Theron M. Terhune

Habitat influences Northern Bobwhite survival at fine spatiotemporal scales

ABSTRACT Habitat quality influences individual survival at widely varying spatial and temporal scales. Understanding interactions between habitat and survival among individuals in declining populations that occupy highly modified landscapes can inform conservation strategies aimed at improving survival and population growth. We used radiotelemetry to monitor space use and daily survival of wintering Northern Bobwhites (Colinus virginianus) at the northern end of their range to test for fine spatial- and temporal-scale relationships between individual survival and habitat composition around radio-locations in agricultural landscapes in Ohio, USA. Habitat composition within daily and seasonal movement ranges of individuals (n = 189) during periods without snow cover did not explain variation in daily survival rates. However, mortality increased substantially in the presence of snow cover, and availability of woody cover and row crops within 95 m of an individual radio-location were positively associated with daily survival during those periods. A similar relationship between row crop availability and survival was supported at a larger scale that reflected composition of seasonal ranges (300-m buffer) but was less influential than fine-scale influences of woody cover and row crops. Our results suggest that previously documented selection for woody cover in our agricultural study areas was an adaptive behavior to improve individual survival during periods of snow cover. Positive associations between survival and row crop cover at daily and seasonal range scales suggest that agricultural landscapes confer improved survival probabilities when underlying constraints on occupancy related to woody cover are met. Collectively, our results suggest that targeted conservation practices focused on provision of suitable woody cover in agricultural landscapes in the northern end of the Northern Bobwhites range has potential to improve winter survival and perhaps abate long-term population declines in the region.

Effects of fire management on northern bobwhite brood ecology

Northern Bobwhite Colinus virginianus chicks require ample invertebrates for growth and feather development. Early successional or resprouting vegetation provides invertebrates for chicks but may not provide other resources such as roosting and loafing cover that is typically provided by later successional stages. Thus, management for bobwhites provides multiple seral stages in close proximity but the effects of landscape interspersion have not been tested for bobwhite broods. During a 2-year study, we explored the effects of landscape complementation and food availability on growth and survival of bobwhite chicks. We found growth of chicks to be negatively related to home range size which was negatively correlated to the amount of area burned. We also found survival of chicks to be positively related to the amount of burned area (i.e., foraging area) within brood home ranges. To maximize the growth and survival of bobwhite chicks, it would be necessary to increase access to foraging areas while decreasing the size of brood home ranges. Access to foraging areas can be created through frequent prescribed fire at small spatial scales.

Factors affecting seasonal movements of juvenile Greater Sage-Grouse: A reconceptualized nest survival model

ABSTRACT Estimating the climatic and habitat factors that affect animal movement patterns (e.g., migration, dispersal, site fidelity) is informative for management and conservation. Juvenile Greater Sage-Grouse (Centrocercus urophasianus) have been identified as having a significant influence on population growth, but relatively little is known about factors that influence survival, movement, and the potential interrelation between the two. Movement out of fall habitat has been suggested to influence the survival of juvenile Greater Sage-Grouse. We reconceptualized the nest survival model (equating movement out of a focal area with failure of a nest) to extend its use to movement data on juveniles in south-central Utah. We found that juveniles seasonal movements were affected by a linear trend in time (β = −0.655, 95% confidence interval [CI]: −1.049 to −0.26) and by precipitation (β = −3.718, 95% CI: −6.687 to −0.749), with an interaction between the parameters (β = 0.360, 95% CI: 0.002–0.718). In the absence of precipitation, the probability of movement increased weekly through time (within a year). Weekly precipitation increased the probability of movement in earlier weeks, but the effect of precipitation attenuated in later weeks (i.e. interaction parameter). The precipitation was likely non-accumulating snowfall, given the observed below-freezing temperatures. Our results suggest that changes in precipitation (mainly snowfall) that result from climate change could influence the timing and duration of seasonal movements (i.e. population-level time to complete movement) in migratory populations of Greater Sage-Grouse. Furthermore, our results demonstrate the utility of the nest survival model for evaluating the factors that affect animal movements with “ragged” data.

Partial meso-mammal predator removal positively affects northern bobwhite reproduction

Perceived changes in predator—prey dynamics along with documented declines of northern bobwhite Colinus virginianus have created a renewed interest from biologists and managers about the role meso-mammals play in shaping bobwhite population trajectories. Therefore, we evaluated the efficacy of meso-mammal trap and removal (MMTR) at reducing meso-mammal activity and increasing bobwhite reproductive success; thus testing the predation limitation hypothesis. During 1999–2006, we monitored bobwhite reproduction on 11 sites in three states across the southeastern United States. Combined, there were 37 site—year combinations when MMTR occurred and 20 combinations when it did not occur. We conducted 57 predator surveys and calculated an index of meso-mammal activity (i.e. predator index), for each site, as the average number of station visits per night by raccoons Procyon lotor, nine-banded armadillos Dasypus novemcinctus, Virginia opossums Didelphis virginiana, bobcats Lynx rufus and foxes Vulpes vulpes, Urocyon cinereoargenteus. The average predator index (predator visits per trap night) across sites was 0.13. We collected bobwhite reproductive information from a total of 3935 radio-tagged bobwhites resulting in 2499 nests. We used generalized linear mixed models to evaluate the relationships between MMTR, predator activity, and bobwhite reproduction. The mean predator index for non-trapped sites was 0.21 (95% CLs: 0.18, 0.24) compared to 0.10 (95% CL: 0.07, 0.13) for trapped sites. Bobwhite nests were 1.33 times (Odds ratio, 95% CL: 1.09, 1.62) more likely to be successful on trapped sites than non-trapped sites. Meso-mammal trap and removal had a positive effect on nests per hen (βtrapped= 0.25 ± 0.06; 95% CL: 0.13, 0.37), broods per hen (βtrapped = 0.37 ± 0.08; 95% CL: 0.21, 0.53), and chicks per hen (βtrapped = 1.09 ± 0.52; 95% CL: 0.07, 2.11). Our results show that MMTR reduces meso-mammal activity and positively affects bobwhite reproduction.