whit! Sorting out the call notes of western Empidonax flycatchers

After a flurry of migrant Empidonax flycatchers this April in California, a number of us engaged in a discussion about their whit! call notes. Specifically, could we tell Willow from Dusky from Gray just by the whit? Personally, I’m not there yet. I usually only hear them a few times a year, which is insufficient experience, and I suspect there’s individual variation as well as the tricks that wind, humidity, and distance play on sound. But what about analyzing their sonograms with a good recording?

I looked at the very best on-line recordings from the Macaulay Library (collected via eBird, and there’s a collection of the best ones at Peterson Bird Sounds) and from xeno-canto. (Warning: the horizontal axis is different between their sonograms. Xeno-canto sonograms fit about two seconds in the space where Macaulay fits one second of recording, thus compressing the sonogram. Here, I stretched the xeno-canto sonograms horizontally to adjust for that.)

Willow whits

Dusky whits

Gray whits

It appears that Willow, with a good recording, is distinctive, with up to three harmonic tones and that downward slope after the upward slow. To the ear, the Willow whit is softer and sweeter than the others. Dusky and Gray, on the other hand, are both dry sharp whits, and virtually indistinguishable on the sonograms. Gray is more likely to go up to 10 kHz or higher, and that echo line on the first Gray sonogram was consistent on all the calls, at least for that individual recording. For the record, Least was similar to Dusky and Gray, although the triangular dark shadow to the right of the main call tended to be thicker and larger.

iPhone whit

iPhone recording

To the right is a typical iPhone recording, probably a Dusky. Based only on this sonogram, just a shadow of the good ones above, it could be any of the species. The take-home lesson is that one could probably diagnostically identify a Willow whit from a sonogram with a very good recording. The Dusky and Gray whits are too close to call.

Our discussion also focused on spring migration timing and incorporated Hammond’s (as many of these birds are silent). Again, I turned to eBird for some trends.

CLICK TO ENLARGE

whit map

Spring migration for western Empids. These maps are based on 2017-18 data. I excluded a few outliers in each case. Nevertheless, these dates represent the earliest arrivals. Most birds were a week later than the dates shown.

The results are that Hammond’s is the earliest, followed by Gray and then Dusky. For all three, however, there was a pulse of records during the last week of April. Willow is a full month behind the other two. In fact, even in southern Arizona there were very few Willow records before May 10.

Kaufmann empidsMuch has been written about Empid identification. Here’s a link to the Rowland 2009 article in Birding. My personal favorite is the chapter in Kenn Kaufmann’s Advanced Birding. The diagram at left is from the old version; the new one is even better, showing variations within species.

For the Hammond’s/Dusky challenge in spring, I put together the diagram below. These identifications were confirmed by calling birds, which are easily separated (Hammond’s says peep rather than whit).

HammondsDusky

Finally, if you’re still confused, there’s this infamous meme:

empid meme

Why are so many Eurasian Collared-Doves leucistic?

0V2A6850In 2006, I wrote a paper about the spread of the non-native Eurasian Collared-Dove into the Central Valley of California. At that time, there were about 43 records. Now, of course, the species is widespread and common. Quoting from that paper, here’s the backstory of their spread throughout North America:

The Eurasian Collared-Dove was first observed in Florida in the late 1970s. These birds likely originated from an accidental release in the Bahamas in 1974. Since then, their spread has been well documented by Christmas Bird Count and by state bird record committees. By the mid 1990s, the species had been recorded throughout the southeast United States. By 2000, Arizona, Idaho, Oregon, Utah, and Washington had documented records. On the 106th CBC (December 2005 – January 2006), over 30,000 individual birds were reported nationwide, compared to just 560 fifteen years earlier. Their rate of increase has averaged 34% per year.

Today, it seems that in any large aggregation of Eurasian Collared-Doves, there are one or two that are unusually pale, blotched with white and cream. They seem to be about 1% of the population or more, though it’s yet to be studied. These birds bare a strong resemblance to African Collared-Doves, which is generally this pale.  However, based on the dark outer web of the outermost tail feather (see below), as well as size and vocalizations, these birds are clearly leucistic Eurasian Collared-Doves.

CLICK TO ENLARGE

EUCD diagram

All of the photos on this page involve the same two darker doves and one pale dove. Above, the tail patterns of the dark dove (left) and pale dove (right) both suggest Eurasian Collared-Dove.  Woodland, California, October 2018.

0V2A6835Many birders suspect this is due to the Founder Effect, a phenomenon that occurs when a small population colonizes a large area. Eventually, all of the birds (or other animal species) are descended from few individuals. In this context, certain recessive traits that were once rare may become more common.

See the Wikipedia account of the Founder Effect for examples of this in human populations.

0V2A6846

Here, one of the darker doves is mating with the pale dove.

 

The basics of Fox Sparrow identification

While there are over a dozen subspecies of Fox Sparrows, they fall into four main groups: Sooty, Red, Slate-colored, and Thick-billed. The images and diagrams below illustrate the main differences.

Sooty is the darkest, usually illustrated as dark chocolate in most guides. Even the darkest Sooties, however, show some gray on the face and rusty tones in the wings and tail– especially in bright light. I’ve chosen a photo in sunlight to show how lighting can change a bird from dark brown to bright rust. Regardless, the back is solid brown.

FOSPsooty

Red is the common form that breeds across the taiga to Nome and Bethel, Alaska, and generally winters in the eastern US.

FOSPred

Slate-colored is the Rocky Mountain version, found throughout much of the mountain West. Note that some consider altivagans, from Alberta, an intergrade swarm between Red and Slate-colored.

FOSPsc

Thick-billed is the southern Cascade and Sierra Fox Sparrow, found in the mountains south and west of Slate-colored range.

FOSPtb

A key distinguishing feature is back color and pattern.

FOSPbacks

Less useful due to variation, but still helpful, are tail and bill length.

FOSPtails

FOSPculmens

FOSPachwhy

Most forms of Fox Sparrow winter in the lower 48, with southern California host to nearly all subspecies. This photograph shows the green chaparral along the Angeles Crest Highway where a wide variety of Fox Sparrows can be found.

For a more detailed analysis, including discussion of Sooty subspecies, see my paper:

Hampton, S.  2016.  Status and Identification of Fox Sparrow Subspecies in the Central Valley of California. Central Valley Bird Club Bulletin 19(2-3): 28-63.