You can click on this link – Bot_gardens_letter – or read the letter below from Dr Bryan Watts (they are both the same).
I wanted to thank all of those who came out to the Norfolk Botanical Garden to the eagle banding event today and all those who tuned in online. I continue to be thrilled and amazed by the number of people monitoring this pair and their broods. In a time with so many distractions, the attention given this pair speaks a great deal about how much we as a global society value wildlife. What a fantastic opportunity that has been provided by the Norfolk Botanical Garden, the Virginia Department of Game and Inland Fisheries, WVEC, Nuckols Tree Care and the other partners to see the intricate and private lives of this spectacular species. It is a privilege to work with them.
The Center for Conservation Biology conducts 30-40 research projects per year focused on birds of conservation concern. We have banded hundreds of eagles and tens of thousands of birds of many species. We have worked toward the recovery of bald eagles in the Chesapeake Bay for more than 40 years and have seen the population in Virginia recover from less than 30 pairs to more than 650 this year. I am one of the lucky ones who has been able to work on more than 50 eagle projects, spending thousands of hours in planes and boats surveying them, handling birds of all ages and banding many, many broods. Even so, I was taken by surprise that two of the chicks were not of banding size today, a clear contradiction to my message just a couple of days ago. Though this may seem on the surface to be a concern, the chicks will be fine and I find this truly fascinating.
The chicks today were 21 days old (1,303 grams), 20 days old (980 grams), and 18 days old (796 grams). This is a typical stagger for a 3-chick brood. Three chicks are the maximum brood size for bald eagles and due to the time difference in hatching the first-hatched chick has quite a head start that it maintains often into the fifth or sixth week. Adults typically are unable to provide the same resources per chick for all three chicks that they can for one or two chick broods and the deficit is mostly borne by the younger chicks resulting in slower growth rates.
Over the past decade we have worked with many broods on the tributaries of the lower Chesapeake Bay. These are some of the most productive waters for eagles in North America. They support some of the highest breeding densities on the continent, the largest average brood sizes, and the fastest growth rates. We have measured many eaglets 15-20 days old and none have been less than 1,000 grams. Most chicks that are 20 days old are more than 2,000 grams and are of perfect banding size. Between 15 and 40 days of age these chicks have an average daily weight gain of 150 grams. The average weight for 15-day old chicks has been 1,350 grams. This is higher than the 21-day old chick today and nearly twice the weight of the youngest chick. Note that the chicks today were perfectly healthy. They are simply growing at a slower rate than those of the lower Chesapeake.
We have no growth data from the outer coastal areas including the Delmarva Peninsula and Lower Tidewater. The difference between this brood and the broods of the lower tributaries lead me to misjudge the early banding date but also invites new research questions. We need more information on the pairs breeding on the outer coastal fringe for comparison. We will measure these chicks again when we return later in the spring to deploy a transmitter. These chicks and others to follow will add to our growing understanding of the ecology of this magnificent species in the hope that it will improve their management in the years to come.
Bryan D. Watts, Ph.D.
Mitchell A. Byrd Professor of Conservation Biology
Director, Center for Conservation Biology
College of William and Mary