This is a very interesting and informative essay by Marge Gibson. It may only be reproduced for non-commercial educational purposes and if attributed to the author. A pertinent excerpt: "We do know that the parents do kill, eat or abandon chicks that are not healthy or will not for some reason develop normally. We see this in rehab often when people find babies that appear to have fallen from the nest but instead were pushed by a parent. We see nothing wrong and raise them only to find they have an abnormality that we were blissfully unaware of until they were grown. Many of our education birds are those that are not releasable to the wild because they are not perfect and therefore should not breed and dilute a perfect gene pool."
Marge Gibson, Executive Director of Raptor Education Group, Inc., offers her insights on the seemingly strange behaviors of bald eagles on nests throughout the United States.
BALD EAGLE BEHAVIOR IN CHANGING TIMES
Marge Gibson, Executive Director, Raptor Education Group,Inc. © 2013
I wish I had a simple explanation; however, the truth is we are entering uncharted water as it relates to bald eagles. Let me offer some ideas. These are only SOME possibilities.
The Bald Eagle population has changed. In 1963, according to FWS there were only 487nesting pairs of bald eagles remaining IN OUR COUNTRY; the species was in danger of extinction.
Due to some quick action in the late 1960’s and early 1970’s on the part of Dept. of the Interior (and the old version of the EPA) the Bald Eagle population recovered. In some parts of the country, including where I live in N. WI, we are now in the enviable position of having a near saturated population of Bald Eagles. That means all the prime territories are occupied. This forces the birds to behave differently.
The fact is when current books and classes were developed that schooled the current experts, and even references, now turned to in efforts to offer explanation, are based on the recovering population of eagles not a saturated population. We know that is true because we have concentrated on the endangered aspects of the eagle. No current working biologist remembers a saturated population of Bald Eagles. Alaska is as close to the dynamics we need to consider, but that state is very different in habitat and prey availability during the breeding season. Having worked in AK with the bald eagles in 1989, their behavior and comfort level even during breeding was much more casual in part due to the spectacular nesting sites as well as over the top plentiful food.
Experts in many parts of the country are still dealing with a threatened or endangered status for Bald Eagles. The references we are used to therefore, apply in those situations, but not so much anymore in areas of strong population.
1. Behaviors change in ways we are only beginning to understand when we have a strong and expanding population. In my part of the world we see many more territorial disputes. Our research at REGI in WI is in the beginning, and is fascinating thus far. In the past these disputes happened pre breeding unless in extraordinary situations. We are now seeing them throughout the spring and summer. A breeding territory must have many criteria to qualify as an adequate “territory” including a safe nesting area, plentiful prey availability and even areas where the birds can go that is a safe area in event they are injured. Those “prime” territories are held by the strongest eagles with the “best” DNA. They will be challenged and fought for. It is important to understand a “territory” is not just a nest site. Some are large and some are not. IN Alaska we had prime territories along Prince William Sound that were only 100 feet wide on the waterside!
2. We have to take into account food availability. A population crash of certain fish or die off/ population change in other prey as one of the many things that happen in the natural world. Plentiful migrating fish such as salmon happen only sporadically and are not a stable food source for breeding birds. Removing certain animals that we consider invasive may in fact affect a population of eagles that has become reliant. We don’t know what may be happening in the ocean in N. CA where the nest of concern is located. We do know that many baby sea lions have been found starving in the area. Perhaps there has been a crash in some species of fish that these eagles prefer to feed on. If there is not enough food, and there was some indication that the male was not supplying the female with adequate food before he disappeared, the eagles cannot raise healthy eaglets. In nature birds must have adequate food to feed their young to rear them. If not, they cannot waste their own energy and calories on feeding chicks that will not be able to survive. Humans have a very different mindset on this. We have to remember we are watching wild eagles behave in a way that is entirely normal and natural way. The term “Survival of the Fittest” is perhaps overused but very true.Eagles have no option when it comes to caring for young that are weak or otherwiseimpaired. Seventy per cent of all raptors die their first year of life. It is a tough life. There are few safely catches for the weak or injured. The pair of eagles not behaving in a normal way is Larry and Lucy, on the Eagles4Kids site in Blair, WI. There the male continues to care for and has nested with a disabled female. He is rewriting the book. We have no idea why. We are learning daily as we watch the nest. Anything is possible even at that site however. They are eagles and we are humans. We can only try to understand their behavior and incorporate it into what we know about eagles now and what we will know in the future.
3. There are many other issues that could cause behavior changes in eagles and other species. They are too numerous to go into and include but are not limited to toxins, pesticides used in the environment and enter the food sources through water and other routes and viruses. Both may affect the brain. West Nile Virus does affect the brain of eagles and other birds and causes aggression, other viruses may as well. We do not know. It was a scientist, Rachel Carson that wrote the book Silent Spring in 1962 and sounded the alarm on DDT. Her ideas were very unpopular at the time, but she was the key to saving many avian species from extinction.
In short we do not have all the answers. Behaviors, even maturation development change with population, food and other pressures. Neurotoxins change behavior because they change brain chemistry. There are other considerations that are yet to be revealed. Science rarely offers absolutes. We can give educated guesses and hope we are right. We can study and do research to see what may be happening at certain sites, but when populations are changing even top experts have to admit to being behind the 8 ball. It is not because of lack of desire but because it is a different situation that we have never seen before. Please be patient as it plays out.
We do know that the parents do kill, eat or abandon chicks that are not healthy or will not for some reason develop normally. We see this in rehab often when people find babies that appear to have fallen from the nest but instead were pushed by a parent. We see nothing wrong and raise them only to find they have an abnormality that we were blissfully unaware of until they were grown. Many of our education birds are those that are not releasable to the wild because they are not perfect and therefore should not breed and dilute a perfect gene pool. That is how wild species remain perfect. Survival of the fittest, strongest, more capable works for them and has from the beginning. It is not our “way” but it has allowed their species to continue and beautifully. Cams are amazing and are allowing scientists and the interested public to watch, and observe the REAL LIFE of eagles will all the good and the bad. It is hard for us to understand sometimes. But please know the reasons are there. In the history of man you will find that our own species coped in these ways to assure the survival of the greatest number. They are eagles and we are humans. It is tempting to want to think of the eagles we are fond of as “humans with wings” but they are not. We need to love and accept them for the magnificent creatures that they are.
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