Dawn Chorus Update #5: Before and After on Sehome Hill

[Stephen Chase]

Hi Whatcom Birds,

Sehome Hill in mid-April really excites me! Our neotropical migrants are just showing up and there seems to be something about this hill that feels just right for stumbling across a first-of-year neotropical passerine. Several members of the WWU Bird Club have made a priority to document the bird life on this hill lately, with some exciting results. It's a great spot for first-of-year warblers, thrushes, vireos, flycatchers, and other migrating passerines. 

I parked below the hill below the Myrtle Street trailhead right at first light (5:56am), and stepped out of my car to the incredible din of dawn chorus song: absolute gobs of American Robins and Pacific Wrens. Once within the arboretum itself - just wow! I did barely make out a beeping Townsend's Solitaire, but otherwise everything my ears were taking in - well, it was all robin and wren! At the reservoir, I recorded a soundscape with my phone - have a listen, and take a look at the sonogram! Between the robins and the wrens, there's hardly room for any other sound!

If you remember back my comments in my last write-up, I suggested that a prevailing theory on the dawn chorus is that breeding birds use it as a "roll call" of sorts to claim territory and get a sense of who is in the area. On Sehome Hill, I'm certain American Robins and Pacific Wrens are among the most numerous breeding species, likely with eggs already being incubated on their territorial claims. The din of robins and wrens on Sehome Hill matches the basic premise of that theory. (By the way, the robins and wrens might be incubating already, but they're well behind owls. Later during my walk, I found two fledged and nearly adult-sized Great Horned Owls chicks doing their whisper-scream begging calls.)

If breeding birds use the dawn chorus as a roll call, it could be assumed that migrants are less likely to be as vocal during the dawn chorus, as the roll call means less to them. That's also what I experienced. The dawn chorus quieted down perhaps only 15 minutes after it started, and a more consistent and diverse morning chorus took over. It included many Yellow-rumped and Orange-crowned Warblers, Ruby-crowned Kinglets, and many others. While many of these species do breed in the county, these specific individuals are likely not on their breeding territory, but belong to the early waves of migrants stopping over on their way further north into their boreal breeding grounds. About an half hour after sunrise, I recorded a second soundscape, again at the reservoir. Note how even though the intensity of the dawn chorus has decreased, the species diversity is much better in this second clip.

I'll admit I wasn't too thrilled with the audio quality of either recording. Too many urban noises - particularly vehicles on I5 and commercial appliances on Western's campus - affected the quality. It's especially noticeable on the sonogram in the 0.5-1 kHz range. I'm going to try to find some places where I can get some cleaner audio clips.

And yes, Sehome Hill came through again! Just about on my way down, I picked out an Empidonax flycatcher. To my relief, it was calling, allowing for an easy confirmation of Hammond's Flycatcher! On eBird, this is the earliest record of this species in the county ever - by an impressive five days! Here's my complete checklist from this morning's walk.

Where to next time? Well, I hear the boardwalk at Tennant Lake has been reopened...

In Everson,

Stephen Chase

[Margarette Grant]

Thanks for the great report of your observations! The difference between the dawn chorus and the later migrant chorus is fascinating. Please keep it up!