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1.
Benjamin J. O'Neal Joshua D. Stafford Ronald P. Larkin 《The Journal of wildlife management》2012,76(2):285-293
The amount of time migrating birds spend at stopover sites, or stopover duration, partially determines an individual's access to resources, the environmental conditions encountered, and the exposure to predation, which in turn affect survival and fecundity. As such, migratory behaviors such as stopover duration can have a considerable effect on populations of migrants and plans for their conservation. This is especially true for migrant waterfowl, which are explicitly conserved through Joint Venture (JV) partnerships under the North American Waterfowl Management Plan. Although waterfowl are one of the most heavily studied taxa, little is known about their stopover behavior due to the scope of migration. Consequently, conservation plans of many mid-migration JVs either omit estimates of stopover duration or rely on antiquated data to estimate energetic requirements. We used weather surveillance radar to identify and enumerate ducks emigrating from an important stopover area in central Illinois. By using radar data in combination with data from weekly aerial inventories, we estimated an average stopover duration for fall-migrating dabbling ducks (tribe Anatini) of 28 days (SD = 12) over 8 years (1996, 1997, 2003, 2005–2009). Our estimate was similar to the historical estimate of 28 days (1940–1966), which serves as the primary reference for the Upper Mississippi River Great Lakes Region JV conservation plan. In addition to a corroborative mean, we also found considerable inter-annual variation in stopover duration. Estimated annual stopover duration was correlated positively with an index of annual foraging habitat quality (Spearman's rank correlation; rs = 0.83), suggesting ducks may have assessed local conditions and adjusted the spatiotemporal course of fall migration. If the stopover behavior of fall-migrating ducks is flexible and forage-dependent, it is possible ducks allocate their time among sites in a somewhat ideal and optimal fashion, which could substantially affect the way resources are allocated within the spatial context of a JV region. © 2012 The Wildlife Society. 相似文献
2.
Adam C. Behney Ryan O'Shaughnessy Michael W. Eichholz Joshua D. Stafford 《Journal of avian biology》2019,50(6)
Life history theory predicts that species with faster life history strategies should be willing to risk their survival more to acquire resources than those with slower life history strategies. Foraging can be a risky behavior and animals generally face a tradeoff between food consumption and predation risk. We predicted that the degree to which animals invest in current versus future reproduction (i.e. life history strategy) would determine how they approach this tradeoff. We manipulated food abundance in wetlands to assess whether life history theory could explain risk taking among females of five duck species with respect to foraging. We found evidence consistent with our prediction based on life history theory; species with a faster life history strategy were willing to engage in riskier behavior, by feeding more intensively, for a greater food reward. Females from species with faster life history strategies devoted 25% more time to feeding when in high food density treatment plots versus control plots. The percentage of time that females from species with slower life history strategies devoted to feeding was not affected by food density. These findings contribute to our understanding of life history theory and represent a possible mechanism to explain differences in life history strategies among species. 相似文献
3.
Richard A. Fischer Sidney A. Gauthreaux Jr. Jonathon J. Valente Michael P. Guilfoyle Michael D. Kaller 《Journal of Field Ornithology》2012,83(1):61-72
ABSTRACT For decades, researchers have successfully used ground‐based surveys to understand localized spatial and temporal patterns in stopover habitat use by migratory birds. Recent technological advances with WSR‐88D radar now allow such investigations on much broader spatial scales. Both methods are assumed to accurately quantify patterns in migrant bird communities, yet information is lacking regarding relationships between radar estimates of migration and different ground‐based monitoring methods. From 2005 to 2007, we monitored migrant communities on or near two Department of Defense installations in the spring (Ft. Polk Military Complex, LA; U.S. Army Test and Evaluation Command, Yuma Proving Ground, AZ) and on two installations in the fall (Ft. Polk Military Complex, LA; Eglin Air Force Base, FL) using both ground‐based transect surveys and radar imagery of birds aloft. We modeled daily changes in migrant abundance and positive and negative species turnover measured on the ground as a function of radar estimates of migrant exodus and input densities. Radar data were not significant predictors of any response variable in any season either in the southeastern or southwestern United States, indicating a disparity between the results obtained using different methods. Multiple unique sources of error associated with each technique likely contributed to the conflicting outcomes, and researchers should take great care when selecting monitoring methods appropriate to address research questions, effects of management practices, or when comparing the results of migration studies using different survey techniques. 相似文献
4.
Benjamin J. O'Neal Joshua D. Stafford Ronald P. Larkin 《Journal of Field Ornithology》2010,81(1):71-82
ABSTRACT Local and migratory movements aloft have important implications for the ecology and conservation of birds, but are difficult to quantify. Weather surveillance radar (WSR) offers a unique tool for observing movements of birds, but until now has been used primarily to address broad taxonomic questions. Herein, we demonstrate how natural history information and ground‐truthing can be used to answer quantitative and taxon‐specific questions regarding bird movements on WSR. We found that super‐resolution Level II data from the National Oceanic and Atmospheric Administration's mass storage system was the most effective format and source of WSR data, and that several software packages were needed for thorough analysis of WSR data. Using WSR, we identified potential movements of birds emigrating from a waterfowl stopover area in Illinois in fall (1 September–31 December) 2006 and 2007. We compared spatial and temporal patterns of these movements to the natural history of taxa occupying the source habitat and classified these radar targets as dabbling ducks (tribe Anatini). A portable X‐band radar measured the cruising heights of ducks at 400–600 m. During fall 2008, we conducted ground‐truthing with a thermal infrared camera to enumerate birds passing over our field site during nocturnal migration events. This estimate of bird density, paired with an associated sample of WSR echo strength, provided a mean radar cross section the same as dabbling ducks (112.5 cm2) and supported our natural‐history‐based classification. Thermal infrared‐estimated duck densities explained most of the variation (R2= 0.91) in WSR echo strength across seven migration events of varying intensities, suggesting that radar cross sections of dabbling ducks and WSR reflectivity can be used to estimate duck numbers in other comparable contexts. Our results suggest that careful investigation of the spatial and temporal patterns of movements on radar, along with field‐based ground‐truthing, can be used to study and quantify the movements of specific bird taxa. 相似文献
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6.
Emily B. Cohen Kyle G. Horton Peter P. Marra Hannah L. Clipp Andrew Farnsworth Jaclyn A. Smolinsky Daniel Sheldon Jeffrey J. Buler 《Ecology letters》2021,24(1):38-49
Migrating birds require en route habitats to rest and refuel. Yet, habitat use has never been integrated with passage to understand the factors that determine where and when birds stopover during spring and autumn migration. Here, we introduce the stopover‐to‐passage ratio (SPR), the percentage of passage migrants that stop in an area, and use 8 years of data from 12 weather surveillance radars to estimate over 50% SPR during spring and autumn through the Gulf of Mexico and Atlantic coasts of the south‐eastern US, the most prominent corridor for North America’s migratory birds. During stopovers, birds concentrated close to the coast during spring and inland in forested landscapes during autumn, suggesting seasonal differences in habitat function and highlighting the vital role of stopover habitats in sustaining migratory communities. Beyond advancing understanding of migration ecology, SPR will facilitate conservation through identification of sites that are disproportionally selected for stopover by migrating birds. 相似文献
7.
Abstract Aim An analysis is presented to examine whether variation in breeding waterfowl estimates can be explained by weather patterns prior to annual surveys. Location The location of the study is north‐western Ontario, Canada. Methods Annual, systematic survey data for breeding waterfowl are available from the 1950s to the present for north‐western Ontario. Regional monthly climate data for this area were compiled using weather data derived from interpolated annual climate surfaces. These data were analysed using stepwise multiple linear regression for each species and for waterfowl functional groups to assess whether monthly climate data accounted for some of the variation in waterfowl numbers. Results For all dabbling ducks pooled, 12% of the variation in annual abundance was explained by April temperatures, with more dabbling ducks observed in years when April was relatively cool. For diving ducks, 23% of the variation in pooled abundance was explained by April temperatures and February precipitation, where more diving ducks were observed in years when February had relatively less precipitation and April was cool. Patterns for individual species varied. Main conclusions Mean monthly weather data for months prior to surveys explained some of the variation in numbers of waterfowl observed in annual surveys. This suggests that future incorporation of weather data into waterfowl population models may help refine population estimates. 相似文献
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A recently developed radar‐based technique permitted empirical re‐evaluation of the established but poorly supported theory that migrating North American waterfowl (Anatidae) use landscape features such as rivers as leading lines. Ducks departing the Illinois River Valley in the autumn of each of 15 years travelled SSE with a mean track that was 68° different from the 220° course of the Illinois River (P ≤ 0.001). We conclude that leading lines were unimportant navigation aids for ducks leaving this major stopover site in autumn and suggest that rivers have less effect on the spatial course of duck migration than previously thought. Timing of departures was examined in a representative subset of 8 years and found to be consistent, with a mean start time of 44 min after civil sunset. 相似文献
10.
We studied the effects of weather and tides on percent feeding and flock positions of wintering redheads (Aythya americana Eyton) in the Chandeleur Sound, Louisiana, USA. Flock scans (n = 750) were made on 55 flocks from November through March of 1988–1989. The percent of the flock that was feeding was negatively correlated with time of day, temperature, water level, and distance of the flock from shore, and was positively correlated with wind velocity, flock size, fetch, and wave height; birds also fed more in early winter and during northerly winds. Flocks were closer to land earlier in the winter on cloudy, rainy, and windy days when waves were high, and those flocks were smaller than flocks farther from shore. Conditions associated with reduced fetch by flocks included later time of day, smaller waves, warmer air temperatures, northerly wind shifts, stronger winds, increasing cloud cover, and rain. Redheads minimized energy expenditure by foraging during low tides and in shallow water closer to shore; they increased feeding and reduced fetch during times of high thermoregulatory demands. 相似文献
11.
Redheads, Aythya americana, concentrate in large numbers annually in traditional wintering areas along the western and northern rim of the Gulf of Mexico.
Two of these areas are the Laguna Madre of Texas and Chandeleur Sound of Louisiana. We collected data on 54,340 activities
from 103 redhead flocks in Texas and 51,650 activities from 57 redhead flocks in Louisiana. Males and females fed similarly,
differing neither in levels of feeding (percent of all birds in flock that were feeding) (p>0.90) nor in percentages of birds feeding by diving, tipping, dipping, or gleaning from the surface (p>0.10). The foraging level of redheads in the upper Laguna Madre region was relatively constant throughout two winters. Foraging
of redheads in early winter in Louisiana was significantly greater than redhead foraging in the upper Laguna Madre, but by
late winter, foraging by redheads in Louisiana had declined to the same level as that shown by redheads foraging in the upper
Laguna Madre. The overall foraging level of redheads from Chandeleur Sound was greater (41%) than that of redheads in the
upper Laguna Madre (26%), yet it was quite similar to the 46% foraging level reported for redheads from the lower Laguna Madre.
Redheads in the upper Laguna Madre region of Texas fed more by diving than did those in the Chandeleur Sound and the lower
Laguna Madre. Diving increased in frequency in late winter. Greater reliance by redheads on diving in January and February
indicates that the birds altered their foraging to feed in deeper water, suggesting that the large concentrations of redheads
staging at this time for spring migration may have displaced some birds to alternative foraging sites. Our results imply that
the most likely period for food resources to become limiting for wintering redheads is when they are staging in late winter. 相似文献
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HANS VAN GASTEREN IWAN HOLLEMAN WILLEM BOUTEN EMIEL VAN LOON JUDY SHAMOUN‐BARANES 《Ibis》2008,150(4):674-686
Although radar has been used in studies of bird migration for 60 years, there is still no network in Europe for comprehensive monitoring of bird migration. Europe has a dense network of military air surveillance radars but most systems are not directly suitable for reliable bird monitoring. Since the early 1990s, Doppler radars and wind profilers have been introduced in meteorology to measure wind. These wind measurements are known to be contaminated with insect and bird echoes. The aim of the present research is to assess how bird migration information can be deduced from meteorological Doppler radar output. We compare the observations on migrating birds using a dedicated X‐band bird radar with those using a C‐band Doppler weather radar. The observations were collected in the Netherlands, from 1 March to 22 May 2003. In this period, the bird radar showed that densities of more than one bird per km3 are present in 20% of all measurements. Among these measurements, the weather radar correctly recognized 86% of the cases when birds were present; in 38% of the cases with no birds detected by the bird radar, the weather radar claimed bird presence (false positive). The comparison showed that in this study reliable altitudinal density profiles of birds cannot be obtained from the weather radar. However, when integrated over altitude, weather radar reflectivity is correlated with bird radar density. Moreover, bird flight speeds from both radars show good agreement in 78% of cases, and flight direction in 73% of cases. The usefulness of the existing network of weather radars for deducing information on bird migration offers a great opportunity for a European‐wide monitoring network of bird migration. 相似文献
14.
- Dispersal of plant seeds by ducks and other waterbirds is of great importance to the ecology of freshwater habitats. To unravel the mechanisms of waterbird‐mediated seed dispersal, numerous laboratory experiments have been conducted, but effects of seed and waterbird traits on dispersal potential have rarely been investigated under field conditions.
- Through analysis of the digestive tracts of 100 wild mallards (Anas platyrhynchos) across a winter season in the Netherlands, we assessed (i) the inter‐individual and seasonal variability of seeds in the digestive tract, (ii) the variability of digestive tract organ size and gizzard grit mass, and (iii) the potential effects of seed species traits and gut traits on the survival potential of ingested seeds.
- We found 4548 ingested seeds of at least 66 plant species from a wide range of habitats, most of which were retained in the gizzard. Nineteen species had not previously been reported from mallard diets. Individual tracts contained anywhere between 0 and 1048 seeds, of up to 14 species (median of three species). Diet composition and digestive tract size varied substantially between individuals and over the course of the winter season. As predicted from controlled feeding studies, we found that also in wild mallards, size‐dependent gut passage survival favours the dispersal of small‐seeded species. Despite the large variation in gizzard and small intestine size in this study, their effect on the dispersal potential of ingested seeds in the field remains unclear. We found no difference in dispersal potential between plants species growing in wet or dry habitats.
- This study demonstrates that wild mallards are opportunistic seed consumers with a very diverse diet as reflected by seed species composition in both the foregut and hindgut. However, we also show that serious limitations of field‐based analyses compared to controlled experiments can impede drawing conclusions about gut passage survival of seeds. The large variability in diet composition among individuals and over time indicates high endozoochorous dispersal potential for a wide range of plant species by wild mallard in aquatic and wetland, as well as surrounding terrestrial habitats.
15.
Concern about the sustainability of intercontinental‐scale migration systems grows apace with global change. Traditional organism‐centred approaches to this problem have provided insights at the population level, but not at the systems level. We are sceptical that an accumulation of data from a species‐by‐species approach will yield an understanding of these systems in the near term. As an alternative, we advocate a new research programme that grows from an explicitly system‐based framework that leverages existing Earth observation infrastructure to make inferences directly at the macrosystem level. We illustrate how this approach can be used to generate and test system‐level predictions, using NEXRAD radar data as an example. We urge organismal ecologists to recognize that some of the most urgent migration questions are at the macrosystem scale and that tackling these questions requires an interdisciplinary approach if we are to make progress at a pace that exceeds that of climate change. 相似文献
16.
Joseph R. Marty J. Brian Davis Richard M. Kaminski Michael G. Brasher Scott A. Rush 《The Journal of wildlife management》2020,84(7):1315-1325
Biomass estimates of potential waterfowl foods are fundamental to estimating foraging carrying capacity of waterfowl habitat by conservation planners and managers of the North American Waterfowl Management Plan-Gulf Coast Joint Venture (GCJV). Rice and moist-soil seeds in Gulf Coast rice fields provide principal sources of energy for waterfowl during migration and winter. We investigated spatio-temporal biomass dynamics of these seeds and modeled their variation in production and idled rice fields in southwestern Louisiana, southeastern Texas, and the Texas Mid-Coast, USA, in August and November 2010–2013. We hypothesized that previous estimates of November rice and moist-soil seed biomass from the Mississippi Alluvial Valley were not applicable to the GCJV region because climate and agricultural production practices (e.g., ratooning, crayfish [Procambrus spp.] aquaculture) are primary inter-regional contrasts. Waste-rice biomass was greatest in November in fields with an unharvested second crop of rice from tillers of original plants (i.e., ratoon crop; 837.7 kg[dry]/ha; CV = 16.7%) and least in fields without a ratoon crop (119.3 kg/ha; CV = 18.5%). Moist-soil seed biomass was greatest in idled rice fields in October (477.3 kg/ha; CV = 24.8%), where substrate and rice stubble were disked at the time of sampling, and in idled fields with standing native vegetation in November (304.8 kg/ha; CV = 17.1%). Field-level variation in waste rice in production fields in November was best explained by an interaction between field management (e.g., harvested ratoon) and rice variety. We were unable identify a reliable predictor of field-level variation in moist-soil seed biomass in idled fields for July–August or November (i.e., null model was best or competitive). Substituting existing seasonal moist-soil and rice seed biomass estimates in GCJV planning models with those from our study would result in a seasonally flooded habitat objective 76% (101,974 ha) greater than the current GCJV estimate for 3 rice-growing planning areas. We encourage conservation planners in the GCJV region to use biomass estimates from our study because they are reasonably precise for planning and implementation (i.e., CV ~ 20%) and represent most contemporary patterns of farming practices and food abundance in this region. Further, programs and incentives that promote production of ratoon rice crops and allow growth of naturally occurring vegetation in idled rice fields, followed by shallow flooding during November–February, would significantly enhance food resources for waterfowl and other waterbirds in this important landscape for North American avifauna. © 2020 The Wildlife Society. 相似文献
17.
Adam C. Behney Ryan O'Shaughnessy Michael W. Eichholz Joshua D. Stafford 《Ecology and evolution》2018,8(2):961-972
Indirect risk effects of predators on prey behavior can have more of an impact on prey populations than direct consumptive effects. Predation risk can elicit more vigilance behavior in prey, reducing the amount of time available for other activities, such as foraging, which could potentially reduce foraging efficiency. Understanding the conditions associated with predation risk and the specific effects predation risk have on prey behavior is important because it has direct influences on the profitability of food items found under various conditions and states of the forager. The goals of this study were to assess how ducks perceived predation risk in various habitat types and how strongly perceived risk versus energetic demand affected foraging behavior. We manipulated food abundance in different wetland types in Illinois, USA to reduce confounding between food abundance and vegetation structure. We conducted focal‐animal behavioral samples on five duck species in treatment and control plots and used generalized linear mixed‐effects models to compare the effects of vegetation structure versus other factors on the intensity with which ducks fed and the duration of feeding stints. Mallards fed more intensively and, along with blue‐winged teal, used longer feeding stints in open habitats, consistent with the hypothesis that limited visibility was perceived to have a greater predation risk than unlimited visibility. The species temporally nearest to nesting, wood ducks, were willing to take more risks for a greater food reward, consistent with an increase in a marginal value of energy as they approached nesting. Our results indicate that some duck species value energy differently based on the surrounding vegetation structure and density. Furthermore, increases in the marginal value of energy can be more influential than perceived risk in shaping foraging behavior patterns. Based on these findings, we conclude that the value of various food items is not solely determined by energy contained in the item but by conditions in which it is found and the state of the forager. 相似文献
18.
Elizabeth S. Bonczek Kevin M. Ringelman Joseph R. Marty Samantha A. Collins 《The Journal of wildlife management》2022,86(6):e22247
Adult survival is a key driver of waterfowl population growth and is subject to temporal and spatial variation. Mottled ducks (Anas fulvigula) are native to the Gulf Coast and peninsular Florida, USA, and have suffered population declines over the past decade, especially in Texas and Louisiana, USA. Although the cause of this decline is not well understood, previous research concluded variation in survival contributed to nearly a third of variation in the species' population growth rate. We used global positioning system-groupe spécial mobile (GPS-GSM) transmitters to study temporal and spatial variation in survival of adult female western Gulf Coast mottled ducks in southwestern Louisiana, 2017–2020. We evaluated weekly survival models parameterized with combinations of hunted and non-hunted periods, biological seasons, and landcover types that were used by mottled ducks. There were 3 competitive survival models, and all contained 4 parameters that parsed the annual cycle into the non-hunted period, first part of the general waterfowl season, and second part of the waterfowl season, and included the proportion of GPS locations in agricultural lands. Weekly survival was 0.979 during the first part of the general waterfowl hunting season, and 0.996 during the second part of the general waterfowl season. Daily survival rate increased with an increasing proportion of locations logged in agricultural lands. Annual survival rates were similar to other waterfowl that are not experiencing population declines, which suggests survival is not limiting population growth of mottled ducks along the western Gulf Coast. Managers should ensure the availability of refuge areas where hunting is prohibited during the first part of the general waterfowl season, when mottled ducks are at an increased risk of mortality, in addition to the targeted conservation of agricultural lands that provide cover and forage. 相似文献
19.
Body size affects foraging and forage intake rates directly via energetic processes and indirectly through interactions with social status and social behaviour. Ambient temperature has a relatively greater effect on the energetics of smaller species, which also generally are more vulnerable to predator attacks than are larger species. We examined variability in an index of intake rates and an index of alertness in Lesser Snow Geese Chen caerulescens caerulescens and Ross's Geese Chen rossii wintering in southwest Louisiana. Specifically we examined variation in these response variables that could be attributed to species, age, family size and ambient temperature. We hypothesized that the smaller Ross's Geese would spend relatively more time feeding, exhibit relatively higher peck rates, spend more time alert or raise their heads up from feeding more frequently, and would respond to declining temperatures by increasing their proportion of time spent feeding. As predicted, we found that Ross's Geese spent more time feeding than did Snow Geese and had slightly higher peck rates than Snow Geese in one of two winters. Ross's Geese spent more time alert than did Snow Geese in one winter, but alert rates differed by family size, independent of species, in contrast to our prediction. In one winter, time spent foraging and walking was inversely related to average daily temperature, but both varied independently of species. Effects of age and family size on time budgets were generally independent of species and in accordance with previous studies. We conclude that body size is a key variable influencing time spent feeding in Ross's Geese, which may require a high time spent feeding at the expense of other activities. 相似文献
20.
Mottled ducks (Anas fulvigula) are endemic to the Gulf Coast of North America, and their range stretches from Alabama to the Laguna Madre of Mexico, with a distinct population in peninsular Florida and an introduced population in South Carolina. As one of the few non-migratory ducks in North America, mottled ducks depend on a variety of locally available habitat throughout the annual cycle, and threats to these landscapes may affect mottled ducks more acutely than migratory species. Annual population monitoring has revealed declines in mottled duck populations in Texas and Louisiana since 2008, and the genetic integrity of the Florida population has been muddled by the presence of large numbers of feral mallards (Anas platyrhynchos) resulting in hybridization. Similar to other closely related dabbling ducks, mottled duck populations are influenced by recruitment and breeding season survival, so changes in these factors may contribute to population decline. Accordingly, researchers have attempted to address various aspects of mottled duck breeding season ecology and population dynamics since the 1950s. We conducted a literature review on this topic by searching a combination of key terms using Google Scholar, including mottled duck, nesting ecology, habitat use, breeding incidence, nest success, brood, and breeding season survival, and followed citation trees to eventually aggregate information from nearly 50 publications on mottled duck breeding ecology. Our review concluded that mottled ducks use brackish and intermediate coastal marsh, including managed impoundments, and agricultural land during the breeding season. Their nests can be found in pastures, levees, dry cordgrass marsh, cutgrass marsh, spoil banks, and small islands. Nesting propensity and nest success estimates are often lower than other waterfowl species that are characterized by stable or increasing populations. Broods use wetlands composed of a mix of open water with submerged and emergent vegetation. Breeding season survival is higher for the Florida population than the western Gulf Coast population, but adult survival in both geographies is comparable to (or higher than) that of other dabbling duck species. Breeding habitat use, breeding season survival, and nest-site selection and success have been studied extensively in mottled ducks, whereas information on nesting propensity, renesting intensity, and post-hatch ecology is lacking. © 2021 The Wildlife Society. 相似文献