More will follow on avian weather challenges, but first, a review of chimney swift biology will help explain why these birds are vulnerable to extreme weather events. Chimney swifts are obligate aerial insectivores. That mouthful means that in order to eat, chimney swifts have to collect insects out of the air column. Unlike purple martins which can drop to the ground and pick up insects (then themselves) if necessary, the long wings of a chimney swift hinder getting airborne again once they land on flat ground. The clinging-adapted feet of a chimney swift are also of little use to cope with horizontal surfaces and chimney swifts cannot perch on branches or wires to wait for prey items to pass by. Chimney swifts are either up in the air flying or inside their nest/roost sites clinging to a vertical surface.
Back to July issues. The type of wet 'n' windy weather we have experienced over the last month can cause a lot of problems for foraging chimney swifts. If rain is steady over many hours, and especially if it is coupled with strong winds, airborne insects are not concentrated or are washed out of the air column. High heat, humidity, and accompanying strong winds, which we also had in July, can disperse the aerial plankton too. The consequence at a nest site is that a patch of bugs may not be close enough for adults to collect food and return to hatchlings in a timely manner; starvation of the juveniles may ensue. Rain can also loosen the bond between nests and the vertical surface of the chimney which results in nest slippage.
Unfortunately, the St. Adolphe breeding flock has had problems in July. Of the 5 primary nesting attempts which were underway, 3 failed by July 21st. The SE Club Amical, Church, and Main St. residence adults stopped using the chimneys during the daytime but they continued to roost at night. The Southeast Club Amical adults recently started a secondary use of the chimney, but time is now too short for a successful nesting outcome. The NE Club Amical site is still active (feeding non-brooded juveniles) and at the Brodeur Bros. there is often manic activity as 1-2 helpers are assisting the breeding adults feed the young (you can tell how many birds are onsite by the sequence of entries and exits). Our fingers and feathers are crossed for successful fledging from the 2 active sites.
Despite the difficulties elsewhere, good news prevails in Selkirk. Ruby and her diligent group of monitors reported an exciting development in the discovery of a new site. On July 7, chimney swifts were observed entering a chimney on Manitoba Ave (i.e. the main west-to-east one-way street in Selkirk, running between Main St and Eveline Ave)". Congratulations on your sleuthing!
The active group of Selkirk monitors does a weekly Monday night monitoring session. Thanks for all of your hard work Ruby (team leader), Andy, Gerald, Carol, Nia, Ralph, Linda, and Virginia (regular volunteers), plus Sybil, Ray, Robert, Maggie, Barry, Jim, and Dorothy (backup crew)!!!
To the north, Ken and Jan continued to track the Dauphin roost site. The latest count on July 22 was 30 roosting swifts.
In Winnipeg, David, Adolf, Anna, and Peter are still reporting exceptionally high roost counts at Assiniboine School. On July 6, 70 swifts entered for the night and on July 14, 54 roosted.
It's hard to believe that August, which is our wrap-up month, will be upon us so soon. What will the home-stretch involve? For roost sites, expect to see counts peak again - although perhaps not as high as seen in the spring - as swifts group in preparation for migration. Ken notes that counts at his northern Dauphin roost site are the highest by August 6 usually. After fledging, the St. Adolphe birds may set up a local pre-migratory group which reflects the breeding adult population and new recruits that have just fledged. Southern roost sites, such as Selkirk, will have peak numbers later into August as northerly swifts may join in before continuing southward. Small numbers of birds may linger into early September.
At nest sites in August, activity will increase in the daytime prior to fledging. At ~21 days of age, juveniles move from the bowl of the nest to the wall of the chimney. Flight training ensues and the youngsters fly up and down the shaft to prepare for free flight. The adults eventually will lure the juveniles close to the rim of the chimney. Fledging (day 28-30) occurs when the juveniles burst out the top of the chimney and experience the open skies. It is not as romantic as it may sound. Free flying is a slow, follow-the-leader process for the fledglings. Getting back inside home base is not necessarily a pretty sight - the fledglings are led back to their natal chimney and entries can be difficult. There is a lot of fluttery, wing flapping to position over the opening and entry "misses" involve some tumbling down the outer surface of the chimney. Despite the breath-sucking drama, I have never seen a fatal entry event (said with wood-clutching superstition). However, flight proficiency is gained quickly and within 36 hours of fledging it may be difficult to distinguish fledglings from adults unless you see the wings. Adults will be in moult so missing wing feathers reveal gaps, while fledglings have intact wing margins.
The dispersal of chimney swifts from the summer range is linked to many factors. Temperature, photoperiod, food availability, and time of fledging all influence the bird's departure. August monitoring sessions - especially within the first two weeks of the month - will be valuable to track production at nest sites and migration from roost sites.
I enjoy reading about your sightings. We have had excellent coverage throughout the province this season and high quality data has been submitted. Thank you all for your efforts and, as we near season's end, keep your observations winging in!
All the best in birding, Barb.
Barb Stewart
St. Adolphe Monitor & MCSI Steering Committee Member
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