Wednesday, March 22, 2006

March 22 notes: eggs over easy ...

You may have noticed that the eagles occasionally take a brief respite from incubation and seem to be arrange items in the middle of the nest. Eagles, like all birds, need to turn their eggs frequently during incubation. An air cell forms in the egg shortly after the egg is layed and grows larger during incubation. The parents need to turn the egg to prevent the developing embryo from adhering to the eggs shell, which stops development. As far as we know, biologists have not documented how often eagles turn their eggs. Perhaps you can gather some information on this behavior by watching the web camera.

Bald eagles typically lay only one clutch per year. Eagles on the coast of Maine may lay a clutch as early as mid-February, although early March is more typical. In northern Maine, where the lakes are still frozen over and the snow pack still has weeks before it melts, egg-laying may be delayed into early to mid-April. We have seen eagles many times blanketed in an early spring snow, but remaining faithful to their incubation duties.

Bald eagles lay one to three eggs, but two is most common. They are dull white in color and about the size of a goose egg. The eggs are layed about 3 or 4 days apart. Incubation begin when the first egg is layed, which means that eggs in a clutch will hatch several days apart. "Asynchronous hatching" is a common in strategy in birds of prey. One chick will always be the oldest and largest and dominant over its siblings. In poor food years, only the oldest chick may survive, but in good years all chicks in a brood survive.

Both the male and female eagle develop a brood patch - a bare area of skin in the center of the chest to keep the eggs warm. the female eagle does most of the incubating, but the male also returns to the nest to help. If you're lucky, you may see a nest exchange occur on the web camera. The male will often bring food to the nest for the female while she is incubating.

Adults show great concern for their fragile eggs and walk very carefully around the nest with clenched feet to avoid breaking the eggs. We would be interested in hearing from you if you observe no eagles on the nest during the incubation period. Adults will occasionally leave the eggs for a brief time (perhaps on warmer days in late incubation). If they do, they sometimes cover the eggs with grass and pine needles from the nest bowl to avoid predation by crows. -- Mark McCollough, U. S. Fish and Wildlife Service

Tuesday, March 14, 2006

March 13 notes: time for diligence

After only a week of watching incubation, perhaps you can see the strategy of nesting eagles is simple, patient diligence to one duty: keeping eggs warm enough to hatch. The incubation period of approximately 35 days requires steadfast attention. For intervals of only a few minutes, the eggs may be unguarded as one adult takes a break and its partner soon resumes the task. The interval during an incubation exchange was 5 minutes long on March 11, an unusually warm spring morning in coastal Maine. During cold spells and spring rain or snowfall, the incubating eagle must endure the elements to safeguard its egg.

Look for subtle behaviors in this period. An adult may rise up, step around the eggs, and reach down to roll them with its beak. If a prolonged absence is planned, a departing adult may cover its eggs with nest lining before departure. When resuming incubation, the female is likely to almost go face down before settling into a position where its brood patch is pressed snugly against the eggs. This is a thinly feathered area on the upper breast enabling an incubating bird to transfer most of its body heat to the eggs.

Incubation duty is not as easy as it sounds. On March 12, I watched an incubating eagle at a Penobscot County nest sit tightly while a crow perched on the edge of the eagle nest: an apparent attempt to lure the incubating eagle into aggressive pursuit and perhaps allow other crows nearby to predate the eagle egg(s). This eagle did not budge, and its mate appeared after a 10-minute standoff to chase away the crows. Raccoons and fisher may also climb into lofty eagle nests for eggs or nestlings, and biologists may prescribe a predator guard to deter them.

Management comments: Eagles have varying levels of tolerance to intrusions. If you or I get too close to a nest, an incubating bird may abandon its primary mission of egg care to circle the nest vicinity (often with an exaggerated flapping flight: not the typical, effortless soaring) and vocalize in protest. This behavior can be misinterpreted as "the eagles are putting on a show for us" when, in fact, they are imploring you to leave. Please do so! -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife

Friday, March 10, 2006

March 6 notes: incubation begins!

The eagles completed nest building last week. For several days they carried grass, sprigs of pine, and other fine materials to line the center of the nest. After home improvements were finished, the female began laying prone in the nest for short periods of time. Late last week the duration of incubation behavior increased, and we knew that egg-laying was not far away. She remained prone for 30% of the time during a 4-hour period on February 27, but periodic absences indicate that eggs had not yet arrived.

Bald eagles have spectacular courtship displays in the weeks leading up to egg-laying. They soar to great heights, lock talons and cartwheel at dizzying speed to the earth, breaking apart just before they hit the ground. They may chase each other, lock talons, roll together in the air, and continue their tandem flight. These behaviors are part of an annual courtship ritual to strengthen the pair bond and encourage mating. Copulation may take place on the nest or a perch nearby. During the last week, we often heard the eagles vocalizing from the nest tree, but out of view of the camera. Our eagles were discreet, and we didn't observe mating. We suspect the couple spent a romantic weekend somewhere on the coast of Maine!

By the morning of March 6, both birds were at the nest for extended periods of time but still left for varying intervals. Charlie stopped at the USFWS office that afternoon to pick up several eagle carcasses sampled by Steve Mierzykowski, our contaminants biologist. We tuned into this web site and were thrilled to see that the female had resumed incubation posture in the nest. A clear, starry night revealed the adult's white head in that same position long after sunset. Nothing had changed by first light March 7. It seems certain an egg was late March 6!

Management comments: Some observers of nesting eagles get the mistaken impression that they are no longer present when, in fact, incubation is underway. One member of the pair is almost always attending the eggs and out of view. Its prone posture is usually not visible from below. The mate may be ranging widely for food or watching nearby but is also less conspicuous to most. Seasonal privacy near the nest is their priority and a good strategy for those who want to co-exist with nesting eagles. -- Mark McCollough, USFWS, and Charlie Todd, MDIFW

Tuesday, March 07, 2006

February 28 notes: nest building

For the last two weeks (since about Valentines Day) this pair of eagles has been sprucing up their home! The web cam provided a unique vantage point to watch this rarely-observed behavior. Check out the archived still photos during this period to observe bald eagle housekeeping.

Nearly every morning both eagles were busy carrying branches to the nest. The female (larger eagle) seems to be the interior decorator and spent the most time arranging the sticks. After two weeks of persistent work, they raised the nest platform about 6 inches. In the last few days, they began carrying small twigs and grass to line the nest bowl. Curiously, nearly all eagle nests contain a sprig of white pine in the nest bowl. We think this is nature's remedy to deter parasites like feather mites.

I've observed bald eagles on the ground in February gathering grass for their nest - an odd behavior for a regal bird that spends much of its time soaring high above the earth. I've also observed eagles snapping large branches from pine snags while in flight and oftened wondered, "what happens if the branch doesn't break?" They seem to have an uncanny ability to judge which branches will snap easily!

Bald eagles are the most sensitive to human disturbance at the final stages of nest building and just prior to egg-laying. Activity close to the nest can result in nest abandonment. - Mark McCollough, U.S. Fish and Wildlife Service

February 15 notes: nest site loyalty

Both adult eagles are making multiple appearances daily at the nest. They feed at the nest occasionally, but meals can be eaten anywhere until food deliveries to young nestling eaglets become necessary. Rearrangement and grooming of small sticks and vegetation lining the center of the nest command most of their attention: apparently readying the nest for eggs.

This is the 11th consecutive year of eagle residency at this site. Construction of this nest began in October, 2005. In just 10 seasons of use, the nest has grown to a two-level structure: each measures 3-4 feet in width and depth. The lower level appears to be residual debris from the original nest that partly fell after damage to supporting limbs. Our eagle 'cam is zoomed in on the "top floor" portion of the nest to optimize views of upcoming breeding activity.

Management comments: Bald eagles are notorious for being highly selective of nest locations. Some Maine nests have been used for more than 35 years and thus were likely home to 2 - 3 generations of breeding eagles. The annual addition of nest materials can lead to enormous structures over time. A Sagadahoc County nest measured 20 feet tall and 7 feet across when first discovered in 1963; it was estimated that eagles resided there for 60 years or more. Even when nests must be relocated to a new tree, the alternate nest is often built nearby. Their loyalty to traditional nesting habitats is the basis for effective land conservation initiatives, environmental regulations, and stewardship efforts of landowners. All habitat protection strategies have proved important to eagle recovery in Maine. -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife

Monday, March 06, 2006

February 9 notes: adult eagles return!

Both adult eagles appeared in the nest today. They likely were never far away. Visits to the nest and the duration of their stay should increase steadily over the next 6 - 8 weeks prior to active nesting (commences with egg-laying). Even when not visible in the nest, one or both are likely keeping a watchful eye from a sentry perch nearby.

Check your audio settings if you are watching the eagle 'cam via live-streaming video. You may hear the shrill vocalizations of adult eagles perched locally. Many are surprised by the sound of an eagle call! I live one-half mile away from an eagle nest in Penobscot County and can sometimes hear the adults vocalizing around their nest while inside my home: often before sunup or during the early morning hours when many birds are most active.

Management comments: Mid-February is traditionally the start of the sensitive period for nesting eagles in coastal Maine. Although bald eagles sometimes acclimate to human activities, new disturbances or abrupt seasonal changes can cause breeding failures or permanent abandonment of nests. Seasonal safeguards are a key safeguard to coexistence with nesting eagles. The timing of nesting events is generally a month later in northern Maine, and therefore the onset of the sensitive period is March 15 there. Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife

February 6 notes: a visitor!

An immature bald eagle landed in the nest today (see archived images). Often called "juveniles" (a term better used for first-year birds) or "young" eagles, immatures are brown-feathered over the entire body with variable white mottling patterns. They do not have the white head and white tail of an adult bald eagle: the highly distinctive plumage that signifies sexual maturity. The buffy highlights in this visitor's head plumage, light feathering of the throat area, dark beak, and brown eye color suggest that it is a second-year bird. It's possible to age immature bald eagles by focusing on these features since head plumage, beak color, and iris color all change in predictable patterns through the first 4 years. Patterns of white on body feathers can be quite varied. Immature eagles are not smaller bodied than their adult counterparts.

This bird could be a visitor to Maine or a native. We have identified eagles from as far away as Florida, Michigan, and Saskatchewan spending time in Maine! Nest intruders may be briefly tolerated at this time of year. Territorial adults usually rudely escort them away during the nesting season, even if is an offspring from previous years attempting to visit home. Only once in more than 50,000 observations of nests here in Maine have I witnessed breeding adults allowing a visiting immature eagle to land on an active nest.

Management comments: Non-breeding eagles (especially immatures) often have a nomadic lifestyle for the first few years but tend to return to their natal area as they approach adulthood at 4 - 5 years of age. Immature eagles from Maine have been seen along the Atlantic seaboard from Nova Scotia to South Carolina. Death rates of eagles are higher in their early years due to inexperience and wide-ranging habits. -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife

January 17, 2006 notes: year-round residency

An adult bald eagle flies in to watch from a shoreline pine 100 yards from the nest as our field crew completes today's installation of the surveillance camera. The nest is often a center of activity (feeding platform, foraging lookout, overnight roost, etc.) even in the "off-season."

Past surveys of wintering eagle distribution revealed frequent use of nests across Maine. Year-round residency is especially prevalent near ice-free coastal waters but occurs even in northernmost interior Maine. Eagles use wintering areas habitually but can patrol a wider area or relocate in response to changes in winter severity and food availability. We found during Mark's research that there may be steady numbers of wintering eagles in a locality, but individual eagles sometimes move broadly across the state or into neighboring New England states.

Management comments: Today's visit was timed to avoid impacts to breeding eagles, but we did not escape their attention. Bald eagles are year-round residents of Maine. Adults appear frequently near nests in all seasons. A territorial presence (even in midwinter) is both a deterrent to other eagles attempting to move in on established nests and an advantage to finding food in familiar foraging habitats. The winter diet influences the fitness of eagles that will soon initiate breeding during March and April. -- Charlie Todd, Maine Dept. of Inland Fisheries and Wildlife