EagleCam Updates - 2011
Click image for the photo gallery:
April 16, 2011
It has been confirmed that the dead eagle found at Antietam did not have a brood patch. This means this eagle was almost certainly not the long-term resident male from NCTC, given that the resident male would probably still have had a brood patch. We will do our best to confirm the gender once the bird has arrived at the National Eagle Repository.
April 14, 2011
The resident female eagle and the new eagle have been observed mating; behavior which indicates the new bird is almost certainly male. We think it is too late in the season for eggs to be laid, but we are keeping an eye on the nest. Eagle behavior is complex, particularly during the breeding season. The behavior we are seeing at NCTC may be unusual, but by no-means is it unheard of.
The absence of the long-time resident male at NCTC has concerned many of our eagle cam viewers, and there are several possible reasons why we aren't seeing him. The most likely reason is that the new male may be in better breeding condition, and as a result, replaced the original male. While we will not be able to know with certainty what happened to the resident male, we do have some new information.
Yesterday, we received a report from our National Park Service neighbors at Antietam National Battlefield that a dead eagle was found inside the park. NCTC sent a team to examine the bird, and based on measurements the team obtained and compared with typical eagle gender patterns, it seems very likely this bird was male. The Fish and Wildlife Service's National Eagle Repository will perform a necropsy, and only then will the gender of the bird be absolutely confirmed. This process is expected to take several weeks. Even if the bird is determined to be male, it will still be impossible to confirm with any certainty whether this bird was the resident male at NCTC.
Below, we've provided some additional information about eagle behavior which may help explain some of what our eagle cam viewers have been witnessing this season:
- Eagles are at risk of agonistic encounters (aggressive social interactions with other members of the same species).
- Aggression and territorial defense behaviors increase during the breeding season.
- Violent exchanges between eagles can result in the exclusion of one bird from the area, and in some cases, serious injury or death.
Mating for life; nesting behavior:
- Eagles do generally mate for life, usually selecting a new mate only when one dies.
- Re-pairing can occur within months or a few days. In one case, a female attracted a new mate in four days. In another documented case, the male of an incubating female disappeared and a replacement male appeared the next day and began delivering prey to the nest.
- Typically eagles prepare nests 1-3 months prior to egg-laying. However, nest repair can continue year round. In some cases Bald Eagles will lay replacement clutches if the first attempt fails.
- Because of the lateness of the season, it is highly unlikely that the NCTC eagles will attempt another nest. Return trips to the nest may indicate an instinctual behavior brought on by the time of year and the individuals' hormone levels.
Local eagle populations by numbers:
- In 2010, the WV Department of Natural Resources located 36 Bald Eagle nests state-wide and MD Department of Natural Resources estimates 500 breeding pairs in Maryland.
- These numbers are extremely encouraging for a bird recently removed from the Endangered Species list. However, with higher populations, there will be additional competition for suitable territories, nest sites, and mates.
April 4, 2011
This morning we confirmed a sighting of two adult eagles in a tree located near the nest tree. While we do not know the current whereabouts of the original male resident eagle, he was seen on March 21st and was not injured. We have not seen the male resident since. The new eagle, we now believe to most likely be a male, has been making trips to the nest on a daily basis. This indicates to us that the resident male eagle has either moved on or is not willing to come within a certain radius of the nest because of the new bird. The resident female is still occupying her territory and is keeping quite close to the nest site. It is very difficult to determine whether an adult eagle as male or female; typically the female is larger (we initially assumed the new adult eagle was a female because of its large size). Without capturing the new adult to examine it- which would pose a potential risk to eagle - it has been difficult to confirm whether it is male or female. One method we're exploring is listening to the eagles' calls: some females have a much lower pitch relative to males. We will continue to provide information as the situations changes. Meanwhile, we encourage those of you who are interested to learn more about eagle biology. (For example, this Cornell University Web page is a good resource: http://bna.birds.cornell.edu/bna/species/506/articles/introduction.) We have a fascinating piece of eagle biology playing out at NCTC. We are glad that you are able to experience this along with us.
March 22, 2011
Earlier this afternoon, NCTC released a statement regarding its resident bald eagles. The statement includes information from a raptor biologist explaining why human intervention is not a good approach when it comes to nesting birds, and eagles in particular. To learn more, you can view the brief statement on the Web at:
March 21, 2011
In upcoming weeks, we will do our very best to post regular, factual updates that are grounded in science. Over the weekend, we were able to confirm the presence of a third adult eagle near the nest, and we are almost certain that it is a breeding age female. Typically, the presence of a new female means she is competing with the established pair of eagles for the current nest. Nest competition is a common occurrence in areas with healthy eagle populations, meaning the total population of eagles near NCTC has likely increased in recent years.
We have also confirmed multiple sightings of the male eagle who is part of the established breeding pair. The male does not appear to be injured, and appears to be in good health. The eaglet which hatched on March 17th has died and the remaining egg is not likely to hatch given that it is not being regularly incubated by the parents.
We do have biologists on staff here at NCTC who have been offering their expert assessments of the situation. In addition, our land manager has been communicating with another raptor biologist based in our Chesapeake Bay field office. There is general agreement among our biologists that if the new female eagle is successful in chasing off the current female, the new female will then need to recruit a male to join her. However, it is likely too late in the nesting season for success in laying, incubating and hatching any new eggs.
You may wonder why there is competition over this nest - and there are several potential factors. Eagles prefer to nest in the tops of large trees located near rivers, lakes, and other wetlands. The NCTC nest is located very close to the Potomac River, which is a plentiful source of fish for nesting eagles to hunt. In addition, eagle nests represent a considerable investment of effort to construct: they can be up to 10 feet in diameter and weigh up to 2,000 lbs. And finally, as mentioned above, nest competition frequently occurs in areas with a significant eagle population.
March 18, 2011 - 3:00 PM
While we are still working to confirm what the current situation is with the adult eagles, we would like to remind all of our dedicated eagle fans that the eagles who nest on the NCTC campus are wild birds. As such, they are exposed to the same environmental pressures any eagle faces in nature. While the NCTC camera provides us with an opportunity to observe these magnificent birds in their natural environment, it is not our policy to interfere with them in any way.
March 18, 2011
The first of two eggs in the nest hatched yesterday, March 17th, in the morning. Two eagles have been confirmed to be present at the nest as of this morning. One has been generally staying higher in the tree (above the camera). The behavior we are seeing from the adult eagles is a little different than is typical. At this point U.S. Fish and Wildlife Service staff are working to confirm whether these two eagles are the mating pair. More information will follow soon.
January 20, 2011 Update
We are excited that the eagles have been working hard to set up the nest for another nesting season. Dawn, midday and dusk seems to be the best time to view them right now. There has been mating activity occuring for more than a week, which is a good sign.
We have been able to adjust the new cam to work fairly well in night vision mode, so we are ready for the eggs to be laid. We are hoping to see the first egg within about about two weeks, toward the beginning of February.