Date: 6/23/20 12:58 pm
From: Chris Rurik <chrisrurik...>
Subject: [Tweeters] Black swift phenomenon
[I tried to send this last week. Better late than never.]

Tweeters,

I too spent an hour [on June 15] transfixed by the black swift phenomenon.
From my perch near NE Seattle's Magnuson Park I could see ~50 concentrated
over Promontory Point, and small groups were almost always breaking away to
arc over the surrounding neighborhoods. At times they were within 50-100
feet of my head. Once or twice I heard the whooshing of their wings. Never
did I expect to have such a wonderful opportunity to study black swifts.

Pondering what might have caused the event has raised a number of questions
for me:

What were they eating? The general black swift birding knowledge around
Puget Sound, in my experience, goes like this: lowland black swift
sightings are the result of weather conditions. Namely low dark cloud cover
that makes foraging impossible in the mountains. Is there more nuance to
the expected weather conditions? For example, last night was incredibly
calm in terms of wind.

In the literature summarized by Birds of the World, far more attention is
paid to prey conditions than climatic conditions (though weather is
mentioned as playing a role in black swift foraging grounds). A number of
studies from different parts of their range show that black swifts
opportunistically seek out areas where flying insects are swarming or at
least abundant. Flying ants are mentioned a number of times as particularly
favored. Often flying swarms of insects are ephemeral mating events lasting
a few days at most and sometimes just an evening. Though black swifts will
take a wide variety of insect types (67 families documented), gut contents
of individual black swifts often show many prey items of a single species,
reinforcing the idea that they seek out areas where a single insect is
having a mass flight event. What could they have been eating last night?
Was there an insect flight event, or were they eating a variety of species?
In my experience you know if an ant flight is on, and I have not seen any
flying ants on the ground yesterday or today. There were a few small clouds
of some tiny insect near my balcony, but I was unable to sample them. When
the black swifts were flying low around me I failed to see any flying
insect activity around them. But they were moving fast and light conditions
were not great. Or perhaps the prey was on the smaller side.

Anyone have any idea what they were eating? Perhaps if we learn what
attracted them here (if it is not merely weather) we can be on the lookout
in the future. Stomach contents of black swifts taken in Washington have
included flying ants, wasps, caddisflies, crane flies, other flies,
beetles, termites, aphids, leafhoppers, treehoppers, moths, and even
spiders (presumably ballooning spiders?).

Did others notice them concentrating over certain spots like the "sky
island" of Promontory Point, where a certain type of prey may have been
originating?

Others reported common nighthawks in Seattle. Were these typical migrants
that were seen because more observers than usual were looking up? Or were
they too attracted by whatever attracted the black swifts?

In response to Larry's question, I did see one Vaux's swift among the black
swifts. From one to five Vaux's swifts has been a near guarantee at
Magnuson Park for at least the last month. I did not see any interaction
between black and Vaux's swift.

Those black swifts sure electrified the sky. The last stragglers departed
by 9:15. On a brief walk the following morning I did not see any swift
action, though it sounds like there were some down by the arboretum. The
sky felt empty without them.

Chris Rurik
Seattle


--
*Chris Rurik*
Writer / Naturalist
(253) 225-7104
<chrisrurik...>

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