Using decoys and camera traps to estimate depredation rates and neonate survival

Ungulate neonates-individuals less than four weeks old-typically experience the greatest predation rates, and variation in their survival can influence ungulate population dynamics. Typical methods to measure neonate survival involve capture and radio-tracking of adults and neonates to discover mortality events. This type of fieldwork is invasive and expensive, can bias results if it leads to neonate abandonment, and may still have high uncertainty about the predator species involved. Here we explore the potential for a non-invasive approach to estimate an index for neonate survival using camera traps paired with decoys that mimic white-tailed deer (Odocoileus virginianus) neonates in the first month of life. We monitored sites with camera traps for two weeks before and after the placement of the neonate decoy and urine scent lure. Predator response to the decoy was classified into three categories: did not approach, approached within 2.5 m but did not touch the decoy, or physically touched the decoy; when conducting survival analyses, we considered these second two categories as dead neonates. The majority (76.3%) of the predators approached the decoy, with 51.1% initiating physical contact. Decoy probability of survival was 0.31 (95% CI = 0.22, 0.35) for a 30-day period. Decoys within the geographic range of American black bear (Ursus americanus) were primarily (75%) attacked by bears. Overall, neonate survival probability decreased as predator abundance increased. The camera-decoy protocol required about ½ the effort and 1/3 the budget of traditional capture-track approaches. We conclude that the camera-decoy approach is a cost-effective method to estimate a neonate survival probability index based on depredation probability and identify which predators are most important.

Effects of body size on estimation of mammalian area requirements

Accurately quantifying species' area requirements is a prerequisite for effective area-based conservation. This typically involves collecting tracking data on species of interest and then conducting home-range analyses. Problematically, autocorrelation in tracking data can result in space needs being severely underestimated. Based on the previous work, we hypothesized the magnitude of underestimation varies with body mass, a relationship that could have serious conservation implications. To evaluate this hypothesis for terrestrial mammals, we estimated home-range areas with global positioning system (GPS) locations from 757 individuals across 61 globally distributed mammalian species with body masses ranging from 0.4 to 4000 kg. We then applied block cross-validation to quantify bias in empirical home-range estimates. Area requirements of mammals <10 kg were underestimated by a mean approximately15%, and species weighing approximately100 kg were underestimated by approximately50% on average. Thus, we found area estimation was subject to autocorrelation-induced bias that was worse for large species. Combined with the fact that extinction risk increases as body mass increases, the allometric scaling of bias we observed suggests the most threatened species are also likely to be those with the least accurate home-range estimates. As a correction, we tested whether data thinning or autocorrelation-informed home-range estimation minimized the scaling effect of autocorrelation on area estimates. Data thinning required an approximately93% data loss to achieve statistical independence with 95% confidence and was, therefore, not a viable solution. In contrast, autocorrelation-informed home-range estimation resulted in consistently accurate estimates irrespective of mass. When relating body mass to home range size, we detected that correcting for autocorrelation resulted in a scaling exponent significantly >1, meaning the scaling of the relationship changed substantially at the upper end of the mass spectrum.

Seasonal space use of transient and resident coyotes (Canis latrans) in North Carolina, USA

Coyote (Canis latrans Say, 1823) is a recent immigrant into eastern United States and little is known about the species’ space use and movement in the region. We compared space use and movement of radio-collared coyotes among biological seasons. We captured and collared 30 coyotes from February through May 2011 and collected 85 386 GPS locations through October 2012 at Fort Bragg Military Installation. We defined four biological seasons according to coyote life history: breeding (December–February), gestation (March–May), pup-rearing (June–August), and dispersal (September–November). Out of 27 radio-collared individuals, we identified 10 as transient and 11 as resident based on home-range size and variability across seasons; 6 switched their status and were classified as intermediate. We observed low variability of core-area size across seasons for resident males and females, whereas we documented high variability for transient males. Movement rate of resident coyotes during spring (449.75 m/h) was greater than summer (295.33 m/h), whereas movement rates did not differ between any other seasons. For transient coyotes, movement rate during summer (283 m/h) was less than fall (374.73 m/h), spring (479.85 m/h), and winter (488.5 m/h). Some coyotes adjusted their residency status seasonally and other individuals dispersed large distances (>200 km).

Invertebrate community response to coarse woody debris removal for bioenergy production from intensively managed forests

Increased market viability of harvest residues as forest bioenergy feedstock may escalate removal of coarse woody debris in managed forests. Meanwhile, many forest invertebrates use coarse woody debris for cover, food, and reproduction. Few studies have explicitly addressed effects of operational-scale woody biomass harvesting on invertebrates following clearcutting. Therefore, we measured invertebrate community response to large-scale harvest residue removal and micro-site manipulations of harvest residue availability in recently clearcut, intensively managed loblolly pine (Pinus taeda) forests in North Carolina (NC; n = 4) and Georgia (GA; n = 4), USA. We captured 39,794 surface-active invertebrates representing 171 taxonomic groups using pitfall traps situated among micro-site locations (i.e., purposefully retained piles of hardwood stems and piles of conifer stems and areas without coarse woody debris in NC; windrows and no windrows in GA). Micro-site locations were located within six, large-scale treatments (7.16-14.3 ha) in clearcuts. Large-scale treatments represented intensive harvest residue removal, 15% and 30% harvest residue retention, and no harvest residue removal. In NC, ground beetles (Coleoptera: Carabidae) and crickets (Orthoptera: Gryllidae) were three times more abundant in treatments with no harvest residue removal than those with the most intensive harvest residue removal and were reduced in treatments that retained 15% or 30% of harvest residues, although not significantly. Invertebrate taxa richness was greater at micro-site locations with retained hardwood and pine (Pinus spp.) harvest residues than those with minimal amounts of coarse woody debris. In both states, relative abundances of several invertebrate taxa, including cave crickets (Orthoptera: Rhaphidophoridae), fungus gnats (Diptera: Mycetophilidae and Sciaridae), millipedes (Diplopoda), and wood roaches (Blattodea: Ectobiidae), were greater at micro-site locations with retained harvest residues than those with minimal coarse woody debris. Intensified woody biomass harvesting without retention of ≥15% of harvest residue volume may reduce invertebrate taxa richness and abundances of some key invertebrate taxa in regenerating stands. Further, harvest residue management during and after woody biomass harvesting may be an important consideration for maintaining invertebrate diversity and conserving invertebrates that are influential in the maintenance of ecosystem function and integrity in young forests.

Setting an evolutionary trap: could the hider strategy be maladaptive for white-tailed deer?

An evolutionary trap occurs when an organism makes a formerly adaptive decision that now results in a maladaptive outcome. Such traps can be induced by anthropogenic environmental changes, with nonnative species introductions being a leading cause. The recent establishment of coyotes (Canis latrans) into the southeastern USA has the potential to change white-tailed deer (Odocoileus virginianus) population dynamics through direct predation and behavioral adaptation. We used movement rate and bedsite characteristics of radiocollared neonates to evaluate their antipredator strategies in the context of novel predation risk in a structurally homogeneous, fire-maintained ecosystem. Neonate bedsites had greater plant cover values compared with random sites (t = 30.136; p < 0.001), indicating bedsite selection was consistent with the hider strategy used to avoid predation. We determined selection gradients of coyote predation on neonate movement rate and plant cover and diversity at bedsites during the first 10 days of life. Interestingly, neonates that moved less and bedded in denser cover were more likely to be depredated by coyotes, meaning that greater neonate movement rate and bedsites located in less dense cover were favored by natural selection. These results are counter to expected antipredator strategies in white-tailed deer and exemplify how an adaptive response could be maladaptive in novel contexts.

Breeding, Early-Successional Bird Response to Forest Harvests for Bioenergy

Forest regeneration following timber harvest is a principal source of habitat for early-successional birds and characterized by influxes of early-successional vegetation and residual downed woody material. Early-successional birds may use harvest residues for communication, cover, foraging, and nesting. Yet, increased market viability of woody biomass as bioenergy feedstock may intensify harvest residue removal. Our objectives were to: 1) evaluate effects of varying intensities of woody biomass harvest on the early-successional bird community; and (2) document early-successional bird use of harvest residues in regenerating stands. We spot-mapped birds from 15 April– 15 July, 2012–2014, in six woody biomass removal treatments within regenerating stands in North Carolina (n = 4) and Georgia (n = 4), USA. Treatments included clearcut harvest followed by: (1) traditional woody biomass harvest with no specific retention target; (2) 15% retention with harvest residues dispersed; (3) 15% retention with harvest residues clustered; (4) 30% retention with harvest residues dispersed; (5) 30% retention with harvest residues clustered; and (6) no woody biomass harvest (i.e., reference site). We tested for treatment-level effects on breeding bird species diversity and richness, early-successional focal species territory density (combined and individual species), counts of breeding birds detected near, in, or on branches of harvest piles/windrows, counts of breeding bird behaviors, and vegetation composition and structure. Pooled across three breeding seasons, we delineated 536 and 654 territories and detected 2,489 and 4,204 birds in the North Carolina and Georgia treatments, respectively. Woody biomass harvest had limited or short-lived effects on the early-successional, breeding bird community. The successional trajectory of vegetation structure, rather than availability of harvest residues, primarily drove avian use of regenerating stands. However, many breeding bird species used downed wood in addition to vegetation, indicating that harvest residues initially may provide food and cover resources for early-successional birds in regenerating stands prior to vegetation regrowth.

Describing a developing hybrid zone between red wolves and coyotes in eastern North Carolina, USA

When hybridizing species come into contact, understanding the processes that regulate their interactions can help predict the future outcome of the system. This is especially relevant in conservation situations where human activities can influence hybridization dynamics. We investigated a developing hybrid zone between red wolves and coyotes in North Carolina, USA to elucidate patterns of hybridization in a system heavily managed for preservation of the red wolf genome. Using noninvasive genetic sampling of scat, we surveyed a 2880 km² region adjacent to the Red Wolf Experimental Population Area (RWEPA). We combined microsatellite genotypes collected from this survey with those from companion studies conducted both within and outside the RWEPA to describe the gradient of red wolf ancestry. A total of 311 individuals were genotyped at 17 loci and red wolf ancestry decreased along an east–west gradient across the RWEPA. No red wolves were found outside the RWEPA, yet half of individuals found within this area were coyotes. Hybrids composed only 4% of individuals within this landscape despite co‐occurrence of the two species throughout the RWEPA. The low proportion of hybrids suggests that a combination of active management and natural isolating mechanisms may be limiting intermixing within this hybrid system.

Resource selection by southeastern fox squirrels in a fire-maintained forest system

Fire is essential to maintain the open forest structure required by the southeastern fox squirrel ( Sciurus niger niger ). In recent decades, managers of the longleaf pine ( Pinus palustris ) ecosystem have transitioned from dormant-season to growing-season burns, which more effectively limit midstory hardwood encroachment. Similarly, aggressive hardwood removal programs have been employed to further reduce hardwood midstory. However, fox squirrels are dependent on oaks ( Quercus spp.) for food and cover; thus, it is unclear how growing-season burns and hardwood removal may affect habitat quality for fox squirrels. We used compositional analysis to investigate selection of home ranges within the study area by 48 radiocollared fox squirrels on the Fort Bragg Military Installation, North Carolina. We used resource utilization functions with growing-season fire history and other habitat covariates as explanatory variables to test whether growing-season fires influenced the selection of habitat components within home ranges. Lastly, using a sample of fox squirrel relocations and paired random points, we performed binomial logistic regression to test whether habitat selection by fox squirrels was influenced by the availability of oaks and longleaf pines and select forest stand structural characteristics. When establishing home ranges, fox squirrels selected southern yellow pine over other cover types. Within home ranges, fox squirrel use increased with decreasing distance to a riparian area but was not affected by the application of growing-season fires. At the population level, fox squirrels selected for greater densities of reproductively mature oak stems. Fox squirrels likely benefit from growing-season fires that maintain expansive upland pine stands but are negatively affected by homogeneous fire application and mechanical hardwood removal that reduce the occurrence of reproductively mature oaks across the landscape. Managers should strive to maintain oaks in riparian areas, fire shadows, and naturally occurring patches within pine stands when managing for fox squirrels.

Do indirect bite count surveys accurately represent diet selection of white-tailed deer in a forested environment?

Context Diet selection is studied in herbivores using three predominant methods: (1) microhistological surveys (identification of plants cell walls remaining in gut contents or faecal excretions); (2) direct bite counts (of tame animals); and (3) indirect bite counts (identifying herbivory on damaged plant tissues). Microhistological surveys and direct bite counts are accurate and provide the potential advantage of linking diet selection to particular individuals. Also, they allow diet selection to be measured in systems with sympatric herbivores more easily than indirect bite counts. However, they require expertise in cell wall structure identification or access to tame animals, and generally require greater expense than indirect bite counts. Conversely, indirect bite counts have the advantages of relatively low cost and time commitment for gathering data and do not require animal observation, but may not be accurate. Aims We tested for similarity between diet-selection estimates calculated by indirect bite counts and microhistological surveys. Methods We performed concurrent indirect bite count and faecal microhistological surveys on white-tailed deer (Odocoileus virginianus) at Fort Bragg Military Installation, NC. Key results The indirect bite count survey assignment of selection was 48% similar to assignments derived from the microhistological survey, based on Jaccard’s similarity index. Out of 23 plant species determined to be selected by indirect bite counts, 15 of those species were selected according to microhistological surveys. According to the microhistological survey, eight of the selected plants made up 51% of the overall diet, and seven of those eight were selected according to the indirect bite counts. Conclusions Our data indicate that indirect bite counts may provide a relatively accurate index of the deer-selected plants most important in the white-tailed deer diet, but may be less appropriate to determine selection of plants that infrequently occur in their diet, plants that are typically consumed in entirety, or plants where herbivory damage is poorly identified. Implications Indirect bite counts are a relatively inexpensive and time-efficient tool that may be useful to determine plant species most important to white-tailed deer within a forested landscape, particularly if additional research can improve on associated inaccuracies.

Do biological and bedsite characteristics influence survival of neonatal white-tailed deer?

Coyotes recently expanded into the eastern U.S. and potentially have caused localized white-tailed deer population declines. Research has focused on quantifying coyote predation on neonates, but little research has addressed the potential influence of bedsite characteristics on survival. In 2011 and 2012, we radiocollared 65 neonates, monitored them intensively for 16 weeks, and assigned mortality causes. We used Program MARK to estimate survival to 16 weeks and included biological covariates (i.e., sex, sibling status [whether or not it had a sibling], birth weight, and Julian date of birth). Survival to 16 weeks was 0.141 (95% CI = 0.075-0.249) and the top model included only sibling status, which indicated survival was lower for neonates that had a sibling. Predation was the leading cause of mortality (35 of 55; 64%) and coyotes were responsible for the majority of depredations (30 of 35; 86%). Additionally, we relocated neonates for the first 10 days of life and measured distance to firebreak, visual obstruction, and plant diversity at bedsites. Survival of predation to 10 days (0.726; 95% CI = 0.586-0.833) was weakly associated with plant diversity at bedsites but not related to visual obstruction. Our results indicate that neonate survival was low and coyote predation was an important source of mortality, which corroborates several recent studies from the region. Additionally, we detected only weak support for bedsite cover as a covariate to neonate survival, which indicates that mitigating effects of coyote predation on neonates may be more complicated than simply managing for increased hiding cover.