Thursday, April 28, 2022

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2021

2021 was the 13th year of the Middleton Island Tree Swallow (TRES) project. The season started off with an inspection of the nest boxes by ISRC-members in April. Five new nest boxes were installed, replacing ones that had rotted away. Thanks to their efforts in 2021 17 boxes were available to the swallows:

Swallow boxes check, conducted by ISRC personnel on April 19, 2021:

Box 1: Good shape, slightly rotten but sturdy. Might need to replace in 2022/2023

Box 2: No more door present, wood very rotten. Needs to be replaced

Box 3: Good shape!

Box 4: Good shape!

Box 5: Old box fell off and was no reparable. Replaced by new box (green one) in exact same location/orientation.

Box 6: Old box replaced by new one (white one) in the exact same location.

Box 7: Good shape!

Box 8: Ok condition, should last through another season but would need to be replaced in 2022.

Box 9: Old box replaced by new one (white one). Exact same location as previous box.

Box 10: Broken (bottom and side panels missing). Needs to be replaced.

Box 11: Replaced with new box (white one). Box on the angled post facing down and angle adjusted using washer to avoid having the box too tilted forward. New box slightly lower than old one as per recommendation.

Box 12: Good condition, slightly rotten but sturdy. Consider changing in 2022/2023

Box 13: Good condition, back corner rotten but box feels sturdy. Nail for the door missing.

Box 14: Box completely broken and rotten. Replaced by new box (green one).

Box 15: Good condition, starting to rot a little bit.

Box 16: No box. Needs new one.

Box 17: Perfect condition!

Box 18: Perfect condition!

Box 19: Good condition. Post slightly angled

Box 20: Unknown

Unfortunately, due to a lack of time the 2021 ISRC-crew did not manage to monitor the TRES during the breeding season, nor conduct a post-breeding season nest box inspection. The following inspection round could only take place in April 2022, during the start of the following ISRC-season. Details on the 2021 TRES-breeding season were derived from what was found in the nest boxes during this inspection:

From this information it can be concluded that in 2021 five TRES-pairs nested in Middleton Island's nest box project.

Notes on the 2021 breeding season (and looking ahead)
As for potential predators, a Peregrine Falcon was recorded on several occasions in spring, in April until May 11th, but not during the period the TRES were nesting on the island (data: The relative large number of dead eggs and chicks found in the nests may be the result of a long period of bad weather taking place at some point in June/early July.

Several of the nest boxes currently present on the island have been out in Middleton's harsh climate for 12 or 13 years now and underwent only a serious renovation (= complete checkup + new layers of paint) in 2016. It's inevitable that they will continue to decay and more and more boxes will be lost. To take care of this problem a number of boxes installed from 2016 onwards are (partially) made from recycled plastic or PVC:

Boxes # 18, 19 and 20 are made from white PVC-planks and were installed by the end of the 2016 summer. These have thus far never been used by the swallows (except for an occasional piece of nest material).

In spring 2021, 3 boxes were installed to replace some of the most popular, but damaged ones (#'s 6, 9 and 11). These new boxes are made from wood and are similar in size to the remaining types constructed for the project, while adding a (recycled) plastic (dark colored) roof and an aluminum mounting bar. In their first year these did not get used, although a single piece of nest material was brought into box #9.

Two of the new boxes that were installed in spring 2021 (to replace #'s 5 and 14), were made entirely from recycled plastic panels. These boxes are green and have much smaller dimensions than a regular TRES nest box. They were already brought to the island in 2016, but were at that time deemed too small for the TRES to use (and too fragile to remain there in winter). These European nest boxes are designed for house sparrows, but have a slightly enlarged entrance. Surprisingly, in 2021 box 14 (the one on the photo above) was used by the TRES! It contained a nest with 3 dead chicks...

With the ongoing decay of the wooden nest boxes in the project, in 2022 the TRES will find a relatively larger number of synthetic nest sites available to them. We will hopefully soon find out whether the TRES are willing to adapt to these boxes, so the amount of maintenance can be reduced significantly.

I thank the 2021 & 2022 ISRC-crew members for their help!

Sunday, October 4, 2020

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2020

Tree Swallow perched above box 7 (facing the FAA weather camera). June 18, 2020. Photo by S. England (

2020 was the 12th year of the Tree Swallow (TRES) nest box project on Middleton. This year again no data could be obtained during the breeding season, but thankfully Martha Hatch (part of the ISRC crew present in September) checked, photographed and cleaned out all nest boxes still present on the island:

Notes on the 2020 breeding season:
- 16 nest boxes were available to the swallows. 4 were either gone or had become unuseable to the birds. 7 boxes currently are in such bad shape that these might not survive the coming winter. This would leave 9 boxes for the next breeding season. This is also the maximum number of occupied nest boxes (9, in 2013). Therefore, for proper continuation of the project, some replacement boxes will have to be installed.
- Instead of wood, nest boxes 18-20 were constructed from PVC planks. These have similar dimensions to the wooden ones, but are white on the inside. Thus far, these have never been used by the swallows. 
- As far as potential predators go: a Peregrine Falcon got recorded on June 22, July 21 and July 22 (
Again, I thank Martha and Scott Hatch for their effort!  

Sunday, April 26, 2020

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2019

2019 was the 11th year for the Tree Swallow (TRES) research project out on the remote Middleton Island. Again, this summer the TRES-population did not get monitored during the breeding season, but thankfully Scott Hatch of the Institute for Seabird Research and Conservation (ISRC) provided me with an overview of the nest boxes’ contents, as found on their annual inspection round after the breeding season:

Field map containing 2019's TRES results (ISRC). Middleton is approximately 7x2 km.

Based on this information I suspect that this year about 6 nesting pairs roamed the island, four of which laid eggs and produced one or more young.

I took the time to organize box occupancy between 2009 - 2019...:

Thursday, September 6, 2018

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2018

2018 was the 10th year for the Tree Swallow nest box project out on the remote Middleton Island (for more information check the previous annual posts). Once again Martha Hatch was kind enough to inspect all 20 boxes shortly after the breeding season:

I thank the Hatch family and ISRC collaborators for keeping an eye out for these beautiful birds during their stay on Middleton, and Tony Rinaud for the photos included.

Let’s end this post with a text about the Tree Swallow on Middleton Island, copied and pasted from the very interesting publication BIRDS OF MIDDLETON ISLAND, A UNIQUE LANDFALL FOR MIGRANTS IN THE GULF OF ALASKA by Lucas H. DeCicco and others of the Fish and Wildlife Service and University of Alaska Museum (Western Birds, Volume 48, Number 4, 2017):

Tachycineta bicolor. Tree Swallow. Casual in fall, but local breeders remain into early Aug (e.g., 30+ from 31 Jul to 5 Aug 1983; PJG, DRN). One was notably late on 9 Sep 2012 (photos ML26887741 and 26887751, LHD, CWW) and the only one recorded after early Aug. The species’ occurrence as a migrant in late Jul and early Aug was difficult to assess because of its status as a local breeder. Uncommon in spring: Earliest dates 12 May (one, 2012; KHE) and 14 May (eight, 1981; DDG). Uncommon as a breeder in summer, when first reported nesting in “cavities in an old building” by Rausch (1958:237); nesting continued into the 2010s (TvN). As of spring 2009 the species had successfully bred in a small number of artificial nest boxes (TvN). Notes: Tree Swallows breed commonly in coastal s-c Alaska, typically departing there by mid-Aug (Isleib and Kessel 1973).

Thursday, September 28, 2017

The Tree Swallows (Tachycineta bicolor) on Middleton Island in 2017

2017 was the ninth year for the Tree Swallow (TRES) research project out on the small (8x2km) and remote Middleton Island, located in the Gulf of Alaska (59°26′59″N 146°18′26″W). It’s one of the most isolated breeding populations and research sites (that’s thus far assumed to be largely predator free) for a beautiful bird that is considered a ‘model species’ in science. This year the Institute for Seabird Research and Conservation (ISRC) provided information on the TRES breeding season after a single nest box inspection (and cleanout) after the breeding season, of the 20 boxes currently present on the island. No in-depth study on their breeding biology this summer, but basic data on box occupancy and an indication for reproduction in 2017 instead. Some additional info and photos came from ISRC 2017 crew members. On 19 September Scott and Martha Hatch recorded the following nest box contents:

1. nothing
2. nothing
3. nothing
4. complete feather-lined nest with feces
5. nothing
6. complete feather-lined nest (feces?)
7. complete feather-lined nest with feces
8. complete nest with 3 dead, nearly fledged chicks
9. large straw nest base but no feather lining
10. nothing
11. complete nest with 5 dead, nearly fledged chicks
12. nothing
13. nothing
14. complete nest with 1 unhatched egg, also feces
15. nothing
16. nothing
17. nothing
18. nothing
19. nothing
20. nothing

(Complete nests with feces are expected to have resulted in fledged young)

Besides these data, I received four photos and some opportunistically noted observations of the birds around their boxes, in particular box 7 (the one facing the FAA weather camera), from which chicks fledged, which seemed to get visited by a TRES as late as July 17 (also the last recorded sighting of a TRES that I received).

Another year added... (By the way, after analyzing the data again and for accuracy I adjusted the number of occupied boxes for 2013 from 10 to 9 (not counting a few straws as an occupied box anymore)).

Distribition of occupied nest boxes in which eggs were laid in 2017.

The FAA weather camera ( was offline throughout most of the summer, due to the installation of a new camera and further maintenance, but it’s up and running agian now and box # 7 is still visible.

Discussion (& some serious speculation...)
2017 was a relatively good year as far as the number of nesting TRES pairs goes. Total reproduction remains unknown, but was likely relatively low due to chick mortality occurring shortly before fledging. During the previous years of the project chick mortality has been low and dead TRES chicks were a rare sight, at least for me. The thought that came to mind among some was that perhaps a predator had been picking off the adults this summer, cutting off food supply to their young. Has predation become an issue for the largely predator free population? ISRC crew members observed a Peregrine Falcon Falco peregrinus, the first predator that would come to mind, on the island but only in May. Additionally, I suspect that an adult TRES would not be an easy prey for a falcon, while around the same time the island would be full with other, more easy prey types (i.e. young sparrows, snipe?) (But Peregrines will lose many larger prey items to the Bald Eagles Haliaeetus leucocephalus there, perhaps the reason they're not nesting there, and this could increase predation risk for the TRES(??)). But no Peregrine was seen in June and July, when the swallows have young.

Previously, on Middleton chick mortality only had a significant influence on reproduction in 2012. The chicks involved that year were also large and close to fledging. Bad weather (cutting off the adults from their food supply) was the obvious cause that year. When looking at the historic climatic data for 2017, the end of June/first half of July appears to be a good period for TRES ( Unfortunately data from this on site weather station appears to be incomplete again and therefore unreliable). The only significant change to bad weather seemed to occur around July 14 - 18 (complete days missing here), but it's the type of weather that I would expect to kill TRES chicks. During my stays, however, TRES chicks fledged by the end of June/first half of July, so were these boxes still occupied by the time real bad weather appeared? Perhaps they were, since the last sighting of a TRES made by the 2017 crew was on July 17, of a bird exiting box # 7. On Middleton, the TRES do not appear to visit their boxes after fledging (and box 7 resulted in fledged chicks). And when looking at the historical data of this project, first eggs can be laid as late as June (June 2, in 2012), which could indicate that boxes can still contain chicks during the second half of July. So, with only little data to support this wild speculation, 2017 was also a late breeding season. It would be interesting to compare these thoughts on the TRES breeding season again with whatever happened at Long Lake (the nearest TRES study site in Southeast Alaska) this summer, but unfortunately I don't seem to be able to get in touch with the responsible there.

Update 10-25: here's what Chris Gates ( wrote me:

Hi Tim,

Thanks for Middleton update. It's always nice to hear some of these hardy birds made it to the island and nested successfully. I put some of your information about the blog and links to it on the facebook group Tree Swallows, so others here in the US can learn of your efforts.

I do have a comment regarding the possibility of predation on TRES by peregrines and other falcons. In eastern North America TRES form very large flocks after nesting, which usually stage for the summer months in and around large marshes. By late summer and autumn the flocks begin to migrate south with heavy concentrations along the Atlantic shore. Here, the swallow flocks are followed by falcons, peregrines and especially merlins, which apparently take them with relative ease. I've attached a photo of a merlin "packing a lunch." Although the swallow in the photo is an adult I expect hatch-year swallows are heavily targeted. Also, in one of my favorite books, "Curious Naturalists," Niko Tinbergen describes behaviors of hobbies hunting swallows along the North Sea coast. So I guess if peregrines or merlins happened to summer at Middleton some year they could be potential predators of both tree and bank swallows there.

Regards, and thanks again,

Chris gates

(I've seen Merlins there regularly in spring, but never in summer. I recall installing two artificial stick-nests for the species in 2006, hoping to attrack a pair...) 

A Merlin taking a TRES... (photo supplied by Chris Gates)

Update 2: Alexandra Rose informed me 2017 was the latest breeding season she's seen in 12 years of TRES monitoring at Long Lake...

A big thank you to Scott and Martha Hatch for their participation in the project, as well as to the 2017 crew members supplying some additional information and these photos of the 2017 MDO TRES breeding season!!

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…