Tuesday, April 25, 2006

April 23 notes: TRIPLETS (3 eaglets hatch!)

Several astute observers of our live-streaming video recently reported glimpses of a third eaglet. We agree!! Finally this morning, I clearly saw a third fuzzy little head rise above the nest rim. Wing Goodale at BRI captured this great shot from the eagle cam archive tape showing a feeding of the triplets later that day.

As Bucky and Mark have both noted earlier in our Biologists' Journal, significant hurdles remain for the survival of all three. Adequate foods for rapid eaglet growth, no disturbances that displace adults from the nest, no adverse weather spells, and low dietary exposure to contaminants are all important to survival of our triplets. Last year, only one nest in Maine successfully reared 3 eaglets to fledging.

For viewers that rely on the still-image updates, extra patience may reveal all 3 young eaglets. There is a slight depression in the nest bowl (the soft lining at nest center) that hides smaller, prone nestlings. Be on the alert at feeding time, because eaglets sit upright and crane their necks upward to be the first in line for feeding. The adults will likely stand to grapple delivered food or may change places with one another: either way, eaglets may suddenly be more visible!

Barb called me to attention at 8:20 this morning as the image update revealed a standing adult with its head turned sharply and beak wide open: something is up! Either this is a greeting to a mate (maybe arriving with a meal) or an alarm call to an intrusion. The next refreshed image 30 seconds later revealed one eaglet straining for the first food morsels shred by an adult bent low over the nest. After 2 more image updates, the head of a second eaglet emerged. After an interval of 6 minutes (12 image updates since the first signs of breakfast), the third eaglet wanted a turn! This order of dominance will likely last for another week or two. By that time, larger eaglets should be visible except when being brooded or shaded by a parent.

Management comments: The availability of foods is a major influence on nesting outcomes. Nest locations close to the food supply are optimal so nesting along shorelines is always preferable. Notes by Edie Miles, a technician observing a Penobscot County nest during our research years ago, reveal a key advantage of nesting close to the food supply: "I had not seen the other adult for several hours when the female arose from her brooding posture over the eaglet. In one fluid motion, she stood and launched into flight over the river .... returning 30 seconds later with a fish! Not only was she guarding the eaglet in the male's absence, the female was also watching for a fish to rise."

When an adult is facing away from the eagle cam at this site, it is scanning adjacent coastal waters and tidal flats. We hope those keen eagle eyes find enough meals for the eagle cam triplets. -- Charlie Todd, Maine Dept. of Inland Fisheries & Wildlife

Monday, April 17, 2006

April 17 notes: two eaglets in our nest!

This morning after a prey delivery (a duck?) we watched the parent eagle feeding two chicks. She meticulously reduced the prey to small morsels and carefully fed both chicks. One chick is older and larger than its sibling and is the first to be fed. The smaller chick will continue to do well as long as plenty of food is available. Sibling competition for food and mortality from starvation or infanticide is greatest in the first two weeks when the size difference between the two chicks is the greatest.

For most of the time, the chicks will remain out of view of the web camera. They cannot maintain their body temperature when they are young and downy. Notice how the parents sit differently on the nest in a more upright posture. On rainy days, the wings of the adult act like an umbrella to keep the chicks dry.

The chicks will remain downy for the next two weeks. At that time, we should start to see some black pin feathers, which will replace the down. If chicks are fed well, they grow about 100 grams per day. Maximum growth occurs when they are about 3 to 4 weeks of age.

For the first two to three weeks after hatching, the female is present at the nest about 90% of the time and the male about 50% of the time (out of view of the camera). You will often hear one of the adults calling to its mate or tilting its head upward to watch its mate soaring overhead. Once the chicks start to grow feathers and can maintain their body temperature, the parents will begin perching off the nest.

Bald eagles are extremely sensitive to disturbance at this critical time. To flush an adult eagle from the nest exposes the chicks to cold, wet weather or predators. When we review development projects, we always request that activity near the nest during the incubation and early chick-rearing period be avoided. -- Mark McCollough, U. S. Fish and Wildlife Service

April 12 notes: we have a hatch!

Charlie Todd's wife, Barbara, saw a small head peak out from under the adult eagle's wing on Wednesday, April 12. Later, at least two little guys were briefly visible in the nest! As Charlie mentioned earlier, this is one of the most successful eagle nests on the coast of Maine, and they've done it again! One adult will brood the chicks almost constantly for the first few weeks because young eaglets are covered only by a light down coat. They are susceptible to cold and rainy weather as we are experiencing right now. Last year's heavy spring rains and exceptionally cold temperatures reduced nesting success statewide, but the population should recover quickly from these random events.

To give you an idea of what a hatchling looks like we've attached a picture of a day-old chick that Barbara raised in 1978. The egg came from a nest on Swan Island (Sagadahoc County) and unexpectedly hatched in an incubator following fostering of an eaglet there. The Swan Island eagles had not hatched their own egg in at least 20 years. Twice, we introduced an egg or eaglet from a captive breeding facility in Maryland to bolster eaglet numbers locally. This young eaglet was raised in captivity until 4 weeks old and then fostered back into another eagle nest where the adoptive adult eagles raised it to fledging!

Young eaglets can only eat very small items so the adults will tear up food into bite-sized portions and gently offer it to the chicks. As with many birds of prey, eagle chicks don't hatch at the same time so one eaglet is larger than its sibling(s). If food is scarce, the oldest eaglet outcompetes others for food and survives, while smaller sibling(s) may not. With ample food, all nestlings will fledge. Food availability has a great deal to do with nest site selection, especially during the nestling period. The presence of anadromous fish, such as alewives, often enhances brood size (the number of eaglets in a successful nest).

Management comments: Food quality is important during this early nesting period. Coastal eagles feed much more on birds, especially fish-eating birds such as gulls and cormorants, than do our inland nesting eagles, which eat a much higher proportion of fish. The result is that our coastal eagles have a greater chance to accumulate contaminants such as DDE, PCPs and mercury. Luckily DDE is rapidly disappearing but the other chemicals are still present in our environment. -- Bucky Owen, University of Maine emeritus

Sunday, April 09, 2006

April 9 notes: precious eggs near hatching?

We are all eager to detect hatching at the nest this coming week. The adult eagles have faithfully tended their egg(s) for nearly 5 weeks. The incubation period for bald eagles is "about 35 days!" Very young nestlings may not be visible initially from our camera angle so watch eagle behaviors closely. There is a subtle difference between the prone posture of an eagle incubating eggs and the slightly raised (but very low) position of one brooding an eaglet. If there is more than 1 egg, hatching dates are days apart identical to the interval between egg-laying dates. In other words, an adult in the nest has to perform both tasks in this challenging time frame!

The first clear evidence of a successful hatch will either be a glimpse of the young eaglet or observations of feeding motions to an unseen, tiny hatchling. Look for food morsels being passed "beak to beak" from the adult to an eaglet.

We have discussed the impacts of disturbance and inclement weather on nesting eagles, but there are many other risks. One that once jeopardized bald eagles across most of their range in the continental U.S. was chronic breeding failures from environmental contaminants. DDE (a by-product of the insecticide DDT) once caused widespread eggshell thinning and breakage before hatching. In the 1960s and 1970s, only 30% of eagle nesting attempts in Maine yielded eaglets. At the time, levels of DDE were higher than any other findings in wildlife tissue sampled in the U.S.

The photo above shows the 1974 transplant of eggs not impaired by DDE into a nest in midocast Maine. Frank Gramlich and Paul Nickerson (both now retired from the U.S. Fish and Wildlife Service) were attempting to bolster the supply of eaglets where eggs failed to hatch at all local nests in the Kennebec River estuary during a 16-year period. It helped hold eagles in areas where the species was nearly extirpated. A limited supply of "precious eggs" was brought in a thermal suitcase from a captive breeding program in Maryland or healthy donor populations in Minnesota and Wisconsin.

Paul Nickerson, former endangered species coordinator in the Northeast, recalls egg transplants during 1974-76. Paul brought 3 eggs from Minnesota's Chippewa National Forest in 1974. Only one of 3 attempts succeeded that year. Addled eggs taken from each nest revealed high levels of contaminants. Egg transplants were about 40% successful. In later years, eaglets were fostered into nests with contaminated eggs. This technique was 90% successful. Desparate circumstances required extreme measures as the decline of Maine eagles continued well into the 1970s.

Our "eagle cam" was placed at this Hancock County nest partly because this location has the best nesting record of any nest in Maine since it was first used in 1995: 100% of ALL nest attempts here have been successful. Eighteen eagles have taken first flight here over the last 11 years: nearly double the average nesting productivity among Maine eagles.

Other nests are less fortunate, and some have continuing problems with environmental contaminants like PCBs and mercury. Another pair of eagles nesting only 30 miles away from the "eagle cam" represents the other extreme. Eagles nesting there have NEVER raised eaglets during 12 years of breeding at a remote location free from disturbances.

Most nests in Maine have nesting statistics somewhere between these two extremes. Since 1996, 60% of all eagle nesting attempts in Maine yielded eaglets that survived to fledging. Some of the 40% failures in the population are due to environmental contaminants. We hope that this problem does not arise at our "eagle cam" nest, and toxics never again threaten the population.

Management comments: Bald eagles are a top-level predator and therefore exposed to concentrated doses of environmental contaminants passed through food webs. Beginning in the mid-1940s, several raptors and fish-eating birds like bald eagles experienced dramatic declines for nearly 3 decades during the height of the DDT era. Banned in 1972, there are still residues in most eagle tissues in Maine, but the impact of DDE has diminished.

Mercury and PCBs still harm some Maine eagles. These contaminants can transport through the atmosphere exposing other regions. Maine is downwind from prevailing westerly winds in North America. Most people value bald eagles as our national symbol or a magnificent part of our wildlife heritage, but their role as an indicator of environmental quality cannot be understated. -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife

Tuesday, April 04, 2006

April 4 notes: hatching one week away?

This morning there is a brisk southeast wind blowing across the Gulf of Maine and buffeting the stand of pines along the shoreline where the nest is located. The web camera, mounted on an adjacent tree, is having trouble staying centered on the eagle nest. A cold rain will fall later today, and we may even see snow by afternoon. How will the inclement weather affect the eagles? The first eagle egg is due to hatch about April 11 (plus or minus a few days).

Bald eagles are one of our earliest nesting birds in Maine. Only great-horned owls nest earlier. We have a relatively short "time in the sun" here in the north and eagles need to get an early start nesting so they have enough time to incubate their eggs (35 days), raise their young to be able to fly (10 to 13 weeks), then allow the young to perfect their flight skills (another 6 to 12 weeks) before leaving their parents in the closing days of summer. Our eagles layed their first egg on March 6, but we've documented some pairs incubating as early as mid-February. Sometimes we've observed eagles incubating their eggs with all but their heads covered in a late-winter snow.

Long periods of adverse weather can have a detrimental effect on the nesting success for eagles. Last year was a good example when we endured one of the coldest and rainiest springs on record. In 2005 we documented 385 breeding areas occupied by paired eagles. Of those, 48% (183 nests) hatched eggs, well below the 58% average success rate we've experienced in the last 15 years. The poor weather not only affected the hatching of eggs, but also reduced chick survival. The longest period of heavy rain occurred in May when chicks were still in the downy stage and have difficulty keeping warm without the constant attention of their parents. In 2005, 253 eagle chicks fledged from 183 nests. Eagle biologists use the ratio of chicks fledged to successful nests, or "brood size," as one of our important measures of the productivity of the population. Last year brood size was only 1.38 chicks fledged/successful nest, nearly 7% below the average for the last 15 years.

This year our spring weather has been unusually mild and dry - perfect conditions for nesting eagles. Charlie Todd and other state biologists have begun their initial aerial monitoring of all known nest sites in the state and occupancy of eagle nests looks good. Barring no major weather events, we may see a downy chick in the nest nest week. If past odds are a guide, we have about a 60% chance that this pair of eagles will hatch one of their eggs. Keep your fingers crossed! --Mark McCollough, U. S. Fish and Wildlife Service