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Large-scale conversion of uncultivated land to agriculture threatens wildlife and can diminish ecosystem services provided by nature. Understanding how wildlife provision ecosystem services may incentivize wildlife conservation in agricultural landscapes. Attracting Barn Owls (Tyto furcata) to nest on farms for pest management has been implemented worldwide but has not been evaluated in vineyard agroecosystems. Napa Valley, California, is a renowned winegrape growing region, and viticulturists encourage Barn Owl occupancy to help minimize damage from Botta's pocket gophers (Thomomys bottae) and voles (Microtus spp.). This study modeled the use of habitats in space and time by hunting Barn Owls, providing information about their potential to provide the critical ecosystem service of pest consumption. We used global positioning system tags to track hunting owls and used a resource selection function to compare used and available habitats. We constructed the intensity of use and home range-movement maps using a time local convex hull analysis from location data. We found that Barn Owls selected uncultivated habitats when hunting, some of which were relatively rare on the landscape. Approximately, one-third of Barn Owl hunting locations occurred in vineyards, but this use was out of proportion to the availability of vineyards, which comprised 50% of the area around nest boxes. The owls' use of vineyards increased with decreasing amount of selected uncultivated habitat in the landscape. However, as reported by a previous study, the occupancy of nest boxes in vineyards increases with uncultivated habitats nearby. Future research should model landscape composition to determine the amount of preferred habitat necessary to support occupancy as well as hunting in vineyards. A true test of pest management by Barn Owls awaits experimentation coupled with monitoring rodent populations.
LAY SUMMARY
Agricultural landscapes are composed of a variety of habitats, both cultivated and uncultivated, and it is vital to understand how wildlife use these areas, especially for predatory birds that may help control agricultural pests.
We used Global Positioning System telemetry to examine the selection of habitats for hunting by Barn Owls breeding in nest boxes in winegrape vineyards.
Barn Owls selected uncultivated habitats, such as oak savanna, riparian forest, and grasslands for hunting, some of which were relatively rare on the landscape.
Nonetheless, approximately, one-third of Barn Owl hunting locations occurred in vineyards, suggesting their predation of rodent pests could be useful for farmers.
A flurry of recently published studies indicates that both insects and birds have experienced wide-scale population declines in the last several decades. Curiously, whether insect and bird declines are causally linked has received little empirical attention. Here, we hypothesize that insect declines are an important factor contributing to the decline of insectivorous birds. We further suggest that insect populations essential to insectivorous birds decline whenever nonnative lumber, ornamental, or invasive plant species replace native plant communities. We support our hypothesis by reviewing studies that show (1) due to host plant specialization, insect herbivores typically do poorly on non-native plants; (2) birds are often food limited; (3) populations of insectivorous bird species fluctuate with the supply of essential insect prey; (4) not all arthropod prey support bird reproduction equally well; and (5) terrestrial birds for which insects are an essential source of food have declined by 2.9 billion individuals over the last 50 years, while terrestrial birds that do not depend on insects during their life history have gained by 26.2 million individuals, a 111-fold difference. Understanding the consequences of insect declines, particularly as they affect charismatic animals like birds, may motivate land managers, homeowners, and restoration ecologists to take actions that reverse these declines by favoring the native plant species that support insect herbivores most productively.
LAY SUMMARY
There may be a link between declining insect populations and bird population declines.
Bird populations are often limited by the amount of insect food available to them.
Most of the bird species that have declined in the last 50 years are those that depend on insects for food.
One cause of insect declines is the widespread use of non-native plants in forestry and horticulture that do not support insects.
The loss of insects, birds, and other forms of life is important because those are the species that run the ecosystems that support humans.
One solution to this problem is to increase the populations of the insects that birds depend on by increasing our use of native plants in managed landscapes.
Worldwide, shorebird populations are declining. Our objectives were to examine abundance trends of shorebirds regularly wintering at Tomales Bay, Marin County, California, accounting for the local effects of rainfall, raptors, and the restoration of part of the bay to tidal wetlands. From November 1989 to February 2019, we conducted 177 comprehensive winter shorebird surveys of Tomales Bay; we averaged 5.7 ± 0.9 (mean ± SD) winter surveys per year. In 30 yr, we counted 1,215,821 shorebirds of 31 species. We used generalized linear models and multi-model inference to evaluate trends in shorebird abundance while accounting for local sources of variation. We conducted separate analyses for 14 species seen in at least 20 of the 30 yr of monitoring and for all shorebird species combined. During the study, the abundance of all species combined declined 66% (52% in the North Bay and 81% in the South Bay) with the most rapid decline in the first 10 yr of monitoring. Of 13 species for which year was in the top model, 10 species decreased in abundance and 3 species increased. Dunlin and Western Sandpiper accounted for the greatest losses in total numbers. The best-supported models to estimate trends in shorebirds included predictors for year and North Bay vs. South Bay. Of the local variables we considered, rainfall was included in 10 of the 15 best-supported models (including all species combined), negatively affecting the numbers of all species except Willets. The wetland restoration project was included in 5 top models, with a short-term positive impact. Raptor abundance was included in 3 top models with mixed results. Our results show that effective conservation and management of local shorebird populations must be linked with regional/global efforts if we are to reverse negative shorebird trends.
LAY SUMMARY
Given declining North American shorebird populations, we analyzed population trends of shorebirds wintering at Tomales Bay, Marin County, California, spanning 30 seasons from November 1989 to February 2019, and reasons for these trends.
Survey teams counted over 1.2 million shorebirds of 31 species, of which we analyzed trends for 14 regularly occurring species.
During this period, overall shorebird numbers declined by 66%; 10 species declined, 3 species increased, and 1 species did not change.
Dunlin and Western Sandpiper suffered the greatest losses, while Least Sandpipers and yellowlegs (predominantly Greater Yellowlegs) increased the most.
Effective conservation and management of local shorebird populations must be linked with regional/global efforts to reverse negative shorebird trends.
Examination of population trends for raptors is a research priority, especially given recent concern for their conservation status. Road counts—in which raptors are counted from a motorized vehicle moving along the ground—might be an effective method to expand the monitoring of raptor populations and estimation of trends. Here, we review past methods used to perform road counts of raptors and present revised recommendations to aid collaboration, data transfer, and interpretation of results across monitoring programs. We performed a standardized keyword search of online literature databases to obtain 148 past road count studies. The number of studies employing road counts increased per year since the 1970s. Most of these studies occurred in North America. The times of day during which road counts were conducted ranged from sunrise to sunset, and maximum speeds ranged from 10 to 113 km hr–1. The number of observers ranged from 1 (the driver) to 5. Most (93) of the studies used unlimited-width transects and fixed-width transects ranging from 0.02 to 2.50 km wide. Sixteen percent of studies calculated or corrected for the probability of detection. Such broad variation in the methodology used during road counts, coupled with infrequent correction for detection, hampers the interpretation of results across road survey programs. We suggest that road count practitioners should emphasize the collection of data, such as speed, number of observers, and distance to observed raptors, which would allow for the calculation of detection-corrected estimates. Such correction would likely improve trend estimation. Recent technology, including mobile apps, allows researchers to collect such data relatively easily, conducting their own studies while contributing to a broader raptor monitoring initiative. Road counts will likely become more useful as statistical analysis of road count data improves and researchers pool their data in a global effort to monitor raptors.
LAY SUMMARY
Raptors provide ecosystem services, are environmental indicators, and their populations are generally declining.
Road counts are commonly used to survey raptors and, therefore, might be an effective method to expand the monitoring of raptor populations.
We review studies employing road counts and demonstrate large variation in methodology, including vehicle speeds, times of day and year, number of observers, and transect width.
We suggest that road count practitioners record information that affects the detectability of raptors, so detection-corrected estimates can be reliably compared within and among monitoring programs.
Advances in technology and statistical methods, along with standardized data collection, will increase the utility of road counts in monitoring population trends of raptors across the globe.
As bio-indicators, seabirds across the globe help us understand how our environment is changing, and how this is affecting our wildlife. Little Penguins (Eudyptula minor) in Australia are a key species in understanding the changes to the Australian environment. However, studies generally focus on the effects of oceanic changes without always accounting for the potential interactions with the environmental conditions experienced on land during breeding. This study examined the relationships between both marine and terrestrial environmental variables and breeding success in South Australian Little Penguins, observing 10 colonies over a nonconsecutive 28-yr time period. Our results showed that South Australian Little Penguins had a lower breeding success (fewer fledglings produced per pair) when sea surface temperatures were higher in the 3 mo before breeding and when high winds occurred during the breeding season. We also observed local variation between the colonies: breeding success was only influenced by environmental variables for colonies located near open waters and not for colonies located in enclosed bays. These results confirm the idea that future oceanographic warming is expected to reduce the breeding success (and population size) of some Australian seabirds, including Little Penguins.
LAY SUMMARY
We showed that increased marine temperatures and high winds have negative effects on the reproductivity of South Australian Little Penguins.
Seabirds are good indicators of changes in their environment because their demographic processes are often affected (either positively or negatively) by environmental variability.
Here, we investigated the relationship between the breeding success of South Australian Little Penguins and environmental variables at 10 colonies over a nonconsecutive 28-year time period.
Climate change is of increasing concern, and our study supports the idea that future environmental warming will have negative impacts on some seabird species, including Little Penguins.
Effective management of wildlife requires a full understanding of population dynamics and knowledge of potential drivers that influence population growth. The Ruffed Grouse (Bonasa umbellus) is a popular upland game bird widely distributed across the northern United States and Canada that has experienced population declines within portions of its range in response to forest maturation and habitat loss. Although the species has been extensively studied, few efforts have been made to synthesize demographic data into a sensitivity analysis to guide management actions. We reviewed the literature and compiled Ruffed Grouse vital rates from 14 field studies conducted across four decades (1982–2018) within the Upper Great Lakes region of Michigan, Minnesota, and Wisconsin, USA. We parameterized a deterministic matrix model to evaluate population dynamics and conducted sensitivity analyses to identify vital rates projected to have the greatest influence on the finite rate of population change (λ). Our modeling effort projected a stable but highly variable annual rate of population change (λ = 1.01; 95% CI = 0.88–1.14) for Ruffed Grouse in the Upper Great Lakes region. Stochastic rates of population change derived from spring drumming surveys (λ = 1.01; 95% CI = 0.61–1.45) and Christmas Bird Count surveys (λ = 0.99; 95% CI = 0.62–1.76) of the corresponding regional population provided validation of stable trends over the same time period as our demographic model. Prospective elasticities and variance-scaled sensitivities suggested λ would be greatly influenced by components of reproductive performance: nesting success, chick survival, and post-fledging juvenile survival. Retrospective analysis indicated that much of the overall variability in λ and annual productivity was also attributed to annual variation in nesting success. Management of this species has often focused on fall and overwinter survival, but population projection models provided little evidence that survival was the predominant factor affecting population growth of Ruffed Grouse in this region. A suite of confounding factors and demographic processes that drive population trends can differ significantly across a species' range. In the Upper Great Lakes region, management efforts aimed at maximizing reproductive success would likely have the greatest potential influence on Ruffed Grouse population growth. Other types of systematic, regional survey data can also be useful for validating population trends derived from demographic modeling studies.
LAY SUMMARY
The Ruffed Grouse (Bonasa umbellus) has been extensively studied, but few efforts have been made to synthesize demographic data into a sensitivity analysis to guide management.
A comprehensive understanding of life history traits and vital rates that influence population growth is crucial for maximizing wildlife conservation and management efforts.
We summarized Ruffed Grouse vital rates from field studies within the Upper Great Lakes region of Michigan, Minnesota, and Wisconsin, USA, to evaluate population growth.
Our analyses projected a stable but highly variable annual rate of population change for Ruffed Grouse in the Upper Great Lakes region.
Management efforts aimed at maximizing reproductive success, particularly nesting success and chick survival, would likely have the greatest potential influence on Ruffed Grouse population growth.
Migration is an important component of some species full annual cycle. California's Central Valley and the Colorado River Delta provide important riparian and wetland habitats for migrating waterbirds in the arid west of North America, but little is known about whether these locations are important at the population level to migrating landbirds. We used eBird Status and Trends abundance data to quantify the importance of the Central Valley and Colorado River Delta to landbirds by estimating the proportion of the breeding population of 112 species that use each site during migration. We found that ∼17 million landbirds use the Colorado River Delta in the spring and ∼14 million in the fall. Across 4 study regions in the Central Valley, up to ∼65 million landbirds migrate through in the spring and up to ∼48 million in the fall. In the spring and fall, respectively, up to 37 and up to 30 species had at least 1% of their continental population migrate through the study regions. We also quantified the spatial concentration of each species across latitudinal transects to determine the extent to which study regions were acting as migratory bottlenecks. Landbird abundances were spatially concentrated in study regions 29.4% of all migration weeks, indicating that each study region acts as a migratory bottleneck. This application of eBird data is a powerful approach to quantifying the importance of sites to migrating birds. Our results provide evidence of population-level importance of the Central Valley and Colorado River Delta for many migratory landbirds.
LAY SUMMARY
Migratory birds are declining throughout North America, and we must identify places birds need during migration so they can safely move between breeding and winter locations.
The Colorado River Delta and the Central Valley are known as important landscapes for wildlife, but their importance to migrating landbirds is not well known.
We used eBird data to measure the importance of the Colorado River Delta and California's Central Valley to birds that migrate through western North America.
Many species have substantial portions of their populations that depend on these locations during migration.
Conservation of the Colorado River Delta and Central Valley are important for the entire populations of many breeding landbird species of North America.
The status and trend estimates derived from the North American Breeding Bird Survey (BBS) are critical sources of information for bird conservation. However, the estimates are partly dependent on the statistical model used. Therefore, multiple models are useful because not all of the varied uses of these estimates (e.g., inferences about long-term change, annual fluctuations, population cycles, and recovery of once-declining populations) are supported equally well by a single statistical model. Here we describe Bayesian hierarchical generalized additive models (GAMs) for the BBS, which share information on the pattern of population change across a species' range. We demonstrate the models and their benefits using data from a selection of species, and we run full cross-validation of the GAMs against 2 other models to compare the predictive fit. The GAMs have a better predictive fit than the standard model for all species studied here and comparable predictive fit to an alternative first difference model. In addition, one version of the GAM described here (GAMYE) estimates a population trajectory that can be decomposed into a smooth component and the annual fluctuations around that smooth component. This decomposition allows trend estimates based only on the smooth component, which are more stable between years and are therefore particularly useful for trend-based status assessments, such as those by the International Union for the Conservation of Nature. It also allows for the easy customization of the model to incorporate covariates that influence the smooth component separately from those that influence annual fluctuations (e.g., climate cycles vs. annual precipitation). For these reasons and more, this GAMYE model is a particularly useful model for the BBS-based status and trend estimates.
LAY SUMMARY
The status and trend estimates derived from the North American Breeding Bird Survey are critical sources of information for bird conservation, but they are partly dependent on the statistical model used.
We describe a model to estimate population status and trends from the North American Breeding Bird Survey data, using a Bayesian hierarchical generalized additive mixed model that allows for flexible population trajectories and shares information on population change across a species' range.
The model generates estimates that are broadly useful for a wide range of common conservation applications, such as International Union for the Conservation of Nature status assessments based on trends or changes in the rates of decline for species of concern, and the estimates have better or similar predictive accuracy to other models.
Natural gas compressor stations emit loud, low-frequency noise that travels hundreds of meters into undisturbed habitat. We used experimental playback of natural gas compressor noise to determine whether and how noise influenced settlement decisions and reproductive output as well as when in the nesting cycle birds were most affected by compressor noise. We established 80 nest boxes to attract Eastern Bluebirds (Sialia sialis) and Tree Swallows (Tachycineta bicolor) to locations where they had not previously nested and experimentally introduced shale gas compressor noise to half the boxes while the other 40 boxes served as controls. Our experimental design allowed us to control for the confounding effects of both physical changes to the environment associated with compressor stations as well as site tenacity or the tendency for birds to return to the specific locations where they had previously bred. We incorporated behavioral observations with video cameras placed within boxes to determine how changes in behavior might lead to any noted changes in fitness. Neither species demonstrated a preference for box type (quiet or noisy), and there was no difference in clutch size between box types. In both species, we observed a reduction in incubation time, hatching success, and fledging success (proportion of all eggs that fledged) between quiet and noisy boxes but no difference in provisioning rates. Nest success (probability of fledging at least one young; calculated from all nests that were initiated) was not affected by noise in either species suggesting that noise did not increase rates of either depredation or abandonment but instead negatively impacted fitness through reduced hatching and fledging success. Compressor noise caused behavioral changes that led to reduced reproductive success; for Eastern Bluebirds and Tree Swallows, gas infrastructure can create an equal-preference ecological trap where birds do not distinguish between lower and higher quality territories even when they incur fitness costs.
LAY SUMMARY
Natural gas is one of the most rapidly growing global energy sources with shale gas resources in particular expected to experience continued expansion.
We used experimental playback of natural gas compressor noise to expose nesting Eastern Bluebirds and Tree Swallows to compressor noise.
Eastern Bluebirds and Tree Swallows nesting in noisy nest boxes spent less time incubating their eggs, had fewer eggs hatch, and produced fewer young than their neighbors nesting in quiet boxes.
Although there was a direct fitness cost, birds did not preferentially select quiet boxes over noisy boxes, suggesting they do not recognize the reduction in habitat quality resulting from the noise.
Because shale gas development often occurs in relatively undisturbed natural areas that provide important habitat for breeding birds, it is imperative that we develop plans to manage and mitigate noise. These practices will also benefit other wildlife and people.
Line markers are widely used to mitigate bird collisions with power lines, but few studies have robustly tested their efficacy. Power line collisions are an escalating problem for several threatened bird species endemic to southern Africa, so it is critical to know whether or not marking works to adequately manage this problem. Over 8 yr, a large-scale experiment was set up on 72 of 117 km of monitored transmission power lines in the eastern Karoo, South Africa, to assess whether line markers reduce bird collision mortality, particularly for Blue Cranes (Grus paradisea) and Ludwig's Bustards (Neotis ludwigii). We tested the 2 marking devices commonly used in South Africa: bird flappers and static bird flight diverters. Using a before-after-control-impact design, we show that line marking reduced collision rates for Blue Cranes by 92% (95% confidence interval [CI]: 77–97%) and all large birds by 51% (95% CI: 23–68%), but had no effect on bustards. Both marker types appeared similarly effective. Given that monitoring at this site also confirmed high levels of mortality of a range of species of conservation concern, we recommend that marking be widely installed on new power lines. However, other options need to be explored urgently to reduce collision mortality of bustards. Five bustard species were in the top 10 list of most frequently found carcasses, and high collision rates of Ludwig's Bustards (0.68 birds km–1 yr–1 uncorrected for survey biases) add to wider concerns about population-level effects for this range-restricted and Endangered species.
LAY SUMMARY
Power line collision mortality is a serious and accelerating bird conservation problem globally, particularly in the developing world with rapidly expanding electricity networks and high avifaunal diversity.
Line marking is the most widespread collision mitigation measure employed worldwide, but there have been relatively few systematic tests of its efficacy.
We set up a large-scale experiment in South Africa with a before-after-control-impact design on 72 km of transmission power line over 8 years to test two marking devices for reducing collisions of large terrestrial birds.
Line marking reduced overall bird mortality by 51%, and Blue Crane mortality by 92%, but was not effective for bustards.
Line marking should therefore be widely deployed, but alternative mitigation measures are urgently required for bustards that are threatened all over the world by collisions.
Temperature at fine spatial scales is an important driver of nest site selection for many avian species during the breeding season and can influence nest success. Sagebrush (Artemisia spp.) communities have areas with high levels of vegetation heterogeneity and high thermal variation; however, fire removes vegetation that provides protection from predators and extreme environmental conditions. To examine the influence of microclimates on Greater Sage-Grouse (Centrocercus urophasianus) nest site selection and nest success in a fire-affected landscape, we measured black bulb temperature (Tbb) and vegetation attributes (e.g., visual obstruction) at 3 spatial scales (i.e. nest bowl, microsite, and landscape) in unburned and burned areas. Nest bowls exhibited greater buffering of Tbb than both nearby microsites and the broader landscape. Notably, nest bowls were warmer in cold temperatures, and cooler in hot temperatures, than nearby microsites and the broader landscape, regardless of burn stage. Nest survival (NS) was higher for nests in unburned areas compared to nests in burned areas (unburned NS = 0.43, 95% confidence interval [CI]: 0.33–0.54; burned NS = 0.24, 95% CI: 0.10–0.46). The amount of bare ground was negatively associated with NS, but effects diminished as the amount of bare ground reached low levels. Shrub height and visual obstruction were positively associated with NS during the entire study period, whereas minimum Tbb had a weaker effect. Our findings demonstrate that thermoregulatory selection by Greater Sage-Grouse at nest sites had marginal effects on their NS. However, given that increases in vegetation structure (e.g., shrub height) provide thermal refuge and increase NS, vegetation remnants or regeneration in a post-fire landscape could be critical to Greater Sage-Grouse nesting ecology.
LAY SUMMARY
Greater Sage-Grouse selection of nest bowls based on background temperature had marginal effects on their nest survival in a fire-affected landscape.
Greater Sage-Grouse nest bowls in unburned and burned areas buffered thermal conditions more than nearby microsites and the broader landscape in the Trout Creek Mountains, Oregon and Nevada.
Nest bowls were warmer in cold temperatures, and cooler in hot temperatures, than nearby microsites and the broader landscape, regardless of burn stage.
Nest survival was higher for nests in unburned areas compared to nests in burned areas.
Amount of bare ground was negatively associated with nest survival; and shrub height and visual obstruction were positively associated with daily nest survival, whereas microclimate had a weak effect.
Determining how site characteristics influence reproductive success can help guide conservation planning for declining wildlife populations. For colonially breeding seabirds, nest survival and predation risk can be influenced by both colony and nest site characteristics such as colony size, nest density, and nest location. We evaluated the reproductive success of a declining population of Roseate Terns (Sterna dougallii) in the United States and British Virgin Islands to identify primary causes of nest failure and investigate the influence of colony and nest site covariates on nest survival. In addition, we measured the influence of colony characteristics on chick provisioning to determine if resource competition in larger colonies affected foraging rates. Monitoring was conducted in 2017–2018 via motion-triggered cameras, which enable 24-hr monitoring with minimal nest disturbance. Nest survival was defined by both hatch success and early chick success, defined as a chick surviving from hatching through the fourth post-hatch day. We monitored 118 nests in 6 colonies over the 2 breeding seasons. We found that predation was the primary cause of nest failure. Both hatch and nest success increased with colony size, and neither nest survival nor predation probability was influenced by individual nest site characteristics. Provisioning rates were comparable among colony sites and did not vary with colony size. Our results suggest that directing management efforts toward enhancing colony size, rather than focusing on nest site characteristics, can be beneficial for tropical seabird conservation.
LAY SUMMARY
Determining how site characteristics enhance nest survival can benefit the conservation of threatened and endangered seabirds like Roseate Terns (Sterna dougallii).
We used nest cameras to determine the effects of colony and nest site covariates on reproductive success, predation probability, and provisioning rates of Roseate Terns breeding in the Virgin Islands in six colonies over two years.
Predation was the primary cause of nest failure. Both hatch and early chick survival increased with colony size but were not otherwise influenced by site characteristics.
Chick provisioning rates were not influenced by colony size.
For tropical seabirds, directing management toward increasing colony size may be an effective strategy for enhancing conservation efforts while maximizing limited management resources.
As avian reproductive success is generally prey limited, identifying important prey types or sizes and understanding mechanisms governing prey availability are important objectives for avian conservation ecology. Irruptive White Ibis (Eudocimus albus) nesting at coastal colonies in the southern Everglades numbered over 100,000 nests in the 1930s. A century of drainage and altered hydrologic patterns reduced aquatic prey availability and eliminated large nesting events; nesting activity in recent decades has been typically less than 5% of historical peaks. Hydrologic restoration is expected to increase ibis nesting activity, but which prey types will support high nesting effort is less clear. In 2017 and 2018, we collected food boluses from White Ibis chicks at coastal colonies in Everglades National Park. We also monitored regional nesting activity from 1999 to 2018. In 2017, the region had 1,075 nests, typical of the past several decades; but in 2018, there were 30,420 nests, representing the highest recorded nesting activity in 87 yr. Prey composition varied between years; estuarine crabs dominated nestling boluses in 2017, while crayfish and fish were dominant prey in 2018. Crayfish, especially Procambarus alleni, were heavily exploited by ibis early in the 2018 breeding season, while fish were used more at the end. Crayfish abundances in wetlands near the colonies were higher prior to 2018, and more crayfish-producing short-hydroperiod wetlands remained available for ibis foraging in 2018. Our results support previous studies indicating that crayfish are important prey for breeding ibises and suggest that unprecedented, extensive flooding of seasonal wetlands promoted crayfish production and initiated the irruptive breeding in 2018. Our observations indicate that rehydration of the southern Everglades could restore ibis nesting activity at coastal colonies, but further investigations of hydrologic variation, crayfish production, and ibis foraging and nesting activity will be helpful to understand these dynamics and the importance of short-hydroperiod wetlands.
LAY SUMMARY
Increasing White Ibis breeding in the southern Everglades and increasing the frequency of large nesting events (tens of thousands of nest attempts) are stated ecological goals of Everglades restoration.
Little is known about which prey support White Ibis breeding and large nesting events in the southern Everglades.
We found that White Ibis nesting in the southern Everglades used freshwater crayfish heavily in a year with extraordinarily high breeding activity and used estuarine crabs heavily in a year with poor breeding activity.
Extensive flooding of seasonal wetlands, following hurricane Irma, was correlated with higher crayfish abundances an foraging habitat availability in the year with higher White Ibis breeding activity.
Our observations indicate that ecological processes supporting large nesting events of White Ibis could be restored with additional freshwater flooding of the southwestern Everglades.
Stopovers comprise a significant proportion of the time that many birds spend migrating, and researchers have long relied on these events to define and classify broader migratory strategies. Analyses of stopovers often assume that individuals stop primarily or exclusively in order to replenish energy stores, but other non-fueling behaviors have also been described during stopover events and can influence stopover incidence and duration. Here, we discuss the growing demand for understanding these non-fueling behaviors and for restoring the inherent behavioral complexity to stopover events. We begin by describing how light-weight tracking technologies allow researchers to follow individuals along their entire migratory journeys, capturing stopovers that controvert the traditional stop–refuel–resume paradigm. We then discuss 5 well-identified non-fueling behaviors—recovering, sleeping, waiting, information gathering, and social interactions—and examine how including these behaviors can alter interpretations of individual movement paths. Finally, we outline emerging directions for identifying these behaviors and look to larger implications for population management and site conservation along migratory flyways.
LAY SUMMARY
Many birds make stops during their migratory journeys, and they may have various reasons for stopping.
In the past, researchers have investigated the role of energy stores in stopping decisions, but birds may also need to stop or prolong their time at a stopping site in order to recover from bodily stress, catch up on lost sleep, wait for travel conditions to improve, or reconvene with other migrants.
Non-fueling behaviors have been more difficult to study, but novel approaches that combine individual movement data with information about ecological and physiological conditions along the way are offering insights into when and where they occur.
Investigating non-fueling stopping behaviors can reveal a more complex story about how birds navigate the challenges of seasonal migration.
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