Keith L. Bildstein

CLIMATE CHANGE, HURRICANES AND TROPICAL STORMS, AND RISING SEA LEVEL IN COASTAL WETLANDS

Global climate change is expected to affect temperature and precipitation patterns, oceanic and atmospheric circulation, rate of rising sea level, and the frequency, intensity, timing, and distribution of hurricanes and tropical storms. The magnitude of these projected physical changes and their subsequent impacts on coastal wetlands will vary regionally. Coastal wetlands in the southeastern United States have naturally evolved under a regime of rising sea level and specific patterns of hurricane frequency, intensity, and timing. A review of known ecological effects of tropical storms and hurricanes indicates that storm timing, frequency, and intensity can alter coastal wetland hydrology, geomorphology, biotic structure, energetics, and nutrient cycling. Research conducted to examine the impacts of Hurricane Hugo on colonial waterbirds highlights the importance of long-term studies for identifying complex interactions that may otherwise be dismissed as stochastic processes. Rising sea level and even modest changes in the frequency, intensity, timing, and distribution of tropical storms and hurricanes are expected to have substantial impacts on coastal wetland patterns and processes. Persistence of coastal wetlands will be determined by the interactions of climate and anthropogenic effects, especially how humans respond to rising sea level and how further human encroachment on coastal wetlands affects resource exploitation, pollution, and water use. Long-term changes in the frequency, intensity, timing, and distribution of hurricanes and tropical storms will likely affect biotic functions (e.g., community structure, natural selection, extinction rates, and biodiversity) as well as underlying processes such as nutrient cycling and primary and secondary productivity. Reliable predictions of global-change impacts on coastal wetlands will require better understanding of the linkages among terrestrial, aquatic, wetland, atmospheric, oceanic, and human components. Developing this comprehensive understanding of the ecological ramifications of global change will necessitate close coordination among scientists from multiple disciplines and a balanced mixture of appropriate scientific approaches. For example, insights may be gained through the careful design and implementation of broad-scale comparative studies that incorporate salient patterns and processes, including treatment of anthropogenic influences. Well-designed, broad-scale comparative studies could serve as the scientific framework for developing relevant and focused long-term ecological research, monitoring programs, experiments, and modeling studies. Two conceptual models of broad-scale comparative research for assessing ecological responses to climate change are presented: utilizing space-for-time substitution coupled with long-term studies to assess impacts of rising sea level and disturbance on coastal wetlands, and utilizing the moisture-continuum model for assessing the effects of global change and associated shifts in moisture regimes on wetland ecosystems. Increased understanding of climate change will require concerted scientific efforts aimed at facilitating interdisciplinary research, enhancing data and information management, and developing new funding strategies.

Conserving migratory land birds in the New World: Do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a birds life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

Estimating updraft velocity components over large spatial scales: contrasting migration strategies of golden eagles and turkey vultures

Soaring birds migrate in massive numbers worldwide. These migrations are complex and dynamic phenomena, strongly influenced by meteorological conditions that produce thermal and orographic uplift as the birds traverse the landscape. Herein we report on how methods were developed to estimate the strength of thermal and orographic uplift using publicly available digital weather and topography datasets at continental scale. We apply these methods to contrast flight strategies of two morphologically similar but behaviourally different species: golden eagle, Aquila chrysaetos, and turkey vulture, Cathartes aura, during autumn migration across eastern North America tracked using GPS tags. We show that turkey vultures nearly exclusively used thermal lift, whereas golden eagles primarily use orographic lift during migration. It has not been shown previously that migration tracks are affected by species-specific specialisation to a particular uplift mode. The methods introduced herein to estimate uplift components and test for differences in weather use can be applied to study movement of any soaring species.

Movement ecology of migration in turkey vultures.

We develop individual-based movement ecology models (MEM) to explore turkey vulture (Cathartes aura) migration decisions at both hourly and daily scales. Vulture movements in 10 migration events were recorded with satellite-reporting GPS sensors, and flight behavior was observed visually, aided by on-the-ground VHF radio-tracking. We used the North American Regional Reanalysis dataset to obtain values for wind speed, turbulent kinetic energy (TKE), and cloud height and used a digital elevation model for a measure of terrain ruggedness. A turkey vulture fitted with a heart-rate logger during 124 h of flight during 38 contiguous days showed only a small increase in mean heart rate as distance traveled per day increased, which suggests that, unlike flapping, soaring flight does not lead to greatly increased metabolic costs. Data from 10 migrations for 724 hourly segments and 152 daily segments showed that vultures depended heavily upon high levels of TKE in the atmospheric boundary layer to increase flight distances and maintain preferred bearings at both hourly and daily scales. We suggest how the MEM can be extended to other spatial and temporal scales of avian migration. Our success in relating model-derived atmospheric variables to migration indicates the potential of using regional reanalysis data, as here, and potentially other regional, higher-resolution, atmospheric models in predicting changing movement patterns of soaring birds under various scenarios of climate and land use change.

Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America.

Variation is key to the adaptability of species and their ability to survive changes to the Earths climate and habitats. Plasticity in movement strategies allows a species to better track spatial dynamics of habitat quality. We describe the mechanisms that shape the movement of a long-distance migrant bird (turkey vulture, Cathartes aura) across two continents using satellite tracking coupled with remote-sensing science. Using nearly 10 years of data from 24 satellite-tracked vultures in four distinct populations, we describe an enormous amount of variation in their movement patterns. We related vulture movement to environmental conditions and found important correlations explaining how far they need to move to find food (indexed by the Normalized Difference Vegetation Index) and how fast they can move based on the prevalence of thermals and temperature. We conclude that the extensive variability in the movement ecology of turkey vultures, facilitated by their energetically efficient thermal soaring, suggests that this species is likely to do well across periods of modest climate change. The large scale and sample sizes needed for such analysis in a widespread migrant emphasizes the need for integrated and collaborative efforts to obtain tracking data and for policies, tools and open datasets to encourage such collaborations and data sharing.

Is pre-breeding prospecting behaviour affected by snow cover in the irruptive snowy owl? A test using state-space modelling and environmental data annotated via Movebank

BackgroundTracking individual animals using satellite telemetry has improved our understanding of animal movements considerably. Nonetheless, thorough statistical treatment of Argos datasets is often jeopardized by their coarse temporal resolution. State-space modelling can circumvent some of the inherent limitations of Argos datasets, such as the limited temporal resolution of locations and the lack of information pertaining to the behavioural state of the tracked individuals at each location. We coupled state-space modelling with environmental characterisation of modelled locations on a 3-year Argos dataset of 9 breeding snowy owls to assess whether searching behaviour for breeding sites was affected by snow cover and depth in an arctic predator that shows a lack of breeding site fidelity.ResultsThe state-space modelling approach allowed the discrimination of two behavioural states (searching and moving) during pre-breeding movements. Tracked snowy owls constantly switched from moving to searching behaviour during pre-breeding movements from mid-March to early June. Searching events were more likely where snow cover and depth was low. This suggests that snowy owls adapt their searching effort to environmental conditions encountered along their path.ConclusionsThis modelling technique increases our understanding of movement ecology and behavioural decisions of individual animals both locally and globally according to environmental variables.

Dietary Salt as a Physiological Constraint in White Ibis Breeding in an Estuary

We monitored the growth and metabolism of 28 nestling white ibis (Eudocimus albus) taken at 21 d of age and hand-reared for 3 wk on ad lib. diets of (1) freshwater crayfish (Procambarus clarkii; salt content 535 mosm kg⁻¹; n = 12), (2) brackishwater fiddler crabs (Uca spp.; 1,080 mosm kg⁻¹; n = 12), and (3)freshwater crayfish salt-loaded to a salt content approximating that of fiddler crabs (1,090 mosm kg⁻¹; n = 4). Brackish water (480 mosm kg⁻¹) or fresh tap water was provided to the birds on an ad lib. basis. Nestlings maintained on the unaltered-crayfish diet gained mass at rates similar to those of parent-reared nestlings. Birds on the fiddler-crab and salt-loaded crayfish diets lost approximately 3% of their body massper day until fresh water was substituted for brackish water 7 d into the experiment. Nestling hematocrits, serum osmolality, and serum electrolyte levels indicated that during the first week of the experiment, nestlings on the two high-salt diets were dehydrated and salt loaded. This occurred even though birds on high-salt diets exhibited hypertrophic development of their salt glands. When birds on the high-salt diets were allowed to drink fresh water, all began gaining mass within 2 d, and their serum osmolality and salt returned to levels similar to those of nestlings on the low-salt diet. Our experiments indicate that a physiological constraint acting on nestling ibis is responsible for the fact that ibis breeding in coastal colonies fly long distances inland to secure freshwater prey for their young.

FEEDING PATTERNS AND AGGRESSIVE BEHAVIOR IN JUVENILE AND ADULT AMERICAN FLAMINGOS

We studied the feeding and aggressive behavior of adult and juvenile American Flamingos (Phoenicopterus ruber ruber) at a coastal salina in Venezuela. Most birds fed in large flocks in early morning, roosted at mid-day, and resumed feeding in late afternoon- early evening. Flamingos rarely flew, except when disturbed. Adults in our study stepped at the same rates while feeding as did Chilean Flamingos (P. chilensis) feeding in the Chilean and Bolivian Andes. Paired observations of birds within mixed-age flocks revealed that adults stepped more during feeding bouts, but less between bouts, and spent more time overall with their bills in the water filter-feeding, than did juveniles. We calculate that the food-intake rate of juveniles was, at most, 82% that of adults. Both adults and juveniles walk-fed and stamp-fed. Juveniles, but not adults, were twice as likely to be supplanted when stamp-feeding than when walk-feeding. Juveniles were more often involved in ag- gression, especially as recipients, than were adults. Aggressive encounters significantly af- fected the amount of time flamingos spent filter feeding.

Long-term counts of migrating raptors : A role for volunteers in wildlife research

The science of conservation biology and the practice of wildlife management depend upon long-term databases, but collecting such data can be difficult, expensive, and labor intensive. Conservation biologists and wildlife managers have long used nonprofessional volunteers to collect much of the information needed to make informed decisions concerning the resources they are attempting to understand and protect. The advent of the modern field guide in the 1930s, together with the growing availability of prismatic binoculars, heralded the modern age of recreational bird watching. Since then, bird watchers have made significant and substantial contributions to our understanding of bird populations in North America. Hawk Mountain Sanctuary in eastern Pennsylvania has used volunteer hawk watchers, in conjunction with its own paid staff, to help create the longest and most complete record of raptor migration in the world. The Sanctuarys annual counts of migrating raptors have proved a critical resource in assessing long-term trends of raptor populations in northeastem North America. The extensive database played a key role in exposing the threat of organochlorine pesticides to bald eagles (Haliaeetus leucocephalus) and other predatory birds earlier this century, as well as in tracking more recent recoveries in many of the same populations. Recent analyses of the database are yielding insights into (1) how cold fronts affect counts of raptors at migration watchsites, (2) the extent to which climate change affects the timing of raptor migration, and (3) changes in the migratory habits of sharp-shinned hawks (Accipiter striatus) in eastern North America. I submit that volunteers will play increasingly important roles in wildlife conservation wherever their efforts can be coupled with those of professional practitioners in the field.

WITHIN- AND AMONG-YEAR EFFECTS OF COLD FRONTS ON MIGRATING RAPTORS AT HAWK MOUNTAIN, PENNSYLVANIA, 1934-1991

ABsTRAcr.--Cold-front passage has long been associated with south-bound raptor migration in northeastern North America. We used Hawk Mountain Sanctuarys 55-year database to calculate abundance indices of 14 raptor species at the site. These indices, together with data taken from coincidental U.S. Department of Commerce daily weather maps, were used to investigate the extent to which raptor migration at Hawk Mountain is associated with the passage of cold fronts. Daily abundance indices for 12 of 14 raptor species exhibited significant increases during one or more of the three days following frontal passage. Three basic patterns emerged, which differed in the number of days after frontal passage on which peak migration occurred. The patterns fit the flight behavior of the species involved. We failed to detect a long-term linear trend in numbers of fall-season cold fronts at the site. Stepwise multipleregression analyses revealed that annual-abundance indices were not influenced by annual variation in the numbers of cold fronts passing the Sanctuary at the time of fall migration. Overall, our analyses confirm the results of earlier, short-term studies demonstrating withinyear effects of frontal passage on raptor migration. Our failure to detect among-year effects of frontal passage rates on annual counts of raptors migrating past the site supports the notion that cold fronts enhance fall migration rather than simply making the birds more visible to observers at such times by forcing them closer to the watch site. Received 6 December 1994, accepted 25 April 1995.