Unusual swifts

Usually there were few or no swifts in evidence from the canopy walkway. 
With patience, we would see small groups of swifts, mostly Short-tailed
and Gray-rumped Swifts and Fork- tailed Palm-Swifts.  One morning,
however, we had the most spectacular display of swifts I have ever seen. 
It had rained hard all night and into the morning.  Because we could not
taperecord in the forest, we climbed to platform 6 where we stood in the
driving rain under umbrellas (there was no thunder to concern us!). 
Suddenly, we were surrounded by swifts swooping low over the canopy and
around emergents.  Often we were looking down on them.  Minna held the
umbrella while I used my binocs in the pouring rain. 

At first most of the swifts were large.  White-collared Swifts were easily
identified -- complete white collars were clearly seen.  Other swifts were
nearly as long but slenderer.  They had longish tails and some had dark
rufous around the neck.  At the time I was puzzled that some lacked
rufous, but I had forgotten that female Chestnut-collared Swifts often
lack the rufous.  Those without rufous had exactly the same size and shape
as those with rufous. 

As the rain eventually slackened to a steady drizzle, the big swifts
disappeared, perhaps by rising higher in the sky, and scores of smaller
swifts replaced them.  There were many Short-tailed Swifts and Gray-rumped
Swifts.  A few were Band-rumped Swifts, very distinctive when seen from
above.  With them were a half dozen black-and-white swallows (see notes on
unusual swallows).  Fork-tailed Palm-Swifts were present also.  

Finally, as the rain slowly ended, the swallows disappeared.  Only small
swifts remained.  These included an occasional (perhaps only one) stocky,
nearly uniformly dark swift (slightly paler on throat and rump),
presumably Chapman's Swift (or Amazonian Swift, if we follow Marin 1997). 
In addition, an occasional swift (again perhaps one individual seen
several times) had much more extensive pale gray on the rump.  Unlike the
Gray-rumped Swifts, the gray extended to the end of the tail, presumably
Ashy-tailed Swifts (or Sick's Swifts, according to Marin 1997).

On other occasions on the canopy walkway, we noted an occasional Chapman's
(Amazonian) Swift.  On one occasion, an individual (or perhaps more) with
Gray-rumped Swifts had noticeably paler (almost whitish rump) and more
contrasty pattern below, possibly Pale- rumped Swift. 

These were the first occasions I had seen Ashy-tailed or Pale-rumped
Swifts.  In addition to those already mentioned, I have seen one other
swift in lowland Loreto.  In February 1997, I watched a flock of Chimney
Swifts bathing early one morning in the Rio Tapiche (see
http://www.unc.edu/ ~rhwiley/ birdsloreto/ tapichelist.html).  These birds
were dark with pale throats and rumps slightly paler than the back. 

Nothing resembling Chimney Swifts was seen at ACEER in July, when Chimney
Swifts should of course be nesting in North America.  The birds called
Ashy-tailed (Sick's) Swifts above were noticeably paler on the rump and
upper tail-coverts than are Chimney Swifts.  The all-dark swifts mentioned
above always looked stocky, a shade larger than other Chaetura present,
and thus were presumably not Vaux's Swift, which in any case would be far
out of its known range.