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Implications for bird aircraft strike hazard by bald eagles: Bald Eagles and Bird Aircraft Strike Hazard
Abstract
Bald eagle (Haliaeetus leucocephalus) aircraft strikes have increased since 1998 because their populations have recovered to near historical sizes. Their attraction to airfields and their large body size makes them a danger to aircraft and therefore important to airfield managers. However, bald eagle management is complicated by their special protected status and the place they hold in the eyes of the public. To help airfield managers plan monitoring efforts and make informed management decisions, we studied the movements of 32 bald eagles telemetered as nestlings in the Chesapeake Bay, Virginia, USA, 2013–2018. Managers often need to know when fledged eagles are most likely to move enough to encounter airfields near nests. As fledglings aged, they moved progressively farther from the nest and spent more time away from the nest. Twenty-eight days after fledging, eagles spent most of the day (81 ± 10% [95% CI]) near the nest (<500 m) and only 7 ± 7% of the daytime away from the nest (>1 km). By day 55 fledglings ventured beyond 2.5 km from the nest and spent 32 ± 15% the day >1 km away from their nest. Distances moved, however, were influenced by proximity of the nest to water, the salinity of that water, and human population density. Eagles left their natal nests and generally migrated out of the Chesapeake Bay 60.5 ± 7.7 days (4 Aug) after fledging and returned to the Chesapeake Bay approximately 220 days later (Mar–Apr). Eighty-four percent (27 of 32) of the eagles that we tracked encountered 164 airfields across the east coast with 91% of those airfields located within 10 km of the Chesapeake Bay. Encounters with airfields outside the Chesapeake Bay occurred mainly during the first 1.5 years of life, peaking in late fall and early spring. We recorded eagles on Chesapeake Bay airfields during each year, but encounters peaked in April of the first year of the bird's life. April coincides with the height of reported strikes of eagles by aircraft in the region. Our results suggest that eagles fledging from the Chesapeake Bay are an issue for airports near the Chesapeake Bay and for airports across the east coast. Given the continued growth of the population, this issue is likely to continue and grow in significance.
... The HCA suggested that the highest risk and hazard groups were separated mainly by their impact history and average mass. A species with the periodical presence of inexperienced juvenile individuals (Mumme et al. 2000;Miller et al. 2019) or with different escape responses to vehicles is more likely involved in bird strikes (Mumme et al. 2000;Legagneux and Ducatez 2013;Miller et al. 2019). The species size is related to the extent of the damage of an impact as the species' mass increases (Atkins Ltd. and Food and Environment Research Agency (FERA) 2009), and then the risk and hazard of a species raised as its mass grows. ...
... The HCA suggested that the highest risk and hazard groups were separated mainly by their impact history and average mass. A species with the periodical presence of inexperienced juvenile individuals (Mumme et al. 2000;Miller et al. 2019) or with different escape responses to vehicles is more likely involved in bird strikes (Mumme et al. 2000;Legagneux and Ducatez 2013;Miller et al. 2019). The species size is related to the extent of the damage of an impact as the species' mass increases (Atkins Ltd. and Food and Environment Research Agency (FERA) 2009), and then the risk and hazard of a species raised as its mass grows. ...
... We propose establishing a national risk and hazard threshold based on more reliable metrics and applicable nation-wide to prioritize the management measures, as is done in other countries (Soldatini et al. 2011). Some studies showed different trends of strikes depending on the species' biology and behavior to an aircraft approach (Blackwell et al. 2019a(Blackwell et al. , b, 2020Miller et al. 2019). Therefore, the BCU personnel should address effective and accepted management measures (Washburn et al. 2015). ...
Bird and other wildlife strikes are an ever-increasing concern in the aeronautic industry. Several countries have developed methods to mitigate wildlife strikes, where indexes are valuable tools to reinforce airport wildlife management plans. Nevertheless, an international consensus on the application of a single method is lacking. Mexico follows the international normative, but there is ample room to develop new strategies to approach the wildlife strike phenomena. We evaluate, contrast, and compare three commonly used indexes in three Mexican airports, the heuristic risk assessment, the R index, and the bird strike risk assessment 2 (BRI2). These indexes use different methods to obtain their assessment value; thus, we use the more informative variables to effectively highlight the species scored as problematic to coincide with the species involved in wildlife strikes. The heuristic risk assessment showed risk values only for two airports, while outcomes of the R index and the BRI2 are similar at all airports. All risk and hazard groups calculated presented coincidences with at least one group involved in a wildlife strike. We suggest using the R index for hazard values and the BRI2 for risk values to obtain better and fastest results. Nevertheless, we encourage developing (a) a standardized survey method, (b) a standardized risk and hazard calculation method, and (c) a publicly available national report system for wildlife strikes.
... We further classified free-flying birds as juveniles (age ~5-12 months), subadults (age 1-4.5 years), or adults (>4.5 years). For additional details on animal capture, handling, permitting, and tagging, see Miller et al. (2019) and Schmuecker et al. (2020). ...
... This period began when a nestling fledged and ended when it dispersed from the natal area. We determined that an eagle dispersed and was no longer dependent on its parents when it took a directed flight away from the natal area and did not return for >7 days (for additional details, see Miller et al., 2019). We used the term "long distance" to describe eagles that engaged in both migratory and directed dispersal movements (as defined in Miller et al., 2016;Poessel et al., 2016). ...
Recent advances in digital data collection have spurred accumulation of immense quantities of data that have potential to lead to remarkable ecological insight, but that also present analytic challenges. In the case of biologging data from birds, common analytical approaches to classifying movement behaviors are largely inappropriate for these massive data sets.
We apply a framework for using K‐means clustering to classify bird behavior using points from short time interval GPS tracks. K‐means clustering is a well‐known and computationally efficient statistical tool that has been used in animal movement studies primarily for clustering segments of consecutive points. To illustrate the utility of our approach, we apply K‐means clustering to six focal variables derived from GPS data collected at 1–11 s intervals from free‐flying bald eagles (Haliaeetus leucocephalus) throughout the state of Iowa, USA. We illustrate how these data can be used to identify behaviors and life‐stage‐ and age‐related variation in behavior.
After filtering for data quality, the K‐means algorithm identified four clusters in >2 million GPS telemetry data points. These four clusters corresponded to three movement states: ascending, flapping, and gliding flight; and one non‐moving state: perching. Mapping these states illustrated how they corresponded tightly to expectations derived from natural history observations; for example, long periods of ascending flight were often followed by long gliding descents, birds alternated between flapping and gliding flight.
The K‐means clustering approach we applied is both an efficient and effective mechanism to classify and interpret short‐interval biologging data to understand movement behaviors. Furthermore, because it can apply to an abundance of very short, irregular, and high‐dimensional movement data, it provides insight into small‐scale variation in behavior that would not be possible with many other analytical approaches.
... 13 We analyzed the accelerations measured by instruments attached to the backs of freely flying wild golden and bald eagles. 52,53 Since bald eagles flap more frequently (≈38% of total flight time) than golden eagles (≈2% of total flight time), we compared the two species to discriminate between the statistical signatures of flapping intermittency, which is concentrated on the timescale of flapping and dominates the bald eagle data, and turbulence intermittency, which is distributed across a broad range of timescales. The relative infrequency of flapping in golden eagles also made it possible to accumulate enough data for conditional statistics to converge. ...
Turbulence grounds aircraft and combating it in flight requires energy, yet volant wildlife fly effortlessly even on windy days. The nature of the interactions between soaring birds and transient turbulent gusts is not clear, especially when compared with our understanding of flight in larger and steadier airflows during thermal or dynamic soaring. We show that soaring golden eagles (Aquila chrysaetos) experienced short upward accelerations indicative of preferential engagement with strong and intermittent turbulent updrafts. The vertical accelerations reflect changes in lift that were as large as 25 standard deviations from the mean, or more than three times the acceleration of gravity, and so large as not to be consistent with gust mitigation or avoidance. These extreme events occurred in short bursts that mimic movement with turbulent vortices. The burst statistics and their symmetries approach those of turbulence toward longer timescales. On the shortest timescales, the bursts break the symmetry of small-scale turbulence in favor of upward accelerations that are more intermittent than turbulence. We introduce a simple nonlinear model that predicts the scale at which symmetry breaks and the stronger intermittency on the smaller scales. These findings suggest a ratcheting mechanism on turbulent gusts and constitute the first quantitative evidence in favor of turbulent gust harvesting by wildlife. An implications is that turbulence is so strong and pervasive as to make unsteady and nonlinear aerodynamics an intrinsic and beneficial aspect of both flapping and soaring flight in the atmospheric boundary layer - one that we need to incorporate in our understanding of the energetics of flight.
... Of studies that have focused on the PFDP, most deal with parental care behavior and its impact on juvenile survival (reviewed by Langen 2000, Cox et al. 2014, or Naef-Daenzer and Grüebler 2016. Its duration, and notably the relation between its duration and flight skill acquisition in juveniles, has been little studied because of technical limitations (Miller et al. 2019, Rymesova et al. 2021). Yet, first flights after departure from the nest do not mean that their flight skills are sufficient to be autonomous. ...
The post‐fledging dependence period (PFDP), which extends from a fledgling's first flight out of the nest to its departure from the parents' territory, is crucial in the lifecycle of birds. During this period, juveniles develop their flight and foraging skills to become fully independent. Despite the importance of this life stage in basic bird ecology and conservation, it remains largely overlooked – notably its link with the acquisition of flight skills. In this study, we modeled the variation in seven proxies describing flight skills of 84 GPS‐tracked golden eagle juveniles in France between 2016 and 2020. Juveniles had a long but highly variable PFDP, averaging 177.9 (± 62.2) days after departure from the nest. This period is divided into two phases: a first phase of rapid increase in flight skills over the first 60 days after departure from the nest, followed by a plateau in which flight skills no longer develop until independence. These results suggest that the full development of flight skills is not a constraining factor during the PFDP and that it is advantageous for juveniles to choose to remain in their natal territory. We posit that parents' tolerance of fledged juveniles is a type of parental care that may maximize their own fitness by improving the survival of their descendants. In future studies, it may be of interest to investigate the factors that may explain the high variability in the duration of this stage between individuals within the same population.
... For example, this behaviour could be the result of nomadic movements in search of foraging opportunities or it could stem from following other non-territory holding birds. Indeed, it is well established that subadult Golden Eagles tend to move at larger scales than adults (Miller et al., 2019;Oppel et al., 2015). Eagles are long-lived, and recent availability of offal from moose hunt has allowed adults to learn during their lifetime. ...
Aim
Animal migrations influence ecosystem structure, dynamics and persistence of predator and prey populations. The theory of migratory coupling postulates that aggregations of migrant prey can induce large‐scale synchronized movements in predators, and this coupling is consequential for the dynamics of ecological communities. The degree to which humans influence these interactions remains largely unknown. We tested whether creation of large resource pulses by humans such as seasonal herding of reindeer Rangifer tarandus and hunting of moose, Alces alces, can induce migratory coupling with Golden Eagles, Aquila chrysaetos, and whether these lead to demographic consequences for the eagles.
Location
Fennoscandia.
Methods
We used movement data from 32 tracked Golden Eagles spanning 125 annual migratory cycles over 8 years. We obtained reindeer distribution data through collaboration with reindeer herders based on satellite tracking of reindeer, and moose harvest data from the national hunting statistics for Sweden. We assessed demographic consequences for eagles from ingesting lead from ammunition fragments in moose carcasses through survival estimates and their links with lead concentrations in eagles' blood.
Results
In spring, eagles migrated hundreds of kilometres to be spatially and temporally coupled with calving reindeer, whereas in autumn, eagles matched their distribution with the location and timing of moose hunt. Juveniles were more likely to couple with reindeer calving, whereas adults were particularly drawn to areas of higher moose harvest. Due to this coupling, eagles ingested lead from spent ammunition in moose offal and carcasses and the resulting lead toxicity increased the risk of mortality by 3.4 times.
Main conclusions
We show how migratory coupling connects landscape processes and that human actions can influence migratory coupling over large spatial scales and increase demographic risks for predators. We provide vital knowledge towards resolving human–wildlife conflicts and the conservation of protected species over a large spatial and temporal scale.
... only absolute age (Nyg ard et al. 2000) or none at all (Whitfield et al. 2009a, The few studies addressing juvenile movements of WTSE did not report any information on excursive behaviour (Whitfield et al. 2009a, 2009b, Nyg ard et al. 2010, mainly because methods with suitable spatio-temporal resolution were not available. Among studies using appropriate methods such as GPS devices, the excursive behaviour of raptors during the post-fledging period has only been marginally addressed (Nyg ard et al. 2000, Balotari-Chiebao et al. 2016, Bragin et al. 2018, Miller et al. 2019). ...
Exploratory movements and natal dispersal form essential processes during early life history stages of raptors, but identifying the factors shaping individual movement decisions is challenging. Global positioning system (GPS) telemetry thereby provides a promising technique to study movement patterns on adequate spatio-temporal scales. We analysed data of juvenile White-tailed Sea Eagles Haliaeetus albicilla (WTSE) in north-east Germany (n = 24) derived from GPS tracking to extensively analyse movements between fledging and emigration from the natal territory. Our goal was to determine the time point of fledging, characterize pre-emigration movements and the onset of natal dispersal while investigating the influence of the natal environment. WTSE fledged at an average age of 72 days and showed strong excursive behaviour during the post-fledging period regarding the number, distance and duration of excursions, yet with high individual variability. Excursive behaviour did not differ between sexes. On average, WTSE left the parental territory 93 days after fledging. The quantity of excursive behaviour delayed the timing of emigration and WTSE tended to postpone their emigration when foraging water was accessible within the boundaries of their parental territory. The overall results suggest that young WTSE assess the quality of the natal environment via pre-emigration movements and stay in their territory of origin for as long as internal and external conditions allow for it. Our study is one of the first to characterize post-fledging and natal dispersal movements of young WTSE to such an extent and applies modern techniques to understand related movements in relation to the natal environment. The results emphasize the urgent necessity for the extension of currently existing nest protection periods and guaranteeing sustainable management of potential breeding and foraging grounds for WTSE. Ultimately, the results are relevant for all large raptor species sensitive to human-related disturbance, as they support the increasing importance of regulations with spatio-temporal specifications for breeding populations of large raptors in densely human-inhabited areas with increasing alteration of land.
Animal responses to unoccupied aircraft systems (UAS) can be exploited to reduce human-wildlife conflicts. We investigated how same-level UAS approaches (0°) would be perceived by Turkey Vultures (Cathartes aura; “vultures”) compared to stoop approaches (20° descent 50 m away) given the directness of the approach. We measured the % of animals that escaped, escape time, flight-initiation distance horizontally and diagonally, vulture remaining index (index of the number of vultures remaining after treatment by the number present before), and latency to return by vultures at a landfill in response to UAS approaches. All vultures exposed to same-level approaches escaped on the first approach, whereas escape occurred in 73% of stoop approaches. When vultures escaped, they did so 1.69 s faster and over 11 and 15 m greater horizontal and diagonal escape distances when exposed to stoop approaches. Vultures exposed to stoop approaches showed over 31 min longer latencies. Our results, though limited by sample size, indicate that stoop approaches might pose greater perceived risk to vultures.
Worldwide anthropogenic changes influence complex aviation-wildlife relationships. Wildlife Hazard Management (WHM) should include nature conservation. The number of bird strikes continuously increases parallel to growth of air traffic and airport infrastructure. In Poland, ca. 200 bird species have been recorded at aerodromes of which some 30 are considered hazardous to aviation. Analysis of wildlife hazard to aviation should be a part of the preliminary documentation for planned aerodromes. Identification and bird strike risk assessment allow preparation of Wildlife Hazard Management plan which includes pro- and reactive mitigation measures. The measures should consider the most up-to-date available WHM tools, including available radar systems. Operational manuals should include the Wildlife Hazard Management as their inherent part already in the planning phase. This requires systemic and interdisciplinary cooperation both at the airport level and at the level of national air traffic safety management. It should include state authorities but also non-governmental organizations involved in nature protection.
Bald Eagle nestlings were equipped with coloured patagial wing markers. This article describes the activities and movements of the marked birds after they fledged and while they were still on Besnard Lake, the lake where their nests were located.
Behavioural responses can help species persist in habitats modified by humans. Roads and traffic greatly affect animals' mortality not only through habitat structure modifications but also through direct mortality owing to collisions. Although species are known to differ in their sensitivity to the risk of collision, whether individuals can change their behaviour in response to this is still unknown. Here, we tested whether common European birds changed their flight initiation distances (FIDs) in response to vehicles according to road speed limit (a known factor affecting killing rates on roads) and vehicle speed. We found that FID increased with speed limit, although vehicle speed had no effect. This suggests that birds adjust their flight distance to speed limit, which may reduce collision risks and decrease mortality maximizing the time allocated to foraging behaviours. Mobility and territory size are likely to affect an individuals' ability to respond adaptively to local speed limits.
All five radiotracked Haliaeetus leucocephalus flights were northerly in direction and were probably aimed at salmon carrion associated with spawning runs in British Columbia and Alaska. -from Authors
This manual contains a compilation of information to assist airport personnel in conducting Wildlife Hazard Assessments and in the development, implementation, and evaluation of Wildlife Hazard Management Plans. This manual includes specific information on the nature of wildlife strikes, legal authority, government agency roles and responsibilities, regulations, wildlife management techniques, Wildlife Hazard Assessments, Wildlife Hazard Management Plans, and sources of help and information. It is emphasized that this manual provides only a starting point for addressing wildlife hazard issues on airports. Wildlife management is a complex, evolving, and public-sensitive discipline, and ecological conditions vary widely across the USA. Therefore, the assessment of wildlife hazards, the development of Wildlife Hazard Management Plans, and the implementation of management actions by airport personnel must be under consultation by qualified wildlife biologists trained in wildlife damage control.
Most known fatalities for both Bald Eagles (Haliaeetus leucocephalus) and Golden Eagles (Aquila chrysaetos) are associated with humans (e.g., collisions with vehicles and artificial structures). Notably, the risk of collisions between eagles and aircraft is an increasing problem at civil airports and military airfields. Of the 234 eagle collisions with civil and military aircraft reported to the Federal Aviation Administration, the U.S. Air Force, and the U.S. Navy during 1990-2013, 52% caused damage to the aircraft. During this 23-yr time period, Bald Eagle-aircraft collisions increased by 2200% and Golden Eagle-aircraft collisions increased by 400%. Eagle-aircraft collisions occur primarily during daylight hours (88%) and typically within the vicinity of the airfield itself; 82.6% of the Bald Eagle-aircraft collisions and 81.0% of Golden Eagle strikes occurred when the aircraft was at or below 305 m aboveground level. Although collision with aircraft is a very minor source of mortality for Golden Eagles, increasing and expanding Bald Eagle populations will likely result in more eagle-aircraft collisions. Currently, there are few mitigation tools and techniques available to reduce eagle-aircraft collisions. Development and evaluation of effective, publically acceptable methods of reducing eagle-human conflicts represent important areas for future research.
Only 55 of 1117 locations of radio-tagged Haliaeetus leucocephalus (4.9%) occurred in the developed land-cover type ≥4 buildings/4 ha), although 18.2% of potential eagle habitat was developed. Eagle use of the shoreline was inversely related to building density and directly related to the development set-back distance. Few eagles used shoreline segments with boats or pedestrians nearby. Only 360 of 2532 segments (14.2%) had neither human activity nor shoreline development. Eagle flush distances because of approaching boats were greater in winter than in summer (mean 264.9 vs. 175.5 m, respectively), but were similar for adult and immature eagles (203.7 vs. 228.6 m, respectively). Of 2472 km of shoreline on the N Chesapeake, 894 km (36.2%) appears to be too developed to be suitable for eagle use, and an additional 996 km (40.3%) had buildings within 500 m, thereby reducing eagle use. The projected increase in developed land in Maryland (74%) and Virginia (80%) from 1878 to 2020 is likely to determine the future of the bald eagle population in this area. (See also 91L/12673). -from Authors
Little information is available on how areas heavily impacted by humans affect habitat use and home range size of bald eagles (Haliaeetus leucocephalus). Thus, we studied home range and seasonal habitat use of bald eagles in the Columbia River estuary (CRE), Oregon and Washington, 1984-86. Aerial and boat surveys of the entire population and intensive observations of 9 breeding pairs were conducted. Most resident pairs were present near their nests year-round. Home range size of resident pairs averaged approximately 22 km2 for both breeding and nonbreeding periods, and ranged from 6 to 47 km2 among pairs. Areas of highest use within home ranges averaged <0.5 km2 (range = 0.1-1.0 km2), and their locations within home ranges varied between breeding and nonbreeding periods. Resident and nonresident migrant bald eagles in the CRE generally selected remnant stands of old-growth forest near the shoreline for nesting habitat, hunted from perches in mixed-mature conifers and bottomland hardwoods on river islands, and primarily used tidal flats as foraging habitat. We recommend a nesting region approach for managing bald eagles in large geographical areas heavily impacted by humans. This addresses the needs of a number of resident nesting pairs and transient wintering eagles, including the identification of high-use areas and key habitat features important to year-round populations.
The first part of this paper provides advice on buying or building equipment, on attaching transmitters to raptors and on field techniques. Three attachment methods are described, and data are given on weight, range and life limitations of transmitter packages. The second part describes the types of information available from the radio-tracking of raptors, to investigate movements, range-sizes and habitat-use, prédation, the survival of released birds and the population dynamics of wild raptors. Other applications have included the use of transmitters with sensors which modulate the radio signal, for telemetry of foraging and incubation behaviour.
Behavioural responses can help species persist in habitats modified by humans. Roads and traffic greatly affect animals' mortality not only through habitat structure modifications but also through direct mortality owing to collisions. Although species are known to differ in their sensitivity to the risk of collision, whether individuals can change their behaviour in response to this is still unknown. Here, we tested whether common European birds changed their flight initiation distances (FIDs) in response to vehicles according to road speed limit (a known factor affecting killing rates on roads) and vehicle speed. We found that FID increased with speed limit, although vehicle speed had no effect. This suggests that birds adjust their flight distance to speed limit, which may reduce collision risks and decrease mortality maximizing the time allocated to foraging behaviours. Mobility and territory size are likely to affect an individuals' ability to respond adaptively to local speed limits.
We measured provisioning and growth patterns in Bald Eagle (Haliaeetus leucocephalus) chicks from nests in two salinity zones in the lower Chesapeake Bay. Nestlings in mesohaline reaches experienced higher per capita consumable energy provisioning rates and had higher instantaneous growth rates compared to nestlings in tidal-fresh salinity zones. These results suggest that Bald Eagles nesting along mesohaline reaches are more successful at meeting the energetic demands of brood rearing compared to pairs nesting along tidal-fresh reaches, a finding consistent with documented higher reproductive rates and proportion of three-chick broods along mesohaline reaches compared to tidal-fresh reaches. The results of this study have important conservation implications for Bald Eagles by addressing issues related to variation in habitat quality within a continuous ecosystem and the determination of core breeding zones.
The size of the home range is examined in mammals. It is determined, mainly, by the amount of energy expended by the species, and, therefore, the home range area may vary according to the direct and indirect influences of weather and climate on the animal. But the kind of food that is utilized will also influence home range size. Those species that must hunt for their food need larger areas for food gathering than those species that feed on the vegetation. As a result the largest hunters appear to have their food habits regulated by considerations of the efficient use of the food materials in their home range. Finally, the home range size affects population density, which in turn influences the behavior in the population.
We evaluated the relationship between salinity and Bald Eagle (Haliaeetus leucocephalus) population parameters using 26 years of survey data for the lower Chesapeake Bay. Tidal tributaries within the study area were stratified according to the Chesapeake Bay Program's segmentation scheme, and segments with the same salinity classification were considered spatial replicates. Salinity categories included tidal fresh, oligohaline, mesohaline, and polyhaline. Four parameters-colonization rate, nesting density, projected carrying capacity, and productivity were derived from nesting data within each shoreline segment and compared across the salinity gradient. The study-wide Bald Eagle population is exhibiting exponential growth, with an average doubling time of 7.9 years. All population parameters showed significant directional variation with salinity. Average population doubling time for tidal fresh reaches was < 6 years, compared with > 16 years for polyhaline areas. Current Bald Eagle nesting density is negatively related to salinity and varies by a factor of 4 across the gradient. Comparison of current densities with projected carrying capacity suggests that these differences will be stable or increasing as the geographic areas approach equilibrium densities. We suggest that fisheries within lower saline reaches, including spring spawning runs of anadromous Clupeidae (shad and herring), are the most likely explanation for salinity effects. Observed distribution patterns suggest that lands along low-salinity waters are the core of the Bald Eagle nesting population within the lower Chesapeake Bay and should be the focus of long-term programs designed to benefit nesting eagles.
The Chesapeake Bay plays a significant role in the life cycle of Bald Eagles (Haliaeetus leucocephalus) along the entire Atlantic coast of the U.S. In addition to supporting a resident breeding population, the Chesapeake Bay is an area of convergence for post-nesting and subadult Bald Eagles from breeding populations in the southeastern and northeastern U.S. The convergence of three geographically distinct populations (northeast, southeast, and Chesapeake Bay) suggests that the Bay plays a particularly important role in the recovery of Bald Eagles in eastern North America. Since the ban on DDT and formal listing under the Endangered Species Act, the Chesapeake Bay breeding population has increased dramatically. Between the early 1970s and 2001 the population within the Bay and vicinity has grown exponentially from 60 to 646 pairs with an average doubling time of just over eight years. Reproductive rates have increased over this time period and are now similar to those documented prior to the DDT era. With the current rate of increase, the population is expected to reach saturation within the next decade. Bald Eagles continue to be vulnerable to the potential introduction of new biocides into the estuary, human disturbance within nesting and foraging areas, and the loss of habitat to urban and industrial development. The tidal fresh reaches of the estuary appear to support core breeding areas, as well as, concentration areas for migrant populations and should be priorities for long-term conservation efforts.
We compared the reproductive biology, dispersal, and subadult survival of bald eagles (Haliaeetus leucocephalus) from nest sites in suburban and rural landscapes in west-central Florida, USA, from 1997 to 2001. We documented the reproductive outcome of randomly selected suburban (n = 60) and rural (n = 60) bald eagle nest attempts. We also used satellite tracking packages on randomly selected rural (n = 35) and suburban (n = 35) bald eagle fledglings. Nest-site occupancy varied among years (range = 75.0–100.0%), but averaged 90% for nests in both land-use categories. The overall mean nesting start date was similar for both groups (suburban = 11 Dec, rural = 13 Dec). Bald eagles occupying nest sites in both land-use categories raised an average of 1.3 young to 8 weeks-of-age, and pairs that fledged ≥1 young raised an average of 1.7 young to 8 weeks-of-age. Most bald eagle fledglings from our study area migrated northward, some as far as Newfoundland, Canada. The core summering area was the Chesapeake Bay and the coastal plain of North Carolina, USA. Successful fledglings started northward migration earlier on average at rural than at suburban nest sites (124 vs. 132 days-of-age). Survival of both groups was similar until dispersal (approx 91%); however, during the first northward migration, mortality of suburban fledglings increased disproportionately. One year after fledging, survival of rural fledglings was 89% compared to 65–72% for suburban fledglings. Survival of the 2 groups was similar (84–90%) thereafter. Suburban bald eagles died more often from anthropogenic factors (primarily electrocution and vehicle collision) than rural bald eagles, though most of these deaths occurred in rural areas after dispersal from natal areas. We suggest that suburban bald eagle fledglings were more acclimated to dangerous anthropogenic landscape features than rural eagles, and as such did not regard them with the same degree of caution. Despite the difference in first-year mortality, population models suggest that both groups are experiencing positive population growth rates.
Entre1987 y 1989, colocamos transmisores VHF y anillas de identificación de colores a 15 pichones de Haliaeetus leucocephalus en el centro de Arizona, para determinar la dirección y la extensión de sus migraciones luego del emplumamiento (abandono del nido). Trece de los juveniles emplumaron exitosamente y uno de los transmisores falló; 11 águilas sobrevivieron el período premigratorio posterior al emplumamiento, el cual duró entre 18 y 65 d (media = 44 d). Un águila no pudo ser seguida por los receptores después de su partida, pero las 10 águilas monitoreadas viajaron entre 925 y 1955 km antes de detenerse por períodos de tiempo extendidos o hasta que el clima impidió los seguimientos posteriores. Los ambientes de las localidades de parada variaron e incluyeron diques y lagos del interior, tierras ganaderas abiertas y la costa marina del Pacífico. Los alimentos en los lugares de parada del interior incluyeron peces desovando (Salmo clarki) y carroña de peces (Cyprinus carpio y Catostomus commersoni). Al menos nueve de los 13 juveniles que emplumaron sobrevivieron ≥1 año (69%) y un mínimo de seis (46%) sobrevivió hasta la edad reproductiva.
We used satellite telemetry locations accurate within 1 km to identify migration routes and stopover sites of 54 migratory sub-adult Bald Eagles (Haliaeetus leucocephalus) hatched in Florida from 1997 to 2001. We measured number of days traveled during migration, path of migration, stopover time and locations, and distance traveled to and from winter and summer areas for each eagle (1–5 years old). Eagles used both Coastal Plain (n = 24) and Appalachian Mountain (n = 26) routes on their first migration north. Mountain migrants traveled farther (x̄ = 2,112 km; 95% CI: 1,815–2,410) than coastal migrants (x̄ = 1,397 km; 95% CI: 1,087–1,706). Eagles changed between migration routes less often on northbound and southbound movements as they matured (χ2 = 13.22, df = 2, P < 0.001). One-year-old eagles changed routes between yearly spring and fall migrations 57% of the time, 2-year-olds 30%, and 3–5-year-olds changed only 17% of the time. About half (n = 25, 46%) used stopovers during migration and stayed 6–31 days (x̄ = 14.8 days; 95% CI: 12.8–16.8). We recommend that migratory stopover site locations be added to GIS data bases for improving conservation of Bald Eagles in the eastern United States.
70% of all wildlife strikes with aircraft occur at ft, where management at the airport can be effective. At least 415 bird and 35 terrestrial mammal species were struck by aircraft from 1990-2009. Overall, 14% of all strikes with birds and 61% of all strikes with mammals caused some damage. But, the severity and probability of damage is species-specific. To better prioritize management (e.g., habitat management, land-use planning, non-lethal dispersal), an improved understanding of which species are most hazardous is needed.
Research questions Which species are most hazardous? That is, which species are most likely to cause some type of damage to the aircraft when struck? How do body mass, body density, and flocking behavior contribute to hazard level?
Building on previous research Dolbeer, R.A., S.E. Wright, and E.C. Cleary. 2000. Ranking the hazard level of wildlife species to aviation. Wildlife Society Bulletin 28:372-378. ~18,000 records in the database 21 wildlife species/groups considered Dolbeer, R.A., and S.E. Wright. 2009. Safety management systems: How useful will the FAA National Wildlife Strike Database be? Human-Wildlife Conflicts 3:167-178. Did not use a composite hazard score Zakrajsek, E.J., and J.A. Bissonette. 2005. Ranking the risk of wildlife species hazardous to military aircraft. Wildlife Society Bulletin 33:258-264. Used the number of damaging strikes and cost as criteria
Methods Used FAA National Wildlife Strike Database records: 1990-2009 99,411 total strikes Summarized strikes for 77 species or groups with ≥20 records Only used strikes ≤500 ft AGL (in the airport environment) Reduced sample size to 23,503 reports Variables used in ranking % of strikes with damage % of strikes with substantial damage % of strikes with effect on flight (EOF) Species were ranked and a relative hazard score was calculated For birds, we assessed effects of body mass, body density, and group size on relative hazard scores
Bird-aircraft collisions (bird strikes) are an increasing safety and economic concern to the civil aviation industry worldwide, costing well over $1 billion each year. To reduce risks associated with strikes, the U.S. Federal Aviation Administration has developed airworthiness standards for airframes, windshields, and engines using a single 4-lb (1.82-kg) bird mass as the maximum that must be tested for most components. We determined that 36 of the approximately 650 bird species that nest in North America have average body masses greater than 4 lbs. Of the 31 species for which population trend data were available, 24 (77%) showed population increases over the past 20-40 years, only 2 showed declines and 5 were stable. Of most importance, 13 of the 14 species with body masses over 8 lbs (3.64 kg) showed population increases. At least 294 strikes with >4-lb birds caused substantial damage to civil aircraft in the USA, 1990-2002; 30% of these strikes involved multiple birds. Over 6,022 strikes occurred at heights >1,000 feet above ground level of which at least 1,986 (33%) involved >4-lb birds. We conclude that airworthiness standards, as well as proposals to allow high-speed (>250 knots [288 miles/hour]) operations below 10,000 feet, should be reevaluated to address the threat posed by increased populations of large flocking birds. Also, increased research and development is needed in the deployment of bird-detecting radar to warn pilots of flocks of migrating birds and in techniques to make aircraft more visible to birds. Finally, wildlife biologists should increase efforts to reduce or disperse populations of these large birds in airport environments. For certain overabundant large species such as non-migratory Canada geese (Branta Canadensis), management programs may be needed to reduce populations regionally.
We measured provisioning and growth patterns in Bald Eagle (Haliaeetus leucocephalus) chicks from nests in two salinity zones in the lower Chesapeake Bay. Nestlings in mesohaline reaches experienced higher per capita consumable energy provisioning rates and had higher instantaneous growth rates compared to nestlings in tidal-fresh salinity zones. These re-sults suggest that Bald Eagles nesting along mesohaline reaches are more successful at meeting the energetic demands of brood rearing compared to pairs nesting along tidal-fresh reaches, a finding consistent with documented higher reproductive rates and proportion of three-chick broods along mesohaline reaches com-pared to tidal-fresh reaches. The results of this study have im-portant conservation implications for Bald Eagles by addressing issues related to variation in habitat quality within a continuous ecosystem and the determination of core breeding zones. La Influencia de la Salinidad sobre las Tasas de Aprovisionamiento y Crecimiento de los Pichones de Haliaeetus leucocephalus en la Parte Baja de la Bahía Chesapeake Resumen. Medimos los patrones de aprovisionamiento y crecimiento de los pichones de Haliaeetus leucocephalus provenientes de nidos de dos zonas salinas de la parte baja de la Bahía Chesapeake. Los pichones de las zonas de salinidad intermedia experimentaron tasas de aprovision-amiento de energía consumible per capita mayores y tuvieron tasas de crecimiento instantáneo mayores comparadas con las de los pichones de las zonas de agua dulce con influencia marina.
Soaring birds that undertake long-distance migration should develop strategies to minimize the energetic costs of endurance flight. This is relevant because condition upon completion of migration has direct consequences for fecundity, fitness and thus, demography. Therefore, strong evolutionary pressures are expected for energy minimization tactics linked to weather and topography. Importantly, the minute-by-minute mechanisms birds use to subsidize migration in variable weather are largely unknown, in large part because of the technological limitations in studying detailed long-distance bird flight. Here, we show golden eagle (Aquila chrysaetos) migratory response to changing meteorological conditions as monitored by high-resolution telemetry. In contrast to expectations, responses to meteorological variability were stereotyped across the 10 individuals studied. Eagles reacted to increased wind speed by using more orographic lift and less thermal lift. Concomitantly, as use of thermals decreased, variation in flight speed and altitude also decreased. These results demonstrate how soaring migrant birds can minimize energetic expenditures, they show the context for avian decisions and choices of specific instantaneous flight mechanisms and they have important implications for design of bird-friendly wind energy.
The factors affecting the population dynamics of seabirds have long intrigued biologists. Current data suggest that density-dependent depletion of prey during the breeding season may regulate population size. However, much of the evidence for this has been circumstantial, and the underlying mechanisms are unclear. Here, we show that the per capita population growth rates of northern gannet Morus bassanus at colonies in Britain and Ireland have declined with increasing population size. Furthermore, direct observations reveal that the mean foraging trip duration of breeding gannets is positively correlated with colony size, both among colonies of different sizes in the same year, and within colonies as they change in size. To understand this phenomenon, we have developed a model which demonstrates that disturbance of fish alone can readily generate conditions under which gannets at larger colonies have to travel further to obtain food.
The first edition of this book has established itself as one of the leading references on generalized additive models (GAMs), and the only book on the topic to be introductory in nature with a wealth of practical examples and software implementation. It is self-contained, providing the necessary background in linear models, linear mixed models, and generalized linear models (GLMs), before presenting a balanced treatment of the theory and applications of GAMs and related models. The author bases his approach on a framework of penalized regression splines, and while firmly focused on the practical aspects of GAMs, discussions include fairly full explanations of the theory underlying the methods. Use of R software helps explain the theory and illustrates the practical application of the methodology. Each chapter contains an extensive set of exercises, with solutions in an appendix or in the book’s R data package gamair, to enable use as a course text or for self-study.
During 1985-95, we documented fledging, migration, and subsequent locations of juvenile bald eagles (Haliaeetus leucocephalus) from Glacier National Park (GNP), Montana. The median fledging date was 1 August (N = 29). We radiotagged 11 fledglings, nine of which also received wing markers. The median date of migration from natal areas was 13 September (N = 15). The interval between fledging and migration varied from 32 to 70 d (median = 42 d, N = 15). Juveniles appeared to migrate alone, joining other eagles at foraging sites. GNP adults remained on their nesting territories when juveniles departed. One juvenile wintered 130 km from GNP. Others migrated as far as 1000 km. Six migrated to southern Montana, Idaho, Wyoming, and California. Three moved west to Washington or British Columbia. Two juveniles from the 1988 Lake McDonald nest migrated separately to the Pacific Coast. By 1991, one Lake McDonald adult had been replaced; the juvenile produced that year migrated south to Idaho. This contrast suggests that juveniles inherited distinct migration direction "programs" from different parents. Early autumn migration departures of GNP juveniles also may be genetically determined; we found no evidence that they remained locally to feed on autumn spawning runs of kokanee salmon (Oncorhynchus nerka) in GNP. At least 10 of the 11 radio-tagged juveniles survived their first winter. During spring migration, four juveniles passed through or near GNP. Nine summering sites or last known spring locations were in Alberta or British Columbia, Canada. There is no evidence to date of marked juveniles returning to breed in GNP natal areas.
We documented complete annual migratory cycles for five hatch-year Bald Eagles (Haliaeetus leucocephalus) from central Labrador, Canada. We attached backpack-mounted Platform Transmitter Terminals (PTT) to track hatch-year eagle movements from their natal areas. The median departure date from natal areas was 26 October 2002, with the earliest departure occurring on 7 October 2002 and the latest on 12 November 2002. All eagles migrated independently of siblings and spent a mean of 62 d on autumn migration at a mean speed of 45 km/hr with a mean of five stopovers. Eagles travelled north in the spring at an estimated speed of 27 km/hr over 32 d, with a maximum of 11 stopovers. One wintered in the Gulf of St. Lawrence, while the remaining eagles migrated to the northeastern U.S.A. Eagles spent a mean of 76 d on their wintering grounds, with a median date of departure for spring migration of 20 March 2003. Two of the eagles returned to Labrador during their first summer and showed some fidelity to their natal areas. We document migration routes and identify stopover areas.
This paper details liability issues inherent in bird–aircraft collisions (bird-strike) incidents at airports and discusses how airport managers and operators must strive to conduct accurate assessments and develop and implement an effective wildlife management plan. Such efforts are mandated by Federal Aviation Administration (FAA) regulations, and failure to follow them may result in loss of human life and property, as well as large financial penalties for managers and operators and adverse media attention and public criticism for the airport authority.
We studied the postfledging dependency period in bald eagles (Haliaeetus leucocephalus), a little studied but important period in the life cycle of avian species. Bald eagles in Florida had a postfledging dependency period of 4-11 weeks (15-22 weeks old). The length of the dependency period did not vary by year of study, sex, number of fledgings, timing of fledging, or hatch order (P > 0.05). Mean distance fledglings ranged from the nest increased with age, but they were observed in the nest or nest tree throughout the postfledging dependency period. Distance from the nest did not vary by sex, number of fledglings, or timing of fledging (P > 0.05). Over 80% of the fledgling observations were within 229 m of the nest. The boundary of the primary protection zone specified in the bald eagle habitat management guidelines for the southeastern United States is 229 m. Restrictions on human disturbance around nest sites should remain in place during the postfledging dependency period because of the close association of fledglings with the nest site. Restrictions also should be flexible because of the varying length of the dependency period.
Survival of 39 radio-tagged Haliaeetus leucocephalus in the Chesapeake Bay region was 100% in the first year of life. Mean minimum survival per year of all eagles was 91%, mean maximum survival 98%. A deterministic life-table model predicted a finite growth rate of 5.8% per year; growth rate based on the maximum survival estimates was 16.6% per year. The breeding population actually increased 12.6% per year from 1986-1990. Intrinsic growth rate was 6.9% based on natality and minimum survival data and 19.2% based on maximum survival data. -from Authors
Haliaeetus leucocephalus nesting biology was studied on Chippewa National Forest. Nests built on developed shoreline were farther from water than nests built on undeveloped shoreline. Nests were farther from houses than random shoreline points. Breeding eagles flushed at 57-991 m (mean 476 m) at the approach of a pedestrian. A multiple regression model including number of previous disturbances, date and time of day explained 82% of the variability in flush distance and predicted a maximum flush distance at the first disturbance of 503 + or - 131 m. Unsuccessful nests had no greater frequency of known human activity within 500 m than successful nests. Fixed-wing aircraft passing 20-200 m from nests did not flush incubating or brooding eagles. Under current management policies, human activities did not have an important impact on bald eagle reproductive success.-from Authors
This Advisory Circular (AC) provides guidance on certain land uses that have the potential to attract hazardous wildlife on or near public-use airports. It also discusses airport development projects (including airport construction, expansion, and renovation) affecting aircraft movement near hazardous wildlife attractants. Appendix 1 provides definitions of terms used in this AC.
There are about a dozen published variations of equidistant conic map projections. They are identical when using the same actual standard parallels, but the parallels are chosen differently. Greater use of the spheroidal form of the equidistant conic with two standard parallels (especially when chosen by minimum-error procedures) is encouraged because of its true meridian scale and low-error compromise between Lambert's conformal conic and Albers' conical equal-area projections. Scale errors and coordinates for the three major conic projections and for their spherical versus spheroidal forms are compared in representative tables for U.S. maps. Relative scale errors using projections based on the sphere rather than the spheroid may also be calculated with relatively simple formulas.
Analizamos los cambios poblacionales de 420 especies con base en los censos de aves reproductivas de Norte América (BBS, por sus siglas en inglés) mediante un modelo jerárquico log-lineal y comparamos los resultados con los obtenidos mediante análisis de regresión por rutas. Los estimados de tendencias a nivel de todos los censos basados en modelos jerárquicos fueron más precisos que los estimados del análisis previo. No existió un patrón consistente de diferencias en la magnitud de las tendencias entre los métodos de análisis. Los estimados de tendencias a nivel de todos los censos cambiaron sustancialmente entre los análisis de regresión y de modelos jerárquicos para 15 especies. Comparamos los estimados regionales para estados, provincias y regiones de conservación de aves; las diferencias observadas en esos análisis regionales probablemente son consecuencia de la consideración inadecuada de las diferencias temporales en el esfuerzo de muestreo que hace el procedimiento de regresión. Utilizamos los resultados de modelos jerárquicos específicos de cada especie para estimar el cambio conjunto de grupos de aves asociadas con los principales ambientes y tipos de migración. Las poblaciones de especies restringidas a pastizales, zonas áridas y a bosques del oriente disminuyeron, mientras que las de aves de ambientes urbanos-suburbanos aumentaron entre 1968 y 2008. Ninguna agrupación basada en el tipo de migración experimentó cambios significativos, aunque las poblaciones de especies migratorias neártico-neotropicales disminuyeron en algunos intervalos y las poblaciones de especies residentes permanentes aumentaron en casi un 20% durante el intervalo. Los resultados de los modelos jerárquicos ilustraron los patrones de cambio poblacional de mejor manera que los resultados de los análisis de regresión. Recomendamos el uso de modelos jerárquicos para analizar datos del BBS.
We examined the demographic consequences of road mortality in the cooperatively breeding Florida Scrub-Jay (Aphelocoma coerulescens), a threatened species restricted to the oak scrub of peninsular Florida. Between May 1986 and July 1995 we monitored the survival and reproductive success of a color-banded population of jays along a two-lane highway at Archbold Biological Station. Annual mortality of breeding adults was 0.38 on road territories, significantly higher than the rate of 0.23 for breeders on nonroad territories. High mortality on road territories appeared to be a direct result of automobile traffic per se and not a consequence of road-induced changes in habitat characteristics. Mortality was especially high for immigrants without previous experience living along the road: in their first two years as breeders on road territories, naive immigrants experienced annual mortality of 0.50 and 0.45. From year 3 onward, however, annual mortality dropped to 0.29, not significantly different from the rate for birds on nonroad territories. This experience-dependent decline in road mortality could be caused either by surviving jays learning to avoid automobiles or by selective mortality operating through time (demographic heterogeneity). Proximity to the road had no effect on nesting success beyond its indirect effects on breeder experience and group size. Because the mortality of 30- to 90-day-old fledglings was significantly higher on road territories than on nonroad territories, however, breeder mortality greatly exceeded production of yearlings on road territories. Roadside territories therefore are sinks that can maintain populations of Florida Scrub-Jays only via immigration. Because Florida Scrub-Jays do not avoid roadside habitats and may even be attracted to them, road mortality presents a difficult challenge for the management and conservation of this threatened and declining species.
Spatio-temporal variability in assemblages of pelagic fish in Chesapeake Bay from 1995 to 2000 was documented based on midwater trawl surveys conducted three times annually (April, July, and October). Numerically dominant pelagic and benthopelagic fishes, 30–256 mm TL, were included in the analysis. Species assemblages, diversity indices, biomass distributions, and a correspondence analysis revealed that physical forcing, primarily driven by freshwater input, shaped the structure of fish communities, both annually and regionally. But, seasonal succession occurred, with adults dominating in the spring and recruited juveniles dominating in the fall. The dominant species were bay anchovy (Anchoa mitchilli), Atlantic croaker (Micropogonias undulatus), white perch (Morone americana), spot (Leiostomus xanthurus), weakfish (Cynoscion regalis), and Atlantic menhaden (Brevoortia tyrannus). Young-of-the-year (YOY) and age-1+ fish were concentrated in different regions and different seasons. A correspondence analysis showed that salinity was the most important environmental factor explaining annual differences in the upbay–downbay gradients in fish community structure. In 1997–2000, following a surge of freshwater input and nutrient loadings in 1996, October baywide fish biomass increased by 120% and mean baywide dissolved oxygen (DO) concentration below the pycnocline in summer decreased by 30%. These interannual variabilities in baywide fish biomass and mean DO suggest a relationship between bay plankton productivity and fish production. Species composition shifted markedly in 1996 when YOY and age-1+ anadromous fishes became dominant, but returned progressively in subsequent years to the usual structure in which bay anchovy and other polyhaline species were dominant.
Conflicts between humans and predators are the product of socio-economic and political landscapes and are particularly controversial because the resources concerned have economic value and the predators involved are high profile and often legally protected. We surveyed the current literature for information on ecological and social factors common to human–predator–prey conflicts. We used this information to examine whether losses to predators and patterns of investment in husbandry could be linked to these factors. We found that livestock losses to predators were low and were negatively associated with net primary productivity and predator home range sizes, but were not affected by predator density, methods of husbandry or human population density. While there was no effect of husbandry on losses, variation in husbandry was explained by net primary productivity, predator density and percentage of stock killed by predators. Inconsistent and sparse data across conflicts may have limited our ability to identify important factors and resolve patterns, and suggests that there is no reliable or consistent framework for assessing and managing human–predator conflicts that involve game and livestock species. Our approach highlights the type of data that could be very informative to management if collected across a range of cases and habitats.
I examined the species involved in bird strikes on the runways at J. F. Kennedy International Airport, Long Island, New York from 1973 to 1981. One-hundred-and-forty-two strikes were recorded although 1202 carcasses were found on the runways. Gulls Larus accounted for 47% of the pilot-reported strikes and 70% of the carcasses. Most of the other pilot-reported strikes were shorebirds, small passerines, or were unidentified. During the period 49 species were found as carcasses. Other than gulls, ducks (9%), shorebirds (4%) and owls (3%) were most common. Over half of the gull strikes involved herring Larus argentatus, followed by laughing L. atricilla, ring-billed. L. delawarensis and great black-backed L. marinus gulls. Herring and great black-backed gulls were hit less than expected on the basis of their percent occurrence. Young gulls were hit proportionally more often than expected. Bird strikes and carcass counts were highest in 1975, decreased in 1976 and 1977, increased from 1978 through 1980, and decreased in 1981. For all years pilot-reported strike rates were low (usually less than 1 per 10 000 movements) compared to other airports. Pilot-reported strike rates peaked in May and November during the spring and autumn migration although carcass counts were high from May through December. Over 50% of the pilot-reported gull strikes occurred from 0500–0900 h, although non-gull strikes occurred evenly throughout the day, despite the fact that 70% of plane movements occurred after 1300 h. The pattern of pilot-reported strikes is similar to that reported from Canadian airports.
1. Caring for offspring beyond leaving the nest is an important but under-studied part of avian life histories. Theory predicts that prolonged post-fledging parental care should yield fitness benefits such as increased fledgling survival. Post-fledging care is also costly in terms of time and energy available for subsequent reproduction, moult or migration. So far, direct measurements of the fitness effects of the duration of post-fledging parental care are lacking.
2. In a partial cross-fostering experiment, barn swallow (Hirundo rustica) chicks were exchanged among broods close to fledging. Thereby, we separated the effects of post-fledging care from those of pre-fledging origin on juvenile survival.
3. Prolonging post-fledging care substantially increased juvenile survival up to 3 weeks post-fledging. Juvenile mortality was maximal in the days following the termination of parental care, and prolonging care delayed and reduced this peak mortality. Survival of fledglings experiencing 6 days of care was Φ = 0·227, whereas fledglings experiencing 14 days of care showed a survival of Φ = 0·571.
4. Offspring from pairs providing short care showed lower post-fledging survival than did offspring from pairs providing long care, irrespective of the actual duration of care experienced. This gives evidence for an additional survival effect of pre-fledging factors associated with the parental duration of care.
5. The results suggest that differential survival in relation to post-fledging parental care is a major fitness component. This relationship has profound effects on the reproductive trade-offs underlying the evolution of avian life histories.
This classification, to be used in a new inventory of wetlands and deepwater habitats of the United States, is intended to describe ecological taxa, arrange them in a system useful to resource managers, furnish units for mapping, and provide uniformity of concepts and terms.Wetlands are defined by plants (hydrophytes), soils (hydric soils), and frequency of flooding. Ecologically related areas of deep water, traditionally not considered wetlands, are included in the classification as deepwater habitats. Systems form the highest level of the classification hierarchy; five are defined—Marine, Estuarine, Riverine, Lacustrine, and Palustrine. Marine and Estuarine Systems each have two Subsystems, Subtidal and Intertidal; the Riverine System has four Subsystems, Tidal, Lower Perennial, Upper Perennial, and Intermittent; the Lacustrine has two, Littoral and Limnetic; and the Palustrine has no Subsystems.
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1989. Vita. Abstract. Includes bibliographical references (leaves 54-60).
A linear model for repeated measurements is proposed in which the correlation structure within each time sequence of measurements includes parameters for measurement error, variation between experimental units, and serial correlation within units. An approach to data analysis is presented which involves preliminary analysis by ordinary least squares, use of the empirical semi-variogram of residuals to suggest a suitable correlation structure, and formal inference using likelihood-based methods. Applications to two biological data sets are described.