown treesnakes ( Boiga irregularis ) on Guam. We used a 5‐ha enclosure containing a known, closed population of brown treesnakes to identify key habitat variables that related to CPUE and mean size of trapped snakes over six years. We then tested the relationship of those variables to CPUE and mean size of trapped snakes at three sites with suppressed snake populations as a proxy for low‐density populations anticipated to occur during early detection of invasive populations. We found that a coarse measure of habitat structure represented by three forest types correlated with trap detections, as well as finer measures of habitat structure, such as distance to nearest branch and the type of trap support structure used. On average, smaller snakes were captured in traps placed higher in the tree canopy. Some, but not all, habitat variables identified as predictive of CPUE and mean size within the enclosed population pre‐suppression were also predictive at the snake‐suppressed (low‐density proxy) sites. Habitat structure around the sampling unit (a trap) affected detection probability and the size of detected individuals independently of the demographic structure of the population. Measuring wildlife‐habitat relationships of invaders in their novel environments may be one method to improve early detection during invasive species management.

Ecosphere↗
USGS2018

Exotic predators may threaten another island ecosystem: A comprehensive assessment of python and boa reports from the Florida Keys

Summarizing historical records of potentially invasive species increases understanding of propagule pressure, spatiotemporal trends, and establishment risk of these species. We compiled records of non-native pythons and boas from the Florida Keys, cross-referenced them to eliminate duplicates, and categorized each record’s credibility. We report on 159 observations of six python and boa species in the Florida Keys over the past 17 years. Burmese pythons (Python bivittatus), boa constrictors (Boa constrictor), and ball pythons (Python regius) are the most frequently reported species, but credible records of three additional species were also reported. Among the most notable records, we report on three hatchling and multiple reproductive Burmese pythons captured on North Key Largo since 2016, indicating that the species is now established on that island. The expanding mainland Burmese python population and ongoing python and boa introductions via pet and cargo pathways are likely to keep propagule pressure high in coming years. Both effective public outreach to solicit reporting of sightings and effective early detection and rapid response networks may help to prevent further establishment and associated ecological impacts of python and boa species in the Florida Keys.

Florida↗
USGS2017

Passive restoration following ungulate removal in a highly disturbed tropical wet forest devoid of native seed dispersers

Overabundant ungulate populations can alter forests. Concurrently, global declines of seed dispersers may threaten native forest structure and function. On an island largely devoid of native vertebrate seed dispersers, we monitored forest succession for 7 years following ungulate exclusion from a 5-ha area and adjacent plots with ungulates still present. We observed succession from open scrub to forest and understory cover by non-native plants declined. Two trees, native Hibiscus tiliaceus and non-native Leucaena leucocephala , accounted for most forest regeneration, with the latter dominant. Neither species is dependent on animal dispersers nor was there strong evidence that plants dependent on dispersers migrated into the 5-ha study area. Passive restoration following ungulate removal may facilitate restoration, but did not show promise for fully restoring native forest on Guam. Restoration of native forest plants in bird depopulated areas will likely require active outplanting of native seedlings, control of factors resulting in bird loss, and reintroduction of seed dispersers.

Guam↗
USGS2017

Experimental landscape reduction of wild rodents increases movements in the invasive brown treesnake (Boiga irregularis)

Experimental studies evaluating the effects of food availability on the movement of free-ranging animals generally involve food supplementation rather than suppression. Both approaches can yield similar insights, but we were interested in the potential for using food suppression for the management and control of invasive predators, in particular, the brown treesnake ( Boiga irregularis ) on Guam. However, understanding a species’ response to food resources is critical before employing such a strategy. We studied the movements of 24 radio-tagged B. irregularis initially caught within four 4-ha unfenced plots in rodent-abundant (control) and rodent-suppressed (treatment) grassland habitats over a 40-day period. Because monitoring duration differed among snakes, we also analyzed short-term (16-day) activity areas. Over the 16 days, snakes associated with rodent-suppressed plots had 86% larger activity areas (ha), 94% greater dispersal distances (m), and 43% greater movement rates (m/h) than snakes associated with control plots. Boiga irregularis moved extensively, but these movements were not always reflected in the size of the snake’s total activity area. Movement rates did not differ between sexes, but snakes in above-average body condition moved greater distances per hour than those in below-average condition irrespective of treatment. Our study indicates that a relatively small prey suppression effort can cause almost immediate and significant changes in B. irregularis movement. On Guam, prey suppression might enhance control efforts by either increasing trap capture success or discouraging snakes from entering areas of conservation or management concern. However, the outcome of using prey suppression as a control tool in areas threatened with the accidental introduction of the brown treesnake is more difficult to predict and might have negative consequences such as elevated dispersal rates.

Management of Biological Invasions↗
USGS2016

Detection rates of geckos in visual surveys: Turning confounding variables into useful knowledge

Transect surveys without some means of estimating detection probabilities generate population size indices prone to bias because survey conditions differ in time and space. Knowing what causes such bias can help guide the collection of relevant survey covariates, correct the survey data, anticipate situations where bias might be unacceptably large, and elucidate the ecology of target species. We used negative binomial regression to evaluate confounding variables for gecko (primarily Hemidactylus frenatus and Lepidodactylus lugubris) counts on 220-m-long transects surveyed at night, primarily for snakes, on 9,475 occasions. Searchers differed in gecko detection rates by up to a factor of six. The worst and best headlamps differed by a factor of at least two. Strong winds had a negative effect potentially as large as those of searchers or headlamps. More geckos were seen during wet weather conditions, but the effect size was small. Compared with a detection nadir during waxing gibbous (nearly full) moons above the horizon, we saw 28% more geckos during waning crescent moons below the horizon. A sine function suggested that we saw 24% more geckos at the end of the wet season than at the end of the dry season. Fluctuations on a longer timescale also were verified. Disturbingly, corrected data exhibited strong short-term fluctuations that covariates apparently failed to capture. Although some biases can be addressed with measured covariates, others will be difficult to eliminate as a significant source of error in longterm monitoring programs.

Andersen Air Force Base↗
USGS2015

The influence of disturbed habitat on the spatial ecology of Argentine black and white tegu ( Tupinambis merianae ), a recent invader in the Everglades ecosystem (Florida, USA)

The threat of invasive species is often intensified in disturbed habitat. To optimize control programs, it is necessary to understand how degraded habitat influences the behavior of invasive species. We conducted a radio telemetry study to characterize movement and habitat use of introduced male Argentine black and white tegus ( Tupinambis merianae ) in the Everglades of southern Florida from May to August 2012 at the core and periphery of the introduced range. Tegus at the periphery moved farther per day (mean 131.7 ± 11.6 m, n = 6) compared to tegus at the core (mean 50.3 ± 12.4 m, n = 6). However, activity ranges were not significantly smaller in the core (mean 19.4 ± 8.4 ha, n = 6) compared to periphery (mean 29.1 ± 5.2 ha, n = 6). Peripheral activity ranges were more linear due to activity being largely restricted to levee habitat surrounded by open water or marsh. Tegus were located in shrub or tree habitat (mean 96%) more often than expected based on random locations (mean 58%), and the percent cover of trees and shrubs was higher in activity ranges (mean 61%) than the general study area (17%). Our study highlighted the ability of tegus to spread across the Florida landscape, especially in linear disturbed habitats where increased movement occurred and in areas of altered hydrology where movement is not restricted by water.

Florida↗
USGS2015

Brumation of introduced Black and White Tegus, Tupinambis merianae (Squamata: Teiidae), in southern Florida

An established population of Tupinambis merianae (Black and White Tegu) in southeastern Florida threatens the Everglades ecosystem. Understanding the behavioral ecology of Black and White Tegus could aid in management and control plans. Black and White Tegus are seasonally active and brumate during the winter in their native range, but brumation behavior is largely unstudied in either the native or the invasive range. We describe the first observations of Black and White Tegu brumation in southeastern Florida after monitoring 5 free-ranging, adult male Black and White Tegus through an inactive season using radiotelemetry and automated cameras. Duration of brumation averaged 137 days, beginning in September and ending by February. One of the 5 Black and White Tegus emerged to bask regularly during brumation, which to our knowledge represents the first documented instance of a free-ranging Black and White Tegu basking during brumation. These preliminary findings provide a basis for future research of brumation behavior.

Florida↗