Availability Of Breeding Habitat Research Articles

Assessing golden‐winged warbler dispersal habitat in a highly parcelized landscape

AbstractGolden‐winged warblers (Vermivora chrysoptera) are facing population declines in the southern Appalachian Mountains. Breeding habitat loss is considered one of the primary reasons for golden‐winged warbler declines in the region. Expanding breeding habitat availability in a manner that promotes population expansion across an interconnected network of habitat patches is particularly problematic in a landscape dominated by private land ownership. We assessed the connectivity of golden‐winged warbler breeding habitat in a 29,680‐ha landscape with 5,664 ownership parcels between 2 state‐owned game lands in northwestern North Carolina, USA, in fall 2021. We created a connectivity map and provided examples of 3 means of prioritizing parcels for golden‐winged warbler habitat maintenance and management based on dispersal distances of fledglings that could return the following spring with prior familiarity of potential nesting areas. Prioritized parcels can guide land acquisition and conservation easement development as well as active management. Despite being highly parcelized, the area has both well‐connected and disjointed clusters of core habitat patches, but habitat management on privately owned parcels would be needed to connect core habitat patches to enable dispersing golden‐winged warbler fledglings to encounter potential breeding habitat that they could use the following spring.

Climate-related range shifts in Arctic-breeding shorebirds.

To test whether the occupancy of shorebirds has changed in the eastern Canadian Arctic, and whether these changes could indicate that shorebird distributions are shifting in response to long-term climate change. Foxe Basin and Rasmussen Lowlands, Nunavut, Canada. We used a unique set of observations, made 25 years apart, using general linear models to test if there was a relationship between changes in shorebird species' occupancy and their species temperature Index, a simple version of a species climate envelope. Changes in occupancy and density varied widely across species, with some increasing and some decreasing. This is despite that overall population trends are known to be negative for all of these species based on surveys during migration. The changes in occupancy that we observed were positively related to the species temperature index, such that the warmer-breeding species appear to be moving into these regions, while colder-breeding species appear to be shifting out of the regions, likely northward. Our results suggest that we should be concerned about declining breeding habitat availability for bird species whose current breeding ranges are centered on higher and colder latitudes.

Balancing ecosystem service outcomes at the ranch-scale in shortgrass steppe: The role of grazing management

• Grazing management for providing multiple ecosystem services at the ranch scale requires balancing desired outcomes. • Abundant challenges involve matching the spatial heterogeneity in soils and associated plant community characteristics with the temporal variability in precipitation. • Prescriptive grazing (season-long continuous and time-controlled rotational grazing) removes the human experiential knowledge to adapt to changing conditions, whereas adaptive multipaddock (AMP) grazing often invokes high stock densities, which reduce livestock weight gain. • A “mix-and-match” or blending of both approaches for grazing management in the shortgrass steppe can result in reduced drought risk, enhanced breeding habitat availability for grassland bird species of concern, and sustained livestock production.

WESTERN TOAD (ANAXYRUS BOREAS) BREEDING TIMING AND LARVAL DEVELOPMENT IN LAKE CUSHMAN RESERVOIR, WASHINGTON STATE

We observed Western Toad (Anaxyrus boreas) breeding from mid-May to late June, coincident with a reservoir rise of ≤1.2 m in Lake Cushman, Washington State. Breeding occurred at 5 sequentially inundated sites and included diverse habitats. Early-spawned clutch-strings remained attached to the lake bottom but became vertically suspended during the lake-level rise. Embryos and hatchlings nearest the bottom were in cooler water than those near the top. Development through hatchling stages took up to 40 d for early spawn. Locations of later spawning were shallower and warmer, and larval development progressed rapidly. Ultimately, the extended spawning season and varied sites and habitats may provide reproductive success resilience. Reservoir water-level management during Western Toad breeding and larval development may effect: (1) breeding habitat availability; (2) larval development rates; and (3) reproductive success.

Incorporating hydrology into climate suitability models changes projections of malaria transmission in Africa

Continental-scale models of malaria climate suitability typically couple well-established temperature-response models with basic estimates of vector habitat availability using rainfall as a proxy. Here we show that across continental Africa, the estimated geographic range of climatic suitability for malaria transmission is more sensitive to the precipitation threshold than the thermal response curve applied. To address this problem we use downscaled daily climate predictions from seven GCMs to run a continental-scale hydrological model for a process-based representation of mosquito breeding habitat availability. A more complex pattern of malaria suitability emerges as water is routed through drainage networks and river corridors serve as year-round transmission foci. The estimated hydro-climatically suitable area for stable malaria transmission is smaller than previous models suggest and shows only a very small increase in state-of-the-art future climate scenarios. However, bigger geographical shifts are observed than with most rainfall threshold models and the pattern of that shift is very different when using a hydrological model to estimate surface water availability for vector breeding.

Restricted breeding habitat of the Critically Endangered White-winged Flufftail in Ethiopia and its conservation implications

The White-winged Flufftail Sarothrura ayresi is considered the most threatened rallid species in Africa and has significant data deficiencies related to population dynamics, ecology and conservation priorities. The Ethiopian Highlands have until recently, been the only known breeding area for this species globally and are being significantly transformed as a result of expanding agricultural activities. Our study aimed to use in situ data collection and spatially explicit modelling, supported with remote sensing, to produce the first quantified estimate of breeding habitat availability and population size for this species in the Ethiopian Highlands. Our results confirm that a significant proportion (c. 95%) of the three wetland catchments known to support the species have been transformed and are no longer suitable. We estimate that given the remaining habitat (c. 232 ha) and recorded nest density (0.24 nests ha−1), the three catchments could support a potential breeding population of 55 pairs. Of the three catchments, Upper Berga was highlighted as a conservation priority for securing the largest intact sections of suitable breeding habitat. The accumulative impact of a small and declining population size, restricted and localised geographic range and a high rate of habitat loss, all contribute to White-winged Flufftail being associated with a very high extinction risk.

AMPHIBIAN DISTRIBUTION IN THE GEORGIA SEA ISLANDS: IMPLICATIONS FROM THE PAST AND FOR THE FUTURE

We summarized amphibian distributions for 12 coastal islands in Georgia, USA. Occurrence among islands was correlated with life history traits, habitats, island size, distance to other islands, and island geological age. Species’ distributions were determined from published literature. Island sizes and vegetation types were derived from 2011 Georgia Department of Natural Resources habitat maps, which included both federal and state vegetation classification systems. Species occurring on more islands tended to have greater total reproductive output (i.e., life span >4 years, and annual egg production >1,000 eggs) and adults had tolerance of brackish environs. Larger islands had great­er area of freshwater wetlands, predominantly short hydroperiod (<6 months). Species tied to long hydroperiod wetlands (>6 months) were more restricted in their distribution across islands. Overall, larger islands supported more species, but the correlation was weaker for geologically younger Ho­locene islands (age <11,000 years). While Euclidean distance between islands does not necessarily preclude inter-island dispersal, inhospitable habitat for amphibians (brackish tidal marshes and creeks interspersed with wide rivers) suggests that inter-island dispersal is very limited. The paucity of recent occurrence data for amphibians in this dynamic coastal region, let alone standardized annual moni­toring data, hinders efforts to model species’ vulnerability in a region susceptible to sea level rise and development pressure. The most common survey method, standardized amphibian vocal surveys, will detect Anuran reproductive efforts, but is unlikely to ascertain if breeding was successful or to detect salamanders. While it will not replace actual population data, consideration of critical life-history traits and breeding habitat availability can be used to direct management to support long-term species per­sistence in changing environs. Even common amphibians in coastal conservation areas of Georgia are vulnerable to increasing population isolation caused by unsuitable habitat.

Density dependence forces divergent population growth rates and alters occupancy patterns of a central place foraging Antarctic seabird.

Density‐dependent regulation is an important process in spatio‐temporal population dynamics because it can alter the effects of synchronizing processes operating over large spatial scales. Most frequently, populations are regulated by density dependence when higher density leads to reduced individual fitness and population growth, but inverse density dependence can also occur when small populations are subject to higher extinction risks. We investigate whether density‐dependent regulation influences population growth for the Antarctic breeding Adélie penguin Pygoscelis adeliae. Understanding the prevalence and nature of density dependence for this species is important because it is considered a sentinel species reflecting the impacts of fisheries and environmental change over large spatial scales in the Southern Ocean, but the presence of density dependence could introduce uncertainty in this role. Using data on population growth and indices of resource availability for seven regional Adélie penguin populations located along the East Antarctic coastline, we find compelling evidence that population growth is constrained at some locations by the amount of breeding habitat available to individuals. Locations with low breeding habitat availability had reduced population growth rates, higher overall occupancy rates, and higher occupancy of steeper slopes that are sparsely occupied or avoided at other locations. Our results are consistent with evolutionary models of avian breeding habitat selection where individuals search for high‐quality nest sites to maximize fitness returns and subsequently occupy poorer habitat as population density increases. Alternate explanations invoking competition for food were not supported by the available evidence, but strong conclusions on food‐related density dependence were constrained by the paucity of food availability data over the large spatial scales of this region. Our study highlights the importance of incorporating nonconstant conditions of species–environment relationships into predictive models of species distributions and population dynamics, and provides guidance for improved monitoring of fisheries and climate change impacts in the Southern Ocean.

Integrating habitat and partial survey data to estimate the regional population of a globally declining seabird species, the sooty shearwater

Many animal populations are thought to be in flux due to anthropogenic impacts. However, censusing organisms to understand such changes is often impractical. For example, while it is thought that over half of pelagic seabird populations are declining, most breed in burrows or on cliffs, in large, remote colonies, making them difficult to count. Burrow-nesting sooty shearwaters (Ardenna grisea) are abundant but declining in their core (South Pacific) breeding range, potentially due to introduced rodents and habitat loss. In contrast, Kidney Island, their largest colony in the Falkland Islands (Southwest Atlantic), purportedly grew by several orders of magnitude since the mid-1900s. This island is rodent-free, and native tussac grass (Poa flabellata) has increased following cessation of historical exploitation. To estimate the sooty shearwater population in the Falkland Islands, and its relationship with breeding habitat availability, we sampled burrow density and occupancy on Kidney Island and modeled these as functions of habitat. Both indices responded positively to a proxy for historical increases in tussac cover. We estimate that breeding sooty shearwaters occupy ∼140,000 (95% CI: 90,000–210,000) burrows on Kidney Island. Moreover, using additional survey data and Generalized Functional Response models to account for intra-island variation in habitat availability, we estimate that 25,000 (95% CI: 20,100 - 30,500) burrows could be occupied on nearby islands from which non-native rodents have been recently eradicated. Our study shows that habitat selection functions, generalized where necessary, not only improve population estimates but provide biological insights needed to reverse declines in seabirds and other species.

Influence of Weather, Wetland Availability, and Mallard Abundance on Productivity of Great Lakes Mallards (Anas platyrhynchos)

Waterfowl rely on breeding habitat availability for successful reproduction. Breeding habitat availability likely changes throughout the season and among years as weather patterns change and thus productivity rates are likely susceptible to these changes. We used data from 1961 to 2011 to investigate effects of weather, breeding habitat availability and abundance of breeding mallards (Anas platyrhynchos) on productivity rates of mallards breeding in the Great Lake states (Michigan, Minnesota, and Wisconsin; hereafter GLS). We hypothesized that productivity rates would increase with wetter and warmer conditions however, extreme temperatures may have a negative impact and that high breeding density may negatively impact productivity rates. Specifically, we looked at the effects of average June and July temperature and precipitation, the Palmer Hydrological Drought Index (hereafter PHDI), and wetland counts to model productivity rates across the three states for the time series. We used a reduced time series model set to evaluate the impacts of wetland counts on productivity. We found that in general, wetter conditions, as indexed by high positive PHDI values and relationships with pond abundance, positively affected productivity. We believe that breeding habitat availability is likely a reasonable predictor of mallard productivity rates in the GLS.

An amphibian species of concern prefers breeding in active beaver ponds

AbstractChanges in water availability threaten to reduce suitable habitat for wildlife in the western United States. Ecosystem engineers, such as beavers (Castor canadensis), potentially mitigate the effects of such habitat changes, particularly in stochastic environments. Our goal was to determine factors driving wetland use of a widespread, declining species, the northern leopard frog (Lithobates pipiens), in southeastern Wyoming. We evaluated hypotheses about habitat preferences of leopard frogs in a healthy population using occupancy modeling. Although leopard frogs may breed in a variety of wetlands, we found that the main drivers of breeding distribution in southeast Wyoming were the degree of beaver activity at wetlands and the ability of a site to retain water throughout the summer. In both years of our study (2012–2013), leopard frogs bred only in beaver ponds, with a preference for those ponds actively used by beavers. Leopard frogs also bred in wetlands that were less likely to dry over the course of the season. This effect was strongest in a dry year when water availability was limiting (2012), but still among the top drivers in the wetter year (2013). The decreased predictive power of water in a high snowpack year corresponded to an increase in the importance of wetland shape complexity, likely representative of breeding habitat availability along wetland edges. Identifying factors driving the distribution of healthy populations of species that are declining elsewhere can uncover limiting factors across the species’ range. We conclude that beavers are one vital conservation and management tool for maintaining declining populations of northern leopard frogs. While site‐level effects may vary, the presence of beaver ponds across the landscape in water‐limited systems, particularly in times of drought, should have positive impacts on many native amphibian species.

Are breeding sites a limiting factor for the Tandilean redbelly toad (Bufonidae) in pampean highland grasslands?

Fil: Cortelezzi, Agustina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Demographic response to perturbations: the role of compensatory density dependence in a North American duck under variable harvest regulations and changing habitat

1. Most wild animal populations are subjected to many perturbations, including environmental forcing and anthropogenic mortality. How population size varies in response to these perturbations largely depends on life-history strategy and density regulation. 2. Using the mid-continent population of redhead Aythya americana (a North American diving duck), we investigated the population response to two major perturbations, changes in breeding habitat availability (number of ponds in the study landscape) and changes in harvest regulations directed at managing mortality patterns (bag limit). We used three types of data collected at the continental scale (capture-recovery, population surveys and age- and sex ratios in the harvest) and combined them into integrated population models to assess the interaction between density dependence and the effect of perturbations. 3. We observed a two-way interaction between the effects on fecundity of pond number and population density. Hatch-year female survival was also density dependent. Matrix modelling showed that population booms could occur after especially wet years. However, the effect of moderate variation in pond number was generally offset by density dependence the following year. 4. Mortality patterns were insensitive to changes in harvest regulations and, in males at least, insensitive to density dependence as well. We discuss potential mechanisms for compensation of hunting mortality as well as possible confounding factors. 5. Our results illustrate the interplay of density dependence and environmental variation both shaping population dynamics in a harvested species, which could be generalized to help guide the dual management of habitat and harvest regulations.

Concurrent habitat and life history influences on effective/census population size ratios in stream‐dwelling trout

Lower effective sizes (Ne) than census sizes (N) are routinely documented in natural populations, but knowledge of how multiple factors interact to lower Ne/N ratios is often limited. We show how combined habitat and life-history influences drive a 2.4- to 6.1-fold difference in Ne/N ratios between two pristine brook trout (Salvelinus fontinalis) populations occupying streams separated by only 750 m. Local habitat features, particularly drainage area and stream depth, govern trout biomass produced in each stream. They also generate higher trout densities in the shallower stream by favoring smaller body size and earlier age-at-maturity. The combination of higher densities and reduced breeding site availability in the shallower stream likely leads to more competition among breeding trout, which results in greater variance in individual reproductive success and a greater reduction in Ne relative to N. A similar disparity between juvenile or adult densities and breeding habitat availability is reported for other species and hence may also result in divergent Ne/N ratios elsewhere. These divergent Ne/N ratios between adjacent populations are also an instructive reminder for species conservation programs that genetic and demographic parameters may differ dramatically within species.

Population Growth and Demography of Common Loons in the Northern United States

ABSTRACT We used recent developments in theoretical population ecology to construct basic models of common loon (Gavia immer) demography and population dynamics. We parameterized these models using existing survival estimates and data from long‐term monitoring of loon productivity and abundance. Our models include deterministic, 2‐stage, density‐independent matrix models, yielding population growth‐rate estimates (λ) of 0.99 and 1.01 for intensively studied populations in our Wisconsin, USA, and New Hampshire, USA, study areas, respectively. Perturbation analysis of these models indicated that estimated growth rate is extremely sensitive to adult survival, as expected for this long‐lived species. Also, we examined 20 years of count data for the 2 areas and evaluated support for a set of count‐based models of population growth. We detected no temporal trend in Wisconsin, which would be consistent with fluctuation around an average equilibrium state but could also result from data limitations. For New Hampshire, the model set included varying formulations of density dependence and partitioning of stochasticity that were enabled by the annual sampling resolution. The best model for New Hampshire included density regulation of population growth and, along with the demographic analyses for both areas, provided insight into the possible importance of breeding habitat availability and the abundance of nonbreeding adults. Based on these results, we recommend that conservation organizations include nonbreeder abundance in common loon monitoring efforts and that additional emphasis be placed on identifying and managing human influences on adult loon survival.

Effects of Forest Disturbance on Breeding Habitat Availability for Two Species of Anurans in the Amazon

Deforestation may cause substantial changes in community structure along freshwater habitat gradients. This study evaluated how biotic and abiotic factors affect the distribution and reproductive success of two frog species in Central Amazon. Ponds in continuous and disturbed forest were surveyed to determine the distribution of their associated aquatic predators and the production of newly metamorphosed frogs. The effect of each predator assemblage on tadpole survival was tested using mesocosms. Newly metamorphosed Osteocephalus taurinus occurred in short hydroperiod ponds in disturbed forest, where they had lower encounter frequencies with aquatic insects and no fish were detected. In contrast, newly metamorphosed Phyllomedusa tarsius were associated with longer hydroperiod ponds in continuous forest where fish and aquatic insects were prevalent. In the experimental study, O. taurinus tadpoles had lower survival rates than P. tarsius tadpoles, suggesting that O. taurinus is more vulnerable to fish and insect predators. These results are consistent with the pattern of metamorphic success along the hydroperiod gradient in the study area. If intact continuous forest continues to be harvested, species that require ponds with longer hydroperiods for successful metamorphosis would be prone to population declines.

BREEDING PHENOLOGY AND SPATIO-TEMPORAL DYNAMICS OF POND USE BY THE YELLOW-BELLIED TOAD (BOMBINA VARIEGATA) POPULATION: THE IMPORTANCE OF POND AVAILABILITY AND DURATION

We analysed the spatial and temporal variation of breeding habitat availability and use by a yellow-bellied toad population in a mixed deciduous forest between 2003n2005. During this period, the number of temporary ponds was highly variable. Toads tended to exploit newly created breeding habitats or those of which hydroperiod increased due to precipitation. Ponds with intermediate and long duration were preferred for reproduction. We found no evidence of predator avoidance behaviour (aquatic inver- tebrates and newts) or reproductive failure in ponds containing aquatic predators. Ponds located in sunny patches of the forest were preferred for reproduction. We suggest that ponds that act as sinks in years with low precipitation could contribute to the demography of toad populations in rainy years, when their hydroperiod increases.

Using satellite imagery to assess breeding habitat availability of the endangered loggerhead shrike in Qu�bec

The loggerhead shrike (Lanius ludovicianus) is a grassland bird species whose preferred nesting habitat in eastern Canada is pastureland. This species has been extirpated from much of its historical range in this region, and breeding habitat loss is suspected to be an important cause of this decline. We evaluated the availability of suitable breeding habitats in Quebec using satellite imagery. Because this species no longer breeds in Quebec, we established habitat selection criteria from known nesting sites in the adjacent province of Ontario, from analysis of a Landsat-TM satellite image, and applied these criteria to Landsat-TM images covering southern Quebec. We developed regional landscape criteria in 100 km2 plots and patch indices criteria at the pasture level. Spatial analyses were conducted to characterize plots and pastures on the basis of pasture availability and spatial distribution. Pastures suitable for nesting loggerhead shrikes were those fulfilling patch criteria at the pasture level and located in plots fulfilling regional landscape criteria. Overall, 310 out of 1700 plots located in the historical breeding range of the loggerhead shrike in Quebec fulfilled landscape criteria, supporting 3988 pastures that fulfilled patch criteria. More than 500 of these pastures were visited to validate their current status. The Outaouais region would be the most suitable region for nesting loggerhead shrikes in southern Quebec, where suitable breeding habitat still remains because more than two-thirds of visited sites were still pastureland, hawthorns were well-distributed in the region, and pastureland fragmentation was lowest. We conclude that the availability of breeding habitat does not limit the establishment of a breeding population of loggerhead shrike in southern Quebec, as we estimated that thousands of hectares of suitable habitat still remain in that province.

Culex restuans (Diptera: Culicidae) oviposition behavior determined by larval habitat quality and quantity in southeastern Michigan.

Oviposition is a critical stage in the mosquito lifecycle, and may determine population levels, distribution, biting behavior, and pathogen transmission. Knowledge of the oviposition behavior of Culex restuans Theobald has become particularly important with the emergence of West Nile virus (WNV) in North America. Laboratory and field studies have examined some factors that contribute to oviposition choice in Culex spp., but few studies have investigated responses to cues of future competition and breeding habitat availability in the field. We hypothesized that female Cx. restuans mosquitoes avoid laying eggs in habitats containing cues of larval competition, and that increased availability of larval habitat decreases egg density. To test these hypotheses, a series of field experiments were conducted in southeastern Michigan during summer 2002. We found that female mosquitoes prefer nutrient-enriched containers and decrease ovipositing in containers with conspecific larvae. In addition, greater habitat abundance decreased egg clutch density per container, although there was considerable aggregation of egg clutches. These results support our hypotheses and have potentially important implications for pathogen transmission by mosquitoes.