Post by thumper59 on Jan 22, 2012 15:51:10 GMT -6
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.
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.