IBRC 55-B-11

Idaho Bird Records Committee
Rarities Report Form

 

Species: Red-throated Loon – 2 immatures

 

Reporter: Jay Carlisle

Idaho Bird Observatory, Boise State University, 1910 University Ave., Boise, ID 83725; jaycarlisle@boisestate.edu

 

Other Observers: Dave Hazelton (first spotted the birds), Heidi Ware, Danette Henderson, John Shortis, Susan Hazelton, Sue Norton, RL Rowland, Mark Collie, and another 15+ participants in a Golden Eagle Audubon Society fieldtrip

 

Date Report Prepared: 10-29-11

 

Date Sighting Occurred:  10-29-11

 

Locality of Observation: open water above dam at CJ Strike Reservoir; viewed from a point between Black Sands and Cove Recreation area

 

Habitat: reservoir

 

Conditions: mostly clear and calm; I used a Swarovski scope with 25-50x zoom; the bird was relatively distant (maybe 500+ meters). 

 

Did you take notes?  no

 

Did you consult a field guide or other reference work?  during and after the observation

           

What guide(s) or reference(s) did you consult?

Sibley & National Geographic

 

Description:  Two relatively small loons (there were about 8 Common Loons in view from this spot) with an overall light gray, black, and white appearance.  The birds had white on the lower throat/upper chest, streaky gray on the sides and back of the neck, and apparently without a clean break between gray & white.  One bird had a noticeably darker area of the central throat – appeared reddish-brown in the right light.  Both birds had slender bills often held pointing upwards when at rest.  Both birds, but especially one of the two, showed white flanks separating the darker back from the water.

 

Behavior:  Floating on surface and actively diving.  The two birds were first observed swimming side by side and they stayed this way for about 10+ minutes – covering a decent amount of water during this time, first swimming away and then perpendicular to us.  When they arrived to an area above the dam, they were separated by 100-200m – both actively diving.

 

How and when did you positively identify the bird, and what clinched the identification for you?   When Dave pointed out the birds to me and I saw the relatively pale gray hindneck, I figured it was two Pacific Loons.  But I soon noticed that the bills appeared to be held above the horizontal and that got me wondering about Red-throated.  As we studied the birds, the opinion/consensus of the group went back and forth between the two species!  (Honestly, having this many observers of varying levels of experience expressing opinions about fieldmarks added to the confusion :-).  Over time, the birds seemed to get a little closer and also turned with their sides to us more often so that we were able to observe more fieldmarks. 

 

I started to notice that there was not a clean break between the gray hindneck and the white throat/neck.  Instead, whereas the upper chest/lower neck area was white on both birds, higher on the neck & throat was covered in dingy gray that extended from the sides.  Also, the head shape did not seem especially round; instead, more flattened across the top and somewhat peaked at the rear.  Other fieldmarks, including the limited pale cheek area, the bill angle, and the white flanks, added to the evidence.

 

How did you eliminate similar species, and what were they?  Possibilities include other loons and, possibly, the larger grebes.  The birds in question swam by numerous Western Grebes; they are separated by their contrasting black & white colors with a clean break along the neck and their more slender neck.  An immature Red-necked Grebe (which we saw about 30 minutes later) would look superficially similar in possessing the dark cap and paler ear patch but they are smaller, have an orange bill, and do not have white on neck.  The most likely species to cause confusion is the similar-sized Pacific Loon which has a more patterned neck with a cleaner division b/t gray & white, a rounder head shape, normally holds it bill more level, and usually does not show extensively white flanks.  Throughout the day, we observed multiple Common Loons – separated by its much larger bill, larger size, darker back & head, and more patterned neck. 

 

Experience with this species (and similar species):  I have observed thousands of Red-throated Loons, mostly on the east coast but also along the west coast; this is my 2nd inland sighting.  I have observed hundreds of Pacific Loons on the west coast and a few in South Dakota; I normally see 1-3 per fall migration in Idaho.  I have seen thousands of Common Loons all over North America.

 

General birding experience: extensive; 15+ years in US and Latin America

 

Were photo(s), video, and/or audio obtained by you? (If yes, please include or attach)    Yes, some low-quality digi-scoped images are attached.

Photos were edited by the webmaster.  To view original file click on the image.