I have visited Deer Creek in Jefferson County these past four evenings to see how the White-throated Swifts conclude the season at their roost in the Lyons hogback. I mentioned a count of 234 on 10/3, which may be a typical number for this site in late September and very early October. But the swifts depart now, in the first week of October, yet with little detailed local study on numbers and roost attendance. Their nightly entry to the roost may be the only time they are countable at this season, when at all other hours they are usually up foraging and typically far from the roost and quite high up.
Numbers at the roost declined, clearly reflecting the last birds moving out.
Oct 3 234
Oct 4. 115 (DFO field trip)
Oct 5. 25
Oct 6. 1
There seems to be a particular pattern of arrival to the roost in these last days before leaving. Earlier during the breeding season and during migration up to late September, swifts usually fly for extended periods in front of the roost cliff or over the area in general, before they actually enter the roost for the evening. But in these last days the birds are not around at all it seems as roosting time approaches. When they decide they are going to enter they suddenly appear. Individuals and small loose groups begin to enter the roost directly. They fly right at the cliff face at an oblique angle, descending, and swoop up into the roost crack from just below it. They are flying in at high speed, but you see them spread their tails and position their wings to slow down at the last moment as they disappear up into the crack. It is some thing to see. I think the "last minute" arrival of the flock before entry into the roost is because the swifts are maximizing foraging time before migrating, perhaps entering the roost when prey availability in the air column changes at the close of the day. The prior 3 days were clear and mid 70s, today same temps but more cloudy.
After tonight's swift activity came quickly its close, I decided to go over to a good Ken Caryl spot for a Common Poorwill to see if one might still be around, rare after September. It has been a very mild entry into October, much more so than in the last few years when I have been paying attention to poorwill occurrence. Indeed, a tardy Poorwill called several times from the Lyons hogback formation. My previous latest in the area was September 29. Perhaps when the weather is mild it is normal for a poorwill to linger to now if prey continues to be available.
David Suddjian
Ken Caryl Valley
Littleton Co
Sent from my iPhone
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