Monday, October 10, 2016

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2016

2016 was the eighth year of the Tree Swallow (TRES) nest box project out on the small (8x2km) and remote Middleton Island, located in the Gulf of Alaska. It provides housing to one of the most isolated TRES breeding populations of North America. I myself had the privilege to monitor them this summer, during a stay on Middleton between May 15 – July 15, covering most of the TRES breeding season.

The first TRES for 2016 was seen shortly before my arrival on May 14 (by employees of Alaska Fish & Game), at the central cluster of boxes near the Military pond. During a first round of nest box checks on May 22, it appeared that three pairs occupied three boxes, all containing nests (one unfinished and two finished)…

… and in box 6 also the first eggs for the season (a single 3-egg clutch). Back calculating (with a rate of one egg laid per day, usually laid in the AM) this would mean a first laying date of May 20. These 3 nests resulted in 3 clutches, all containing 6 eggs. Clutches in box 8 and 11 were initiated on May 25 and 29 respectively.

All of these eggs hatched the following weeks…

… allowing to have banding of 18 circa 12 day old TRES-chicks take place between June 18 – 27...

...under the watchful eyes of their parents, which during the operation found their entrance hole blocked by paper tissue. All 18 chicks fledged by the end of June/first half of July.

But things didn’t go this easy for all TRES on the island. An additional number of lonely males (probably 3 - 4) occupied single or clusters of nest boxes. These birds spent most of their days perched on top of their box in the hopes of attracting a partner for the season. The male on the photo above occupied the northern box cluster. It must have gotten quite desperate, as it was observed displaying towards Bank Swallows on a few occasions during the second half of June. The opening photo of this post shows a male that spent most of its summer on top of box 7 (facing the FAA weather camera). It never found a mate, but none the less brought a 5 cm thick layer of white gull feathers into the box (which I don't record as nest). Other places where a lonely male was seen regularly were box 13 and the southern cluster (boxes 15 - 17).

The late appearance of a second calendar year female on the island, first recorded together with a male around box 14 on June 8 (not known to be occupied before that date), must have caused excitement among the lonely males on the island. The two birds would make up Middleton’s fourth and final nesting pair for 2016. On June 9 this female copulated on the box, which on that day contained some feathers as nest material. On June 16 their nests was finished, but instead of them, a total of 4 very noisy birds (including 3 adults and 1 2cy female, photo above) got recorded, harassing each other around the box. On June 20 the nest contained 3 eggs (first laying date: June 18), but the two birds present appeared to both be adults… When on June 27 3 cold eggs and no birds get recorded in or around box 14, the breeding attempt had apparently failed.

What exactly made the pair from box 14 fail remains unknown, but when on July 8 the unoccupied box 15 (located 2 km from box 14) was opened for maintenance, the decomposing remains of an non-banded second calendar year (born in 2015) female TRES were found (thanks to Chris Gates for confirming the ID). Since this box hadn’t been opened since June 16, a time of death remains hard to determine, but the state of decomposition indicated that ‘weeks’ seems more likely than days, making it reasonable to assume that this was the young female from box 14 (last seen on June 16). Were it the lonely male TRES that harassed her to death?

Bank Swallows Riparia riparia were abundant breeders this summer. In 2005, 2006, 2009 and 2010 I counted the total number of nest holes, resulting in a varying amount per year (112, 48, 65 and 106, respectively). This summer a total of 203 holes was counted! In 1956 Robert Rausch recorded the species for a first time, with only a few pairs.
And many young Bank Swallows fledged this summer, which would often hang out together with the young TRES, making it very difficult to catch a glimpse of the young TRES in a brown mass of young swallows. I believe that among the swallows on this stick above the Military pond there´s at least a few young TRES… (or maybe all are?).

The 17 nest boxes withstood the 7 – 8 years of exposure to the Gulf’s extreme weather conditions quite well. But the scheduled maintenance of the project’s hardware took up an unexpected large amount of time. In the end all boxes got a fresh layer of paint, but two needed to be replaced, one repaired...

…and several had to be provided with a new swallow perch (a bended metal pipe at the top), also a measure to keep eagles and gulls away from the boxes. In the absence of this device, this Glaucous-winged Gull Larus glaucescens managed to put its feet on wet paint…

Three new boxes were added to the project this summer, including this one along the Dump Road, making a total of 20 nest boxes currently present on the island. As a tryout, two of these were constructed from white PVC planks, in order to see whether this material suits the TRES needs, and if it has a longer life span than wood. I thank Scott Hatch (ISRC) for providing the materials for this project!

A new map of the new situation, and the boxes used by the four breeding pairs in 2016’s. Boxes 18 – 20 were placed later in the breeding season and were therefore not available to the birds.

Now it's all set up and ready for a new season…

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