SEARCH · Geology Reports

Results for “Predator”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64Linked to original sources

USGS2025

Mercury speciation and stable isotopes in emperor penguins: First evidence for biochemical demethylation of methylmercury to mercury-dithiolate and mercury-tetraselenolate complexes

Apex marine predators, such as toothed whales and large petrels and albatrosses, ingest mercury (Hg) primarily in the form of methylmercury (MeHg) via prey consumption, which they detoxify as tiemannite (HgSe). One of the most intriguing current questions in Hg research is how more abundant lower trophic level predators detoxify MeHg, particularly in marine environments where tissue Hg burdens can be elevated. To address this need, we used high energy-resolution X-ray absorption near edge structure spectroscopy paired with nitrogen (N) and Hg stable isotopes to identify the chemical forms of Hg, Hg source, and species-specific δ 202 Hg isotopic values in emperor penguin, a mesopredator feeding primarily on Antarctic silverfish. The penguin liver contains variable proportions of MeHg and two inorganic Hg species (IHg), Hg-dithiolate (Hg(SR) 2 ) and Hg-tetraselenolate (Hg(Sec) 4 ) complexes, each characterized by a specific isotopic value (δ 202 MeHg = 0.3 ± 0.2‰, δ 202 Hg(SR) 2 = −1.6 ± 0.2‰, δ 202 Hg(Sec) 4 = −2.0 ± 0.1‰). Using δ 15 N as tracer of food source, we show that Hg(SR) 2 is not dietary but a biochemical demethylation product of MeHg metabolism. Penguin females transfer Hg to the egg as MeHg in the egg albumen, 89% MeHg and 11% IHg in the membrane, and 32% MeHg and 68% Hg(Sec) 4 in the yolk, on average (n = 15). Despite IHg species in eggs, MeHg is the main species quantitatively transferred by the mother to the chick because of the disproportionate mass of the MeHg-rich albumen compared to the yolk (n = 18). Further research is needed to elucidate the MeHg to Hg(SR) 2 demethylation pathway firmly documented here for the first time in multicellular organisms, and to understand why the thiolate ligands are not exchanged for Se ligands to form Hg(Sec) 4 , as the liver does not suffer from Se deficiency.

Adelie Land↗

USGS2012

Keanakākoʻi Tephra produced by 300 years of explosive eruptions following collapse of Kīlauea's caldera in about 1500 CE

The Keanakākoʻi Tephra at Kīlauea Volcano has previously been interpreted by some as the product of a caldera-forming eruption in 1790 CE. Our study, however, finds stratigraphic and 14 C evidence that the tephra instead results from numerous eruptions throughout a 300-year period between about 1500 and 1800. The stratigraphic evidence includes: (1) as many as six pure lithic ash beds interleaved in sand dunes made of earlier Keanakākoʻi vitric ash, (2) three lava flows from Kīlauea and Mauna Loa interbedded with the tephra, (3) buried syneruptive cultural structures, (4) numerous intraformational water-cut gullies, and (5) abundant organic layers rich in charcoal within the tephra section. Interpretation of 97 new accelerator mass spectrometry (AMS) 14 C ages and 4 previous conventional ages suggests that explosive eruptions began in 1470–1510 CE, and that explosive activity continued episodically until the early 1800s, probably with two periods of quiescence lasting several decades. Kīlauea's caldera, rather than forming in 1790, predates the first eruption of the Keanakākoʻi and collapsed in 1470–1510, immediately following, and perhaps causing, the end of the 60-year-long, 4–6 km 3 ʻAilāʻau eruption from the east side of Kīlauea's summit area. The caldera was several hundred meters deep when the Keanakākoʻi began erupting, consistent with oral tradition, and probably had a volume of 4–6 km3. The caldera formed by collapse, but no eruption of lava coincided with its formation. A large volume of magma may have quickly drained from the summit reservoir and intruded into the east rift zone, perhaps in response to a major south-flank slip event, leading to summit collapse. Alternatively, magma may have slowly drained from the reservoir during the prolonged ʻAilāʻau eruption, causing episodic collapses before the final, largest downdrop took place. Two prolonged periods of episodic explosive eruptions are known at Kīlauea, the Keanakākoʻi and the Uwēkahuna Tephra (Fiske et al., 2009), and both occurred when a deep caldera existed, probably with a floor at or below the water table, and external water could readily interact with the magmatic system. The next period of intense explosive activity will probably have to await the drastic deepening of the present caldera (or Halemaʻumaʻu Crater) or the formation of a new caldera.

Hawai'i↗

USGS2022

Sclerochronological records of environmental variability and bivalve growth in the Pacific Arctic

The Pacific Arctic region has experienced, and is projected to continue experiencing, rapid climate change. Large uncertainties exist in our understanding of the impact these physical changes have on the region’s ecology. This is, in part, due to the lack of long-term data. Here we investigate bivalve mollusc growth increment width chronologies (sclerochronologies) to develop a long-term biological data series in an Arctic species and address the hypothesis that benthic production in the Pacific Arctic region is in decline with implications for predators (e.g., walrus, whales, seals, and sea ducks). Growth increments formed in the shells of two bivalve mollusc species, Astarte borealis and Liocyma fluctuosa, were examined using conventional sclerochronological techniques. The A. borealis and L. fluctuosa samples exhibited measured longevities of >148 and >18 years, respectively, in the coastal waters of Alaska’s Chukchi Sea. Dendrochronology crossdating techniques facilitated the development of two robust (expressed population signal >0.85) independent growth increment width chronologies. These chronologies provide evidence of the growth conditions through time for each species (1985-2015 for A. borealis and 1997-2014 for L. fluctuosa) . Linear regression analyses identified that both species grew more rapidly in years with warmer sea surface temperature and lower sea ice concentration. The results provide evidence that benthic ecosystems are benefiting from the warmer conditions and reduced sea ice that have accompanied recent Arctic climate trends. This result is encouraging for benthic predators in the eastern Chukchi Sea as it alleviates the concern that their benthic prey has already become food limited by weakened pelagic-benthic coupling. More broadly, this initial A. borealis chronology is among the longest biological data series for any Arctic species and highlights the feasibility of multicentennial biological data for the Arctic.

Progress in Oceanography↗

USGS2019

Life history, genetics, range expansion and new frontiers of the lionfish (Pterois volitans, Perciformes: Pteroidae) in Latin America

Pterois volitans (lionfish) is a midsize predatory fish commonly found in waters of the western Pacific and Indian Ocean. The species was first documented in Dania Beach, Florida (northwestern Caribbean) in 1985. Since that time the species has expanded its range rapidly to the Northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. Since its introduction P. volitans has changed community structure and biodiversity of Caribbean reef communities and other coastal tropical ecosystems. Continuous introductions (accidental or intentional), limited natural predators, naïve-range prey behavior, high predation rates on competitors, continuous reproduction, and an extended period of larval dispersal have been the keys for successful invasion and rapid range extension of P. volitans . This invasion has become so severe that it has been recognized as one of the world’s top conservation issues. Here, we review the life history, behavior, and historical and contemporary genetic patterns that facilitate expansion and the colonization process. A greater understanding of lionfish biology, ecology, and the changes related to its present condition as a super-invader could improve current and future management strategies and new detection and response methodologies. We also examine new invasion frontiers that this species has the potential to colonize such as the eastern Pacific. This information will provide managers, the scientific community, and the civil society better tools for eradication, control and management of future invasions of this and other invasive species.

Caribbean Sea, Latin America↗

USGS1997

Recovery strategies for the California clapper rail (Rallus longirostris obsoletus) in the heavily-urbanized San Francisco estuarine ecosystem

The California clapper rail ( Rallus longirostris obsoletus ), a Federal- and State-listed endangered marsh bird, has a geographic range restricted to one of the most heavily-urbanized estuaries in the world. The rail population has long been in a state of decline, although the exact contribution of each of the many contributing causes remains unclear. The rail is one of the key targets of emerging plans to conserve and restore tidal marshlands. Reduction of tidal marsh habitat, estimated at 85–95%, has been the major historical cause of rail decline. Increased predation intensity may be the more important present problem, because habitat fragmentation and alteration coupled with the invasion of the red fox have made the remaining populations more vulnerable to predators. Population viability analysis shows that adult survivorship is the key demographic variable; reversals in population fate occur over a narrow range of ecologically realistic values. Analysis of habitat requirements and population dynamics of the clapper rail in the San Francisco Estuary shows that decreased within-marsh habitat quality, particularly reduction of tidal flows and alteration of drainage, is an important barrier to population recovery. Management and restoration activities should emphasize the development of well-channelized high tidal marsh, because this is the key requirement of rail habitat. Developing effective restoration programs depends upon having information that field research will not provide. The effect of spatial pattern of reserves requires accurate estimation of the effects of prédation and inter-marsh movement, both of which are practically impossible to measure adequately. It will be necessary to develop and use simulation models that can be applied to geographic data to accomplish this task.

Landscape and Urban Planning↗

USGS1996

Biology of Amur sleeper ( Perccottus glehni ) in the Delta of the Selenga River, Buryatia, Russia

We determined the fecundity, growth, diet, and density of the Amur sleeper ( Perccottus glehni ) in the Selenga River Delta on Lake Baikal during 1986-1991 to better understand how this invading exotic will affect Baikal's endemic fishes. We also compared the Amur sleeper's diet with that of other fishes living in the delta. The largest Amur sleepers were about 200 mm long and weighed 200 g; the oldest were age 7. All females were mature at age 2. Fecundity ranged from 884 eggs at age 1 to 37,056 eggs at age 7. Highest densities of Amur sleepers were found in oxbow lakes where densities sometimes exceeded 4,000 fish per ha. The bulk of the diet of Amur sleeper age 2 and older was chironomids, fish, and fish eggs. Chironomids were also important in the diet of the commercially valuable Siberian roach ( Rutilus rutilus lacustris ) and Siberian dace ( Leuciscus leuciscus baicalensis ). Thus the Amur sleeper may cause population declines of these important endemic fishes through resource competition and predation on their juvenile life stages. However, Amur sleepers were the species of fish most frequently eaten by Eurasian perch ( Perca fluviatilis ) and northern pike ( Esox lucius ). So, maintaining vigorous populations of these two predators may well be an effective strategy for limiting the size of Amur sleeper populations.

Lake Baikai;Selenga River↗

USGS2021

Recent recovery and expansion of Guam’s locally endangered Såli (Micronesian Starling) Aplonis opaca population in the presence of the invasive brown treesnake

Assessing the impacts of invasive predators on the demography and distribution of native species is critical for understanding mechanisms of species persistence and informing the design of recovery programmes. On the oceanic island of Guam, the introduction of the predatory brown treesnake Boiga irregularis after World War II caused the near-total loss of the native forest avifauna. Localised snake control measures have been implemented since the early 1990s, yet it remains poorly understood how they have impacted Guam’s remaining native bird populations. To address this question, we combined intensive area searches of Andersen Air Force Base (AAFB) with island-wide transect surveys and opportunistic sightings to provide a comprehensive update on the distribution and abundance of Såli (Micronesian Starling, Aplonis opaca ) – one of Guam’s last extant native bird species. Area searches of AAFB, where the largest remnant of the Såli population persists, revealed a 15-fold population increase since the last survey in the early 1990s, and transect surveys and opportunistic sightings indicate incipient recolonisation of other urbanised areas of northern and central Guam. We estimate the current island-wide population size at ~1,400 individuals. The population increase can likely be attributed to a combination of snake control measures and the Såli’s ability to exploit urban refugia for nesting and roosting. Although these trends demonstrate some population recovery, a skewed age ratio (>90% adults and subadults) at AAFB and a highly urbanised distribution and low abundance outside AAFB indicate that snake predation continues to strongly impact the population. More intensive snake suppression efforts, particularly in forested areas, may allow for the Såli population to attain its former distribution and abundance on Guam. More broadly, our findings reinforce the importance of urban areas as refugia for some threatened species.

Bird Conservation International↗

USGS2004

Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study

Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, k e = 0.025, 0.155, and 0.25 d -1 , respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se >15 μg g - 1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.

California↗

USGS2002

Ontogenetic behavior and migration of Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, and shortnose sturgeon, A. brevirostrum, with notes on social behavior

Ontogenetic behavior of Hudson River Atlantic sturgeon and Connecticut River shortnose sturgeon early life intervals were similar during laboratory observations. After hatching, free embryos were photonegative and sought cover. When embryos developed into larvae, fish left cover, were photopositive, and initiated downstream migration. Free embryos may remain at the spawning site instead of migrating downstream because the risk of predation at spawning sites is low. The two species are sympatric, but not closely related, so the similarities in innate behaviors suggest common adaptations, not phylogenetlc relationship. Atlantic sturgeon migrated downstream for 12 days (peak, first 6 days), shortnose sturgeon migrated for 3 days, and year-0 juveniles of both species did not resume downstream migration. Short or long migrations of larvae may reflect different styles related to the total migratory distance from spawning sites to juvenile rearing areas. Atlantic sturgeon need to move a short distance to reach rearing areas and they had a long 1-step migration of 6-12 days. In contrast, shortnose sturgeon need to move a long distance to reach all rearing areas. This may be accomplished by a 2-step migration, of which the brief migration of larvae is only the first step. Early migrant Atlantic sturgeon were nocturnal, while late migrants were diurnal, and shortnose sturgeon were diurnal. These diel differences may also be adaptations for long (Atlantic sturgeon) or short (shortnose sturgeon) migrations. Cultured shortnose sturgeon, and possibly Atlantic sturgeon, have a dominance hierarchy with large fish dominant when competing for limited foraging space. Social behavior may be more important in the life history of wild sturgeons than is generally recognized.

Environmental Biology of Fishes↗

USGS2002

Persistence of an unusual pelagic zooplankton assemblage in a clear, mountain lake

The planktonic zooplankton assemblage in Mowich Lake, Mount Rainier National Park (MORA), was composed almost entirely of rotifers in 1966 and 1967. Adult pelagic crustacean taxa were rare. Their paucity was attributed to predation by kokanee salmon (Oncorhynchus nerka), which had been stocked in 1961. During a park-wide survey of 24 lakes in 1988, Mowich Lake was the only one that did not contain at least one planktonic crustacean species. Given the apparent persistence of the unusual pelagic zooplankton assemblage in Mowich Lake, the first objective of this study was to document the interannual variation in the taxonomic structure of the zooplankton assemblages in the lake from 1988 through 1999. A second objective was to determine if it was possible to predict the taxonomic composition of the pelagic crustacean zooplankton assemblage in Mowich Lake prior to the stocking of kokanee salmon. The Mowich Lake zooplankton assemblages in 1988-1999 were consistent with those in 1966 and 1967. Crustacean taxa were extremely rare, but they included most of the primary taxa collected from 23 MORA lakes surveyed in 1988. Nonetheless, the 1988 collections showed that the September rotifer assemblage in Mowich Lake was similar to 10 of the 24 lakes sampled. Seven of the 10 lakes were dominated by cladocerans, primarily Daphnia rosea and Holopedium gibberum. Therefore, it appeared that either one or both of these species may have numerically dominated the crustacean zooplankton assemblage in the lake prior to 1961.

Hydrobiologia↗

USGS2012

Climate impacts on bird and plant communities from altered animal-plant interactions

The contribution of climate change to declining populations of organisms remains a question of outstanding concern. Much attention to declining populations has focused on how changing climate drives phenological mismatches between animals and their food. Effects of climate on plant communities may provide an alternative, but particularly powerful, influence on animal populations because plants provide their habitats. Here, we show that abundances of deciduous trees and associated songbirds have declined with decreasing snowfall over 22 years of study in montane Arizona, USA. We experimentally tested the hypothesis that declining snowfall indirectly influences plants and associated birds by allowing greater over-winter herbivory by elk (Cervus canadensis). We excluded elk from one of two paired snowmelt drainages (10 ha per drainage), and replicated this paired experiment across three distant canyons. Over six years, we reversed multi-decade declines in plant and bird populations by experimentally inhibiting heavy winter herbivory associated with declining snowfall. Moreover, predation rates on songbird nests decreased in exclosures, despite higher abundances of nest predators, demonstrating the over-riding importance of habitat quality to avian recruitment. Thus, our results suggest that climate impacts on plant–animal interactions can have forceful ramifying effects on plants, birds, and ecological interactions.

Arizona↗

USGS2023

Masting is uncommon in trees that depend on mutualist dispersers in the context of global climate and fertility gradients

The benefits of masting (volatile, quasi-synchronous seed production at lagged intervals) include satiation of seed predators, but these benefits come with a cost to mutualist pollen and seed dispersers. If the evolution of masting represents a balance between these benefits and costs, we expect mast avoidance in species that are heavily reliant on mutualist dispersers. These effects play out in the context of variable climate and site fertility among species that vary widely in nutrient demand. Meta-analyses of published data have focused on variation at the population scale, thus omitting periodicity within trees and synchronicity between trees. From raw data on 12 million tree-years worldwide, we quantified three components of masting that have not previously been analysed together: (i) volatility, defined as the frequency-weighted year-to-year variation; (ii) periodicity, representing the lag between high-seed years; and (iii) synchronicity, indicating the tree-to-tree correlation. Results show that mast avoidance (low volatility and low synchronicity) by species dependent on mutualist dispersers explains more variation than any other effect. Nutrient-demanding species have low volatility, and species that are most common on nutrient-rich and warm/wet sites exhibit short periods. The prevalence of masting in cold/dry sites coincides with climatic conditions where dependence on vertebrate dispersers is less common than in the wet tropics. Mutualist dispersers neutralize the benefits of masting for predator satiation, further balancing the effects of climate, site fertility and nutrient demands.

Nature Plants↗

USGS2021

A food web including parasites for kelp forests of the Santa Barbara Channel, California

We built a high-resolution topological food web for the kelp forests of the Santa Barbara Channel, California, USA that includes parasites and significantly improves resolution compared to previous webs. The 1,098 nodes and 21,956 links in the web describe an economically, socially, and ecologically vital system. Nodes are broken into life-stages, with 549 free-living life-stages (492 species from 21 Phyla) and 549 parasitic life-stages (450 species from 10 Phyla). Links represent three kinds of trophic interactions, with 9,352 predator-prey links, 2,733 parasite-host links and 9,871 predator-parasite links. All decisions for including nodes and links are documented, and extensive metadata in the node list allows users to filter the node list to suit their research questions. The kelp-forest food web is more species-rich than any other published food web with parasites, and it has the largest proportion of parasites. Our food web may be used to predict how kelp forests may respond to change, will advance our understanding of parasites in ecosystems, and fosters development of theory that incorporates large networks.

California↗

USGS2024

Detection of prions from spiked and free-ranging carnivore feces

Chronic wasting disease (CWD) is a highly contagious, fatal neurodegenerative disease caused by infectious prions (PrP CWD ) affecting wild and captive cervids. Although experimental feeding studies have demonstrated prions in feces of crows ( Corvus brachyrhynchos ), coyotes ( Canis latrans ), and cougars ( Puma concolor ), the role of scavengers and predators in CWD epidemiology remains poorly understood. Here we applied the real-time quaking-induced conversion (RT-QuIC) assay to detect PrP CWD in feces from cervid consumers, to advance surveillance approaches, which could be used to improve disease research and adaptive management of CWD. We assessed recovery and detection of PrP CWD by experimental spiking of PrP CWD into carnivore feces from 9 species sourced from CWD-free populations or captive facilities. We then applied this technique to detect PrP CWD from feces of predators and scavengers in free-ranging populations. Our results demonstrate that spiked PrP CWD is detectable from feces of free-ranging mammalian and avian carnivores using RT-QuIC. Results show that PrP CWD acquired in natural settings is detectable in feces from free-ranging carnivores, and that PrP CWD rates of detection in carnivore feces reflect relative prevalence estimates observed in the corresponding cervid populations. This study adapts an important diagnostic tool for CWD, allowing investigation of the epidemiology of CWD at the community-level.

Scientific Reports↗

USGS2025

American alligators (Alligator mississippiensis) as wetland ecosystem carbon stock regulators

Blue carbon refers to organic carbon sequestered by oceanic and coastal ecosystems. This stock has gained global attention as a high organic carbon repository relative to other ecosystems. Within blue carbon ecosystems, tidally influenced wetlands alone store a disproportionately higher amount of organic carbon than other blue carbon systems. North America harbors 42% of tidally influenced global wetland area, which has been identified as a critical carbon stock in the context of climate change mitigation. However, quantified associations between vertebrate biota and carbon sequestration within ecosystems are in their infancy and have been incidental, given that microbial trophic levels are thought to drive nutrient dynamics. Here, we assess the relationship between American alligator ( Alligator mississippiensis ) demography and tidally influenced wetland soil carbon stock among habitats at continental, biogeographically-relevant, and local scales. We used soil core profile data from the Smithsonian’s Coastal Carbon Network and filtered for continuous core profiles in tidally influenced wetland areas along the Gulf and Atlantic Coasts of the United States. Results indicate that American alligator presence is positively correlated with soil carbon stock across habitats within their native distribution. Further, American alligator demographic variables are positively correlated with soil carbon stock at local scales. These conclusions are concordant with previous findings that apex predators, through trophic cascade theory, play a key role in regulating soil carbon stock and that alligators are functional apex predators in carbon dynamics and a key commercialized natural resource.

Connecticut, Delaware, Florida, Georgia, Louisiana↗

USGS2002

Evaluating causes of population change in North American insectivorous songbirds

Although the North American Breeding Bird Survey (BBS) is a principal source of information regarding populations of most North American bird species, many features of the survey complicate analysis of population change. Correlation studies based on BBS data cannot be used to unambiguously define cause and effect relationships. Recently, Bohning-Gaese et al. (1993) presented an analysis of population trends in insectivorous songbirds using data from the BBS. They concluded that predation has played an important role in influencing population trends. We review aspects of the analysis methods for estimating population trends (e.g., observer effects, data subset) and for associating mean trends with species attributes (e.g., confounding of attributes). Using alternative analyses of the same BBS data, we demonstrate that the evidence that predation is associated with population declines is weaker than they suggested. Based on our analyses the only factor among those tested that is consistently associated with population trends is migration status (i.e., short-distance migrant/resident vs. long-distance migrant) during the period 1978-1987. Also, we present evidence that the harsh winters of the mid-1970's severely depressed populations of short-distance migrant species, and may be responsible for the observed associations between migration status and population trends.

Conservation Biology↗

USGS1997

Translocation of the Palila, an endangered Hawaiian honeycreeper

The Palila Loxioides bailleui is an endangered Hawaiian honeycreeper that is restricted to high-elevation dry woodlands on Mauna Kea volcano, Hawaii. Palila are absent or occur in small numbers throughout most of their historic range because of habitat loss, predation and avian disease. The Palila's habitat is regenerating as a result of feral ungulate control, but the species is likely to be slow in recolonizing former ranges because of strong site tenacity. In March 1993, we translocated 35 Palila to Kanakaleonui on the eastern slope of Mauna Kea to determine whether we could speed recovery by releasing adult birds in new areas where predators were controlled. At least two pairs of translocated Palila successfully nested at the release site during their first breeding season, and two other pairs constructed nests. The density of Palila at Kanakaleonui in the three years following the translocation was higher than that before translocation. Approximately half of the translocated birds remained at the release site for 2?6 weeks and then homed back to their capture site, >20 km away. Translocations of adult birds and release of captive-reared juvenile Palila, in combination with additional habitat restoration, may be an effective management tool for speeding the recovery of this species.

Pacific Conservation Biology↗

USGS2010

Impact of harvest on survival of a heavily hunted game bird population

Context . Despite their economic importance and intensive management, many game bird species, including the northern bobwhite Colinus virginianus , are in decline. Declines may be explained, at least in part, by low survival due perhaps to poor habitat quality, high predation or excessive hunting pressure. Aims . This study sought to estimate and model annual/seasonal survival probabilities, to evaluate factors influencing them and to determine the cause-specific mortality rates for northern bobwhites subject to varying levels of harvest on the Babcock–Webb Wildlife Management Area (BW area), south Florida, USA. Methods . We applied Cox’s proportional hazard models to data collected from 2066 radio-tagged bobwhites during 2002–2008 to test for intrinsic and extrinsic factors affecting survival and the non-parametric cumulative incidence function estimator to estimate cause-specific mortality rates. Key results . Mean annual survival (0.091 ± 0.006) in the BW area was lower than most estimates reported for other bobwhite populations. Annual survival differed between adults (0.111 ± 0.008) and juveniles (0.052 ± 0.008), and varied among years. Survival in winter (October–March; 0.295 ± 0.014) was similar to that in summer (April–September; 0.307 ± 0.013). Density of food strips (i.e. long and narrow food plots) did not influence survival, but hunting effort (number of hunters per day per km 2 ) had a substantial negative impact on survival. In the lightly hunted field trial zone, winter (October–March) survival was significantly higher (0.414 ± 0.035) than in the other more heavily hunted management zones (0.319 ± 0.016). Cause-specific mortality analyses revealed that bobwhite mortality during summer (April–September) was mainly due to raptor (39.7%) and mammalian predation (35.6%), whereas hunting was the primary cause of mortality during winter (47.1%). Conclusions . Our results highlight the potential role of harvest as an important cause of the northern bobwhite population declines in south Florida. High mortality during winter may reduce recruitment of juveniles to the reproductive segment of the population, and ultimately the population growth. Implications . Our results suggest that reduction in hunting pressure may be necessary to reverse the declining population trends in heavily hunted game species in public lands, such as the northern bobwhites in the BW area.

Florida↗