Spotted Towhee subspecies in the Pacific Northwest: From nearly-spotless to pretty messy

Posted on March 18, 2024 by Stephen Carr Hampton

There are 21 subspecies of Spotted Towhees, but only three of them occur in the Pacific Northwest. Even then, there is confusion.

Our local oregonus birds, like so many PNW subspecies, are dark and dusky. I call them Nearly-spotless Towhees. But sometimes in winter we see more spotted ones. In my quest to uncover the differences between curtatus and arcticus, the most likely candidates, I discovered there are more questions than answers.

Figure 1: The breeding ranges of *oregonus, curtatus*, and *arcticus*, the only three subspecies that occur in the northern US and southern Canada. The data (in red) is from summer eBird reports. The solid lines reflect the crude subspecies map in *Birds of the World* (in Figure 2 below). The dotted lines and question marks were added by me; the dotted lines reflect obvious breaks in breeding densities along the Continental Divide, rather than transecting riparian corridors where there are lots of towhees. An analysis of their songs (at the bottom of this post) suggest my dotted lines are more accurate, and the breeding birds in interior British Columbia, Washington, and Idaho are actually *curtatus*, not *arcticus*.

The confusion goes back to the 1800s. To quote from Rick Wright’s Sparrows of North America (2019), the taxonomy of Spotted Towhees is a source of “much confusion.” He’s actually quoting William Brewster from 1882. Yet, 137 years later, Wright spent the next 15 paragraphs describing decades of confusion – which persists to this day.

According to the Birds of the World (BOW) species account: “There exists no review of subspecies and no modern, quantitative study of geographic variation” outside of Mexico and the Pacific Coast (which was studied by Swarth in 1913).

Because there are so many subspecies – some of questionable legitimacy – they are grouped. Even the groupings are confused.

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Figure 2: Spotted Towhee subspecies with BOW and Pyle groupings.

At present, BOW divides the 21 subspecies into 5 groups. Of relevance to the PNW, oregonus is in the oregonus Group, curtatus is in the maculatus Group, and arcticus is by itself, presumably because it the only Spotted Towhee that is entirely migratory and it also shows the most sexual dimorphism – that is, the female arcticus is quite distinctive.

(There are other Mexican subspecies separate from all of this, such as soccorroensis, which has been considered a separate species altogether.)

Because eBird uses the BOW approach, birders in PNW coastal regions encountering a heavily-spotted Spotted Towhee typically see these options on their app:

By “maculatus Group,” eBird, at least in the PNW, implies curtatus. Though arcticus is not listed, it does tempt birders to figure out how to distinguish arcticus from curtatus, because simply using “maculatus Group” on eBird implies the bird is not arcticus.

Oregonus is largely resident (though some go south in winter). Curtatus retracts from the northernmost part of its breeding range. Highly migratory, arcticus winters entirely south of its breeding range. Both are candidates to visit the West Coast of Cascadia, though curtatus is far more likely.

Despite its proximity (and the BOW range map), there are no confirmed eBird records of arcticus in Washington, and Wahl et al (2005), Birds of Washington, assert only oregonus and curtatus are expected. British Columbia has just two winter records for arcticus (2014 and 2016), both from south Vancouver Island, and one July record from just north of the Washington/Idaho border (perhaps based on the BOW map?).

Peter Pyle’s Identification Guide to North American Birds, 2^nd Edition (2023) suggests a very different taxonomy (though tentative, as we all still await a DNA study). His 1^st edition was similar to BOW, but even then he had arcticus with curtatus in what he called the Interior Group. In his 2^nd edition, oregonus is limited to just itself; the rest are in the coastal megalonyx Group. (Peter tells me he’s suggesting reducing Spotted Towhee’s 21 subspecies down to seven, based on morphology.) As with his 1^st edition, all the interior subspecies north of Mexico City are in the same group, which he now calls the arcticus Group. The maculatus Group is reduced to just four subspecies in southern Mexico and Guatemala.

By putting curtatus and arcticus together in the same group (and suggesting they be merged?), Pyle makes our lives easier – we don’t need to worry about the identification challenge to use the eBird subspecies offerings. Except Pyle calls it the arcticus Group, while eBird calls it the maculatus Group.

Let’s set aside the taxonomic and range map questions. Can we even tell them apart? Answer: sometimes.

Identification

Focusing on oregonus, curtatus, and arcticus, I’m relying on BOW, Wright, Pyle 1^st and 2^nd editions, photos on eBird, and personal observations (at least for the first two subspecies). Note that upperpart color tone varies depending on lighting, and the differences are subtle. Likewise, dorsal spotting appears to vary tremendously across individuals, and varies with angle of view and posture of the bird due to feather ruffling. Tail spots (the big white spots on the underside) may be the most definitive, yet there is overlap between forms and often they are difficult to see.

These sources also discuss how pale or bright the rufous flanks are. I’ve not included this, as the photos seem quite variable in this regard, probably due to lighting.

Of all the Spotted Towhee subspecies, Sibley only illustrates oregonus (which he calls the Pacific Northwest form) and arcticus (the Great Plains form), the least- and most-spotted forms.

	oregonus	curtatus	arcticus
Upperpart color tone	Male: glossy black; any streaking/mottling variable, but often quite limited. Female: dull black, sometimes with a hint of brown, with faint bold black and dark gray streaks on the back.	Similar to oregonus, but less glossy, more flat black in male.	Male: dull to grayish black with bold black and gray streaks on back. Faint olive tone to rump. Female: brownish; with narrow blonde streaks on back.
Dorsal spotting	White spots largely limited to the shoulder area, with a line of white spots along the scapulars; back largely dark.	White spots coalescing into bright white streaks in shoulder area, with smaller spots extending onto back.	Similar to curtatus with even more white spotting.
Tail spots	About ¼ to 40% the length of the tail. (Pyle: 12-25 mm long on r6)	About 1/3 to ½ the length of the tail. (Pyle: 22-35 mm long on r6)	Can be ½ the length of the tail or more. (Pyle: 27-42 mm long on r6)

The National Geographic Society guide, 3rd edition, illustrates these tail spots and undertail coverts – dark in *oregonus*; paler in every other form. I assume *curtatus* would be similar to *montanus*. Note that tail spot sizes have considerable variability (see chart above). Thanks to Dave Irons for alerting me to this illustration.

The photos below are mine or from eBird. It is frustratingly difficult to find photos of females in summer when they should be on their breeding range, and thus known.

Figure 3a: *oregonus* male; Port Townsend, WA; 6 Jan 2022. A typical nearly-spotted look. Note slight mottling on back.

Figure 3b: *oregonus* male; Port Townsend, WA; 4 Mar 2024.

Figure 3c: *oregonus* male; near Issaquah, WA; 21 Jun 2019 (from https://ebird.org/checklist/S67832978 Glen Chapman). This is bird showing a lot of white.

Figure 3d: *oregonus* male; Port Townsend, WA; 27 Jun, 2023 (from https://ebird.org/checklist/S142894263 Michael Long). Illustrating rather small tail spots, only about 1/4 the length of the tail.

Figure 3e: *oregonus* male; Port Townsend, WA; 16 Mar 2024. This one has larger tail spots, about 40% of the length of the tail, which would overlap with *curtatus*. But the undertail coverts are dark rufous.

Figure 3f: *oregonus* female; Port Townsend, WA; 10 Mar 2024. A typical female, showing some back streaking, visible in good light.

Figure 4a: *curtatus* male; near La Grande, OR; 30 Jun 2023 (from https://ebird.org/checklist/S143142401 Glenn Pannier). Much more boldly streaked white than any *oregonus*.

Figure 4b: *curtatus* male; near Summer Lake, OR; 25 Jun, 2012 (from https://ebird.org/checklist/S100771094 Scott Carpenter). Note the tail spot, nearly 1/2 the length of the tail, and the undertail coverts are paler.

Figure 4c: *curtatus* female; south of Asotin, WA; 25 May, 2023 (from https://ebird.org/checklist/S139221422 Dave Koehler).

Figure 5a: *arcticus* male; near Crawford, NE; 15 Jun 2019 (from https://ebird.org/checklist/S57397630 Steven Mlodinow). Note the tail spots over 1/2 the length of the tail, and the paler undertail coverts.

Figure 5b: *arcticus* male; South Sioux City, NE; 27 Oct, 2022 (from https://ebird.org/checklist/S121410819 Bill Huser). Note the boldly streaked back, though this bird is currently showing only modest white spots, which could be due to ruffled feathers. Many *arcticus* pics on eBird are wintering in areas where Eastern Towhee occurs. That’s why they got their picture taken and were identified to subspecies.

Figure 5c: *arcticus* male; south of Bismarck, ND; 16 Jun, 2021 (from https://ebird.org/checklist/S90269105 Ted Wolff). Note the large white tail spots, well over 1/2 the length of the tail.

Figure 5d: *arcticus* female; near Dickinson, ND; 4 May, 2018 (from https://ebird.org/checklist/S45246538 Jesse Kolar). Note the brownish hood and buffy streaks on the back.

Figure 5e: *arcticus* female; Ontario, CAN; 12 Feb 2021 (from https://ebird.org/checklist/S81352507 Brad Carey). Another out-of-range *arcticus* pic, illustrating the distinctive fawn brown female with buffy streaking on the back.

Songs

An analysis of songs of their songs suggest a different story — that oregonus and curtatus are very close to each other, but arcticus is quite separate, and with aspects similar to Eastern Towhee.

Spotted Towhees give two types of songs: a buzz or trill; and a slower electronic rattle or what I call the “shaka-shaka” song (example: https://macaulaylibrary.org/asset/587645701). I focus only on the former, and limit my window to May thru July, focusing on breeding birds in their summer range. They all give a distinctive “mew” call, quite different from Eastern Towhee, and rarely a few odd calls, such is a sharp “piew” that sounds like an Evening Grosbeak (example: https://macaulaylibrary.org/asset/447207011)

On to the buzz or trill songs. There are basically three different types:

The buzz (dark green on the map). Example: https://macaulaylibrary.org/asset/584320661. This is often too fast to see the distinctive notes (vertical lines) on an eBird sonagram, unless it’s a very high quality recording. It seems more common on the Pacific slope (thus, oregonus), but is also given in the curtatus range. I could lump #1 and #2 here, as there seems to be a cline between them.
The fast trill, often with a high-pitched introductory accent note or squeak (light green on the map). Example: https://macaulaylibrary.org/asset/464938911. The accent note seems more common and pronounced in the interior (the curtatus range). The same bird can give both the buzz and the fast trill.
The trill with 2 to 6 sweet or scratchy intro notes, or even an intro trill (light blue on the map). Example: https://macaulaylibrary.org/asset/104621711. This song is the only one recorded on eBird in the arcticus zone, and it may be diagnostic for arcticus. Birds further east and around the Black Hills seem more likely to have more than two intro notes or an intro rattle. This song can be quite similar to Eastern Towhee, though Eastern typically has two different intro notes. With arcticus, the intro notes are alike. I found one exception, an arcticus with two different intro notes: https://macaulaylibrary.org/asset/220722981.

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Figure 6: Trill songs by type, as posted to eBird, using only data from May – July, all years.

The map of song types also suggests the BOW map of subspecies is indeed off. The song type I’m associating with arcticus seems largely limited to east of the Rockies, though it does cross the Continental Divide and extend further west near Idaho Falls and also into eastern Utah near Dinosaur National Monument (not on map). That is beyond the scope of this post.

Summary

A heavily-spotted Spotted Towhee in western British Columbia or Washington, presumably in winter, is far more likely to be curtatus than arcticus. In eBird you would choose “maculatus Group,” even though, for Pyle, that would mean a form from Oaxaca or further south. Identification can be made by the back spotting and size of tail spots, though both are subject to overlap in appearance.

Figure 7: apparent *curtatus* male; Port Townsend, WA; 22 Nov 2022. Out-of-range winter bird in my backyard.

arcticus vs curtatus

arcticus can be separated from curtatus if: 1) it sang its distinctive song (unlikely in winter?); 2) the tail spots were large, more than 1/2 the tail length; 3) this was supported by a streaked back; and/or 4) it was a female, which are distinctive.

Thanks to David Bell and the Cascadia Advanced Birding Facebook group for alerting me to Pyle’s treatment of these birds, and for inspiring me to do this deep dive. And thanks to all who posted pics and audio to eBird! I’ll never looks at towhees the same again.

References

Bartos Smith, S. and J. S. Greenlaw (2020). Spotted Towhee (Pipilo maculatus), version 1.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.spotow.01

Dunn, J.L. and Alderfer, J. eds., 1999. Field guide to the birds of North America, Third Edition. National Geographic Books.

Pyle, P., 2023. Identification guide to North American birds: a compendium of information on identifying, ageing, and sexing” near-passerines” and passerines in the hand. 2nd Edition. Slate Creek Press.

Pyle, P., 1997. Identification guide to North American birds: a compendium of information on identifying, ageing, and sexing” near-passerines” and passerines in the hand. Slate Creek Press.

Wahl, T.R., Tweit, B. and Mlodinow, S., 2005. Birds of Washington.

Wright, R., 2019. Peterson reference guide to sparrows of North America. Peterson Reference Guides.

Restoring Southeast Farallon Island thru mouse eradication: Yes

Posted on December 5, 2021 by Stephen Carr Hampton

Islands are special

In contrast to continents, their ecosystems have much fewer moving parts. It’s not unusual for an island to have only a few plant species and often no land bird or mammal species. All of New Zealand has no native land mammals except for bats. The Channel Islands off southern California have only a native deer mouse and the island fox, and that’s only on some of the islands. Southeast Farallon Island has no native land mammals.

I’ve had the privilege of being on Southeast Farallon twice. It’s a magical place, home to thousands of seabirds and marine mammals.

Yet islands are critical refuges for marine mammals and seabirds. It’s not unusual for over 90% of a single species to come from a single island, or just a few islands. For example, over 99% of the world’s Heermann’s Gulls breed only on Isla Raza, a 1.5 acre postage stamp in the Sea of Cortez. 95% of the world’s Black-vented Shearwaters breed only on San Benito Island off Baja California. 99% of the world’s Scripps’s Murrelets come from four islands off southern California and Baja California. And probably 50% of the world’s Ashy Storm-Petrels nest in burrows on a single hillside on Southeast Farallon Island. There are similar examples from all over the world.

A new 4-minute video by Point Blue, summarizing the project.

Islands are vulnerable

This gets us to the final characteristic about islands; they are vulnerable to perturbations. Add one more moving part, and things can fall apart quickly. 75% of all bird, mammal, amphibian, and reptile extinctions have occurred on islands. More bird species have gone extinct on the Hawaiian Islands than on North America, South America, Europe, Africa, Asia, and Australasia combined.

The introduction of a single non-native species, such as rats or mice or cats or even rabbits, can result in massive changes to an island’s ecology, leading to the extinction of native or breeding species. Rats, arriving as stowaways on ships, are the number one cause of bird extinctions worldwide.

Scripps’s Murrelet nest success on Anacapa Island, before and after rat eradication.

When I worked for the California Department of Fish and Wildlife, I was involved in over 300 restoration projects. The best one, the one with the most obvious and dramatic benefits, was when we eradicated non-native black rats from Anacapa Island. In addition to benefitting Scripps’s Murrelets, other seabirds such as Cassin’s Auklets began nesting on the island. The native lizard and even the sea stars and mussels and vegetation rebounded; the rats had been eating them all out of house and home.

Here’s the 4-minute version about Anacapa restoration ten years after rat eradication.

The mouse problem on Southeast Farallon Island

Today, the non-native house mouse is impacting the Farallon Islands, one of the most important seabird nesting colonies south of Alaska.

Southeast Farallon Island, the main island, is infested with the mouse. In fact, there are higher densities of house mice there (more than one per square foot) than anywhere in the world. They eat seabird eggs and spread the seeds of non-native weeds around the island. More significantly, they attract a few migrating Burrowing Owls each fall. The owls, lost over the ocean, would normally stop on the island and then leave. But with the mice there, the owls stay and feast. When the winter rains come, the mouse population crashes and the owls begin to starve. Right about then, the declining Ashy Storm-Petrels begin returning to the island to nest. The owls catch them and stack them like cordwood. (In the most recent review, they were not listed an “endangered” based on the assumption that this project would be implemented.)

One thing to know about Ashy Storm-Petrels is that they are long-lived and slow-reproducing, like most seabirds. With the owls killing the adults, the storm-petrel population cannot recover.

Eventually, the owls starve to death. Then the mouse population rebounds in the spring and the cycle starts over, while the storm-petrel population spirals down. This happens every year on the Farallones.

Restoring the island thru mouse eradication

The plan is to eradicate the house mouse from Southeast Farallon Island, as we eradicated rats on Anacapa, and as has been done on over 600 islands worldwide.

Locations of all of the recorded eradications of invasive vertebrates from islands for which location data are available (n=664).

The key is to get every last mouse—thousands of them. The only way to do this is to use rodenticide bait pellets. It will be done in the late fall, when the mouse population is at its low point, and when there are very few birds or mammals on the island. The few gulls present can be hazed with a laser (we’ve tested this). Any pellets that fall in the water will quickly decompose. On Anacapa, there were few secondary impacts; the benefits were far greater than we ever dreamed.

This project has been researched by dedicated biologists who know and love the island. We have explored all alternatives. (Contraceptives are not feasible. Introducing more raptors is NOT the answer.) We have researched possible harms and benefits. We’ve seen the amazing restoration of the ecosystem on Anacapa and on 600 islands worldwide, and we’ve worked with experts from New Zealand.

Supporters

Here is a list of organizations and experts in support of the project:

National Audubon Society
Audubon California
American Bird Conservancy
BirdLife International
The Nature Conservancy
California Native Plant Society
California Invasive Plant Council

David Ainley; author of Seabirds of the Farallon Islands; Ashy Storm-Petrel species account in Birds of North America
Peter Pyle; Institute for Bird Populations; author of Identification Guide to North American Birds and over 100 journal articles
Peter Harrison; author of Seabirds: An Identification Guide.
Mark Rauzon, Marine Endeavors; author of Isles of Amnesia: The History, Geography, and Restoration of America’s Forgotten Pacific Islands.
Hadoram Shirihai, Tubenoses Project; author of A complete guide to Antarctic wildlife: the birds and marine mammals of the Antarctic continent and the Southern Ocean; Whales, dolphins and seals: A field guide to the marine mammals of the world; The Macmillan birder’s guide to European and Middle Eastern birds.
Debi Shearwater, Shearwater Journeys, 44 years of offshore experience; co-author of Distribution patterns and population size of the Ashy Storm-Petrel
Dianne Feinstein, US Senator

Point Blue Conservation Science (formerly Point Reyes Bird Observatory)
Institute for Bird Populations
Pacific Seabird Group
Agreement on the Conservation of Albatrosses and Petrels
Island Conservation
Oikonos

California Academy of Sciences
California Institute of Environmental Studies

Oiled Wildlife Care Network
International Bird Rescue

Golden Gate Audubon Society
Marin Audubon Society
Monterey Audubon Society
San Diego Audubon Society
Sequoia Audubon Society

Marin County Supervisor
Santa Cruz County Supervisor
National Refuge Association
Save the Bay
Farallon Islands Foundation
Citizens Committee to Complete the Refuge
Coastal Conservation Action Lab
Freshwater Life
Marin Conservation League
Marine Endeavors
Natural Heritage Institute
South Georgia Heritage Trust

More details about the project and the public process

More details about the project, the process, and all relevant documents can be found here. The project will come before the California Coastal Commission on Dec 16, 2021. Letters to the Commission should be emailed to farallonislands@coastal.ca.gov. The deadline for letters is 5pm on Friday, December 10.

Related reports and videos

Here are some videos and reports about past similar projects:

Paper: The Global Islands Invasive Vertebrate Eradication Database: A tool to improve and facilitate restoration of island ecosystems

Article: 169 Islands that Offer Hope for Stemming the Extinction Crisis: Nearly 10% of island extinctions can be prevented through the eradication of invasive mammals on 169 islands

Anacapa Island Rat Eradication

Achieving Balance: Anacapa Island Ten Years After the Removal of the Black Rat (15 min)

Final Report: Responses by Breeding Xantus’s Murrelets Eight Years after Eradication of Black Rats from Anacapa Island, California

All the reports on the Anacapa rat eradication

Short documentaries/reports of rodent eradications from islands around the world

Night Birds Returning: eradication of rats by Haida Nation and Parks Canada

The Rakiura Titi Islands Restoration Project: Community action to eradicate rats for ecological restoration and cultural wellbeing

Million Dollar Mouse: the eradication of mice from Antipodes Island