Date: 4/6/21 6:26 pm
From: DAVID A LEATHERMAN <daleatherman...>
Subject: [cobirds] Rigden Reservoir (Larimer) today
I visited Rigden Reservoir on this rather cool, progressively deteriorating weather day. Best birds were peregrine falcon flyover at 7:30am, one lesser yellowlegs, grebes (horned, eared and pied-billed), both grackles, heard only Virginia rail, flock of tree swallows, FOY for me barn swallow, yellow-headed blackbirds, Savannah sparrow, and about a half dozen Franklin's gulls.

But to me the best thing was the bird response to a food "happening". Chironomid midges, those mosquitolike insects that buzzily swarm in front of you on the trail, were emerging and being deposited on the south shore by the increasingly strong north winds. Like an arthropod version of D-Day, larvae (aka "bloodworms"), pupae and adults wriggled and wiggled on the small pebble beach. Here is a list of the 23 bird species eating them in the air (adults), out on the water as they emerged (adults and rising pupae), but mostly where concentrated along the south shore (larvae, mostly pupae, adults): Gadwall, Mallard, Pied-billed Grebe, Eared Grebe, Horned Grebe, Killdeer, Greater Yellowlegs, Lesser Yellowlegs, Franklin's Gull, Ring-billed Gull, California Gull, Herring Gull (maybe), Horned Lark, Tree Swallow, Bark Swallow, American Robin, European Starling, Savannah Sparrow, Yellow-headed Blackbird, Western Meadowlark, Red-winged Blackbird, Common Grackle, Great-tailed Grackle. Don't recall seeing that many species of birds eating the same thing at one site before.

Photos (from top to bottom): adult midge (not taken today and probably a difference species than that shown in the pupal photo but just to give an idea of their body style & general appearance), midge pupae present today at Rigden, yhblackbird at water's edge with pupa, close-up of yhblackbird with pupa in beak, ring-bills on the beach (they were getting midges out in the water where they occurred at a density of 1 per square foot and then decided to try the beach where midges were 5 per square inch).




[cid:ea505996-58ae-4adc-b94d-d402ff9a028a] [cid:e43af0f9-ff1d-466b-991f-f36703134722]

Dave Leatherman
Fort Collins

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