Roseburg might be able to get us that data. We do know that once we sealed the Old Northern State bottom access the evening bird counts immediately changed from single digits to thousands.
4. It's made out of brick. Besides being effective at storing and releasing heat energy common bricks are just the right size for Vaux's Swift overlapping. One row
old chimney as its vent. The swifts might be able to deal with this if its mostly water vapor that isn't too warm or if the heat is not on during migration. Rio Lindo is one such site and the word is that the heat is turned off until the swifts depart.
3. It's very much open at the top but not at the bottom. If the roost is light tight at the bottom the swifts should feel secure that no rodent will be crawling up from below to get them in the middle of the night. It may also be a lot cooler inside a chimney that is sucking cold air in at the bottom.
changed the path of their migration because of the presence or lack of suitable roost sites.
2. It is no longer passing gas. A common practice after replacing a smoky furnace that burned wood, coal or corncobs with a not so dirty new oil or gas furnace is to use the
1. It is located on a migration route. One wonders how much the swifts have
How does a migrating Vaux's Swift decide where it will spend the night? It's likely that if last night's accommodations were suitable it will return to the same roost site. But If this was a travel day the bird has to locate a new one. Do these birds have some sort of memory of the location of suitable roost sites along a migration route they traveled before? What if this is a young swifts first migration? If that's the case he better be traveling in a flock and the bigger the greater the probability that one of them knows where the closest safe and warm roost is when the sun is getting low.
As the day is ending Vaux's Swifts spend a lot of time circling their chosen roost site calling out. Is this to help other migrating Vaux's find the roost? During the summer when a group of non-breeders uses the same site every night they usually just fly right in without much circling and calling. We have multiple observations of a group of 50 Vaux's that over wintered in San Diego and It was usually 3 laps around the bricks and then down the hole.
Churches and schools are the right stuff. Vaux's Happening has yet to discover a residence that consistently attracts large numbers of these birds.
than three feet square inside because its walls are so thick. Once that pile of bricks gets warmed up its inside temperature might drop less than a degree during the night.
6. Having a taper is a positive. If the bottom of the structure is wider than
the top when there is no wind, no spot in the roost will get rained on. But there is a point when the angle is so much that the birds would be hanging rather than clinging.
7. The inside needs to be large enough to hold a lot of little birds but small enough so hawks and owls will not want to fly inside.
The 31 vertical feet of four-foot square Monroe Wagner has enough surface area inside to accommodate 14,000 Vaux's. If there are more they can go two or three deep. The Wagner inside camera caught the blur of a Cooper's Hawk about three feet
down. A Barn Owl flew into the widest of the three San Francisco Brick Plant smoke stacks, which is the one the swifts usually don't use. Then again, our camera inside a Detroit smoke stack with a ten foot hole has yet to show anything inside but insects, snow, and thousands of Chimney Swifts.
8. It's old, being constructed before 1941. Being old isn't always a good thing
but chimneys erected after 1941 have a smooth liner, which swifts can't cling to. Wagner was built in 1940 with great bricks and mortar. Those good old chimneys crumble more every day.
9. The swifts have a clear approach to the roost opening.
This is usually not a problem and we've never seen a swift strike a utility wire.
10. The lower part of the chimney is inside a temperature controlled building. The only roost constructed this way that we have temperature measurements from is Johnson Auto Glass in Yakima.
Unfortunately for the birds this building is not air conditioned and not only is it hot in the human work area on a warm sunny late afternoon, the inside chimney bricks transfer that heat to the swifts.
11. There is little predation. Small birds circling and calling out attracts predators and the more swifts the more predators. Merlins and Coopers Hawks are the most common. Once crows learn how to take a swift they keep coming back and a Peregrine Falcon is bad news. We seldom see what the predation level is in the morning, but the swifts are not as swift and easier to catch when they're coming out. The swifts will abandon their roost site out of predation fear and the Vaux's know exactly where the nearest back up roost is. If it's getting dark they hustle right over and may stick with this new roost until the predators adjust or there's been a complete migration turnover. Eugene has had at least three different main roost sites.
Vaux's Happening has experience using walls and spikes to mess up hawks and crows sitting on the top of the chimney. Wagner's crow pokers have been wildly successful for the last six years. Constructing and installing a crow poker isn't especially difficult but accessing the top of the roost can be. You may enjoy our
12. It has been used a lot in the past and the swifts are aware of it. Some of
our current sites have had continual use for 40 years and we've watched flock after flock of Vaux's drop through low heavy rain clouds into their shelter. A suitable roost can probably be bird-confirmed by its smell.
13. There is not a nasty guano build up. This stuff can really stink but I've also had some up close and personal encounters when it seems well, not sweet, but not really that bad. No idea why.
Perhaps there's a master's thesis here. With poultry poop you can get a deadly ammonia release but I've never smelled ammonia inside a swift roost. If the site is small to start with you could actually and eventually run out of space. The fake Sumas Old Customs House chimney that is no longer used may be an example.
14. There's an abundant food supply close by. As the swifts may spend a day or
keeps the chin warm resting on the above row of rumps. But rough concrete works too. Old Northern State and the Roseburg Clay Place are concrete.
5. It's made out of lots of bricks so it has thick walls. This is a major attraction of the Portland Chapman School chimney. It's big on the outside but not much larger
two fueling up on bugs before continuing their migration, a dependable and prolific supply right down the street is a big plus.
What makes a good roost site?
Illustrations by Dale Rutter.