Explorations of an Ecologist: Blue Grosbeak at Pelee? May 18, 2015

Tuesday, 23 June 2015

Blue Grosbeak at Pelee? May 18, 2015

During the morning of May 18, I stationed myself at the tip once again, to see what interesting reverse migrants we could turn up on the light south winds. For some reason, light south winds create good conditions for some species of passerines and other small songbirds to fly out over the lake from the tip of Point Pelee, a phenomenon seen at other points jutting south into Lake Erie, most notably Pelee Island. The long points of both Fish Point at Pelee Island and the tip of Point Pelee National Park funnel birds south, and from there during certain days in the spring hundreds of birds may fly off the tip. Some of these birds continue on south, while other ones loop back north, sometimes returning to the tip and repeating this process over and over again. There are many theories behind this phenomenon dubbed 'reverse migration', and lots that we still do not know about it, but I don't want to get into that here. I just wanted to post some photos of a bird that I've tentatively identified as a Blue Grosbeak, and see if anyone agrees with me based on the poor photos!

The following sections I have taken directly from the report I wrote up for the OBRC:

Circumstances of the observation:
I had stationed myself at the tip early in the morning with several others, anticipating a good reverse migration as the winds were light out of the south. A moderate reverse migration was taking place, not big numbers by any means. Indigo Buntings dominated the reverse migration, with smaller numbers of Warbling Vireo and occasional warblers and other songbirds. Around 7:45 AM I noticed an “interesting” bird flying over, so I started taking photos and alerted those near me to its presence. Kory Renaud, Luke Berg and I studied the bird, but due to the height it flying at it was tough to get a good read on it. It was slightly larger than most of the songbirds we were seeing (Indigo Bunting, warblers, Chipping Sparrows, etc), and smaller than a Blue Jay or American Robin. I was on the alert for Blue Grosbeaks that morning as it is one that very occasionally is seen in a reverse migration, and lots of Indigo Buntings were on the move. After zooming in on my photos it became apparent that the bird in question was likely a Blue Grosbeak. I called it out as a possible Blue Grosbeak and several others got on the bird and watched it circle the tip a couple of times. It was last seen flying south over the lake, though given the behaviour of many passerines during a reverse migration in these conditions, it likely looped back into the park. We didn’t see it go over the tip any other times. I showed the photos on the back of my camera to several others present and Blue Grosbeak seemed like the best fit. I’ve cropped several of the photos when the bird was at its closest point and attached them to this report. The photos are very poor but look like a female Blue Grosbeak to me.

Description (including how similar species were eliminated):
Some thoughts on its identification:

The bird was noticeably larger than Indigo Bunting. We had lots of INBU to compare it to that morning at the tip and I can say for sure that this bird was definitely larger.

Overall the bird appeared to be a warm brown passerine, with darker primaries and tail. It appeared to be unstreaked below, though of course with such a heavy crop on the photos it is tough to be certain. I think photo 2 show this reasonably well.

The bird appeared to show two distinct buffy wingbars. In photos 1 and 3 this can be seen somewhat on the bird’s left wing.

The size and shape of the bill are what I think are the most diagnostic features in the photos for Blue Grosbeak. Photo 3 is the best shot showing the bill, while in the other two photos the bird is facing away and the bill is tough to see. The bill is clearly quite large, and the lower mandible appears to be paler than the upper mandible.

We did not hear the bird call, possibly due to wave noise and the height that it was flying at.

I think the only bird that it could be confused with from the photos is female Brown-headed Cowbird. Compared to female BHCO:

-the body colour is a much warmer brown. I find that female BHCOs appear more of a gray-brown, noticeable in flight during a reverse migration. BHCOs have light streaking underneath. To be honest I’ve never photographed one in flight before, but I would imagine that this might appear in a photograph, even as poor quality as the ones I’ve provided.

-the bill seems much too large to suit BHCO, and the lower mandible was definitely paler. Female BHCO’s bill appears dark, and the upper and lower mandibles often appear to be the same colour (though looking at photos online, this feature is variable and some birds show a slightly paler lower mandible).

-the buffy wingbars look too prominent to fit female BHCO. When looking at photos online, most female BHCOs did not show any hint of a wingbar, though some showed some light edging to the flight feathers. I couldn’t find any photos showing buffy wingbars.

-the tail does not appear as rounded as BLGR shown in Sibley, and most of my photos don’t show the tail really well. This is one point of contention I have with convincing myself it is a BLGR.

BHCOs are seen fairly regularly during reverse migrations, but they usually seem to appear in small groups with other BHCOs, or with other blackbirds such as Red-winged Blackbird and Common Grackle. I think it is pretty rare to get a female by itself go over, or at least I haven’t seen it too often. BHCOs also seem to fly a little lower and faster than what this bird showed. Obviously not really a feature to be used in identification, but anecdotally this is worth mentioning. This bird was acting similar to the young male Blue Grosbeak that several of us observed flying over the tip on May 20, 2012. It was flying slowly into the headwind, looping back around over the tip and then flying out again in the same manner, repeating this several times.

Photo 1 (moderate crop with minimal editing):