Novel management tools for subsidized avian predators and a case study in the conservation of a threatened species

Shields, Timothy A.; Currylow, Andrea; Hanley, Brenda J.; Boland, Stephen; Boarman, William I.; Vaughn, Mercy

doi:10.1002/ecs2.2895

Cited by 11 publications

(11 citation statements)

References 28 publications

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“…The posterior estimates of the TFD and AWT models presented herein are directly incorporable for designing and implementing new occupancy surveys within cliff habitat of the Appalachian region and eastern United States. The effectiveness of the time‐to‐detection method for estimating detectability and abundance makes this framework conducive to raven monitoring not only for targeted species conservation but also for management and control in ecosystems where ravens depredate species of concern, such as the threatened desert tortoise ( Gopherus agassizii , Cooper) in the Mojave Desert, USA (Kristan & Boarman, 2003; Shields et al, 2019); spur‐thighed tortoise ( Testudo graeca L.) in Morocco (Segura et al, 2020); and greater sage‐grouse ( Centrocercus urophasianus , Bonaparte) in the western United States (O'Neil et al, 2018). To utilize the time‐to‐detection framework for survey planning in other geographic areas, studies similar to ours that evaluate detection patterns should be repeated to derive accurate location‐specific detectability curves and recommendations of required survey effort.…”

Section: Discussionmentioning

confidence: 99%

Detectability of common ravens (Corvus corax) in the eastern USA: Rapid assessment of a recolonizing species

et al. 2022

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Common ravens (Corvus corax) inhabited much of the eastern United States prior to European colonization but were nearly extirpated by the mid‐1900s. Although remnant raven populations have since begun recolonizing portions of their historic range in the eastern United States, the extent of recovery remains largely unknown because of the species' elusive behavior. To aid development of targeted monitoring programs for this rare and cryptic species, we investigated factors that may influence detectability of ravens in natural cliff habitat during the nesting season in the Central Appalachian Mountains. Using a time‐to‐detection framework, we performed surveys at cliff sites with positive raven occupancy and recorded time to first detection (TFD) and confirmed cliff occupancy (i.e., occupied detection) to estimate detection probability curves as a function of survey time. We further compared multiscale habitat features of occupied and unoccupied cliff sites to characterize regional nesting habitat. Mean TFD at occupied cliffs was 14 ± 2 (SE) min. The TFD and subsequent detection probability increased with warming temperatures, likely as a result of heightened activity at nests as the reproductive season progressed. Shorter distances from observation point to the surveyed cliff resulted in longer TFD, indicating that ravens are likely sensitive to disturbance at nest sites. Analysis of cliff‐nesting habitat data identified raven selection of cliffs with large, exposed faces positioned on predominant west‐facing aspects. Mean detection probability calculated from detectability curves was ≥0.8 after the first 30 min. Using a probability‐based model and empirical detection probabilities, we estimated that raven absence from a cliff site during the nesting season may be inferred with p = 0.99 after three independent 30‐min surveys. Although ravens have been considered elusive and rare in the eastern United States, we find that their detectability at occupied cliff sites during the nesting season is relatively high and that observation of distributional changes may be easier for this species than for other, more cryptic birds.

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Section: Discussionmentioning

confidence: 99%

Detectability of common ravens (Corvus corax) in the eastern USA: Rapid assessment of a recolonizing species

et al. 2022

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“…Based on the artificial nest predation experiments, corvids are often perceived as efficient nest predators that directly impact the populations of other bird species [ 153 , 154 ]. Despite this perception, relatively few experimental removal or population control studies have been performed in corvids [ 151 , 155 , 156 , 157 ]. Most of these studies found that the overall impact of corvid species on nest predation rate of other species is rather small, and that the populations of other bird species are less likely to be limited by corvid predation than suspected before.…”

Section: Discussionmentioning

confidence: 99%

“…The wide range of these birds and their high flexibility makes them targets to persecution by shooting [ 26 , 125 , 162 , 163 , 164 ]. Other examples of management include the destruction of Chihuahuan ( Corvus cryptoleucus ) and Common Ravens nests on electric poles [ 156 , 169 , 170 ], scaring away winter roosts of American Crows in U.S. cities [ 124 , 165 ] and trapping and removal of Hooded Crow and Carrion Crow individuals in cities in Europe [ 166 , 167 , 170 ]. However, the current population status of these species indicates that the success of these management efforts so far is limited.…”

Section: Discussionmentioning

confidence: 99%

“…With numerous studies carried out in Europe and North America since the beginning of the previous century, we found only nine and two studies on the colonization/invasion of a non-native corvid (House Crow) in sub-Saharan Africa and Latin America, respectively. In addition, some species have been the object of numerous management studies, especially the House Crow [ 10 , 125 , 162 , 164 , 171 ], the American Crow [ 124 , 165 , 172 ], the Eurasian Magpie [ 138 , 173 , 174 ] and, to a smaller extent, the Common Raven [ 76 , 156 ], the Hooded Crow [ 100 , 168 , 175 ] and the Rook [ 168 ]. Studies of management have reported on the use of different methods ranging from direct shooting [ 171 ], trapping [ 14 , 100 , 175 ], egg removal [ 164 ], poisoning [ 164 ], pruning roost trees [ 125 ], acoustic scaring of birds [ 124 , 176 ], dispersing roosts with lasers [ 165 ] and refuse management in cities [ 177 ].…”

Section: Discussionmentioning

confidence: 99%

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Corvids in Urban Environments: A Systematic Global Literature Review

Benmazouz

Jokimäki

Lengyel

et al. 2021

Animals

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Urbanization is one of the most prevalent drivers of biodiversity loss, yet few taxonomic groups are remarkably successful at adapting to urban environments. We systematically surveyed the global literature on the effects of urbanization on species of family Corvidae (crows, choughs, jackdaws, jays, magpies, nutcrackers, ravens, rooks, treepies) to assess the occurrence of corvids in urban environments and the factors affecting their success. We found a total of 424 primary research articles, and the number of articles has increased exponentially since the 1970s. Most studies were carried out in cities of Europe and North America (45.5% and 31.4%, respectively) and were directed on a single species (75.2). We found that 30 corvid species (23% of 133 total) regularly occur in urban environments. The majority (72%) of the studies reported positive effects of urbanization on corvids, with 85% of studies detecting population increases and 64% of studies detecting higher breeding success with urbanization. Of the factors proposed to explain corvids’ success (availability of nesting sites and food sources, low predation and persecution), food availability coupled with diet shifts emerged as the most important factors promoting Corvidae to live in urban settings. The breeding of corvids in urban environments was further associated with earlier nesting, similar or larger clutches, lower hatching but higher fledging success, reduced home range size and limited territoriality, increased tolerance towards humans and increasing frequency of conflicts with humans. Despite geographic and taxonomic biases in our literature sample, our review indicates that corvids show both flexibility in resource use and behavioral plasticity that enable them to exploit novel resources for nesting and feeding. Corvids can thus be urban exploiters of the large-scale modifications of ecosystems caused by urbanization.

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“…Few ravens were killed or removed in the western Mojave Desert or Natural Area during our study, however (USFWS, Desert Tortoise Recovery Office, Reno, Nevada, unpublished reports). The latest effort of oiling eggs in raven nests using drones was confined to natural surfaces (cliffs, Joshua trees; Shields et al 2019). Excluded were utility towers or humanconstructed facilities where nests are common Kawashima 1993, Knight et al 1999).…”

Section: Management Implicationsmentioning

confidence: 99%

The Catastrophic Decline of Tortoises at a Fenced Natural Area

Berry

Yee

Shields³

et al. 2020

Wildlife Monographs

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Agassiz's desert tortoise (Gopherus agassizii), a threatened species of the southwestern United States, has severely declined to the point where 76% of populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery of wild populations is low because females require 12-20 years to reach reproductive maturity and produce few eggs annually. We report on a 34-year mark-recapture study of tortoises initiated in 1979 at the Desert Tortoise Research Natural Area in the western Mojave Desert, California, USA, and provide substantive data on challenges faced by the species. In 1980, the United States Congress designated the Research Natural Area and protected the land from recreational vehicles, livestock grazing, and mining with a wildlife-permeable fence. The 7.77-km 2 study area, centered on interpretive facilities, included land both within the Natural Area and outside the fence. We expected greater benefits to accrue to the tortoises and habitat inside compared to outside. Our objectives were to conduct a demographic study, analyze and model changes in the tortoise population and habitat, and compare the effectiveness of fencing to protect populations and habitat inside the fence versus outside, where populations and habitat were unprotected. We conducted surveys in spring in each of 7 survey years from 1979, when the fence was under construction, through 2012. We compared populations inside to those outside the fence by survey year for changes in distribution, structure by size and relative age, sex ratios, death rates of adults, and causes of death for all sizes of tortoises. We used a Bayesian implementation of a Jolly Seber model for mark-recapture data. We modeled detection, density, growth and transition of tortoises to larger size-age classes, movements from inside the protective fence to outside and vice versa, and survival. After the second and subsequent survey years, we added surveys to monitor vegetation and habitat changes, conduct health assessments, and collect data on counts of predators and predator sign. At the beginning of the study, counts and densities for all sizes of tortoises were high, but densities were approximately 24% higher inside the fence than outside. By 2002, the low point in densities, densities had declined 90% inside the fence and 95% outside. Between 2002 and 2012, the population inside the fence showed signs of improving with a 54% increase in density. Outside the fence, densities remained low. At the end of the study, when we considered the initial differences in location, densities inside the fence were roughly 2.5 times higher than outside. The pattern of densities was similar for male and female adults. When evaluating survival by blocks of years, survivorship was higher in 1979-1989 than in 1989-2002 (the low point) and highest from 2002 to 2012. Recruitment and survival of adult females into the population was important for growing the population, but survival of all sizes, including juveniles, was also critical.Major ...

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Novel management tools for subsidized avian predators and a case study in the conservation of a threatened species

Cited by 11 publications

References 28 publications

Detectability of common ravens (Corvus corax) in the eastern USA: Rapid assessment of a recolonizing species

Detectability of common ravens (Corvus corax) in the eastern USA: Rapid assessment of a recolonizing species

Corvids in Urban Environments: A Systematic Global Literature Review

The Catastrophic Decline of Tortoises at a Fenced Natural Area

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