Geology topics

Ben R. Skipper

Publications and source records attributed to Ben R. Skipper.

6 recordsLinked to original sources

USGS2025

Daily survival rate and nest-site selection of Zone-tailed Hawks (Buteo albonotatus) in the Chihuahuan Desert ecoregion of Texas

The Zone-tailed Hawk ( Buteo albonotatus ) is one of the least studied raptors in North America and lacks contemporary literature allowing informed management decisions for this species. Zone-tailed Hawks occupy rugged areas in the southwestern region of the United States and are listed as state threatened in Texas. Our objectives were to assess habitat, productivity, and daily survival rate (DSR) of Zone-tailed Hawk nests in riparian zones of the Chihuahuan Desert Ecoregion of Texas. We surveyed for Zone-tailed Hawk nests along ∼30 km of 12 riparian corridors in Brewster, Jeff Davis, and Presidio Counties, Texas. We monitored 11 and 15 Zone-tailed Hawk nests in 2018 and 2019, respectively, and conducted vegetation surveys at the nest tree, nest site (11.3-m radius), and paired random locations. We used nest survival modeling to evaluate the effects of eight habitat variables (nest tree diameter at breast height [DBH], nest tree height, nest height, nest distance to main stem, nest to tree height ratio, mean stand height, number of trees within nest site, and mean nest site DBH) on nest DSR. DSR was positively correlated with nest to tree height ratio and nest tree DBH. Zone-tailed Hawk nests had an estimated 0.991 (standard error [SE] = 0.004, 95% CI = 0.980–0.996) constant DSR and ultimately a 51.4% chance of nest success (SE = 0.0943) across the nesting season. Our results suggest that by selecting larger trees for nesting as well as placing nests higher within the tree, Zone-tailed Hawks may increase their chances of successfully fledging young.

Texas↗

USGS2022

Mississippi Kite nest defense: Is there an influence of nest phenology or human activity?

Birds that have adapted to urban landscapes often display changes in their behavioral responses to human disturbance. This habituation may result in a decreased wariness and secrecy near their nest and an increased inclination to engage in aggressive nest defenses. Aggressive defense of nests has been noted among Mississippi Kites ( Ictinia mississippiensis ), a raptor that has become a common and abundant urban nesting species across the Southern Great Plains. Defensive behaviors include swoops at, and occasional physical contact with, humans who venture close to nests. Previous research found aggressive responses by kites in 16–20% of experimental passes under nests. However, the type of human pedestrian activity around nests may influence the occurrence of aggressive responses. We assessed adult Mississippi Kite responses to experimental nest area intrusions during each week of the first four weeks of nestling development to explore increases or attenuation of aggressive behaviors. We also assessed responses in context of three types of pedestrian passes to nests. We conducted 84 trials consisting of 252 passes and found 90% elicited no response from the attending kite, 8% elicited a flight response, and 2% elicited an attack. There was no difference in response to pass type, but we found evidence that responsiveness may be associated with nestling age. Our results suggest aggression by Mississippi Kites is uncommon, but infrequent events that gain local attention may increase the perceived risk from the species due to the availability heuristic. Additionally, individual nesting pairs may tend toward aggression and become persistent nuisance birds that gain attention but are not representative of the majority of nesting pairs.

Journal of Raptor Research↗

USGS2017

Assessment of frequency and duration of point counts when surveying for golden eagle presence

We assessed the utility of the recommended golden eagle ( Aquila chrysaetos ) survey methodology in the U.S. Fish and Wildlife Service 2013 Eagle Conservation Plan Guidance. We conducted 800-m radius, 1-hr point-count surveys broken into 20-min segments, during 2 sampling periods in 3 areas within the Intermountain West of the United States over 2 consecutive breeding seasons during 2012 and 2013. Our goal was to measure the influence of different survey time intervals and sampling periods on detectability and use estimates of golden eagles among different locations. Our results suggest that a less intensive effort (i.e., survey duration shorter than 1 hr and point-count survey radii smaller than 800 m) would likely be inadequate for rigorous documentation of golden eagle occurrence pre- or postconstruction of wind energy facilities. Results from a simulation analysis of detection probabilities and survey effort suggest that greater temporal and spatial effort could make point-count surveys more applicable for evaluating golden eagle occurrence in survey areas; however, increased effort would increase financial costs associated with additional person-hours and logistics (e.g., fuel, lodging). Future surveys can benefit from a pilot study and careful consideration of prior information about counts or densities of golden eagles in the survey area before developing a survey design. If information is lacking, survey planning may be best served by assuming low detection rates and increasing the temporal and spatial effort.

Idaho, New Mexico, Wyoming↗

USGS2017

Environmental influences on the nesting phenology and productivity of Mississippi Kites (Ictinia mississippiensis)

Identifying sources of annual variation in the reproductive success of a species may provide valuable insights into how the species may be affected by future environmental or climatic conditions. We examined annual variation in the nesting phenology, productivity, and apparent nest success of Mississippi Kites (Ictinia mississippiensis), a species common in urban areas in the southern Great Plains, from May through August. We monitored 498 Mississippi Kite nesting attempts in Lubbock, Texas, USA, between 2004 and 2015, from which we modeled daily survival rate as a function of local weather conditions, drought severity, and the state of the El Niño Southern Oscillation. We observed significant annual variation in median incubation initiation date (range = May 20 to June 5), the probability of nest success (range = 0.31–0.90), and productivity (range = 0.25–1.00 fledglings per nest). Our models of daily survival rate suggested that higher daily temperatures, severe storm events, extreme drought conditions, and La Niña events negatively influenced nest survival. These results suggest that increasing storm frequency and higher temperatures associated with climate change are likely to decrease the nesting success of Mississippi Kites in the southern Great Plains.

Texas↗

USGS2013

Diurnal activity patterns of Black-Necked Stilts (Himantopus mexicanus) during the non-breeding season in the eastern Caribbean

Diurnal activity patterns of resident Black-necked Stilts ( Himantopus mexicanus ) were observed on Guana Island, British Virgin Islands, during October 2010. Stilts were principally engaged in foraging and idle behaviors. The amount of time engaged in particular behaviors was relatively constant throughout the day, except during mid-afternoon when idleness increased and foraging decreased, with a subsequent increase in foraging in the evening. We speculate that the increase in foraging activity was a result of changing prey activity.

Journal of Caribbean Ornithology↗

USGS2013

Non-overlapping distributions of feral sheep (Ovis aries) and Stout Iguanas (Cyclura pinguis) on Guana Island, British Virgin Islands

Stout Iguanas (Cyclura pinguis) remain one of the most critically endangered reptiles in the world. Factors contributing to that status include habitat loss, predation by introduced species, and competition with introduced herbivores. On Guana Island, British Virgin Islands, the presence of feral sheep (Ovis aries) has been a hypothesized detriment to iguanas. Using motion sensitive cameras, we documented the distribution of feral sheep on Guana Island in 2010. We also quantified the impact of feral sheep on ground vegetation by comparing plant abundance at longterm sheep exclosures and areas where sheep were absent to areas where sheep were present. Finally, we compared sheep distribution to iguana distribution on the island. The co-occurrence of sheep and Stout Iguanas was less than expected, indicating possible competition. Although we detected no difference in vegetative cover between areas where sheep were present and absent, the long-term exclosures showed that the exclusion of sheep allowed the abundance of many plant species to increase. Our data support the hypothesis that feral sheep are altering the abundance of ground-level vegetation and limiting iguana distribution on the island.

Guana Island↗