Bald Eagle Monitoring at Lake Chabot

By Mary Malec

I first heard about the new Bald Eagle nest at Lake Chabot in early March.  There had been a couple of reports of Bald Eagles at the lake, and then one of the rangers was fishing with his son and spotted an eagle carrying nesting material.  Doug Bell, the Wildlife Specialist for the East Bay Regional Park District, was notified and in turn informed the California Department of Fish and Game and the U.S. Fish and Wildlife Service.

The park district had contracted for fire suppression timbering in the area surrounding the nest, and people were concerned that the cutting, grinding and helicopter log removal might disturb the nest. Monitors started watching the nest immediately, noting all noise from timbering, boating, planes and people, and tracking the birds’ response. The timber contractors agreed not to do any fly-overs of the nest, and to stop all activity if the pair seemed bothered.

The female of the pair was a four-year-old, looking like a dirty blond and not very much like an adult Bald Eagle. In fact, there had been a report of a Golden Eagle diving into Lake Chabot and pulling out a fish.  Clearly it was this immature bald female who had been spotted that day.  Everyone doubted that she would be able to nest successfully, and when it was determined the male was about five years old (still young for breeding), it appeared to be even more of a long shot.

I was oriented to the site one rainy day in March.  We hiked in to the Observation Point where volunteer monitor Harv Wilson was already at work.  He had brought  his tent and was inside with his scope focused on the nest across the cove.  The O.P. is about 1,000 feet from the nest and it was a challenge to be a nest monitor that day, watching activity so far away while rain dripped off the front flap of the tent.

The female was having a difficult time of it during those early weeks.  Either her lack of experience or her immature hormone levels were getting in her way.  She would settle down on the nest but never stay long.  The male would immediately take her place, or he would find her and chase her back to the nest, where again she would sit for a while and then leave.  He did most of the incubating in the first 3-4 weeks and then she started to do about 50 percent of the work.

I had to catch up on my reading about eagle nesting behavior before I started.  Eagles do things that I’ve never seen before:

When they want a stick for the nest, they fly at a branch and grab it with their beaks, then continue to fly and take the branch with them.  (They bring a stick almost every time they return to the nest.) One day the female flew at a branch and ended upside-down for a period of four minutes.

I‘m not sure what went wrong.  I’d been taking notes when she flew by and grabbed the branch and flipped upside-down. I knocked my notes out of the way and moved my scope and started pacing as I watched her hanging and flapping her wings.  Three ravens came by and harassed her as she hung there.  At one point, she flipped upright onto a branch and immediately fell back again.  Again she righted herself and this time stayed upright.  She roused (shook herself and fluffed up, then smoothed out, her feathers) and flew toward the nest, plucking a stick from a tree on the way.

As time went by, they continued to build up the sides of the nest — for some reason, building the west side higher than the rest of it.  That turned out to be the side that the adults (and later the baby) most often stood on: Whether they stood there because it was higher or whether they built it higher because that was the best view of the lake, I don’t know.

A pair of House Finches built their nest in one side of the eagle nest.  We could see the adult eagles watching the finches’ movements as they came and went on their nest.

One morning as I was monitoring, the male brought a fish to the nest.  It was about the time hatch was due so I watched him carefully.  He seemed to settle down on the nest, not eating and not feeding anything, just incubating.  Despite the distance, the sides of the nest nearly obscuring him, and the tree branches in the way, I continued to watch through the scope.  After eight minutes he got up and started to pull off pieces of fish.  I could see him bending over and making feeding motions toward the bottom of the nest but couldn’t see anything there.  It was nearly two more weeks before we were able to confirm one baby, when it was finally big enough for its head to show over the rim of the nest.

The young female caught on quickly to the process of feeding the eyas, although I think the male did more of the feeding than she did.

One day the female flew over the O.P., and I heard eagle calls from the trees behind me.  I didn’t think it possible she had landed so close to me but I carefully got up and crept around the brush so I could see the tops of the trees.  It was not the eagle, but Steller’s Jays who had learned to imitate the eagle’s call nearly perfectly.

The remainder of the season was uneventful until the baby fledged.  Raptors “branch” before they’re ready to fly.  The baby branched on or about July 10th.  I went to monitor in the morning of July 13th and found the nest empty.  I could not see or hear the eyas.  I didn’t see or hear the adults either.  We monitors had gotten to know the places where the adults like to perch, and I had scanned all of them in the first half hour I was there that day.  With no baby calls and no adults in sight, I was getting worried.  I’d scanned the tree branches, and I’d spent a lot of time looking at the ground below the nest.

Then I saw the baby hop up onto the far end of a deadfall log directly under the nest tree.  It looked good, walking around on the log, hop-flying off, walking around on the ground and returning to hop onto the log.  The adult female flew into the nest with some food and the baby started to call.  The adult sat on a branch high in the tree above the baby on the ground.  After an hour of walking around and picking at grubs in the log, the baby flew out of sight.  I saw it later walking around higher up the hill, disappearing behind a tree into some thick brush.  I could hear it calling periodically, getting farther away from the nest tree.  I left that day a little worried about it being on the ground.  Doug Bell went to the site later in the day and saw both adults and could hear the baby calling.

I went in by boat the next day and spent a couple of hours listening and looking, finally seeing the baby about 15 feet off the ground on a partially fallen tree.  It flew from there up and over the crest of the hill in a strong flight.  It was spotted again the next day higher off the ground and making at least two strong flights.  It continues to do well.

After a lot of worry about a too-young mother eagle and several months of monitoring,  we have the first recorded successful nesting of a Bald Eagle in the East Bay Regional Park District.

By the way… it’s a girl.

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This video shows the just-fledged young eagle on a log under the nest tree on July 13, 2012. By the next day it was about 15-20 feet off the ground and making short but strong flights

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Mary Malec has been a volunteer with Golden Gate Raptor Observatory for seven years, counting and identifying migrating raptors.  She has monitored raptor nests in the Bay Area for six years.