Ideal free eagles: Bald Eagle distribution in relation to salmon availability on four salmon spawning rivers

2021 ◽  
Author(s):  
Kristen E. Walters ◽  
John D. Reynolds ◽  
Ronald C. Ydenberg
Keyword(s):  
Pacific Northwest ◽  
Pacific Salmon ◽  
Ideal Free Distribution ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Breeding Period ◽  
Bald Eagles ◽  
Post Spawning ◽  
Salmon Carcass ◽  
Ideal Free

The movement of individuals according to the availability of resources has a fundamental effect on animal distributions. In the Pacific Northwest, Bald Eagles (Haliaeetus leucocephalus (Linneaus, 1766)) rely heavily on scavenging opportunities during the non-breeding period, and their distribution and movements are thought to be strongly influenced by the availability of post-spawning Pacific salmon (genus Oncorhynchus Suckley, 1861) carcasses. We surveyed the abundance of eagles and salmon on four adjacent rivers on Vancouver Island, British Columbia, Canada, during the 2017 fall spawning season. Salmon began to arrive in late September, peaked in abundance in mid-November, and were absent after early December. The seasonal progression of Bald Eagle abundance matched that of salmon carcass availability. The slope of proportional eagle – salmon relationship was significantly positive, though lower than the 1:1 match predicted by Ideal Free Distribution theory. The numerical response of Bald Eagles to salmon abundance was elevated on one of the rivers, potentially due to physical features such as sandbars and mudflats that increased the availability of carcasses and provided access points for eagles.

scholarly journals Numerical and Functional Responses of Migrant Bald Eagles Exploiting a Seasonally Concentrated Food Source

The Condor ◽  
2000 ◽  
Vol 102 (3) ◽  
pp. 561-568 ◽  
Author(s):  
Marco Restani ◽  
Alan R. Harmata ◽  
Elizabeth M. Madden
Keyword(s):  
Age Groups ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Type I ◽  
Functional Responses ◽  
Bald Eagles ◽  
Kokanee Salmon ◽  
Consumption Rates ◽  
Salmon Carcass ◽  
Salmon Carcasses

AbstractWe determined the numerical and functional responses of migrant Bald Eagles (Haliaeetus leucocephalus) feeding on spawning kokanee salmon (Oncorhynchus nerka) at Hauser Reservoir, Montana from 1991–1995. Number of Bald Eagles was positively correlated with the fluctuating number of salmon carcasses during four of five years. Immigration and emigration rates were similar across years and were facilitated by several behavioral and physical characteristics of eagles: group foraging, communal roosting, and keen eyesight. Number of subadult eagles showed closer synchrony with density of salmon carcasses than did adult eagles. Eagles scavenging for salmon exhibited a Type II functional response. Handling times of scavenging eagles remained constant across the range of salmon carcass densities, whereas daily attack rates increased. Functional responses of scavenging eagles differed between age groups; adults exhibited a Type I response, whereas that of subadults could not be characterized. Handling times of scavenging adults were constant, but those of subadults increased with salmon density. Attack rates of scavenging adults increased with salmon carcass density. Consumption rates differed between age groups and among eagles using foraging modes of scavenging, stooping, and pirating, which suggests that eagles viewed live and dead salmon as alternative prey types. Bald Eagle scavenging of kokanee salmon was inversely density dependent.

Recent switch by the Great Blue Heron Ardea herodias fannini in the Pacific northwest to associative nesting with Bald Eagles (Haliaeetus leucocephalus) to gain predator protection

2013 ◽  
Vol 91 (7) ◽  
pp. 489-495 ◽  
Author(s):  
I.M. Jones ◽  
R.W. Butler ◽  
R.C. Ydenberg
Keyword(s):  
Reproductive Success ◽  
Pacific Northwest ◽  
Close Association ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Safe Place ◽  
Ardea Herodias ◽  
Great Blue Heron ◽  
The Pacific

The Great Blue Heron Ardea herodias fannini Chapman, 1901 in the Pacific northwest appears to have modified nesting behaviour in response to the strong recent recovery of the Bald Eagle (Haliaeetus leucocephalus (L., 1766)) population. Previously undescribed, herons now often nest in close association with some breeding eagles, even though eagles depredate heron nestlings, are implicated in the recent reproductive decline of herons, and may induce abandonment of heron breeding colonies. We tested the hypothesis that breeding herons gain protection from the territorial behaviour of eagles. Natural observations and simulated incursions showed that nesting eagles actively repel other eagles within at least 250 m around the nest site, thereby establishing a relatively safe place for herons to nest. Surveys showed that 70% of heron nests and 19% of heron colonies were located within 200 m of eagle nests with high reproductive success. These herons had greater reproductive success than those nesting far from eagle nests.

Bald Eagle Lead Exposure in the Upper Midwest

2014 ◽  
Vol 5 (2) ◽  
pp. 208-216 ◽  
Author(s):  
Sarah E. Warner ◽  
Edward E. Britton ◽  
Drew N. Becker ◽  
Michael J. Coffey
Keyword(s):  
Lead Poisoning ◽  
Lead Exposure ◽  
Clinical Signs ◽  
Local Environment ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Upper Midwest ◽  
Bald Eagles ◽  
Potential Source ◽  
Liver Lead Concentration

Abstract In 2012, we examined lead exposure in 58 bald eagles Haliaeetus leucocephalus found dead in Iowa, Minnesota, and Wisconsin. We determined lead concentrations in livers, examined differences in exposure among ages and between sexes, and recorded clinical signs consistent with lead poisoning. Most (60%) of the bald eagles had detectable lead concentrations, and 38% of the 58 had concentrations within the lethal range for lead poisoning. We found no differences in exposure based on sex or age, but we did find an inverse relationship between body and liver mass and liver lead concentration. The high percentage of lead-exposed bald eagles encouraged us to further examine potential sources of lead in our local environment. We initiated a study on the Fish and Wildlife Service's Upper Mississippi River National Wildlife and Fish Refuge to investigate if discarded offal piles from hunter-killed deer were a potential source of lead exposure to scavenging wildlife such as the bald eagle. Radiographs showed that 36% of offal piles in our sample area contained lead fragments ranging from 1 to 107 particles per pile. Our study indicated that 1) lead exposure rates for bald eagles found dead in our Upper Midwest study area were high, 2) more than one-third of the bald eagles found dead in Iowa, Minnesota, and Wisconsin had liver lead concentrations consistent with lead poisoning, and 3) discarded offal piles from deer shot with lead ammunition can be a potential source of lead exposure for bald eagles.

Neutron activation analysis of bald eagle feathers: analytical precision and sources of sampling variation

1985 ◽  
Vol 63 (12) ◽  
pp. 2707-2718 ◽  
Author(s):  
Gary R. Bortolotti ◽  
Jon C. Barlow
Keyword(s):  
Neutron Activation Analysis ◽  
Activation Analysis ◽  
Neutron Activation ◽  
Chemical Elements ◽  
The Body ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Chemical Profiles ◽  
Significant Patterns

Instrumental neutron activation analysis was used to investigate the feather chemistry of wild and captive bald eagles (Haliaeetus leucocephalus). This paper documents variation that may be attributable to method of feather collection, laundering of samples, and precision of the analysis, as well as the variability within and among feathers from different locations on the body of individual birds. For most samples, reliable estimates could be made of the concentrations of bromine, magnesium. manganese, sodium, vanadium, aluminum, chlorine, calcium, and sulphur. Iodine and copper were detected but could not be measured precisely. There were highly significant patterns of variation along the length of a single feather for most chemical elements. The vane and calamus portions of feathers differed in chemical composition and the concentrations of the elements in the two parts were not correlated. Feathers belonging to the same molt but collected several months apart had similar chemical profiles. Variation within an individual feather and among feathers from different parts of the body necessitates rigorous consistency in the method of sampling feathers. Possible explanations for the observed patterns of elemental composition are discussed.

scholarly journals Enrichment Preferences of Raptors at Elmwood Park Zoo

2018 ◽  
Vol 1 (1) ◽  
pp. 21-27
Author(s):  
Elisa Tyler Tyler
Keyword(s):  
Environmental Enrichment ◽  
Well Being ◽  
Bald Eagle ◽  
Future Research ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Buteo Jamaicensis ◽  
In Captivity ◽  
Natural Enrichment

Environmental enrichment is often offered to animals in captivity to aid in enhancing quality of life by providing appropriate environmental stimuli that improve psychological and physiological well-being. Due to the limited amount of research conducted on raptors and enrichment, I sought to determine raptor preferences of enrichment types through the observation of captive bald eagles (Haliaeetus leucocephalus) and red-tailed hawks (Buteo jamaicensis) in the education department at Elmwood Park Zoo. I predicted that the raptors would interact more with natural enrichment items compared to ones that were man-made. Although results showed only the female bald eagle to interact enough with the enrichment items to gather an adequate number of observations, she was found to interact significantly more frequently with natural enrichment items compared to ones that were man-made (p 0.0001, FET). These results are not meant to infer that all female bald eagles prefer natural enrichment items over man-made ones, or that all male bald eagles and female and male red-tailed hawks do not prefer any enrichment items. Nonetheless, they justify future research on environmental enrichment preferences involving many more individuals and many more taxa to determine more appropriate enrichment regimens for captive birds of prey.

scholarly journals Remotely-sensed tornado signatures indicate an ecological threshold for eagle nest destruction

2016 ◽  
Author(s):  
Jeremy D. Ross ◽  
Cheryl L. Cavert ◽  
Lena C. Larsson
Keyword(s):  
Wind Shear ◽  
Severe Weather ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Climate Change Scenarios ◽  
Bald Eagles ◽  
Arkansas River ◽  
Weather Patterns ◽  
Ecological Threshold ◽  
Azimuthal Shear

AbstractBald Eagles (Haliaeetus leucocephalus) will reuse massive nests placed high in trees over multiple years, potentially exposing them to catastrophe loss during severe storms. The stochasticity of localized weather, however, has traditionally been viewed as impeding the quantitative study of such risks. In March 2015 a severe weather outbreak along the Arkansas River near Tulsa, Oklahoma caused widespread damage among a highly-concentrated and long-monitored population of nesting Bald Eagles. We conducted field surveys on the extent of nest loss and consulted weather and observer records to determine what characteristics of the storm (maximum azimuthal wind shear) or nests (years of use) might have been associated with nest destruction. We found 5 of 9 nests along a ~24km stretch of the river were destroyed during the storm, causing the death of at least 8 eaglets. Mean years of use was higher among destroyed nests (4.8) than surviving nests (4.0), though not significantly so within this limited sample. The degree of maximum azimuthal shear (i.e., wind rotation) during the storm within 800m of the nests, however, did significantly differ both in terms of maximums (15.8 vs 9.5 ms−1) and means (9.4 vs 6.6 ms−1) for destroyed versus persisting nests, respectively. Our findings suggest a threshold of tornadic wind shear beyond which Bald Eagle nests, irrespective of age, could be prone to catastrophe. Such insights are key to developing accurate models of population persistence, especially in light of potential shifts in severe weather patterns under various climate change scenarios.

Foraging behaviour of four avian species feeding on the same temporarily available prey

2020 ◽  
Vol 98 (9) ◽  
pp. 581-590 ◽  
Author(s):  
N.S.B. Houpt ◽  
A.P.H. Bose ◽  
T. Warriner ◽  
N.A.W. Brown ◽  
J.S. Quinn ◽  
...  
Keyword(s):  
North America ◽  
Census Data ◽  
Prey Availability ◽  
Bird Species ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Western North America ◽  
Bald Eagles ◽  
Tidal Cycles ◽  
Plainfin Midshipman

Low tide events provide terrestrial predators with ephemeral, but predictable and abundant sources of prey. Understanding the relationships between tidal cycles, prey availability, and predator abundances is vital to characterizing the ecological relationship between terrestrial predators and their marine prey. Here, we describe the foraging tactics of four common bird species in western North America — Bald Eagles (Haliaeetus leucocephalus (Linnaeus, 1766)), Great Blue Herons (Ardea herodias Linnaeus, 1758), Glaucous-winged Gulls (Larus glaucescens J.F. Naumann, 1840), and Northwestern Crows (Corvus caurinus S.F. Baird, 1858) — feeding on the same transiently accessible fish species, the plainfin midshipman (Porichthys notatus Girard, 1854). We conducted avian predator surveys at breeding beaches of plainfin midshipman across multiple years and sites. Our census data showed that Bald Eagle and Great Blue Heron abundances were higher when the tides were receding than incoming at Ladysmith Harbour, British Columbia, Canada, but the opposite trend was found for total predator abundance at a second site in Dabob Bay, Washington, USA. Glaucous-winged Gull abundance decreased over the course of the plainfin midshipman breeding season (April–July), whereas the abundances of the other three species remained stable. Our data suggest that the foraging activities of birds in the intertidal zones of western North America are linked with the tidal cycles, corresponding to periods of high prey vulnerability.

Some sources of variation in the elemental composition of Bald Eagle feathers

1988 ◽  
Vol 66 (9) ◽  
pp. 1948-1951 ◽  
Author(s):  
Gary R. Bortolotti ◽  
Jon C. Barlow
Keyword(s):  
Neutron Activation Analysis ◽  
Instrumental Neutron Activation Analysis ◽  
Activation Analysis ◽  
Neutron Activation ◽  
Annual Variation ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Physiological Basis ◽  
Sources Of Variation

Concentrations of Br, Mn, Na, Al, and Cl were measured in back and tail feathers and concentrations of Mg and Ca were measured in tail feathers of wild and captive Bald Eagles (Haliaeetus leucocephalus) using instrumental neutron activation analysis. Feather chemistry of four eagles sampled over 3 years showed considerable annual variation. The profiles of tail feathers, however, appeared distinct for each individual. The mineral profiles of feathers of wild nestlings were usually significantly variable among years. A sex difference was evident for Cl, and perhaps Br and Na, in back feathers of nestlings. Mn and Al concentrations were significantly influenced by the species of prey on which the eaglets had fed. Variation attributable to sex likely has a physiological basis, while much of annual variation can likely be explained by diet.

scholarly journals Bacterial Diversity in Feces of Wild Bald Eagles, Turkey Vultures and Common Ravens from the Pacific Northwest Coast, U.S.A

2019 ◽  
Author(s):  
Rocio Crespo ◽  
Scot E Dowd ◽  
Daniel E. Varland ◽  
Scott Ford ◽  
Thomas E. Hamer
Keyword(s):  
Bacterial Diversity ◽  
Pacific Northwest ◽  
Pathogenic Bacteria ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Cathartes Aura ◽  
Pacific Northwest Coast ◽  
16S Gene ◽  
The Pacific ◽  
Turkey Vultures

AbstractBirds harbor diverse microorganisms in their guts, which collectively fulfill important roles in providing their hosts with nutrition and protection from pathogens. Although numerous studies have investigated the presence of certain pathogenic bacteria in the feces of wild birds, only a few have attempted to investigate the microbiota of the gut. This study analyzed the avian bacteria present in the cloaca of avian scavengers captured on coastal beaches of Washington and Oregon between 2013 and 2015: 10 turkey vultures (Cathartes aura), 9 bald eagles (Haliaeetus leucocephalus), and 2 common ravens (Corvus corax). We used illumina sequencing based on the V4 region of the 16s gene was to characterize the bacterial diversity. Our investigation revealed phylum-level differences in the microbiome of turkey vultures, compared with bald eagles and common ravens. Substantial microbiome differences were found between bald eagles and ravens below the phylum level. Although little is known about the possible relations among these microorganisms, our analyses provides the first integrated look at the composition of the avian microbiota and serves as a foundation for future studies in this area.

scholarly journals Lead Poisoning in Bald Eagles Admitted to Wildlife Rehabilitation Facilities in Iowa, 2004–2014

2017 ◽  
Vol 8 (2) ◽  
pp. 465-473 ◽  
Author(s):  
Taylor Yaw ◽  
Kay Neumann ◽  
Linette Bernard ◽  
Jodeane Cancilla ◽  
Terese Evans ◽  
...  
Keyword(s):  
Clinical Outcome ◽  
Blood Lead ◽  
Bald Eagle ◽  
Haliaeetus Leucocephalus ◽  
Bald Eagles ◽  
Tissue Samples ◽  
Independent State ◽  
Negative Results ◽  
Rehabilitation Facilities ◽  
Lead Levels

Abstract Eleven years (2004–2014) of bald eagle Haliaeetus leucocephalus data from four independent, state and federally permitted wildlife rehabilitators in Iowa were assessed for the prevalence of elevated lead levels in blood or tissue samples. The relationship between blood lead concentrations and recorded information (age, season, radiographs, and clinical outcome) was investigated. Adult birds had higher blood lead concentrations than immature and juvenile birds. Highest blood lead levels were found during October–January. Bald eagles with positive radiographs for metallic opacities in the digestive tract had higher blood and tissue lead concentrations than those with negative results or those on which no radiograph was performed. Metallic opacities were identified through necropsy. Bald eagles with elevated levels of lead were associated with poor clinical outcomes, indicating that blood lead concentrations could be used as a predictor of clinical outcome.

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