Food Resources for Wintering and Spring Staging Black Ducks

Abstract: A bioenergetic approach has been adopted as a planning tool to set habitat management objectives by several United States Fish and Wildlife Service North American Waterfowl Management Plan Joint Ventures. A bioenergetics model can be simplified into 2 major components, energetic demand and energetic supply. Our goal was to estimate habitat-specific food availability, information necessary for estimating energy supply for black ducks (Anas rubripes) wintering on Long Island, New York, USA. We collected both nektonic and benthic samples from 85 wetland sites dispersed among 5 habitat types (salt marsh, mud flat, submersed aquatic vegetation, brackish bay, and freshwater) commonly used by black ducks in proportion to expected use. Biomass varied among habitats (F_4,5 > 7.46, P < 0.03) in 2004–2005, but there was only marginal variation in 2005–2006 (F_3,4 = 5.75, P = 0.06). Mud flats had the greatest biomass (1,204 kg/ha, SE = 532), followed by submersed aquatic vegetation (61 kg/ha, SE = 18), and salt marsh (34 kg/ha, SE = 6). In the second year of the study, freshwater had the greatest biomass (306 kg/ha, SE = 286), followed by mud flats (85 kg/ha, SE = 63), and salt marsh (35 kg/ha, SE = 4). Our results suggest food density on wintering grounds of black ducks on coastal Long Island is considerably lower than for dabbling ducks using inland freshwater habitats, indicating black duck populations are more likely than other species of dabbling ducks to be limited by winter habitat. We recommend targeting preservation, restoration, and enhancement efforts on salt marsh habitat.     

Apparent seed use by ducks in moist-soil wetlands of the Mississippi Alluvial Valley

Scientists, conservation planners, and resource managers who estimate energetic carrying capacity of foraging habitats for wintering waterfowl require accurate data on food availability and use. We estimated seed and tuber abundance in moist-soil wetlands commonly used and foraged in by dabbling ducks (Anas spp.) in and near the Mississippi Alluvial Valley (MAV). To identify foods potentially used by dabbling ducks, we surveyed food-use literature from studies conducted in or near the MAV and compared estimated seed decline rates from core samples to predicted decline rates using published and measured estimates of decomposition. We inferred seed use when observed declines in mass exceeded that predicted by decomposition. In our analyses, we identified 15 taxa of moist-soil seeds apparently used and 6 taxa apparently not used by dabbling ducks. From our analyses and literature review, we identified 25 taxa of moist-soil seeds and tubers commonly consumed and apparently used by dabbling ducks in or near the MAV. Removal of seeds apparently not used by dabbling ducks resulted in a 30.9% (SE = 1.3) reduction in estimates of seed and tuber mass in managed moist-soil wetlands in the MAV. When we retained 3 seed taxa reported by previous studies as consumed by dabbling ducks, but which did not decline faster than predicted in our experimental wetlands, seed and tuber estimates were reduced by 26.8% (SE = 1.3). Inclusion of seeds not consumed by dabbling ducks in models of carrying capacity would result in overestimation of existence energy days by the Lower Mississippi Valley Joint Venture and underestimation of moist-soil habitat requirements in the MAV. We suggest scientists conduct food-use and selection studies by collecting actively foraging ducks in the MAV to confirm our results and increase accuracy of carrying capacity estimates for dabbling ducks in autumn and winter. © 2011 The Wildlife Society.     

Occupancy Patterns of Breeding American Black Ducks

Occupancy patterns can assist with the determination of habitat limitation during breeding or wintering periods and can help guide population and habitat management efforts. American black ducks (Anas rubripes; black ducks) are thought to be limited by habitat and food availability during the winter, but breeding sites may also limit the size or growth potential of the population. The Canadian Wildlife Service conducts an annual breeding waterfowl survey that we used to explore the hypothesis that black duck carrying capacity is limited by wetlands available for breeding in Québec, Canada. We applied single-visit, multi-species occupancy models to the 1990–2015 population survey data to determine if there was evidence the black duck population was limited by breeding habitat. Using a dynamic (multi-season) occupancy modeling approach, we estimated latent occupancy (occupancy accounting for imperfect detection) of black ducks and then used latent occupancy estimates to derive occupancy, colonization, and extirpation rates. We jointly modeled the occupancy dynamics of black ducks and other duck species in wetlands where both species were present. Throughout the duration of the survey, 44% of wetlands were never observed to be occupied by black ducks. Occupancy models showed wetland size was positively associated with occupancy at the first time step (initial occupancy) and colonization. All 2-species models indicated initial black duck occupancy, persistence (continued occupancy), and colonization were positively associated with the presence of a second species. Colonization rate over the 26-year period ranged from 7% to 27% across all models. Extirpation rates were similar and were constant through time within each model. Low occupancy rates, combined with approximately equal colonization and extirpation rates, suggest there are available wetlands for breeding black ducks in their core breeding area. If breeding habitats are not saturated, this suggests migration or wintering areas may be more limiting to black duck population abundance. © 2019 The Wildlife Society.     

The Effect of Sea Level Rise on Dabbling Duck Energetic Carrying Capacity

Waterfowl migrating and overwintering in the Atlantic Flyway depend on adequate availability of wetland plant communities to survive winter and fuel reproduction in the subsequent breeding season. Energetics models are the primary tool employed by conservation planners to estimate energetic carrying capacity based on energy supply and demand in different wetlands to assist with effective habitat conservation. Coastal impoundments have been used to provide a consistent, annual source of energy for migrating and wintering waterfowl. But few studies have attempted to comprehensively assess the relative value of managed coastal impoundments compared with unmanaged tidal salt marshes to wintering waterfowl in the Mid-Atlantic region with further consideration to the effect of sea level rise changing availability. We estimated biomass and energy of preferred foods for 5 dabbling duck species in 7 impoundments and 3 tidal salt marshes over winter by collecting soil core (n = 1,364), nekton (n = 426), and salt marsh snail (Melampus spp.; n = 87) samples in October, January, and April 2011–2013. Food-energy density was greater in freshwater impoundments for nearly all dabbling ducks (range = 183,344–562,089 kcal/ha), and typically greater in brackish impoundments (range = 169,665–357,160 kcal/ha) than most tidal salt marsh communities (range = 55,693–361,429 kcal/ha), whereas mudflat (range = 96,223–137,473 kcal/ha) and subtidal (range = 55,693–136,326 kcal/ha) communities typically contained the least energy. Extrapolating to the state level, we estimated 7.60 × 10⁹–1.14 × 10¹⁰ kcal available within a 16-km buffer from the Delaware Bayshore, depending on species. Combining estimates for daily energy expenditure and food energy, we estimated 2.86 × 10⁷–7.06 × 10⁷ duck energy days currently available to dabbling ducks over winter. We estimated that in the next century, dabbling duck carrying capacities are likely to decrease under all but the most conservative sea level rise scenarios because of the gradual replacement of land-cover types that provide high energy density (i.e., low marsh, high marsh communities) with those that provide low energy density (i.e., subtidal, mudflat communities). Coastal impoundments in Delaware, USA, will provide increasingly important habitat for wintering dabbling ducks in the coming decades provided they are properly maintained and retain their current energetic density because they will contain a growing proportion of the available duck energy days on the landscape. Our research will assist managers in meeting target population goals for dabbling ducks in Delaware and the Mid-Atlantic region by highlighting key differences in the function and value of various wetlands. © 2021 The Wildlife Society.     

Origins of harvested American black ducks: stable isotopes support the flyover hypothesis

Waterfowl management is more effective when based on detailed information on population connectivity between breeding, wintering, and stopover sites. For the American black duck (Anas rubripes), a species of conservation concern, estimates for the fall age ratio at harvest differed depending on whether harvest data were derived from Canada or the United States, suggesting regional differences. Within Canada, hunters in Atlantic Canada were more likely to harvest black ducks from nearby breeding locations compared to hunters in southern Ontario and Quebec, Canada, who were more likely to harvest individuals from the Boreal Softwood and Taiga Shield of eastern Canada. Black ducks harvested in the United States are thought to originate predominantly from northern portions of the breeding range, leading to the flyover hypothesis, which postulates that black ducks produced in the Boreal Softwood and Taiga Shield region are less susceptible to harvest by hunters in Atlantic Canada and northeastern United States. To test the flyover hypothesis, we examined regional and temporal differences in the origins of harvested black ducks using feathers from wings (n = 664) submitted by hunters to the species composition and parts collection surveys across 3 hunting seasons (2017–2018, 2018–2019, 2019–2020). We used a likelihood-based assignment method that relied on feather stable-hydrogen isotopes (δ²H) and stable-carbon isotopes (δ¹³C) to determine the natal or molt origin of individuals harvested within eastern Canada and the United States. We also used a spatial clustering technique to group harvested individuals by area of origin without a priori knowledge of such regions. Adult female black ducks originated farther south compared to males and juveniles. All sexes and ages of black ducks harvested in Atlantic Canada showed predominantly southern origins, while those harvested in the United States and other Canadian provinces primarily originated farther north within the boreal, supporting the flyover hypothesis. By contrast, we found no relationship between timing of harvest or peaks of migration and individual origin. After combining band returns and stable isotopes, we inferred 2 distinct stocks: the Mississippi flyway stock and the Atlantic flyway stock. We recommend that regional demographic parameters, particularly for Atlantic Canada, be directly measured to promote more effective conservation of black ducks and optimize harvest opportunities in the United States and Canada.     

Acorn and aquatic invertebrate biomass in Mississippi Alluvial Valley hardwood bottomlands

The Mississippi Alluvial Valley (MAV) is an internationally important migration and wintering region for Nearctic waterfowl. Most of the MAV is a lowland forested floodplain that contains vast stands of red oaks (Quercus spp.). These trees produce acorns and, when forests flood, diverse communities of aquatic invertebrates emerge, providing diverse nutritious foods for wintering ducks. The MAV is within the Lower Mississippi Valley Joint Venture (LMV JV) region of the North American Waterfowl Management Plan, but no combined MAV-wide estimates of acorn and invertebrate biomass exist to determine foraging carrying capacity for conservation planning or actions by the LMV JV or other partners in regions containing southern red oaks. We sampled acorns that fell to the ground or were submersed under shallow water deemed accessible to foraging ducks and aquatic invertebrates in the MAV of Louisiana, Mississippi, Missouri, and Tennessee, USA, during fall-winter 2009–2011. In good and poor masting years, acorn abundance was non-linearly related to the percentage of the forest canopy made up of red oaks and peaked in late autumn or winter when most other waterfowl resources are depleted or decomposed. This finding is novel and represents a deviation from how the LMV JV has traditionally assumed food resources exist for waterfowl in hardwood bottomlands. We used a daily ration model to estimate energy use days (EUDs) from combined acorn and invertebrate biomasses relative to red oak canopy coverage. For good and poor acorn masting years at the mean MAV-wide red oak canopy coverage of 45%, EUD = 2,273.1 days/ha and 161.2 days/ha, respectively. The LMV JV currently uses EUD = 385–502 days/ha for forests with 40–50% red oak canopy coverage. Because acorns and aquatic macro-invertebrates are a food resource that persists through winter and reaches peak abundance later in winter, we contend conservation planners have undervalued the potential of bottomland hardwoods to provide energy for wintering ducks.     

Potential use of weather radar to study movements of wintering waterfowl

To protect and restore wintering waterfowl habitat, managers require knowledge of routine wintering waterfowl movements and habitat use. During preliminary screening of Doppler weather radar data we observed biological movements consistent with routine foraging flights of wintering waterfowl known to occur near Lacassine National Wildlife Refuge (NWR), Louisiana. During the winters of 2004–2005 and 2005–2006, we conducted field surveys to identify the source of the radar echoes emanating from Lacassine NWR. We compared field data to weather radar reflectivity data. Spatial and temporal patterns consistent with foraging flight movements appeared in weather radar data on all dates of field surveys. Dabbling ducks were the dominant taxa flying within the radar beam during the foraging flight period. Using linear regression, we found a positive log-linear relationship between average radar reflectivity (Z) and number of birds detected over the study area (P < 0.001, r² = 0.62, n = 40). Ground observations and the statistically significant relationship between radar data and field data confirm that Doppler weather radar recorded the foraging flights of dabbling ducks. Weather radars may be effective tools for wintering waterfowl management because they provide broad-scale views of both diurnal and nocturnal movements. In addition, an extensive data archive enables the study of wintering waterfowl response to habitat loss, agricultural practices, wetland restoration, and other research questions that require multiple years of data. © 2011 The Wildlife Society.     

Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics

Twelve species of North American sea ducks (Tribe Mergini) winter off the eastern coast of the United States and Canada. Yet, despite their seasonal proximity to urbanized areas in this region, there is limited information on patterns of wintering sea duck habitat use. It is difficult to gather information on sea ducks because of the relative inaccessibility of their offshore locations, their high degree of mobility, and their aggregated distributions. To characterize environmental conditions that affect wintering distributions, as well as their geographic ranges, we analyzed count data on five species of sea ducks (black scoters Melanitta nigra americana, surf scoters M. perspicillata, white-winged scoters M. fusca, common eiders Somateria mollissima, and long-tailed ducks Clangula hyemalis) that were collected during the Atlantic Flyway Sea Duck Survey for ten years starting in the early 1990s. We modeled count data for each species within ten-nautical-mile linear survey segments using a zero-inflated negative binomial model that included four local-scale habitat covariates (sea surface temperature, mean bottom depth, maximum bottom slope, and a variable to indicate if the segment was in a bay or not), one broad-scale covariate (the North Atlantic Oscillation), and a temporal correlation component. Our results indicate that species distributions have strong latitudinal gradients and consistency in local habitat use. The North Atlantic Oscillation was the only environmental covariate that had a significant (but variable) effect on the expected count for all five species, suggesting that broad-scale climatic conditions may be directly or indirectly important to the distributions of wintering sea ducks. Our results provide critical information on species–habitat associations, elucidate the complicated relationship between the North Atlantic Oscillation, sea surface temperature, and local sea duck abundances, and should be useful in assessing the impacts of climate change on seabirds.     

Evidence for Black Duck Winter Distribution Change

ABSTRACT The Mississippi Flyway midwinter population survey (MWS) indicates that American black ducks (Anas rubripes) have been rapidly declining for the last 10 years. We found a negative relationship between MWS and Ontario (Canada) midwinter counts for black ducks. Thus, as number of black ducks in the MWS decreased, Ontario midwinter counts increased. A shift in midwinter distribution of black ducks may be partly responsible for the decreasing trend in MWS counts. We recommend that midwinter black duck surveys be expanded to more sites in southern Canada and northeastern United States that currently are not sampled to better assess winter habitat use and improve the midwinter black-duck population index.     

Patterns of seasonal occurrence,distribution, and site fidelity of coastal bottlenose dolphins (Tursiops truncatus) in southern New Jersey,U.S.A.

Coastal bottlenose dolphins (Tursiops truncatus) form a mosaic of resident and seasonal migratory populations along the United States Atlantic seaboard. Seasonal, poorly known migrants (identified as a separate stock) move as far north as New Jersey. During 2003–2005, 73 boat‐based photo‐identification surveys were conducted in southern New Jersey to discern seasonal occurrence, distribution, and patterns of movement and site fidelity. Neonates, young‐of‐year, and adults occurred in the study area from late May through late September, corresponding to water temperatures of 14.0–16.3°C. Of 205 individuals identified, 44% (n= 90) were sighted multiple times within or among years, including 10% (n= 20) of individuals identified in all 3 yr. Almost half (47%) of the multiple sightings were observed along a core area encompassed by the southern part of the Jacques Cousteau National Estuarine Research Reserve. In contrast to stocks studied in southern coastal areas of the U.S. Atlantic and Gulf of Mexico, estuaries were used significantly less than open‐beach habitat, which is consistent with the relative prey abundance in these habitats. Research at additional sites will help confirm whether bottlenose dolphins at the northern end of their migratory range exhibit local site fidelity and habitat preferences similar to those found in this study.     

Evaluation of an Aerial Survey to Estimate Abundance of Wintering Ducks in Mississippi

Abstract: Researchers have successfully designed aerial surveys that provided precise estimates of wintering populations of ducks over large physiographic regions, yet few conservation agencies have adopted these probability-based sampling designs for their surveys. We designed and evaluated an aerial survey to estimate abundance of wintering mallards (Anas platyrhynchos), dabbling ducks (tribe Anatini) other than mallards, diving ducks (tribes Aythini, Mergini, and Oxyurini), and total ducks in western Mississippi, USA. We used design-based sampling of fixed width transects to estimate population indices (Ǐ), and we used model-based methods to correct population indices for visibility bias and estimate population abundance (Ň) for 14 surveys during winters 2002–2004. Correcting for bias increased estimates of mallards, other dabbling ducks, and diving ducks by an average of 40–48% among all surveys and contributed 48–61% of the estimated variance of Ň. However, mean-squared errors were consistently less for Ň than Ǐ. Estimates of Ň met our goals for precision (CV ≤ 15%) in 7 of 14 surveys for mallards, 5 surveys for other dabbling ducks, no surveys for diving ducks, and 10 surveys for total ducks. Generally, we estimated more mallards and other dabbling ducks in mid- and late winter (Jan-Feb) than early winter (Nov-Dec) and determined that population indices from the late 1980s were nearly 3 times greater than those from our study. We developed a method to display relative densities of ducks spatially as an additional application of survey data. Our study advanced methods of estimating abundance of wintering waterfowl, and we recommend this design for continued monitoring of wintering ducks in western Mississippi and similar physiographic regions.     

Black-backed jackal diet at Mokolodi Nature Reserve, Botswana

We examined the feeding habits of black‐backed jackals at Mokolodi Nature Reserve, Botswana, by analysing 237 scats collected between November 1995 and February 1997. Jackal dietary habits reflected the availability of a wide variety of food items and the differential vulnerability of prey. Potential animal and plant food available to jackals varies throughout the year because of its seasonal character. Seasonality of prey occurrence in scats was pronounced for small mammals, miscellaneous fruits and invertebrates. Across all seasons, mammals were the most common food resource (32.4%, n = 168), followed by anthropogenic items (14.8%), fruits (12.9%), invertebrates (10.8%), birds (8.5%), unidentified items (3.5%) and reptiles (1.4%). The presence of domestic mammals and poultry remains in scats reveals their importance in the diet of jackals and the tendency of jackals to frequent human settlements in search of food. Some ecological implications of jackal dietary habits are also explored.     

Foraging conditions ‘at the end of the world’ in the context of long‐distance migration and population declines in red knots

The long‐distance migrant red knot (Calidris canutus ssp. rufa– Scolopacidae) alternates between the northern and southern ends of the New World, one of the longest yearly migrations of any bird and paradoxically overflying apparently suitable habitat at lower latitudes. This subspecies is sharply declining, with a major mortality event following 2000, attributed to commercial overharvesting of food resources at its Delaware Bay (USA) stop‐over site. A full understanding of this peculiar migrant requires an assessment of the foraging conditions at its southern hemisphere wintering sites. Here, for a major wintering site in Argentinean Tierra del Fuego (Río Grande), we describe and compare food abundance, diet and intake rates during January–February in 1995, 2000 and 2008. The two main prey types were the burrowing clam Darina solenoides and three species of epibenthic mussels Mytilidae. In the year 2000, food availability and intake rate were higher than those recorded at other sites used by knots anywhere else in the world, contributing to the explanation of why red knots carry out this impressive migration. Intake rate in 2008 on the two main prey types was dramatically reduced as a result of birds eating smaller prey and strongly increased human disturbance; the same year we also found a high prevalence of a digenean parasite in Darina. We suggest that during the strongly enhanced winter mortality in 2000, knots did not yet face ecological problems in their southernmost wintering area, consistent with the previous evidence that problems at northern stop‐overs negatively affected their numbers. However, in 2008 the ecological conditions at Río Grande were such that they would have facilitated a further decline, emphasizing the importance of a hemispheric approach to research and management.     

Frequency of mallard-black duck hybrids along the atlantic coast determined by electrophoresis and plumage analysis

The frequency of mallard and black duck hybrids along the Atlantic flyway was estimated based on serum protein and serum esterase electrophoresis and plumage analysis. Hybrid frequencies for black ducks were low (below 10%) in Nova Scotia - Maine, Ontario and New Jersey and high (above 10%) in Maryland and Massachusetts. Plumage estimates tended to be higher for black ducks in Massachusetts and Maryland than estimates based on the electrophoretic work.     

Food Items Consumed by White-headed Langurs in Fusui, China

We studied the socioecology of white-headed langurs (Trachypithecus leucocephalus) from September 1997 to September 1998 in Fusui Precious Animal Reserve, SW Guangxi, China. We collected data on climate, phenology of food plant species, and foods consumed by langurs living in habitats with different levels of human disturbance. Feeding records showed that the most food is from less common plant species. Young leaves were the staple food item in all langur groups, and consumption correlates with availability. Consumption of mature leaves is not significantly correlated with their availability, but the langurs fed on them, and other food items such as fruits and seeds, when the availability of young leaves was low. Langurs in different areas had broadly similar diets, but they varied most in the proportion of supplementary items such as fruit. Groups in more disturbed habitat did not increase the overall proportion of mature leaves in their diet, but instead maintained their intake of young leaves from a greater diversity of species, and incorporated more immature fruit. Conservationists should direct efforts toward protection of rare plant species providing preferred food items, particularly supplementary foods at times when, and in areas where, preferred food items are less available.     

Marine prey processed with stone tools by burmese long‐tailed macaques (Macaca fascicularis aurea) in intertidal habitats

Long‐tailed macaques (Macaca fascicularis) feed opportunistically in many habitats. The Burmese subspecies (M. f. aurea) inhabits coastal areas in southwestern Thailand and Myanmar, and some of their populations have adapted lithic customs for processing encased foods in intertidal habitats. We investigated the diet of such macaques in Laemson National Park, Thailand, and identified the variety of foods they processed with stones. We conducted 36 shore surveys to study tool sites following feeding activity, during which we counted the minimum number of individual (MNI) food items found at each site. We identified 47 food species (43 animals and four plants), from 37 genera. We counted 1,991 food items during surveys. Nearly all were mollusks (n = 1,924), with the small remainder primarily consisting of crustaceans and nuts. The two most common foods, rock oysters (Saccostrea cucullata; n = 1,062) and nerite snails (Nerita spp.; n = 538), composed 80.2% of our sample. Four prey species comprised 83.2% of the sample (MNI = 1,656), S. cucullata (n = 1,062), Nerita chamaeleon (n = 419), Thais bitubercularis (n = 95), and Monodonta labio (n = 80). Macaques selected a wide variety of foods. However, they heavily concentrated on those that were abundant, easy to access, and sufficiently sized. The Burmese long‐tailed macaque stone‐processed diet, which focuses on intertidal marine prey, differs from Sapajus and Pan, who use stones primarily for encased nuts and fruits. In terms of diversity of foods exploited, coastal stone‐based predation by macaques resembles the diet of coastal‐foraging humans (Homo sapiens sapiens). Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Unveiling trade‐offs in resource selection of migratory caribou using a mechanistic movement model of availability

Habitat selection is a multi‐level, hierarchical process that should be a key component in the balance between food acquisition and predation risk avoidance (food–predation trade‐off). However, to date, studies have not fully elucidated how fine‐ and broad‐scale habitat decisions by individual prey can help balance food versus risk. We studied broad‐scale habitat selection by Newfoundland caribou Rangifer tarandus, focusing on trade‐offs between predation risk versus access to forage during the calving and post‐calving period. We improved traditional measures of habitat availability by incorporating fine‐scale movement patterns of caribou into the availability kernel, thus enabling separation of broad and fine scales of selection. Remote sensing and field surveys served to create a spatio‐temporal model of forage availability, whereas GPS telemetry locations from 66 black bears Ursus americanus and 59 coyotes Canis latrans provided models of predation risk. We then used GPS telemetry locations from 114 female caribou to assess food–predation trade‐offs through the prism of our refined model of caribou habitat availability. We noted that migratory movements of caribou were oriented mainly towards habitats with abundant forage and lower risk of bear and (to a lesser extent) coyote encounter. These findings were generally consistent across caribou herds and would not have been evident had we used traditional methods instead of our refined model when estimating habitat availability. We interpret these findings in the context of stereotypical migratory behaviour observed in Newfoundland caribou, which occurs despite the extirpation of wolves Canis lupus nearly a century ago. We submit that caribou are able to balance food acquisition against predation risk using a complex set of factors involving both finer and broader scale selection. Accordingly, our study provides a strong argument for using refined habitat availability estimates when assessing food–predation trade‐offs.     

Feeding ecology and activity pattern of black-fronted titi monkeys (<Emphasis Type="Italic">Callicebus nigrifrons</Emphasis>) in a semideciduous tropical forest of southern Brazil

Most aspects of the ecology and behavior of Callicebus nigrifrons are still unknown. The information available about this species is mainly based on a few studies that also focused on other Callicebus. We examined the feeding behavior and activity pattern of a free-ranging pair of C. nigrifrons between March and November 2007 in an area of semideciduous tropical forest of southeastern Brazil. The study site is located at the southern limit of the Tropical Zone and is characterized by pronounced seasonality. As observed for other Callicebus monkeys, fruits were the most consumed food resource, accounting for 53% of the diet, which was complemented mainly by leaves (16%) but also by invertebrates and flowers (10% of each). A great variety of plant families (28) and species (62) were included in the diet. The titis spent 35% of their time feeding, distributing the remaining time between resting (30%) and traveling (24%). Data presented here indicate that C. nigrifrons prefer high-quality food items (fruit pulp), adding low-quality food items (such as leaves) as the availability of the higher-quality foods decreases. The amount of time spent traveling and resting did not change between seasons, but the time invested in feeding increased during the lean period. The activity pattern was not related to fruit availability, but in months with lower temperatures, monkeys spent more time feeding. We suggest that the feeding ecology and activity pattern of C. nigrifrons reflect adaptations related to annual fluctuations in food availability and temperature, respectively.     

Spatial heterogeneity and scale‐dependent habitat selection for two sympatric raptors in mixed‐grass prairie

Sympatric predators are predicted to partition resources, especially under conditions of food limitation. Spatial heterogeneity that influences prey availability might play an important role in the scales at which potential competitors select habitat. We assessed potential mechanisms for coexistence by examining the role of heterogeneity in resource partitioning between sympatric raptors overwintering in the southern Great Plains. We conducted surveys for wintering Red‐tailed hawk (Buteo jamaicensis) and Northern Harrier (Circus cyanea) at two state wildlife management areas in Oklahoma, USA. We used information from repeated distance sampling to project use locations in a GIS. We applied resource selection functions to model habitat selection at three scales and analyzed for niche partitioning using the outlying mean index. Habitat selection of the two predators was mediated by spatial heterogeneity. The two predators demonstrated significant fine‐scale discrimination in habitat selection in homogeneous landscapes, but were more sympatric in heterogeneous landscapes. Red‐tailed hawk used a variety of cover types in heterogeneous landscapes but specialized on riparian forest in homogeneous landscapes. Northern Harrier specialized on upland grasslands in homogeneous landscapes but selected more cover types in heterogeneous landscapes. Our study supports the growing body of evidence that landscapes can affect animal behaviors. In the system we studied, larger patches of primary land cover types were associated with greater allopatry in habitat selection between two potentially competing predators. Heterogeneity within the scale of raptor home ranges was associated with greater sympatry in use and less specialization in land cover types selected.     

Feeding Strategies of Brown Howler Monkeys in Response to Variations in Food Availability

Primates display varying degrees of behavioral flexibility that allow them to adjust their diet to temporal changes in food availability. This trait might be critical for the survival of folivorous-frugivorous species inhabiting small forest fragments, where the availability of food resources tends to be lower than in large fragments and continuous forests. However, the scarcity of studies addressing this issue hampers our understanding of the adaptive behaviors that favor the survival of these primates in low-quality habitats. We conducted a 36-mo study testing the hypothesis that brown howler monkeys (Alouatta guariba clamitans) are able to adjust their diet in response to local and seasonal changes in resource availability. We compared the diet of six free-ranging groups inhabiting three small (<10 ha) and three large (>90 ha) Atlantic forest fragments in southern Brazil and estimated the temporal availability of their top food species (i.e., those species that together contribute ≥80% of total feeding records). We found that brown howlers exploited similarly rich diets in small (45, 54, and 57 plant species) and large (48, 51, and 56 species) fragments. However, intermonth diet similarity was higher for groups in small fragments, where howlers also fed on plant items from nine alien species. Fruits and leaves were the most consumed plant items in both small (42% and 49% of feeding records, respectively) and large (51% and 41%, respectively) fragments. The consumption of young leaves was higher in small than in large fragments, whereas the consumption of other plant items did not show a pattern related to fragment size. Regarding the contribution of growth forms as food sources, only the exploitation of palms showed a pattern related to fragment size. Palms contributed more to the diet of groups inhabiting large fragments. The availability of seasonal food items–ripe fruits and young leaves–influenced their consumption in both habitat types. Therefore, brown howlers cope with local and seasonal fluctuations in food availability by opportunistically exploiting resources. We believe that this feeding flexibility is a key component of the phenotypic plasticity that enables howlers to thrive in disturbed habitat patches, where periods of scarcity of preferred foods shall be more common.