Journal Article

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Animal Dispersal in Fragmented Habitat: Measuring Habitat Connectivity, Corridor Use, and Dispersal Mortality
(1999) Brooker, Lesley; Brooker, Michael; Cole, Peter
"We used a spatially explicit dispersal simulation to generate movement frequencies and distances for comparison with real dispersal frequencies collected in the field from two habitat-specific, sedentary bird species. The relationship between these two data sets allowed us to (1) test the hypothesis that the study species used corridor routes during dispersal; (2) measure the degree of reliance on corridor continuity; (3) estimate the rate of dispersal mortality with respect to distance traveled, and (4) give examples of how the model can be used to assess habitat connectivity with respect to similarly behaved species. We found that Blue-breasted Fairy-wrens and White-browed Babblers both used corridor routes during dispersal. Blue-breasted Fairy-wrens were inhibited by gaps greater than about 60 m, whereas White-browed Babblers crossed gaps of at least 270 m wide. For each species, the rate of dispersal mortality per unit distance traveled was about the same. Because we have effectively partitioned the risk of dispersal mortality from the chance of outside dispersal, and because our mortality estimates are model dependent but landscape independent, they can be transported to other landscapes on which simulations have been run and, therefore, can be used in population viability assessment of unstudied or hypothetical animal populations."
Bioaccumulation Pattern of Heavy Metals in Commercially Important Fishes in and Around Indian Sundarbans
(2014) Abhijit Mitra, Abhijit; Rajrupa Ghosh, Rajrupa
"Concentrations of Zn, Cu, Pb and Cd were determined in edible finfish species (Polynemus paradiseus, Tenualosa ilisha, Liza parsia, Liza tade and Stolephorus commersonii) collected from four stations in and around Indian Sundarbans. Levels of the selected heavy metals were determined in the muscle of edible finfish species in the Gangetic delta region using a Perkin-Elmer Sciex ELAN 5000 ICP mass spectrometer and expressed as mg kg-1 dry weight. To determine whether heavy metal concentrations varied significantly between sites and species, Duncan multiple range test was performed. In finfish species the concentrations of Zn, Cu, Pb and Cd ranged from 15.89±0.58 – 124.12 ±1.63, 13.68±0.83 – 75.91±0.49, 3.34±0.90–19.89±0.54 and BDL–4.01±0.03 respectively.For Zn and Cu, accumulated metal concentration in Stn. 4 is significantly lower than accumulated metal concentration in Stn. 1 and Stn. 2. For Pb, significant difference between stations was not found. Among the selected species, lowest metal accumulation values was found for S. commersonii (p<0.05). The selected heavy metals in finfish muscle (except Zn in Liza parsia and Liza tade in Stn. 1) were also within the permissible limits for human consumption as indicated by the Food and Agricultural Organization."
Can Local Ecological Knowledge Contribute to Wildlife Management? Case Studies of Migratory Birds
(2005) Gilchrist, Grant; Mallory, Mark; Merkel, Flemming
"Sound management of wildlife species, particularly those that are harvested, requires extensive information on their natural history and demography. For many global wildlife populations, however, insufficient scientific information exists, and alternative data sources may need to be considered in management decisions. In some circumstances, local ecological knowledge (LEK) can serve as a useful, complementary data source, and may be particularly valuable when managing wildlife populations that occur in remote locations inhabited by indigenous peoples. Although several published papers discuss the general benefits of LEK, few attempt to examine the reliability of information generated through this approach. We review four case studies of marine birds in which we gathered LEK for each species and then compared this information to empirical data derived from independent scientific studies of the same populations. We then discuss how we attempted to integrate LEK into our own conservation and management efforts of these bird species with variable success. Although LEK proved to be a useful source of information for three of four species, we conclude that management decisions based primarily on LEK, in the absence of scientific scrutiny, should be treated with caution."
Cost-effective Sampling Design Applied to Large-Scale Monitoring of Boreal Birds
(2002) Carlson, Matthew; Schmiegelow, Fiona
"Despite their important roles in biodiversity conservation, large-scale ecological monitoring programs are scarce, in large part due to the difficulty of achieving an effective design under fiscal constraints. Using long-term avian monitoring in the boreal forest of Alberta, Canada as an example, we present a methodology that uses power analysis, statistical modeling, and partial derivatives to identify cost-effective sampling strategies for ecological monitoring programs. Empirical parameter estimates were used in simulations that estimated the power of sampling designs to detect trend in a variety of species' populations and community metrics. The ability to detect trend with increased sample effort depended on the monitoring target's variability and how effort was allocated to sampling parameters. Power estimates were used to develop nonlinear models of the relationship between sample effort and power. A cost model was also developed, and partial derivatives of the power and cost models were evaluated to identify two cost-effective avian sampling strategies. For decreasing sample error, sampling multiple plots at a site is preferable to multiple within-year visits to the site, and many sites should be sampled relatively infrequently rather than sampling few sites frequently, although the importance of frequent sampling increases for variable targets. We end by stressing the need for long-term, spatially extensive data for additional taxa, and by introducing optimal design as an alternative to power analysis for the evaluation of ecological monitoring program designs."
The Energetic Cost of Path Sinuosity Related to Road Density in the Wolf Community of Jasper National Park
(2004) Lusseau, David
"In their recent article, Whittington et al. (2004) show that wolf packs increase their path sinuosity in the vicinity of roads and highly used trails. This path variable is defined as the relationship between the length of the path traveled (L) and the net displacement of the animal (R). The authors present a model that explains path sinuosity using the distance to prey and the density of roads and trails. Such studies demonstrate the potential impact of human developments on wild animals. However, wildlife management often requires assessing whether a proposed human activity presents a significant risk for a species. Assessing long-term risks is difficult in studies that occur over brief ecological time scales. The type of response variables collected by Whittington et al. (2004) can help to relate the short-term effects of anthropogenic activities to their long-term consequences. Path sinuosity can be related to an individual's cost of transport, i.e., the amount of energy the individual needs to travel a given distance. This in turn can be related to road and trail density thanks to Whittington et al.'s model. This forecasting model can then be used to assess the added cost of transport (in kcal • kg-1 • km-1) for each individual wolf in terms of roads and trails. This value can then be extrapolated for the two packs (13 individuals), and the added energetic cost to the ecosystem, i.e., the amount of energy wolves need to consume to meet the added cost of transport, can be balanced with the known amount of energy, i.e., prey, available. This approach greatly simplifies reality, but it can help approximate the cost of road and trail construction at a population level."
Galapagos Birds and Diseases: Invasive Pathogens as Threats for Island Species
(2004) Wikelski, Martin; Foufopoulos, Johannes; Vargas, Hernan; Snell, Howard
"Exotic diseases and parasites have caused extinctions on islands and continents, particularly when they spread through assemblages of immunologically naive species. Hawaii has lost a substantial part of its endemic bird fauna since the introduction of avian malaria at the beginning of the 20th century. In contrast, the Galapagos archipelago still possesses its entire endemic avifauna. Several of these Galapagos bird populations are in decline, however, and wildlife managers seek guidance to counteract a potential man-made ecological disaster. We recommend that endemic birds be tested for susceptibility to disease outside the Galapagos so that protection efforts can be better designed to deal with actual threats. At present, the best and perhaps only management option is to protect the isolation of these island communities because treating or vaccinating wild bird populations against diseases is almost impossible. If the isolation of the Galapagos Islands is successful, we will preserve the complete avifauna of an archipelago for the first time in the history of human colonization in the Pacific eco-region."
Human-Caused Disturbance Stimuli as a Form of Predation Risk
(2002) Frid, Alejandro; Dill, Lawrence M.
"A growing number of studies quantify the impact of nonlethal human disturbance on the behavior and reproductive success of animals. Athough many are well designed and analytically sophisticated, most lack a theoretical framework for making predictions and for understanding why particular responses occur. Behavioral ecologists have recently begun to fill this theoretical vacuum by applying economic models of antipredator behavior to disturbance studies. In this emerging paradigm, predation and nonlethal disturbance stimuli create similar trade-offs between avoiding perceived risk and other fitness-enhancing activities, such as feeding, parental care, or mating. A vast literature supports the hypothesis that antipredator behavior has a cost to other activities, and that this trade-off is optimized when investment in antipredator behavior tracks short-term changes in predation risk. Prey have evolved antipredator responses to generalized threatening stimuli, such as loud noises and rapidly approaching objects. Thus, when encountering disturbance stimuli ranging from the dramatic, lowflying helicopter to the quiet wildlife photographer, animal responses are likely to follow the same economic principles used by prey encountering predators. Some authors have argued that, similar to predation risk, disturbance stimuli can indirectly affect fitness and population dynamics via the energetic and lost opportunity costs of risk avoidance. We elaborate on this argument by discussing why, from an evolutionary perspective, disturbance stimuli should be analogous to predation risk. We then consider disturbance effects on the behavior of individuals--vigilance, fleeing, habitat selection, mating displays, and parental investment--as well as indirect effects on populations and communities. A wider application of predation risk theory to disturbance studies should increase the generality of predictions and make mitigation more effective without over-regulating human activities."
In Situ Behavioral Response of Common Loons Associated with Elevated Mercury (Hg) Exposure
(1998) Nocera, Joseph J.; Taylor, Philip D.
"Common Loons (Gavia immer) in Nova Scotia, Canada have the highest blood mercury (Hg) concentrations of any loon population in North America. Previous studies have shown that exposure to varying levels of Hg in prey is associated with changes in pre-nesting adult behavior. We report here the first association of sublethal blood Hg contamination with changes in behavior of Common Loon young. As Hg levels in their blood rise, the amount of time that chicks spend brooding (by back-riding) decreases (P = 0.004) and time spent preening increases (P = 0.003). The sum increase in energy expenditure is not being compensated for with expected increases in feeding rates or begging. We suggest that such altered time-activity budgets may disrupt the energetic balance of young. Our results show that variation in time spent back-riding is associated with changes in fledging rates. Adult behavior did not significantly vary with Hg, but results are suggestive that an association may exist. We also show that monitoring the time-activity budgets of very young chicks can serve to indicate the effects Hg concentrations in their blood. We confirm the hypothesis that loons and other upper trophic level predators could be at risk from elevated levels of bioavailable Hg. This may help to explain the chronically low productivity of such contaminated sites as Kejimkujik and allow for more focused management initiatives."
Landscape Connectivity as a Function of Scale and Organism Vagility in a Real Forested Landscape
(2002) D'Eon, Robert G; Glenn, Susan M.; Parfitt, Ian; Fortin, Marie-Josee
"Landscape connectivity is considered a vital element of landscape structure because of its importance to population survival. The difficulty surrounding the notion of landscape connectivity is that it must be assessed at the scale of the interaction between an organism and the landscape. We present a unique method for measuring connectivity between patches as a function of organism vagility. We used this approach to assess connectivity between harvest, old-growth, and recent wildfire patches in a real forested landscape in southeast British Columbia. By varying a distance criterion, habitat patches were considered connected and formed habitat clusters if they fell within this critical distance. The amount of area and distance to edge within clusters at each critical distance formed the basis of connectivity between patches. We then assessed landscape connectivity relative to old-growth associates within our study area based on species' dispersal abilities. Connectivity was greatest between harvest patches, followed by old-growth, and then wildfire patches. In old-growth patches, we found significant trends between increased connectivity and increased total habitat amount, and between decreased connectivity and increased old-growth harvesting. Highly vagile old-growth associates, such as carnivorous birds, perceive this landscape as connected and are able to access all patches. Smaller, less vagile species, such as woodpeckers, chickadees, and nuthatches, may be affected by a lack of landscape connectivity at the scale of their interaction with old-growth patches. Of particular concern is the northern flying squirrel (Glaucomys sabrinus), which we predict is limited in this landscape due to relatively weak dispersal abilities."
Modeling the Geography of Migratory Pathways and Stopover Habitats for Neotropical Migratory Birds
(2003) Tankersley, Roger; Orvis, Kenneth
"Intact migratory routes are critical for the stability of forest-dwelling, neotropical, migratory bird populations, and mortality along migratory pathways may be significant. Yet we know almost nothing about the geography of available stopovers or the possible migratory pathways that connect optimal stopovers. We undertake a spatial analysis of stopover habitat availability and then model potential migratory pathways between optimal stopovers in the eastern United States. Using models of fixed orientation and fixed nightly flight distance between stopovers during spring migration, we explore whether a simple endogenous migratory program is sufficient to ensure successful migration across the modern landscape. "Our model runs suggest that the modern distribution of optimum stopovers in the eastern United States can be adequately exploited by birds following migratory pathways defined by fixed-orientation and fixed-distance nightly flights. Longer flight distances may increase the chances of success by enabling migrants to bypass locales offering little habitat. Our results also suggest that most southwestÃ¢Â Â northeast migratory pathways through the Appalachian mountains are intact. Lack of optimal habitat at key locations in the Southeast causes many modeled pathways to fail. We present a speculative view of regional migration patterns implied by predominant ideas found in stopover ecology literature, and demonstrate the need for broad-scale migration research, in the hope that our approach will foster other continental- and regional-scale projects."
On Using Expert-Based Science to 'Test' Local Ecological Knowledge: A response to: Gilchrist et al. 2005. 'Can Local Ecological Knowledge Contribute to Wildlife Management? Case Studies of Migratory Birds'
(2005) Brook, Ryan K.; McLachlan, Stephane M.
"The challenges and opportunities of incorporating information collected through scientific studies with the experience-based knowledge of resource dependent communities have been the focus of numerous studies. However, there are relatively few examples in which ecological science and local knowledge have both been successfully incorporated to provide meaningful input into resource management. In their recent article in Ecology and Society, Gilchrist et al. provide a thorough evaluation of Local Ecological Knowledge (LEK) using expert-based ecological studies often referred to as 'western science.' Although we applaud their recognition of the value of and desire to promote LEK, it is unfortunate that they use expert-based ecological data as a 'test' to determine the 'reliability' of LEK. Even though the authors indicate their wish to use the two different approaches to identify 'constraints and limitations of both approaches,' they fail to discuss the assumptions, limitations, or constraints of the ecological studies that they use. We do not take issue with their ecological studies; we presume they are of the highest quality. However, to assume that the ecological studies are error free and without any bias or limitation is perhaps somewhat misguided, albeit an assumption that many scientists still make. Indeed, Freeman (1992) provides examples in which conflicts occurred in the Canadian Arctic between LEK and expert-based science over aerial surveys of bowhead whales in the Beaufort Sea and caribou in what is now Nunavut, where local perceptions of the state of these wildlife populations were initially considered 'unreliable' but were resolved when biases in ecological studies were corrected using local knowledge. These case studies illustrate the limitations of ecological research and monitoring, and provide a cautionary tale against accepting them as 'truth.'"
Predator-Resembling Aversive Conditioning for Managing Habituated Wildlife
(2005) Kloppers, Elsabe Louise; St. Clair, Colleen Cassady; Hurd, Thomas Eric
"Wildlife habituation near urban centers can disrupt natural ecological processes, destroy habitat, and threaten public safety. Consequently, management of habituated animals is typically invasive and often includes translocation of these animals to remote areas and sometimes even their destruction. Techniques to prevent or reverse habituation and other forms of in situ management are necessary to balance ecological and social requirements, but they have received very little experimental attention to date. This study compared the efficacy of two aversive conditioning treatments that used either humans or dogs to create sequences resembling chases by predators, which, along with a control category, were repeatedly and individually applied to 24 moderately habituated, radio-collared elk in Banff National Park during the winter of 2001-2002. Three response variables were measured before and after treatment. Relative to untreated animals, the distance at which elk fled from approaching humans, i.e., the flight response distance, increased following both human and dog treatments, but there was no difference between the two treatments. The proportion of time spent in vigilance postures decreased for all treatment groups, without differences among groups, suggesting that this behavior responded mainly to seasonal effects. The average distance between elk locations and the town boundary, measured once daily by telemetry, significantly increased for human-conditioned elk. One of the co-variates we measured, wolf activity, exerted counteracting effects on conditioning effects; flight response distances and proximity to the town site were both lower when wolf activity was high. This research demonstrates that it is possible to temporarily modify aspects of the behavior of moderately habituated elk using aversive conditioning, suggests a method for reducing habituation in the first place, and provides a solution for Banff and other jurisdictions to manage hyperabundant and habituated urban wildlife."
Shopping Centers as Panther Habitat: Inferring Animal Locations from Models
(2004) Maehr, David S.; Larkin, Jeffery L.; Cox, John J.
"A recent model of Florida panther (Puma concolor coryi) habitat erred in arbitrarily creating buffers around radio locations collected during daylight hours on the assumption that study animals were only at rest during these times. The buffers generated by this method likely cause an overestimation of the amounts and kinds of habitats that are used by the panther. This, and other errors, could lead to the impression that unfragmented forest cover is unimportant to panther conservation, and could encourage inaccurate characterizations of panther habitat. Previous 24-hour monitoring of activity and activity readings made during routine telemetry flights indicate that high levels of activity occur in the early morning hours. Literature on the behavior of the species does not support the creation of large buffers around telemetry locations to compensate for the lack of nighttime telemetry data. A thorough examination of ongoing studies that use global positioning systems may help calibrate future Florida panther habitat models."
Should Ecosystem Management Involve Active Control of Species Abundances?
(2005) Lessard, Robert B.; Martell, Steven J. D.; Walters, Carl J.; Essington, Timothy E.; Kitchell, James F.
"We review four case studies in which there is a risk of extinction or severe reduction in highly valued species if we ignore either, or both, of two ecosystem control options. 'Symptomatic control' implies direct control of extinction risk through direct harvesting or culling of competitors and predators. 'Systemic control' implies treating the causes of the problem that led to an unnaturally high abundance in the first place. We demonstrate, with a discussion of historically observed population trends, how surprising trophic interactions can emerge as a result of alterations to a system. Simulation models were developed for two of the case studies as aids to adaptive policy design, to expose possible abundance changes caused by trophic interactions and to highlight key uncertainties about possible responses to ecosystem management policies involving active intervention to control abundances. With reasonable parameter values, these models predict a wide range of possible responses given available data, but do indicate a good chance that active control would reverse declines and reverse extinction risks. We find that controlling seal (Phoca vitulina) populations in the Georgia Strait increases juvenile survival rates of commercial salmon (Oncorhynchus spp.) species, but that commensurate increases in hake populations from decreased seal predation could be a compensatory source of predation on juvenile salmon. We also show that wolf (Canis lupus) control and moose (Alces alces) harvest bring about a recovery in caribou (Rangifer tarandus caribou) populations, where simple habitat protection policies fail to recover caribou before wolf predation causes severe declines. The results help address a common problem in disturbed ecosystems, where controlling extinction risks can mean choosing between active control of species abundance or establishing policies of protection, and allowing threatened species to recover naturally."
Systems Ecology of Radiocesium Dispersal in Forest Landscapes and Food
(1990) Olson, Jerry S.
"Persisting radiocesium in food of humans, reindeer, or other wildlife calls for research and assessments of the future. What trends in Cs are likely in forest and shrubland, as well as crops and pasture? Soon after Chernobyl fallout in 1986, Swedish berry plants, tree parts, organic and sandy soil were analysed. Now we can infer rates of transfer among a typical ecosystem's parts. Cs in food chains in Nordic woodlands seems likely to remain high for many years. I predicted such Cs would be removed to less available forms in soil minerals more slowly than Cs in Nordic crop systems, or in deciduous forest tagged with Cs-137 at Oak Ridge National Laboratory, Tennessee* Cooler climate, partly evergreen plant habit, and many peat and sandy soils are among factors shared by Nordic countries that keep their Cs actively circulating in the ecosystem. Reindeer food chains in lichen woodlands (pine or birch) and seasonal pastures seem important for testing improved modeling of natural processes of the system and predicting alternative scenarios, without waiting to see the real future. For this purpose, we need help in estimating lower and upper bounds for RATES: e.g. fractions per week of Cs in important parts (vegetation, consumers, residues, soils) moving to the other parts. Calculations using the resulting table (matrix) of sources and destinations would show net change (turnover) per week. Models combining many steps should imitate nature's redistribution of Cs. Displaying a range of possible future conditions and problems, and filling gaps in field or lab research, could clarify policy issues for reindeer and other ecological management."
Three Flying Fox (Pteropodidae: Pteropus Rufus) Roosts, Three Conservation Challenges in South-Eastern Madagascar
(2008) Rahaingodrahety, Volana N.; Andriafidison, Daudet; Ratsimbazafy, Jonah H.; Racey, Paul A.; Jenkins, Richard K. B.
"We visited three roosts of the Madagascar flying fox Pteropus rufus in December 2005 in the Anosy Region. Colony size was 900 at Berenty Private Reserve, 412 at Amborabao and 54 at Sainte Luce, based on single counts at each site. Hunting at the roost is prohibited at Berenty but P. rufus is trapped at night in the area surrounding the reserve, where it feeds on sisal. At Amborabao, the bats roost in a sacred forest and hunting is forbidden. At Sainte Luce, the forest is highly degraded and the bats are hunted frequently, despite efforts to engage the local community in for- est conservation. Questionnaires with people living near the roosts revealed the flying foxes were regarded as pests of litchis in Amborabao and Sainte Luce. Berenty is the only site where tourists are able to observe roosting P. rufus. The role of sacred forests and local taboos (fady) is very relevant for P. rufus conservation and might be the only practical mechanism in sites where legislation on hunting and land use is not being enforced."
Urban Bird Diversity and Landscape Complexity: Species-Environment Associations Along a Multiscale Habitat Gradient
(2003) Melles, Stephanie; Glenn, Susan M.; Martin, Kathy
"For birds in urban environments, the configuration of local habitat within the landscape may be as critical as the composition of the local habitat itself. We examined the relative importance of environmental attributes (e.g., tree cover, composition, and number of tree species) measured at different spatial scales in relation to urban bird species richness and abundance. We expected that some bird species and nesting guilds would have a closer association with landscape-level features (within 1000 m), such as proximity to large forested areas, than with local-scale habitat measures (within 50 m). To investigate this, avian community data were collected at 285 point-count stations in 1997 and 1998 along four roadside transects located in Vancouver and Burnaby, British Columbia, Canada. Transects (5-25 km in length) bisected three large parks (>324 ha) and proceeded along residential streets in urban and suburban areas. In total, 48 bird species were observed, including 25 common species. Species richness declined in relation to a gradient of increasing urbanization, as measured by local- and landscape-level habitat features. We further examined the significance and importance of local- vs. landscape-level habitat attributes using logistic regression and found that both scales explained the presence/absence distributions of residential birds. Local-scale habitat features such as large coniferous trees, berry-producing shrubs, and freshwater streams were of particular importance in estimating the likelihood of finding bird species. Landscape measures, particularly forest cover (within 500 m) and park area (measured at different scales as a function of distance from point-count stations) significantly improved likelihood estimations based solely on local-scale habitat features. Our results suggest that both local- and landscape-scale resources were important in determining the distribution of birds in urban areas. Parks, reserves, and the surrounding residential areas should be integrated into urban planning and development designs to maintain resident avifauna and overall species diversity in urban environments."
Why Did the Snake Cross the Road? Effects of Roads on Movement and Location of Mates by Garter Snakes (Thamnophis Sirtalis Parietalis)
(2004) Shine, Richard; Lemaster, Michael; Wall, Michael; Langkilde, Tracy; Mason, Robert
"If animals avoid road surfaces or are unable to follow conspecific trails across such surfaces, previously continuous populations may be fragmented. We gathered data on the effects of a small (4-m wide) gravel road on the behavior and trail-following abilities of garter snakes (Thamnophis sirtalis parietalis) in Manitoba, central Canada. As expected, the road surface had less vegetation cover, a more open canopy and, thus, higher incident radiation than did the surrounding grassland. Contrary to expectations, however, substrate temperatures were lower on the road than in its surrounds, because of the higher reflectivity of the road's surface. On a nearby asphalt road, substrate temperatures were relatively high on the road surface only in the evening, as surrounding areas cooled. Focal sampling showed that snakes avoided the gravel road, typically changing direction when they encountered it. If they crossed the road, they did so by the shortest possible route (straight across). Mate-searching male snakes were less able to follow substrate-deposited pheromonal trails left by females if those trails crossed a road than if the trails were entirely within the surrounding grassland. Thus, roads may significantly modify snake movement patterns, as well as the ability of males to locate reproductive females. Our study provides the first detailed information on the effects of roads on snake behavior."
Winter Responses of Forest Birds to Habitat Corridors and Gaps
(1998) St. Clair, Colleen Cassady; Belisle, Marc; Desrochers, Andre; Hannon, Susan
"Forest fragmentation and habitat loss may disrupt the movement or dispersal of forest-dwelling birds. Despite much interest in the severity of these effects and ways of mitigating them, little is known about actual movement patterns in different habitat types. We studied the movement of wintering resident birds, lured by playbacks of mobbing calls, to compare the willingness of forest birds to travel various distances in continuous forest, along narrow corridors (fencerows), and across gaps in forest cover. We also quantified the willingness of Black-capped Chickadees (Poecile atricapillus) to cross gaps when alternative forested detour routes were available. All species were less likely to respond to the calls as distance increased to 200 m, although White-breasted Nuthatches (Sitta carolinensis) and Hairy Woodpeckers (Picoides villosus) were generally less likely to respond than chickadees and Downy Woodpeckers (P. pubescens). Chickadees were as likely to travel in corridors as in continuous forest, but were less likely to cross gaps as the gap distance increased. The other species were less willing to travel in corridors and gaps relative to forest, and the differences among habitats also increased with distance. For chickadees, gap-crossing decisions in the presence of forested detours varied over the range of distances that we tested, and were primarily influenced by detour efficiency (the length of the shortcut relative to the available detour). Over short distances, birds used forested detours, regardless of their efficiency. As absolute distances increased, birds tended to employ larger shortcuts in the open when detour efficiency was low or initial distance in the open was high, but they limited their distance from the nearest forest edge to 25 m. Thus, chickadees were unwilling to cross gaps of > 50 m when they had forested alternatives, yet they sometimes crossed gaps as large as 200 m when no such choice existed. Our results suggest that the presence of corridors enhanced the movement of some, but not all, forest birds, and that even chickadees, which were less sensitive to gap width, preferred not to venture far from forest cover."

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