Arlington Eagles Update 8/2/23

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About a month ago the nest built by MK and KZ in the Mt. Pleasant Cemetery in Arlington in 2020-21 came tumbling to the ground. The nest had been maintained and expanded by FAE (Female Adult Eagle, unbanded) who in March 2023 had mated with KZ very shortly after MK was removed from the cemetery due to illness and subsequently died. Fae and KZ appear to have built up the walls and expanded the nest, though this year there were no juveniles to tear it apart earlier. The additional build-up of the nest combined with the weight of heavy rains flooding the nest was too much for the relatively thin branches that held the nest in place. It was perfect for a Redtail nest, but the foundation was just too small to support an ever expanding eagle nest.  

 

 When FAE and KZ’s enhanced nest collapsed to the ground, the question was how would this new pair respond?  Would they attempt to rebuild the nest on the old site? Look to build a new nest nearby in the cemetery or vicinity? Look to the handyman’s delight of an old dilapidated nest on the western shore of the lower Mystic Lake, the first nest built by MK and KZ in 20190-20? Or just split and seek new mates?

 

The decrepit nest on the lake had been abandoned by MK and KZ in 2021, likely because MK’s first nestling had been stolen from that nest and killed by an intruding “floater” adult male eagle. Furthermore, KZ had endured challenges from at least six “floater” males, one of whom had defeated him multiple times, driving him from his territory and mate. Many observers thought the intruder had killed KZ after they had locked talons and tumbled beneath the horizon. Only the intruder had returned that day and took possession of the lakes, nominally including KZ’s mate MK. (KZ reappeared roughly a month later and reclaimed his territory and mate, a totally different story.)  

 

Although KZ and MK were restored to “supremacy” on the lakes, I think MK made the decision to abandon their first nest and build a new more secluded nest some distance from the immediate waterfront. She and KZ took over a successful Red-tailed Hawk nest in Mt. Pleasant Cemetery, began clear-cutting small branches in the top of the tree, and built a truly eagle-sized nest. The original nest on the lake was not maintained.

 

When it became clear that FAE and KZ’s attempts to breed this spring had failed, the question was how would this new pair respond? Would the nest failure doom their relationship, or would they remain together to try again in a “normal” year? The only thing we knew for certain was that they began repairing and expanding the nest where they had just failed.   

 

Shortly after that cemetery nest collapsed, the same questions resurfaced. Almost immediately KZ began carrying sticks to the old lakeside nest, where FAE appeared to be laying them on top of the remnants of the old nest. This was not a major surprise because FAE had spent a lot of time in the old nest tree on the lake when she was on “nest exchange breaks” during incubation in the preceding months. The nest area was shaded, relatively cool, and provided great views of the lakes with some sense of privacy. The tree seems to be an ideal nest site, located back a bit from the lakeshore, providing strong horizontal branches under the canopy and good cover. FAE had spent perhaps more time in the old nest tree than anywhere else outside the Mt. Pleasant nest over several months.

 

In late spring/early summer the reproductive systems of eagles atrophy and related hormones decline, so they are not carrying the additional weight needlessly for about six months and it minimizes post-nesting territorial and breeding conflicts. Thus, males are not as inclined to bring sticks to a new nest expecting copulation with the female as a reward, a common occurrence in winter and early spring. But bonding can be encouraged, strengthened, by sharing work on the nest.  

 

Apparently unseen except by the homeowners on whose property the nest tree is located and their immediate neighbors, FAE and KZ soon began tearing apart the remnants of the old nest built by MK and KZ. Much of it simply fell to the ground, but some of it apparently became entangled with lower branches, visible from the dam’s observation platform. One of the homeowners joked to a friend that FAE did not like what KZ’s previous spouse had done with the nest, so she preferred a complete remake. KZ brought in new sticks, small and large, while FAE worked them into a latticework forming the basic shell of a large nest.

 

They tend to work for 30 – 90 minutes at a time, usually in the morning; apparently earlier on hotter days.  They tend to spend several hours most mornings relaxing on their favorite perches. FAE often sits in a short tree at ” MK’s Beach” on the west side of the upper lake, or perches out of sight in the adjacent woods. KZ sits on a spruce on the eastern point of the upper lake. They’re generally too far away to photograph or enjoy seeing even with binoculars, as the photos on my Facebook page illustrate. Eleven days ago they both spent some time in the nest, and then posed for a family photo just outside the nest.

 

 For several months, both eagles have assiduously avoided the famous tree next to the Medford Boat Club, variously known as THE tree, or the EAGLE tree because it is usually the favorite perch of any eagles in the area, affording great views of both lakes and any fish near the dam. FAE and KZ avoided THE tree because a pair of Eastern Kingbirds was nesting there.

 

The eagles and kingbirds have a tacit timeshare arrangement regarding THE tree. The kingbirds (and their young) essentially own THE Tree when they nest in THE Tree from early May to late July. When KZ, FAE, or any other predators try to perch in THE tree, while the kingbirds (scientific name Tyrannus tyrannus) are nesting, the adults and later their young attack them mercilessly, driving them off time and again. They attack Great Blue Herons that try to perch in THE tree, (Great Blues will eat kingbird nestlings should the opportunity arise.) It is not just THE tree they defend; it is the air space for several hundred yards in every direction. They attack raptors who attempt to even cross the lake not far from the tree when the kingbird kids are flying in the neighborhood. Last week a one-year-old male Red-tailed Hawk in heavy molt shot out of the eastern cove by the Osprey tree. It had three kingbirds attacking it simultaneously, hitting it relentlessly. I called out to Julie, my wife, who was sitting on the dam observation deck with the Redtail heading right at her, trying to shed its attackers. Before the Redtail reached her he executed a 180-degree turn and retreated back to the eastern cove harried by the vicious kingbirds. The next day Jim Renault had a kingbird standing on the back pulling at feathers on the neck of a different Redtail attempting to fly across the lake near the tree. Four days ago KZ was perched briefly on the Tufts Boat House. An adult kingbird flew over a hundred yards from THE tree across the dam to make several passes at the head of KZ, who objected loudly. The kingbird could have hit the eagle if it had wanted to; it was just reminding KZ who owned the area.

 

 Four days ago I was amazed as I saw an adult Bald Eagle sitting on a bare branch in the middle of THE tree. KZ! A few minutes later I saw a second adult eagle land on the top of THE tree; FAE. No sign of kingbirds. Neither eagle was attacked. I thought the adult kingbirds must have migrated already, but I saw them a day later hunting with and feeding the kids near the Osprey tree. It appears that the young kingbirds no longer spend much time in their nest tree so it is rarely defended.

 

If you look at the photos of the “original” nest pine on the lakeshore, they might not inspire confidence. From the dam It looks like a house built on sand, but this is because some of the old nest jumble is still visible below the main branches on which the new nest is built, and which obscures your view of the new nest structure.   

 

FAE and KZ might still look for other suitable nest locations and perhaps build a new nest nearby in September or October with plenty of time to complete it before egg laying in February or March. But right now it looks like they are building an all-new nest on the exact spot MK and KZ selected for their first nest. We can only wait and watch to see what happens.

 

An array of photos of KZ, FAE, and the fallen and the ‘new” lakeshore nests are posted on my Facebook page, which is open to the public at https://www.facebook.com/paul.m.roberts.10

 

Best,

Paul

 

Paul M. Roberts
Medford, MA 
phaw...@comcast.net