Giancarlo Sadoti

HABITAT USE AND NEST SITE SELECTION BY NESTING LESSER PRAIRIE-CHICKENS IN SOUTHEASTERN NEW MEXICO

Abstract Lesser prairie-chickens (Tympanuchus pallidicinctus) occur in shinnery oak (Quercus havardii) and sand sagebrush (Artemisia filifolia) grassland habitats in New Mexico, Texas, Oklahoma, Kansas, and Colorado. Range-wide population reductions since the 1800s have been attributed to habitat loss, especially of nesting habitat. Using radio-telemetry and a vegetation map of the study area, we investigated habitat use by lesser prairie-chicken hens during the nesting season in herbicide-treated and untreated pastures (each about 1,000 ha in size). Herbicide treatment was effective in reducing shinnery oak cover. The most common vegetation types in hen home ranges were those dominated by shinnery oak. Hens were detected more often than randomly in or near untreated pastures. Although hens were detected in both treated and untreated habitats, 13 of 14 nests were located in untreated pastures, and all nests were located in areas dominated by shinnery oak. Areas immediately surrounding nests had higher shrub composition than the surrounding pastures. This study suggests that herbicide treatment to control shinnery oak might adversely impact nesting lesser prairie-chickens.

Nonideal habitat selection by a North American cavity excavator: pecking up the wrong tree?

Nonideal habitat selection occurs when preferred habitat attributes differ from those associated with increased fitness. These mismatches have been widely studied in open cup-nesting birds, but the relationship between habitat-associated preferences and fitness in cavity-nesting birds has received relatively little attention. We studied patterns of preference and fitness during 2006–2007 in an Idaho, USA, population of Red-naped Sapsuckers (Sphyrapicus nuchalis S.F. Baird, 1858). Using a suite of nonparametric tests, we examined the associations between habitat attributes and both nesting-area preferences and nest productivity (number of fledglings per pair) across four spatial scales. Nest productivity was associated with tree- and cavity-scale attributes, whereas preference was associated with attributes of home ranges. Live trees and southeasterly oriented cavities had higher nest productivity but were not preferred. Microclimates in nests with these attributes may enhance nestling survival, whereas no...

Variogram models reveal habitat gradients predicting patterns of territory occupancy and nest survival among vesper sparrows

Characterizing landscapes as gradients may help illuminate animal—habitat relationships that are either 1) masked by or 2) impractical to investigate using a purely patch-based perspective. Among other methods, variogram models may reveal these gradients in the environment by quantifying spatial dependence among point samples, yet few analyses of animal habitat relationships employing variograms have been undertaken. Using vegetation volume measurements from 4-m2 plots within breeding vesper sparrow Pooecetes gramineus territories, we calculated four territory-scale gradients: 1) mean volume, 2) standard deviation of volume, 3) nugget (a measure of fine-scale variation), and 4) range (an index of patch size). The first two gradients are more commonly employed in animal ecology while the second two were derived using variogram models and are infrequently employed. We next used these gradients in generalized linear models predicting territory occupancy and daily nest survival. We found overwhelming support for employing the range parameter and models indicated 1) birds selected areas with lower average vegetation volume and smaller patch sizes and 2) had lower rates of nest predation in areas with larger patch sizes. While these results indicate a pattern of non-ideal habitat selection, there was no indication that territories which experienced nest predation were selected disproportionately. Our results underscore the utility of 1) variograms among other methods for quantifying gradients in animal habitat and 2) variogram model parameters in investigating the habitat ecology of animals.

Discriminating patterns and drivers of multiscale movement in herpetofauna: The dynamic and changing environment of the Mojave desert tortoise

Abstract Changes to animal movement in response to human‐induced changes to the environment are of growing concern in conservation. Most research on this problem has focused on terrestrial endotherms, but changes to herpetofaunal movement are also of concern given their limited dispersal abilities and specialized thermophysiological requirements. Animals in the desert region of the southwestern United States are faced with environmental alterations driven by development (e.g., solar energy facilities) and climate change. Here, we study the movement ecology of a desert species of conservation concern, the Mojave desert tortoise (Gopherus agassizii). We collected weekly encounter locations of marked desert tortoises during the active (nonhibernation) seasons in 2013–2015, and used those data to discriminate movements among activity centers from those within them. We then modeled the probability of movement among activity centers using a suite of covariates describing characteristics of tortoises, natural and anthropogenic landscape features, vegetation, and weather. Multimodel inference indicated greatest support for a model that included individual tortoise characteristics, landscape features, and weather. After controlling for season, date, age, and sex, we found that desert tortoises were more likely to move among activity centers when they were further from minor roads and in the vicinity of barrier fencing; we also found that movement between activity centers was more common during periods of greater rainfall and during periods where cooler temperatures coincided with lower rainfall. Our findings indicate that landscape alterations and climate change both have the potential to impact movements by desert tortoises during the active season. This study provides an important baseline against which we can detect future changes in tortoise movement behavior.

Spatial Dependence in Northern Flicker Habitat—Reproduction Relationships: An Application of Dutilleul's Modified t-Test

Abstract. While there is growing awareness in ecology of spatial dependency, the application in avian ecology of spatially explicit statistical methods is rare in areas such as habitat—reproduction relationships. We compared nonspatial vs. spatially explicit tests of correlation between a measure of reproduction and a habitat attribute associated with Northern Flicker (Colaptes auratus) nests. While nonspatial tests showed a significant positive correlation between nest productivity and canopy cover of conifers, Dutilleuls modified t-test, which reduces the effective sample size by accounting for dependence among sampled nest trees, showed no significant correlation. These results may be due to spatial autocorrelation of both canopy cover of conifers and nest productivity at the scale of <1 km. Low localized nest productivity appears to have been driven by nest predation rather than by conifer cover. Our results illustrate the utility of this simple modification for examining ecological correlations in the presence of spatial structure. We encourage further use of this and other spatially explicit statistical tests in avian ecology. Failing to do so risks potentially spurious and overstated conclusions, as we demonstrate here.