Dawn Chorus Update #4: Let's Talk Science on the Gold Mine Trail

[Stephen Chase]

Hi Whatcom Birds,

This morning at first light I hiked Sumas Mountain's Gold Mine Trail. This trail was for years a local secret, but during the Covid-19 pandemic, it was "discovered" thanks to its unique status of having a trailhead on private property, thus escaping pandemic-era restrictions that closed most trailheads in the cause of social distancing. Today the trail is muddy but well travelled. I showed up at first light, only to find three vehicles already on site. When I left around 8am, there were about 15 cars parked somewhat haphazardly along the short access driveway. I am very grateful to the homeowners for access to this trail, and I hope us hikers don't wear out our welcome! If you do come, consider leaving a donation in the designated box at the trailhead, which goes towards trail maintenance managed by a volunteer group.

Notwithstanding a side route to a rustic cabin, the trail's primary destination is the remnants of a turn-of-the-20th-century mine with an exciting history. The rumor goes that the initial miners, on finding their claim devoid of gold, salted the mine with a shotgun, won over investors using less than respectable means, and then high-tailed it out of the area. Michael G. Impero's Dreams of Gold is a great read on this and other historic mines in the area. Evidence of the old mine can be found in several places along the trail, but here in the Pacific Northwest history gets buried quickly under our thick forest floors.

But we're here to talk birds, not history. My goal on today's installment is specifically to talk bird science: Why do birds sing more vehemently at first light? Well, there doesn't appear to be a single clear answer for this question. Some theories remain. Perhaps the prevailing theory is that birds sing at first light in what we might consider a "roll call" which establishes who is in the area and on what plot of land. This might reduce tensions over breeding territory, potential mates, and food access during the day. It also allows other birds to find available "unclaimed" land and lets those birds who forage together get a sense of who is in the area. One theory that appears unlikely is that birds sing more at dawn because the sound travels further in humid air. Another theory that appears to be disproven by the same study is that birds sing more at dawn because food is harder to find in low light. But I'll admit, in researching this topic, I found many theories, but few which have been confirmed or disproven with actual scientific data. We've got some science opportunities just waiting to happen!

What studies have confirmed is pretty interesting! A study in India showed that birds that are more territorial, along with birds with an omnivorous diet, are more likely to be vocal at dawn. Another study in Ecuador showed that birds which are generally found higher in the canopy, along with birds with larger eyes tend to sing earlier than their respective counterparts. Perhaps my favorite is what happens after a total solar eclipse: many species repeat the dawn chorus, even if the darkness was only a few minutes long!

This morning's hike featured not only some of our classic resident birds, but also an excellent representative sample of the first wave of incoming migrants: Rufous Hummingbird, Violet-Green Swallow, Hermit Thrush, Band-tailed Pigeon, Orange-crowned Warbler, and Savannah Sparrow. Savannah Sparrows in particular seem to have arrived on their breeding grounds in excellent numbers just this past week - I'm suddenly hearing them everywhere! The dawn chorus doesn't have to be all vocals either; mechanical sounds such as Red-breasted Sapsucker and Northern Flicker tapping, along with Ruffed Grouse wingbeat drumming added to the (beautiful) cacophony this morning! I've uploaded some audio links from my hike on the checklist, including a dawn chorus soundscape consisting of five different species. You can listen to them on my eBird checklist link here.

I'd love to hear from others about what they know about the dawn chorus. Most of the above studies come from tropical locations. I'm curious if there are any studies that are more local. Please share what you know!

In Everson,

Stephen Chase