spacer
Home About Us Kids' Zone Help Wildlife Webcam  Support Contact
The Eagles of Hornby Island
spacer15 Facebook chat forum cafe press

Frequently Asked Questions

Please click on a topic heading to read the information in that category. If you have questions that are not addressed here please visit our Forum, where specific questions can be answered and additional information found.

FAQs prepared by AJL, November 2009


eagle on tree

 



A: General Questions

Name
Numbers
Distribution


eagles beak-to-beak

 


B: Physical Characteristics

Size
Appearance (differences between the sexes; eye colour; feathers, beaks and talons).
Senses (smell, taste, hearing, vision)
Grooming (bathing, preening, beak feaking)

eaglet with full crop

C: Feeding
Diet
Hunting and foraging
Feeding strategy
Function of the crop
Casting pellets


reproduction


D: Reproduction

Pair bond
Nest building
Copulation
Eggs (production, clutch size, laying interval, hatching interval
Incubation


young eaglets


E: Young

Stages (hatchling, nestling, fledgling, juvenile)
Parental care and feeding
Behaviours and learning (play, sibling competition, mantling, self-feeding)
Fledging process (perching, branching, nest departure, parental care)
Human impact on nest success


eagle on beach


F: Survival

Predators
Lifespan
Statistics
Threats to survival

A. General Questions

Q. What does the bald eagle's name mean?
A. Its scientific name is Haliaeetus leucocephalus (Latin: Haliaeetus or "sea eagle"; leucocephalus or "white head").
Its common name, bald eagle, may be from the old English word balde (white), or may be a derivation of piebald, which describes the eagle's white head and tail feathers and dark body feathers.

Q. How many bald eagles are there?
A. Scientists estimate that there may be more than 70,000 bald eagles in the wild.

Q. Where are bald eagles found?
A. Canada, the continental United States (including Alaska), and northern Mexico (small population). More than 50% of the population occurs in Alaska and British Columbia.

top

B. Physical Characteristics

Q. How big are bald eagles?
A. Sizes and weights vary greatly:

  • Southern birds are smaller and lighter than northern birds; an Alaskan male can weigh about the same as a southern female.
  • Average lengths range from 71 to 96 centimetres (2.3 to 3.1 feet).
  • Average weights range from just under 3 kilograms to 6.3 kilograms (6.6 pounds to 14 pounds) although weights as high as 7.7 kilograms (17 pounds) have been recorded for Alaskan females.
  • Averaged across their entire range, male weights range from 3.6 to 4.1 kilograms (8 to 9 pounds); female weights range from 4.5 to 6.4 kilograms (10 to 14 pounds).
  • Average wingspans range from 168 to 244 centimetres (5.5 to 8 feet).

Q. How can I tell the adult female and male bald eagles apart?
A. The female is about 25% to 30% larger than the male. Her beak looks somewhat deeper than his, and has a more pronounced hook. Plumage is the same in both sexes.
Mom Hornby is larger than Dad. Her head feathers appear longer and less 'groomed' than his; at the back of her head, the feathers have a unique growth pattern, making it look like she has a dark part.

Q. What colour are an eagle's eyes?
A. The eaglet's and juvenile's eyes are dark brown. They begin to fade to a buffy brown and gradually to a creamy colour; when the bird reaches sexual maturity, its eyes are yellow.

Q. How does the eagle's vision compare with human vision?
A. The eagle's vision is about 3 to 4 times sharper than ours. Flying at 305 metres (1000 feet), it can see a 4.8 kilometre (three-mile) radius; it can spot prey that is about 1.6 kilometres (1 mile) away.

Q. Can eagles see at night and do they fly at night?
A. They can see at night, but not nearly as well as they can see during the day. We have, however, seen Mom Hornby and several other eagles fly to their nests after nightfall.

Q. How well do eagles hear?
A. It is thought that their hearing is similar to ours.

Q. Do eagles have a sense of smell and taste?
A. Eagles are thought not to have a strongly developed sense of smell but this is under review for all birds.

Q. Do eagles sweat?
A. No; birds cool themselves by panting.

Q. What are an eagle's feathers, beaks, and talons made of?
A. They (as well as the scales that cover the foot) are made of keratin, a fibrous protein. Our hair and nails are also made of keratin.

Q. How many feathers does a bald eagle have?
A. The bald eagle has about 7200 feathers.

Q. When do bald eagles attain adult plumage?
A. The transition from first year to adult plumage (as well as beak and eye colour) is gradual; the distinctive adult colouration is achieved at around 5 years of age. You can see photographs of the phases here: http://www.swbemc.org/plummage.html

Q. When do bald eagles moult?
A. They moult gradually from spring through autumn. They do not moult all their feathers each year; some of the feathers moult over two (or possibly more) years.

Q. How do bald eagles groom themselves?
A. Most eagles fish and wade (and often swim), so they have opportunity to bathe. They preen their feathers (using the tips of their beaks) to remove food or debris, to distribute oils and to 'zip' the feathers for waterproofing. They remove food from their beaks by 'feaking' (rubbing them back and forth) along hard branches. Feaking also helps keep the beak trimmed.

top

C. Feeding

Q. How does the bald eagle get its food?
A. The eagle soars over water and the ground looking for prey, and also looks for prey while it is perched. It tries to catch its prey while flying but isn't always that successful, so it relies heavily upon dead and dying fish, birds, and mammals. The bald eagle will also steal (pirate) food from other birds and mammals.

Q. How much force do eagle's feet or talons have for grabbing prey?
A. It is said to be about 2600 pounds per square inch.

Q. What are bald eagles' favourite foods?
A. Their favourite food is fish but they are opportunistic feeders and the menu can include mammals, birds, reptiles and amphibians.
The Hornby eagles primarily eat fish; they can be fresh-caught, stolen from other birds, or scavenged. During the 2009 nesting season, in addition to fish they also delivered the remains of several opossums, a mink, a partial waterfowl, a crow, and possibly a gull to the nest.

Q. How much food do bald eagles need to eat in a day?
A. It depends on the bird's size, weight, level of activity, general health, weather, and other stressors. An adult might need about 5 to 10 percent of its body weight, depending on circumstances.

Q. Where do bald eagles usually eat?
A. If they find a larger carcass they will eat some at the site; manageable chunks can be flown off to a tree, rock, or other spots where the eagles can eat in privacy. They will sometimes eat in the nest, especially while breeding or incubating eggs; they also eat the parts that are tough and less digestible or nutritious for the eaglets.

Q. Do bald eagles bring carrion to the nest?
A. Much of their food is scavenged (dead) and they do indeed bring carrion to the nest.

Q. What size of prey will a bald eagle be able to take and carry?
A. A strong bird might be able to fly off an item that is about 1.8 kilograms (four pounds). A smaller bird would be able to carry less weight than would a larger bird.

Q. Do bald eagles and eaglets need to drink water?
No; they derive water from their food. Fledged birds and adults will sometimes drink while bathing, if fresh water is available.

Q. Do bald eagles eat bones?
A. Yes, eagles of all ages eat (and require) bones for calcium.

Q. How do bald eagles deal with bacteria that would be in the road kill that they eat?
A. Their stomachs are highly acidic, and most organisms are killed in that environment.

Q. What is a crop? What is its purpose?
A. The eagle's crop is a sac-like out-pouching of the oesophagus and it functions as a storage area, allowing the bird to eat large quantities of food when it is available (a.k.a. gorging).

Q. Why does an eagle throw its head back and open its beak several times and stretch and twist around?
A. Eagles of all ages stretch and twist in this way in order to move pieces of food from the crop to the stomach.

Q. I saw an eaglet that seemed to be choking; then it threw up something. What was that?
A. Eaglets and eagles of all ages egest (cast) pellets, and when they are doing so they can appear to be vomiting or choking. The pellets are prey parts that could not be digested (bits of feathers, fur, fish scales, etc.); such items are squeezed into a pellet in the bird's gizzard and then expelled.

top

D. Reproduction

Q. Do eagles mate for life?
A. Bald eagles are monogamous; a pair will mate for life if all is well. A partnership may be broken if one of the birds is infertile, and a widow or widower will take a new partner.

Q. Do bald eagles stay together every day throughout the year or only during nesting season?
A. This is not yet clear, but banded or tagged bald eagles that migrate (spend part of their year in breeding grounds and part in wintering grounds) have been seen together in the wintering area. Eagles that are year-round residents (eagles that breed and winter in their territories, leaving only for the salmon runs) appear to stay together throughout the year, although one may leave for the salmon run and return from it before the other.
Mom and Dad Hornby winter together as well as breed on Hornby Island.

Q. Do bald eagles build nests only in trees?
A. Most eagles build their nests in trees, but those that nest in treeless areas will build ground nests on cliffs and ridges. Eagles will also use man-made nest structures.

Q. What are bald eagles' nests made of, and how big are they?
A. They are made of interwoven branches, with fillers like grass and moss. The birds repair and add to the structures every year.
The largest nest recorded so far was 2.7 metres (8.9 feet) in diameter and 3.6 metres (11.8 feet) high; its estimated weight was almost 2 metric tons. Most nests are about 1.5 to 1.8 metres (4.9 to 5.9 feet) in diameter and 0.7 to 1.2 metres (2.3 to 3.9 feet) tall.
The Hornby's nest is 36.6 metres (120 feet) from the ground, in an old Douglas Fir tree that is about 5.5 metres (18 feet) in diameter.

Q. What affects the reproduction of bald eagles?
A. Food supply, weather, chemical-induced infertility, general health, and age (too young or old) can affect reproduction.

Q. Do bald eagles mate only to make eggs?
A. They mate to reproduce, but some of the mating efforts in breeding season strengthen the pair bond; not all efforts result in eggs.

Q. Why do some eggs fail to hatch?
A. Some eggs are not fertilized. Some fertilized eggs fail to develop normally due to extreme cold, soft shells, and microorganisms that can cause embryonic death.

Q. Will bald eagles produce more eggs if the first ones fail?
A. Birds that breed at southern latitudes lay earlier than those that breed at higher latitudes; this gives them a larger window of opportunity, thus southern females attempt second clutches if the first eggs are lost in the early stage of incubation. Females that breed further north have a smaller window of opportunity and appear to attempt second clutches rarely.

Q. How long is it from copulation to egg laying?
A. Reported intervals for bald eagles range from 5 to 10 days.

Q. How many eggs are average for one bald eagle nest?
A. Two-egg clutches are most common (79 %). One-egg clutches are less common (17 %). Three-egg clutches occur sometimes (4 %), but 4-egg clutches are rare.
Mom Hornby usually lays two eggs.

Q. How big are bald eagle eggs?
A. On average, the eggs are 7.0 to 7.6 centimetres (2.8 to 3 inches) long and 5.3 to 5.6 centimetres (2.1 to 2.2 inches) wide. Reported weights range from 110 grams to as much as 130 grams (3.9 to 4.6 ounces), with Alaskan birds producing the largest and heaviest eggs.

Q. How long are the laying and hatching intervals for bald eagles?
A. The interval between eggs is usually two to four days, depending upon how many eggs are laid. In 2009, Mom Hornby laid her second egg three days after the first.
The hatching interval usually corresponds with the laying interval. Mom Hornby's eggs hatched three days apart in 2009.

Q. When does incubation of bald eagle eggs begin?
A. Incubation begins as soon as the egg is laid; the first chick will have the size and developmental advantage because it is older than its sibling or siblings.

Q. What is the incubation period for bald eagle eggs?
A. The average period is 35 days, give or take a few days.
In 2009, the Hornbys incubated the first egg for 35 days; the chick began to vocalize in the shell late that day. The pip (hole) was evident on the morning of the 36th day and the chick was fully hatched in the early morning of the 37th day. The second egg followed suit.

Q. Do male and female bald eagles spend the same amount of time incubating the eggs? How does one partner know when the other wants a break?
A. The female does most of the incubating, but the male takes his turn so that the female can feed, groom, stretch, and fly. When a partner wants a break, he or she will call for the other but a partner often also just flies in to check on the spouse.

Q. Are bald eagle eggs and young in danger from predators?
A: They can be; larger birds (crows, ravens, birds of prey) and some mammals (e.g., raccoons, bears) will take eggs and some can take young nestlings. The parents are always on guard.

top

E. Young

Q. How much food does an eaglet require daily?
A. That would depend upon the eaglet's age, weight, growth stage, level of activity, and other physiological factors; requirement thus varies or changes from day to day.

Q. How much of an impact do humans have on the feeding and care of the eaglets?
A. Human activity has significant impact. Studies show that parents spend much more time on the nest protecting their young than foraging and feeding on weekends and other times of heavy recreational use near the nest and hunting areas. Bald eagles prefer to nest away from built-up areas and human activity for this reason.

Q. Please explain sibling aggression in bald eagles.
A. The older bird is larger, heavier, and more developed than the younger bird, so it requires more food and is avid for its share. Siblings will thus compete for food and parental attention, with one bird attempting to out-compete or dominate the other. The younger bird soon learns to keep a low profile until the older has been satisfied and quickly learns to use its wits, making grabs for food or doing 'end runs' around the larger bird. This behaviour occurs more within the first two weeks of life, declining as the siblings learn. Siblicide (one eaglet killing or causing the starvation of another) appears to be rare in bald eagles.

Q. Is the smaller eaglet able to get enough to eat?
A. The smaller eaglet normally gets enough to eat over the course of the day.

Q. How does the eaglet learn to feed itself?
A. The eaglet learns by watching the parents prepare and pull off pieces of food; when the eaglet's ability to move about improves, it will begin to pick up small pieces of food that have been dropped and gradually will try to pull off pieces of food.

Q. Is it normal for bald eagle parents to be gone for a long time between feedings?
A. In the first weeks, there is almost always a parent on the nest. As the eaglet's ability to regulate its body temperature improves and as it grows and requires more room, the 'parent on duty' will begin to perch outside the nest, either somewhere on the nest tree or beside it. It may appear that the parents are gone a long time, but a parent is actually there, if out of camera range.
The Hornbys watch over the nest from atop the cam boxes, from the top of the tree stump, from the 'babysitting tree', and from another tree right beside the nest tree.

Q. What is mantling and why does the eagle/eaglet do this?
A. Mantling describes a display; the eagle or eaglet will hunker over the food with its wings outspread, often vocalizing to warn off competitors (i.e., "This is mine, go away").

Q. Why do eaglets lie down on the nest?
A. Eaglets, like all growing babies, sleep a lot and conserve energy by resting and lying down. The development of leg and foot muscles takes time; like human infants, young eaglets don't yet have the muscle strength to sit up or move about at first.

Q. Are eagles or eaglets adversely affected by prolonged and heavy rain?
A. Adults are less affected by weather, as they are protected by their (waterproof) feathers and can go without a meal for some time. Nestlings, especially those under two weeks of age who can't regulate body temperature and whose first down doesn't offer protection, can succumb to hypothermia in extreme weather.

Q. Why do some eaglets seem to rub their behinds on the nest?
A. Sometimes a bird is just itchy or irritated by a bit of grass or a food particle around the vent, but this can also be a sign that the bird (young or adult) has 'worms'.

Q. Do young eagles play?
A. Yes; scientists believe that picking up and moving sticks and other objects (and passing them back and forth) are a form of play. Eagles of all ages have been seen passing sticks while flying and 'playing' with objects; it is thought that they learn skills in this way.

Q. How old are the eaglets when they fledge?
A. Nest departure as early as 8 weeks of age has been reported, but 11 to 13 weeks appear to be the most common ages.
The Hornby eaglets have usually fledged at 12 weeks of age. In 2009, the chick fledged at 85 days of age (the exact age reported in Doug Carrick's book).

Q. Do bald eagle siblings fledge at the same time?
A. They fledge a few (or more) days apart, depending on hatching interval and sex.

Q. When they fledge, are the eaglets just pushed out of the nest?
A. No. While some eaglets fledge 'prematurely' (have a mishap when over- or underestimating distance to a branch), the majority take their first flights by choice and under their own control.

Q. Is it true that 40% of bald eaglets do not survive their first flight?
A. While this is widely reported on some websites and in some books, more recent studies (and nest cam studies) indicate that this is not the case. (See "survival", below).

Q. Do bald eagle parents starve out the eaglets to force them to fledge?
A. No; they continue to bring food to the nest.
In 2009, Mom and Dad Hornby delivered 19 fish to the nest the day before their chick fledged.

Q. Do the eaglets try to follow the adult when they leave the nest?
A. Yes; once the eaglet has flown from the nest and landed, the parents will coax it to follow (luring it with food). The eaglets will follow the adults back to the nest and feed there until such time as they begin to feed alongside the parents; at that point, their foraging abilities improve quickly and they become less and less dependent upon their parents.

Q How long will bald eagle parents continue to feed the chicks after they fledge?
A. Studies indicate that this period varies; the average across the entire range is about six weeks.

Q. How does an eaglet learn what food items to hunt? Do eaglets learn to hunt from their parent or is this instinct?
A. The eaglet first learns to recognize foods in the nest; when it fledges and follows the parents, it learns by watching them and other eagles. It continues to learn by observation and through trial and error. The predator's instinct to pursue prey is innate and is fine-tuned through learning and experience.

Q. How do you sex eaglets?
A. Biologists measure beaks and feet to determine sex but this method, while good, is not always accurate. Eaglets in studies are weighed and measured prior to banding and many biologists now also take blood samples to confirm sex.

top

F. Survival

Q. How long can bald eagles live?
A. Their potential lifespan appears to be 40+ years of age. A pair in the Winnipeg Zoo was still reproducing and fledging young at 41 years of age.
Free-ranging eagles face more challenges; 30 years is considered to be a long lifespan in the wild. Studies suggest that resident populations may live longer than those that migrate.
In 2009, the Hornby eagles were thought to be around 26 years of age.

Q. Do bald eagles have any predators?
A. The adult bald eagle's only predator is the human. Small eaglets are vulnerable to larger birds of prey, ravens, and larger climbing mammals such as bears and raccoons. Grounded non-flying young are vulnerable to other mammalian predators (e.g., wolves, coyotes) as well.

Q. Is it true that 50% of bald eagle fledglings will not survive their first year?
A. This may not be the case; some scientists say that earlier estimates were speculative. As radio telemetry study data increase, it appears that first-year survival is better in some areas than in others, with urban eaglets not faring quite as well as those from rural areas.
Findings from some of these studies (all of which had good sample size):
  • Chesapeake Bay: 100% survived from 8 weeks of age to nest departure at 10–12 weeks of age; 100% survived their first year
  • Texas: 97% survived to nest departure
  • Florida: 93% survived to nest departure; a minimum of 63% survived their first year
  • California: 77% survived the first year
  • Montana: 91% survived their first year
  • Yellowstone National Park: 87% survived their first year
  • Maine: minimum of 73% survived their first year

Survival chances improve with each succeeding year.

Q. What are the main causes of death in bald eagles?
A. The most common causes of death are human-related and include collisions (e.g., vehicles, power lines), electrocution (from power lines), toxins (pesticides and other chemicals), lead poisoning (from ingested lead pellets, bullets, and fishing sinkers) and rodenticides (eating poisoned rodents and other poisoned animals). Eagles are still illegally shot and trapped by people who see them as nuisances, or for their feathers, beaks, or talons. Natural causes include diseases like West Nile Virus.

Q. What are the threats that bald eagles are now facing?
A. Habitat loss (due to forestry and human habitation) and degradation are serious threats. Nest trees and roosting habitat are lost to developers and logging, and increased recreational use and human activity in these areas as well as in hunting and fishing areas, have negative impact. According to studies, human activity can lead to permanent displacement from suitable habitat and can reduce survival, notably in winter when food and good hunting areas are no longer available to the birds.

top

Resources

Saving the Bald Eagle

"The bald eagle has been a major player in American conservation history. Chosen by Congress as the nation’s symbol in 1782, it was soon to become a casualty of the country’s social and technological transformation. Eagles were subject to widespread extermination efforts by settlers, and even fed to hogs in Maine. When the story of its poisoning by DDT was popularized in Rachel Carson's Silent Spring, a nascent environmental movement rallied around it: the great raptor was one of the first species listed under the 1967 precursor to today’s Endangered Species Act." ~ Learn about the Bald Eagle from the Center for Biological Diversity

The number of nesting bald eagle pairs has been monitored throughout the lower 48 states since 1967, when the species was listed as endangered. The Center for Biological Diversity published its 2007 Population Report online. It is the first-ever report on numbers of eagle pairs and long-term trends for every U.S. state. Read the report here: Bald Eagle Populations in the United States

The Eagle Nature Foundation provides results of the most recent Bald eagle counts as well as counts for the past 50 years and publishes an annual Status of the Bald Eagle report: Eagle Facts Report


Bald Eagle Trackers

Bald eagle telemetry, tracking, and movement reports

Ontario, Canada: follow the Great Lakes eaglets: Bird Studies Canada

New York State, USA: Journey North Bald Eagle Migration

Virginia, USA: Center for Conservation Biology Eagle Trak


Bald Eagle Information

For the young and young-at-heart, from some fine eagle biologists: Journey North

The Bald Eagle
by Mark V. Stalmaster
Published in 1987 and out-of-print, but may be available through used book dealers on Amazon.com

The Bald Eagle: Haunts and Habits of a Wilderness Monarch
by Jon M. Gerrard and Gary R. Bortolotti
Published in 1988 and available new or used through Amazon.com

Field Guide to the Bald Eagle
by Audubon Society
Published in 2002 and available new or used through Amazon.com


Make a Difference for Bald Eagles

Do you have a large nest in a tree on you property? Check this advice from the Islands Trust in British Columbia on protecting large bird nests

You too can participate in programs that monitor bald eagles!

USA: Eagle count volunteers: Eagle Nature Foundation Midwinter Count

USA: Nest monitoring volunteers: Eagle Nature Foundation Nest Monitoring Program

Canada: Choose from several volunteer programs with Bird Studies Canada

 

Make a Difference for All Wildlife

Know the issues- Read about breaking news at Environmental News Service

Take action - even your signature can save a wild life. Defenders of Wildlife.

See the big picture - Understanding and preserving biodiversity is the only way in which we can help nature regain balance. To learn more about biodiversity, ecosystems, and refuges that offer wildlife protected habitat, go to Wildlife International.

Act locally - Backyard habitats offer shelter, food, and water to many species that are trying to adjust to losses of native habitat due to human encroachment.

Advice for people in British Columbia is valid in other parts of Canada and the US: Identify and Protect Nests on Your land

Learn how to make your garden into a wildlife habitat at home from the National Wildlife Federation and the Humane Society of the United States (HSUS).

Human encroachment can also result in some conflicts with wild neighbours. Find solutions to conflicts, learn about wildlife safety, and read about ways you can create habitat and support for our dwindling wildlife from the International Wildlife Rehabilitation Council
and
the Humane Society of the United States (HSUS).


Citizen Scientists!

Project Feeder Watch
Help gather data on songbirds in your own back yard:

Canada: Bird Studies Canada

USA: Cornell Lab of Ornithology

Other bird monitoring projects:

Canada: Bird Studies Canada Volunteer Programs

USA: Audubon Society Christmas Bird Count


Report a Banded Bird
Have you spotted a bird with a silver (US Federal) or a colored (state) leg band?
Report your sighting to the USGS


Read the annual report on The State of the Birds:
"The state of our birds is a measurable indicator of how well we are doing as stewards of our environment. The signal is clear."

 

Enjoy!

Now that you've been smitten with eagles, you may want to grab your binoculars and camera. For rare bird alerts, identification aids, birding organizations in your area and even information on gadgets and gear, go to Wildlife International Birding page

For fun kinds of eagle gear, visit our Cafe Press gift shop.



   

Home  |   About Us  |   Help Wildlife  |   Forum |   Kids' Zone  |   Contact  |   Webcam  |  Eagle FAQ
Resources  |   Gallery |   Hornby Island |   Our Artists  |   Support Chat   Terms of UseSitemap

The Hornby Eagle Group Projects Society - Contact info@hornbyeagles.com
All content copyright ©Hornby Eagle Group Projects Society