Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
764
result(s) for
"Swainson"
Sort by:
Estimating apparent survival of songbirds crossing the Gulf of Mexico during autumn migration
Many migratory bird species are declining, and the migratory period may limit populations because of the risk in traversing large geographical features during passage. Using automated radio-telemetry, we tracked 139 Swainson's thrushes ( Catharus ustulatus ) departing coastal Alabama, USA and crossing the Gulf of Mexico to arrive in the Yucatan Peninsula, Mexico during autumn. We estimated apparent survival and examined how extrinsic (weather variables and day of year) and intrinsic (fat load, sex and age) factors influenced survival using a mark-recapture approach. We also examined how favourability of winds for crossing the Gulf varied over the past 25 years. Fat load, day of year and wind profit were important factors in predicting which individuals survived crossing the Gulf. Survival estimates varied with wind profit and fat, but generally, fat birds departing on days with favourable wind profits had an apparent survival probability of greater than 0.90, while lean individuals with no or negative wind profits had less than 0.33. The proportion of favourable nights varied within and among years, but has increased over the last 25 years. While conservation strategies cannot improve extrinsic factors, they can provide opportunities for birds to refuel before crossing large geographical features through protecting and creating high-quality stopover sites.
Journal Article
Wounded Warrior
Few people today remember John Swainson. As a teenage soldier he lost both legs in a WWII landmine explosion. Back in the United States, following a meteoric political rise in the Michigan State Senate, Swainson was elected as Michigan's youngest governor since Stevens T. Mason.In 1970 Swainson was elected to the Michigan Supreme Court, becoming one of the few public officials to have served in the legislative, executive, and judicial branches of state government. Then, in 1957, he was indicted on federal charges of bribery and perjury, and convicted of lying to a federal grand jury. Forced to leave the state Supreme Court and disbarred from practicing law, he became a pariah, sinking into depression and alcoholism. He virtually disappeared from public view.Lawrence M. Glazer re-examines the FBI's investigation of Swainson and delves into his 1975 trial in detail. He reveals new information from eye-witnesses who never testified and, in a poignant coda, relates the little-known story of Swainson's rehabilitation and return to public life as a historian.
eBook
Repeatable Selection on Large Ancestry Blocks in an Avian Hybrid Zone
Hybrid zones create natural tests of genetic incompatibilities by combining loci from 2 species in the same genetic background in the wild, making them useful for identifying loci involved in both intrinsic and ecological (extrinsic) isolation. Two Swainson's thrush subspecies form a hybrid zone in western North America. These coastal and inland subspecies exhibit dramatic differences in migration routes; their hybrids exhibit poor migratory survival, suggesting that ecological incompatibilities maintain this zone. We used a panel of ancestry informative markers to identify repeated patterns of selection and introgression across 4 hybrid populations that span the entire length of the Swainson's thrush hybrid zone. Two repeatable patterns consistent with selection against incompatibilities—steep genomic clines and few transitions between ancestry states—were found in large genetic blocks on chromosomes 1 and 5. The block on chromosome 1 showed evidence for inland subspecies introgression while the block on chromosome 5 exhibited coastal subspecies introgression. Some regions previously associated with migratory phenotypes, including migratory orientation, or exhibiting misexpression between the subspecies exhibited signatures of selection in the hybrid zone. Both selection and introgression across the genome were shaped by genomic structural features and evolutionary history, with stronger selection and reduced introgression in regions of low recombination, high subspecies differentiation, positive selection within the subspecies, and on macrochromosomes. Cumulatively, these results suggest that linkage among loci interacts with divergent selection and past divergent evolution between species to strengthen barriers to gene flow within hybrid zones.
Journal Article
Identifying predators clarifies predictors of nest success in a temperate passerine
1. Nest predation negatively affects most avian populations. Studies of nest predation usually group all nest failures when attempting to determine temporal and parental activities, habitat or landscape predictors of success. Often these studies find few significant predictors and interpret patterns as essentially random. 2. Relatively little is known about the importance of individual predator species or groups on observed patterns of nest success, and how the ecology of these predators may influence patterns of success and failure. 3. In 2006 and 2007, time-lapse, infrared video systems were deployed at nests of Swainson's warblers (Limnothlypis swainsonii Audubon) in east-central Arkansas to identify dominant nest predators and determine whether factors predicting predation differed among these predators. 4. Analysis of pooled data yielded few predictors of predation risk, whereas separate analyses for the three major predator groups revealed clear, but often conflicting, patterns. 5. Predation by ratsnakes (Elaphe obsoleta) and raptors was more common during the nestling period, whereas predation by brown-headed cowbirds (Molothrus ater) occurred more during incubation. Additionally, the risk of predation by raptors and cowbirds decreased throughout the breeding season, whereas ratsnake predation risk increased. 6. Contrary to expectations, predation by ratsnakes and cowbirds was more common far from edges, whereas raptor predation was more common close to agricultural edges. 7. Collectively, our results suggest that associating specific predators with the nests they prey on is necessary to understand underlying mechanisms.
Journal Article
The role of humidity and metabolic status on lean mass catabolism in migratory Swainson's thrushes (Catharus ustulatus)
Migratory birds use protein as a fuel source during flight, but the mechanisms and benefits of protein catabolism during migration are poorly understood. The tissue-specific turnover rate hypothesis proposes that lean mass loss depends solely on the constitutive rate of protein degradation for a given tissue, and is therefore independent of metabolic rate or environmental stimuli. However, it has been demonstrated that environmental stressors such as humidity affect the rate of lean mass catabolism during flight, a finding that seemingly contradicts the tissue-specific turnover rate hypothesis. In order to resolve this, we placed migratory Swainson's thrushes in either high (HEWL) or low (LEWL) evaporative water loss conditions at rest and while undergoing simulated migratory flight at 8 m s −1 in a wind tunnel to test the impact of both environmental stressors and metabolic rate on the rate of protein breakdown. The total quantity and rate of lean mass loss was not different between flight and rest birds, but was affected by humidity condition, with HEWL losing significantly more lean mass. These results show that the rate of protein breakdown in migratory birds is independent of metabolic rate, but it can be augmented in response to environmental stressors.
Journal Article
Reproductive Success and Diet of the Swainson’s Hawk (Buteo swainsoni) in the Grasslands of Janos, Chihuahua, Mexico
Understanding the breeding ecology and trophic dynamics of the Swainson’s Hawk (Buteo swainsoni) is essential for conserving grassland raptor populations in northern Mexico. We evaluated reproductive success, nest-site characteristics, and diet of the species in the grasslands of Janos, Chihuahua, during the 2006 breeding season. Eighteen nests were monitored to estimate daily survival rates (DSRs) using the Mayfield method. Overall nest success was 44.4%. DSR declined significantly from incubation (0.99 ± 0.00079) to the nestling stage (0.98 ± 0.00087; z = 8.5, p < 0.001), resulting in cumulative survival of 79.9% and 56.2%, respectively. Successful nests tended to occur farther from towns, although this trend was not statistically significant. Most nests were built in mesquite trees at intermediate elevations and in areas with low human disturbance. Diet analyses of 56 pellets and 91 prey remains revealed a predominance of vertebrates (63.17%), mainly mammals and reptiles, with vertebrate frequency significantly exceeding that of invertebrates (χ2 = 23.19, p < 0.001). These results highlight the species’ reliance on vertebrate prey and the vulnerability of the nestling stage, underscoring the importance of long-term monitoring in semi-arid grasslands.
Journal Article
Response of migrating raptors to an increasing number of wind farms
1. Flying birds have been documented to respond in different ways to the presence of wind farms. Such responses are species-and site-specific, with wind farm design playing an important role. Between 2009 and 2014, the length of rows of wind turbines within our study area increased from 3-4 km to ~ 7.5 km, and the total area occupied by wind farms increased from 6.47 km² to 14-21 km². This area is located on an important migratory corridor in southern Mexico. 2. We used marine radar and hawk-watch monitoring stations to collect data during six consecutive autumn seasons from a single wind farm. We analysed the response of migrating raptors to the presence of two new wind farms by comparing the mean bearing of flight trajectories and the number of intersections km⁻¹ of trajectories with wind farm areas between 2009-2011 and 2012-2014, representing the pre-and post-construction stages of the new wind farms. 3. Mean raptor count was > 600 000 individuals for the six seasons. The most abundant species were Turkey Vulture Cathartes aura, Swainson's Hawk Buteo swainsoni and Broadwinged hawk Buteo platypterus. Between 79% and 97% of migration occurred in October. Radar monitoring overlapped with the peak migratory activity each season. 4. We observed significant differences between periods, involving more scattering in flight bearings and less intersections km\" 1 of trajectory in the post-than in the pre-construction period, implying an avoidance of the new wind farms. 5. Synthesis and applications. We show that migrating raptors adjusted their flight trajectories to avoid new wind farms, but also discuss the extent and limitations of our findings. Our results from our hawk-watch monitoring station, which represent the first published account about the seasonality and intensity of raptor migration in the area, could be used by decision-makers for careful planning of future wind energy developments in the area. Our results might aid in the conservation of those species of raptors that migrate through the Isthmus of Tehuantepee.
Journal Article
Factors influencing the movement biology of migrant songbirds confronted with an ecological barrier
Whether or not a migratory songbird embarks on a long-distance flight across an ecological barrier is likely a response to a number of endogenous and exogenous factors. During autumn 2008 and 2009, we used automated radio tracking to investigate how energetic condition, age, and weather influenced the departure timing and direction of Swainson's thrushes (Catharus ustulatus) during migratory stopover along the northern coast of the Gulf of Mexico. Most birds left within 1 h after sunset on the evening following capture. Those birds that departed later on the first night or remained longer than 1 day were lean. Birds that carried fat loads sufficient to cross the Gulf of Mexico generally departed in a seasonally appropriate southerly direction, whereas lean birds nearly always flew inland in a northerly direction. We did not detect an effect of age or weather on departures. The decision by lean birds to reorient movement inland may reflect the suitability of the coastal stopover site for deposition of fuel stores and the motivation to seek food among more extensive forested habitat away from the barrier.
Journal Article
Anthropogenic subsidies and wildfire influence density, occupancy, and species interactions of three avian predators
Anthropogenic subsidies and disturbance can benefit generalist avian species by providing additional food, nesting, and perching resources. In the sagebrush biome, anthropogenic subsidies have led to increases in the number of common ravens (Corvus corax; hereafter ravens), red‐tailed hawks (Buteo jamaicensis), and Swainson's hawks (Buteo swainsoni), but it is unclear how wildfire disturbance may be affecting these species. We used 6 years of count data (2017–2022) to investigate the effects of anthropogenic subsidies and wildfire on density, occupancy, interspecific density dependence, and interactions of these three sympatric predators in five study areas in eastern Oregon. Estimated mean relative densities for all species varied annually, ranging from 1.00 to 2.05 km−2 for ravens, from 0.46 to 1.09 km−2 for red‐tailed hawks, and from 0.07 to 0.38 km−2 for Swainson's hawks. Mean occupancy probability was 0.78 across all study areas for red‐tailed hawks and varied by study area for ravens and Swainson's hawks, ranging from 0.62 to 0.94 and from 0.70 to 0.97, respectively. N‐mixture and occupancy models indicated that anthropogenic subsidies and recent wildfires (≤10 years) were positively associated with the density and occupancy of ravens and red‐tailed hawks. However, only road density was associated with the occupancy of Swainson's hawks. There were no interspecific density‐dependent effects for ravens and red‐tailed hawks, but Swainson's hawk density decreased as densities of ravens and red‐tailed hawks increased. Multispecies occupancy models indicated that most occupancy probabilities associated with anthropogenic subsidies were independent of allospecific presence. However, occupancy probabilities were influenced by wildfire, indicating negative interactions between Swainson's hawks and ravens but positive interactions between Swainson's and red‐tailed hawks. Our results provide evidence that anthropogenic subsidies create hotspots of generalist predators in sagebrush ecosystems fragmented by wildfire. These increased densities may lead to human–wildlife conflicts, displacement of specialist predator species, and greater risk of predation to prey species of conservation concern.
Journal Article