Fine-scale resource selection and behavioral tradeoffs of eastern wild turkey broods

Resource heterogeneity across the landscape prompts animals to make behavioral tradeoffs to survive and reproduce. Behavioral thermoregulation can buffer organisms from thermal extremes but may conflict with other essential activities such as predator avoidance or foraging, and necessitate tradeoffs among resource requirements. We evaluated patterns of habitat selection relative to thermal conditions, forage availability, and concealment cover for female eastern wild turkeys (Meleagris gallopavo silvestris) with broods to assess potential tradeoffs among resource requirements. We quantified air temperature (°C), vegetation characteristics (e.g., visual obstruction), and arthropod biomass (g/m²) at locations used by broods across 5 study sites in the southeastern United States during May–July 2019–2020. We used conditional logistic regression to estimate brooding female resource selection at the second (home range) and third (within home range) orders. Specifically, we identified differences in selection between brooding and non-brooding females (second order), and factors influencing selection of sites used by brooding females during the day (when loafing and foraging) and night (roosting; third order). Brooding females selected sites with cooler temperatures (β = −0.22; 95% CI = −0.338–−0.102) and greater ground cover vegetation (β = 0.02; 95% CI = 0.013–0.033) than non-brooding females. Additionally, biomass of large prey (Orthoptera) was positively related to ambient temperature, suggesting that use of thermal refuge by brooding females may limit availability of large prey. Brooding females appeared to balance the tradeoff between thermal refuge and forage availability by altering habitat selection patterns within home ranges. Brooding females selected for herbaceous areas that provided greater biomass of large arthropods during the day, and avoided areas dominated by woody vegetation during both the day and night. We did not observe brooding females using locations where woody cover exceeded 27% of understory vegetation. Thermal refuge is an important component of brood habitat, but within thermally suitable areas brooding females can select sites with greater availability of large prey to meet energetic demands of broods. Evaluation of multiple spatial scales is key when assessing tradeoffs among resource needs and determining the potential of behavioral thermoregulation to buffer an organism's thermal environment and allow persistence in a warming climate.     

Gobbling across landscapes: Eastern wild turkey distribution and occupancy–habitat associations

Extensive restoration and translocation efforts beginning in the mid‐20th century helped to reestablish eastern wild turkeys (Meleagris gallopavo silvestris) throughout their ancestral range. The adaptability of wild turkeys resulted in further population expansion in regions that were considered unfavorable during initial reintroductions across the northern United States. Identification and understanding of species distributions and contemporary habitat associations are important for guiding effective conservation and management strategies across different ecological landscapes. To investigate differences in wild turkey distribution across two contrasting regions, heavily forested northern Wisconsin, USA, and predominately agricultural southeast Wisconsin, we conducted 3050 gobbling call‐count surveys from March to May of 2014–2018 and used multiseason correlated‐replicate occupancy models to evaluate occupancy–habitat associations and distributions of wild turkeys in each study region. Detection probabilities varied widely and were influenced by sampling period, time of day, and wind speed. Spatial autocorrelation between successive stations was prevalent along survey routes but was stronger in our northern study area. In heavily forested northern Wisconsin, turkeys were more likely to occupy areas characterized by moderate availability of open land cover. Conversely, large agricultural fields decreased the likelihood of turkey occupancy in southeast Wisconsin, but occupancy probability increased as upland hardwood forest cover became more aggregated on the landscape. Turkeys in northern Wisconsin were more likely to occupy landscapes with less snow cover and a higher percentage of row crops planted in corn. However, we were unable to find supporting evidence in either study area that the abandonment of turkeys from survey routes was associated with snow depth or with the percentage of agricultural cover. Spatially, model‐predicted estimates of patch‐specific occupancy indicated turkey distribution was nonuniform across northern and southeast Wisconsin. Our findings demonstrated that the environmental constraints of turkey occupancy varied across the latitudinal gradient of the state with open cover, snow, and row crops being influential in the north, and agricultural areas and hardwood forest cover important in the southeast. These forces contribute to nonstationarity in wild turkey–environment relationships. Key habitat–occupancy associations identified in our results can be used to prioritize and strategically target management efforts and resources in areas that are more likely to harbor sustainable turkey populations.     

Factors influencing rate of decline in a Merriam's wild turkey population

We investigated population growth rate (λ) for a Merriam's wild turkey (Meleagris gallopavo merriami) population in the northern Black Hills, South Dakota, USA. We constructed and evaluated a females-only matrix population model. Our estimate of asymptotic λ, derived from estimates of vital rates obtained from 2016–2018 was 0.74 (95% CI = 0.60, 0.88), which indicates that the vital rates were inadequate to sustain the population. Elasticity values were highest for changes in adult survival probability followed by, in order, changes in juvenile survival, yearling survival, and adult reproduction. We could only achieve stable or growing populations (i.e., λ ≥ 1) by increasing the probability of adult and yearling survival (holding all other vital rates constant). Estimated adult survival rate in the work reported here was lower than values reported for other populations in the Black Hills; therefore, managing for increased female survival (≥0.68) may be the most practical strategy for promoting wild turkey population growth in this system. We recommend no female harvest during any open turkey season.     

Winter and summer weather modulate the demography of wild turkeys at the northern edge of the species distribution

Temperate species occupying habitats at the northern limit of their geographical distribution are limited by weather and climatic conditions. Such conditions often directly affect population dynamics, and thus, influence shifts in distribution via changes in demographic parameters. We examined this question by following three distinct populations of wild turkeys inhabiting areas exposed to a gradient of meteorological conditions at the northern limit of the species distribution. Four years of radio-telemetry on 181 birds and monitoring of 95 nests revealed that population demographics of wild turkeys were influenced by snow depth, winter temperature and summer rainfall. During winter, survival of turkeys decreased drastically when snow depth remained >30 cm for >10 days and also decreased as temperatures got colder. In the spring, snow persistence delayed nest initiation, whereas nest survival was negatively affected by rainfall. Our findings show that the effects of critical meteorological factors such as snow and temperature can be compounded when both reach the limit of a species tolerance simultaneously.     

Nest site fidelity and dispersal of Rio Grande wild turkey hens in Texas

Rio Grande wild turkey (Meleagris gallopavo intermedia) nests suffer high predation rates exceeding 65%, which may limit recruitment. We evaluated post-nesting movements of reproductively active female Rio Grande wild turkeys. We monitored 194 nesting attempts between 2005 and 2010 and documented 17% and 32% overall apparent nest success for the Edwards Plateau and Central Rio Grande Plains study regions, respectively. Rio Grande wild turkey hens move approximately 1.2 km (SD = 0.7) between nesting attempts within a nesting season and approximately 1.4 km (SD = 1.6) between initial nesting attempts among years. Rio Grande wild turkey hens selected open areas with moderate woody cover for nesting ( = 37.7%; range = 3.0–88.2%). Patchiness of vegetation in the nesting landscape also was borne out by typically low edge-to-area ratios ( = 0.20; range = 0.040–0.732). We found no clear pattern in movement distance and either landscape composition or edge-to-area ratio for within or between breeding season nest site selection for either the Edwards Plateau or Central Rio Grande Plains study region. Based on our results, movement distances post-nest failure do not seem to influence habitat selection. © 2012 The Wildlife Society.     

Timing of vegetation sampling does not influence associations between visual obstruction and turkey nest survival in a montane forest

Evaluating relationships between ecological processes that occur concurrently is complicated by the potential for such processes to covary. Ground‐nesting birds rely on habitat characteristics that provide visual and olfactory concealment from predators; this protection often is provided by vegetation at the nest site. Recently, researchers have raised concern that measuring vegetation characteristics at nest fate (success or failure) introduces a bias, as vegetation at successful nests is measured later in the growing season (and has more time to grow) compared with failed nests. In some systems, this bias can lead to an erroneous conclusion that plant height is positively associated with nest survival. However, if the features that provide concealment are invariant during the incubation period, no bias should be expected, and the timing of measurement is less influential. We used data collected from 98 nests to evaluate whether there is evidence that such a bias exists in a study of wild turkey (Meleagris gallopavo) nesting in a montane forest ecosystem. We modeled nest survival as a function of visual obstruction and other covariates of interest. At unsuccessful nests, we collected visual obstruction readings at both the date of nest failure and the projected hatch date and compared survival estimates generated using both sets of vegetation data. In contrast to studies in grassland and shrubland systems, we found little evidence that the timing of vegetation sampling influenced conclusions regarding the association between visual obstruction and nest survival; model selection and estimates of nest survival were similar regardless of when vegetation data were collected. The dominant hiding cover at most of our nests was provided by evergreen shrubs; retention of leaves and slow growth of these plants likely prevent appreciable changes in visual obstruction during the incubation period. When considered in aggregate with a growing body of literature, our results suggest that the influence of timing of vegetation sampling depends on the study system. When designing future studies, investigators should carefully consider the type of structures that provide nest concealment and whether plant phenology is confounded with nest survival.     

Changes in breeding phenology of eastern Ontario frogs over four decades

Global climate change has been implicated in phenological shifts for a variety of taxa. Amphibian species in particular are sensitive to changes in their environment due to their biphasic life history and restricted reproductive requirements. Previous research has shown that not all temperate amphibian species respond similarly to the same suite of climatic or environmental cues, nor are individual species necessarily uniform in their responses across their range. We examined both the timing of spring emergence and calling phenology of eight anuran species in southeastern Ontario, Canada, using an approximately 40‐year dataset of historical records of amphibian activity. Rana pipiens was the only species out of eight considered to emerge significantly earlier, by an estimated 22 days over four decades. Both R. pipiens and Bufo americanus have advanced initiation of calling over a four‐decade span significantly earlier by an estimated 37.2 and 19.2 days, respectively. Rana sylvatica showed a trend toward earlier emergence by 19 days, whereas we did not detect changes in emergence phenology for the remaining five species. This significant shift in breeding behavior for two species correlates to significant regional increases in spring temperatures of an estimated 2.7–2.8°C overall over four decades. Our study suggests that local temperature increases have affected the timing of emergence and the onset of calling activity in some Ontario anuran species. Global decline or range shifts ultimately may be related to changes in reproductive behavior and timing mediated by shifting climate.     

Effects of environmental conditions on reproductive effort and nest success of Arctic‐breeding shorebirds

The Arctic is experiencing rapidly warming conditions, increasing predator abundance, and diminishing population cycles of keystone species such as lemmings. However, it is still not known how many Arctic animals will respond to a changing climate with altered trophic interactions. We studied clutch size, incubation duration and nest survival of 17 taxa of Arctic‐breeding shorebirds at 16 field sites over 7 years. We predicted that physiological benefits of higher temperatures and earlier snowmelt would increase reproductive effort and nest survival, and we expected increasing predator abundance and decreasing abundance of alternative prey (arvicoline rodents) to have a negative effect on reproduction. Although we observed wide ranges of conditions during our study, we found no effects of covariates on reproductive traits in 12 of 17 taxa. In the remaining taxa, most relationships agreed with our predictions. Earlier snowmelt increased the probability of laying a full clutch from 0.61 to 0.91 for Western Sandpipers, and shortened incubation by 1.42 days for arcticola Dunlin and 0.77 days for Red Phalaropes. Higher temperatures increased the probability of a full clutch from 0.60 to 0.93 for Western Sandpipers and from 0.76 to 0.97 for Red‐necked Phalaropes, and increased daily nest survival rates from 0.9634 to 0.9890 for Semipalmated Sandpipers and 0.9546 to 0.9880 for Western Sandpipers. Higher abundance of predators (foxes) reduced daily nest survival rates only in Western Sandpipers (0.9821–0.9031). In contrast to our predictions, the probability of a full clutch was lowest (0.83) for Semipalmated Sandpipers at moderate abundance of alternative prey, rather than low abundance (0.90). Our findings suggest that in the short‐term, climate warming may have neutral or positive effects on the nesting cycle of most Arctic‐breeding shorebirds.     

Seasonal weather patterns drive population vital rates and persistence in a stream fish

Climate change affects seasonal weather patterns, but little is known about the relative importance of seasonal weather patterns on animal population vital rates. Even when such information exists, data are typically only available from intensive fieldwork (e.g., mark–recapture studies) at a limited spatial extent. Here, we investigated effects of seasonal air temperature and precipitation (fall, winter, and spring) on survival and recruitment of brook trout (Salvelinus fontinalis) at a broad spatial scale using a novel stage‐structured population model. The data were a 15‐year record of brook trout abundance from 72 sites distributed across a 170‐km‐long mountain range in Shenandoah National Park, Virginia, USA. Population vital rates responded differently to weather and site‐specific conditions. Specifically, young‐of‐year survival was most strongly affected by spring temperature, adult survival by elevation and per‐capita recruitment by winter precipitation. Low fall precipitation and high winter precipitation, the latter of which is predicted to increase under climate change for the study region, had the strongest negative effects on trout populations. Simulations show that trout abundance could be greatly reduced under constant high winter precipitation, consistent with the expected effects of gravel‐scouring flows on eggs and newly hatched individuals. However, high‐elevation sites would be less vulnerable to local extinction because they supported higher adult survival. Furthermore, the majority of brook trout populations are projected to persist if high winter precipitation occurs only intermittently (≤3 of 5 years) due to density‐dependent recruitment. Variable drivers of vital rates should be commonly found in animal populations characterized by ontogenetic changes in habitat, and such stage‐structured effects may increase population persistence to changing climate by not affecting all life stages simultaneously. Yet, our results also demonstrate that weather patterns during seemingly less consequential seasons (e.g., winter precipitation) can have major impacts on animal population dynamics.     

Spring temperature, clutch initiation date and duck nest success: a test of the mismatch hypothesis

1. Increases in average global temperature during the twentieth century have prompted calls for research on the effect of temperature variation on avian population dynamics. Particular attention has been paid to the hypothesis that increased temperatures may affect a species' ability to shift their breeding efforts to match the phenology of their prey, and thus result in reduced reproductive success (the 'mismatch hypothesis'). 2. We used data from a long-term study of breeding ducks to investigate how duck nest success varied with clutch initiation date, and to test whether spring temperature affected this relationship in a manner consistent with the mismatch hypothesis. We modelled five possible functional forms of how nest success might vary with clutch initiation date and spring temperature, and used an information-theoretic approach to determine which model best described the nesting outcomes of five dabbling duck species nesting in Saskatchewan, Canada. 3. Probability of nest success for the five species did not vary strongly with clutch initiation date, and we found evidence consistent with the mismatch hypothesis for one species, northern pintail Anas acuta, although weight of evidence was weak. 4. Overall nest success of all five species was positively associated with spring temperature. These results suggest that increasing spring temperature alone (within the range observed in this study) may not affect nest success in a manner that would result in lower populations of breeding ducks.     

Geographic patterns and dynamics of Alaskan climate interpolated from a sparse station record

Data from a sparse network of climate stations in Alaska were interpolated to provide 1‐km resolution maps of mean monthly temperature and precipitation–‐variables that are required at high spatial resolution for input into regional models of ecological processes and resource management. The interpolation model is based on thin‐plate smoothing splines, which uses the spatial data along with a digital elevation model to incorporate local topography. The model provides maps that are consistent with regional climatology and with patterns recognized by experienced weather forecasters. The broad patterns of Alaskan climate are well represented and include latitudinal and altitudinal trends in temperature and precipitation and gradients in continentality. Variations within these broad patterns reflect both the weakening and reduction in frequency of low‐pressure centres in their eastward movement across southern Alaska during the summer, and the shift of the storm tracks into central and northern Alaska in late summer. Not surprisingly, apparent artifacts of the interpolated climate occur primarily in regions with few or no stations. The interpolation model did not accurately represent low‐level winter temperature inversions that occur within large valleys and basins. Along with well‐recognized climate patterns, the model captures local topographic effects that would not be depicted using standard interpolation techniques. This suggests that similar procedures could be used to generate high‐ resolution maps for other high‐latitude regions with a sparse density of data.     

Spatial extent of winter thaw events in eastern North America: historical weather records in relation to yellow birch decline

An algorithm (Weather Reader) was developed and used to analyze daily weather records from all existing Canadian and American weather stations of eastern North America (in excess of 2100 stations), from 1930 through 2000. Specifically, the Weather Reader was used to compile daily minimum, mean, and maximum air temperatures for weather stations with at least 30 years of data, and was used to calculate accumulated degree days for winter thaw–freeze events relevant to yellow birch (Betula alleghaniensis Britt.) from beginning to end. A thaw–freeze event relevant to yellow birch was considered to take place when (i) the station daily maximum temperature reached or exceeded +4°C after being below freezing for at least 2 months of the winter, (ii) sufficient growing degree days accumulated (>50 growing degree days) to cause the affected yellow birch trees to prematurely deharden, and (iii) the daily minimum temperature dropped below ?4°C causing roots and/or shoots of dehardened trees to experience freeze‐induced injury and possibly dieback. The threshold temperature of +4°C represents the daily temperature above which biological activity occurs in yellow birch. The station growing degree day summaries were subsequently spatially interpolated with the Kriging function in GS+^? and mapped in ArcView^? GIS in order to display the geographic extent of the most severe thaw–freeze events. The ArcView^? maps were then compared with the extent of historically observed yellow birch decline. It was found that the years 1936, 1944, and 1945 were particularly uncharacteristic in terms of region‐wide winter thaw–freeze extremes, and also in terms of observed birch decline events during 1930–1960. An overlay of suspected accumulated birch decline based on thaw–freeze mapping and observed decline maps prepared by Braathe (1995), Auclair (1987) , and Auclair et al. (1997) for 1930–1960 demonstrated similar geographic patterns. The thaw–freeze projection for 1930–1960 was shown to coincide with 83% of the birch decline map appearing in Braathe (1995) and 55% of the geographic range of yellow birch in eastern North America. Thaw–freeze mapping was also applied to two significant events in 1981. Greatest impact was recorded to occur mostly in southern Quebec and Ontario, and several American Great Lake States, specifically in northern Michigan and New York, where the greatest growing degree day accumulation prior to refreeze in late February (February 28th) was projected to have occurred; and in southern Quebec, most of Atlantic Canada, and Maine, prior to a late spring frost in mid‐April (April 17).     

温度和降水对森林生物量分配的影响研究进展

森林生物量分配策略是全球变化背景下群落保持生产力的重要机制.温度和降水会影响森林生物量的分配格局.文章基于文献分析,总结了增温、低温和降水对森林地上、地下生物量分配的影响机制,以及温度和降水对森林生物量分配的交互作用,并对未来温度和降水影响森林生物量分配的研究进行了展望,提出该领域今后的研究重点为:(1)加强生物量分配...