Rusty and Brewer’s Blackbirds are close relatives in the family Icteridae, the blackbirds of the Americas. While Rusty Blackbirds are far more common in Chicagoland, every year we see small numbers of Brewer’s during spring and fall migration. Aside from the fun of finding a rare species, it’s important to keep an accurate tally of Rusty’s more generally as they are rapidly declining. Learning about this identification will also add a new layer of appreciation for these unique birds.

Identification of the females of these two species is usually pretty easy, as Brewer’s females usually have dark irises (about 90% of the time, according to Birds of the World). The identification of males in our region is usually aided by this fact, as these birds are often seen in groups, with males and females of the same species traveling and foraging together. However, this leaves out the case of a lone male, as well the instances where both species may be present at the same location (it happens!).

Rusty Blackbird male (left) with three Rusty females (right). Females of either species never get as dark black as the males, with Rusty females turning all sorts of brown and gray in the spring. Pale irises on three females, with smaller, thinner bills, and paler overall than Grackles, and you know you have a group of Rusty’s. Chicago, IL April 3rd, 2023.

A dark-eyed brown bird foraging with a pale-eyed black bird in a field, you probably have a male and female pair of Brewer’s Blackbirds (these are). Chicago, IL April 16th, 2023.

The dreaded Brewer’s Blackbird female with a pale iris. Usually the pale-eyed females are kinder and have a little red in the iris, but sometimes they look like this. This is one of the summering birds in Illinois State Beach Park, from mid-June, 2023. Outside of the time and place this photo was taken, eliminating a female Rusty Blackbird here might only be possible with shape and sound, i.e. not plumage, as far as I know.

What about males?

During the fall, most males are easy to separate by species. Rusty Blackbirds have a ton of bright, warm fringing to their feathers. Young male Brewer’s can have pale fringes, but they are a different color (check out the photos on page three here).

A male Rusty Blackbird in fresh fall plumage is not likely to be confused with anything else. Like most songbirds we see, blackbirds grow an entirely new set of feathers sometime from the late summer to fall, and in this case most of these feathers will be with them for the whole year. Despite the incredible variety seen in male Rusty’s in the spring, all those birds started out looking something like this. Wilmette, IL September 22, 2022.

The difficulty with identification of males arises from the gradual wearing of those rusty and pale-yellowish fringes throughout the remainder of the year. By the time we see Rusty’s in the spring, they have many different looks, with some having much fringing still intact, while others have virtually all their fringing worn off, leaving a mostly dark bird. You would think the latter, more worn birds, would become obviously more frequent later in the season, but there is a surprising variety of wear levels seen throughout the spring.

Rusty Blackbird male with a fair amount of fringing still intact. Chicago, IL April 4, 2023.

Rusty Blackbird male with less fringing. Chicago, IL March 15, 2024. Even though this is from a few weeks earlier than the previous photo, this individual has worn off more fringes.

Brewer’s Blackbirds are very unlikely to be walking around a flooded woodland turning over leaves and picking out invertebrates like the bird above–that is typical Rusty habitat and behavior. When Brewer’s are seen near Chicago, they are usually on a grass field, or in some open area, and sometimes can be seen perched in trees in between flights–but these are all places one could also see a Rusty Blackbird.

Which brings me to the juice of this blog: what do you do with birds like this^??

Based on location, this could be either species. If there were any rusty fringes on this bird, they have worn off. There are a number of field marks outlined in various guides re: tail length, body shape, bill shape, and posture. I’m not knocking those (although I have some words about bill shape), but here I’m going to focus on plumage–specifically the “glossy” concept, and color–which I think can benefit from a more nuanced description.

But first, look for some fringes.

Because they can be hiding. On this bird, there are still a few hard to see rusty fringes on the mantle, and some pale (not really rusty) fringes on the undertail coverts.

Rusty Blackbird. Wilmette, IL March 30, 2024.

Fringes like these, however subtle, should not be present in a Brewer’s Blackbird in the spring. You’ll notice I’m not pointing to the primaries, i.e. the folded wing feathers on the top side just in front of the tail; those are showing faded edges due to wear (I’m sorry, but yes: wear taketh away pale fringes, but wear also giveth pale edges), and faded primaries like these can certainly be seen in Brewer’s in the spring. Here’s a more obviously fringed Rusty example:

Rusty Blackbird Chicago, IL April 17, 2022. The mantle is the last place that obvious rusty fringes remain, and a Brewer’s Blackbird won’t have any fringes like this in the spring.

Gloss and Color

What the previous two birds show, and one of the major points I want to make, is that the wings on Rusty Blackbirds can be darn shiny, even, dare I say, “glossy.” They also have a subtle green color, similar to the same feathers in Brewer’s Blackbirds. I went through a few museum specimens of spring males in these species, and I can confirm this is not an illusion or photographic effect. In the same lighting, the wing panels, and to a lesser degree the tails, are pretty similar in color and glossiness in both species. So where do the two species differ?

Brewer’s Blackbird male. Monterey, CA December 6, 2023. A different time and place, but adult male Brewer’s show very little change in appearance from winter to spring.

One of the joys of a recent trip to California was getting to take a bunch of my own photos of Brewer’s Blackbirds in different lighting. For something like this, I don’t trust what I see on eBird. When people get a hold of those sliders in Adobe, they just can’t help themselves… Anyway, above is a nice Brewer’s male with somewhat soft and diffuse lighting. What do you see? For one, it is still easily glossy, with “specular” highlights (the very pale reflective spots) even in lower light. The other thing, which may be more obvious, are the colors: clear purple throughout the head and nape, fading to greenish-blue or green on the back, underside, and elsewhere. Compare to this Rusty:

Rusty Blackbird. Wilmette, IL March 30, 2024. This is the same bird as the one in the photo with the arrows. Notice how the scant fringing on the back, which was hard to see before, is effectively invisible at this angle and lighting.

The Rusty above is in full sun, and is more illuminated than the previous Brewer’s. Aside from a dull greenish-blue where the sun hits the upper wing coverts, there is very little color, and especially obvious, no saturated purple on the head or nape.

Brewer’s Blackbird. Monterey, CA December 4, 2023. Is this bird “glossy”?

The Brewer’s above, which is in shadow so lit by diffuse ambient light, still shows more color than the well-lit Rusty Blackbirds shown previously, even when there is not enough direct light to appear glossy. In particular, the purple on the head, nape, and chest are still noticeable. You might be thinking, I’m from Chicago, I don’t need to worry about seeing a lone male Brewer’s Blackbird walking around in the shadows.

Brewer’s Blackbird. Chicago, IL April 16, 2023. This bird was in a field on the lakefront which hosted both Rusty and Brewer’s Blackbirds, among other blackbird species.

The photo above, taken under overcast skies in between rain showers, still shows a discernible purple hood around this bird’s head, however subtle, and I highly doubt a Rusty Blackbird would do the same in this setting. The term “glossy” does not enter one’s mind here. Compare this to a Rusty in low light:

Rusty Blackbird. Chicago, IL April 4, 2023.

Back to the swamp. Ignoring the obvious rusty fringes on the back, the bird above is in diffuse light, and not much of it. A Brewer’s in this same low-light setting would show more saturated colors, more purple in and around the head.

Brewer’s Blackbird. Monterey, CA December 6, 2023. Notice the fairly discrete border between the purple bib and blue below on the chest.

Do Rusty Blackbirds actually have pretty colors in the spring and summer?

Kind of. Like I said previously, I tend to avoid eBird for questions like this when the flick of a mouse can totally change the answer, especially when that flick makes your photograph more appealing to a human audience. I found some of my go-to field guides to be oddly misleading re: this topic (one very reliable source said the head was green in Rusty’s, while two other guides said it was purple). So I went to the Field Museum and shined a light on some study skins, and wiggled them around to make sure the angle wasn’t doing anything drastic (it wasn’t, by the way, like the neck feathers in pigeons). For those hungry for more, here’s some photo comparisons of study skins and a more detailed description of color in Rusty and Brewer’s males. I looked at about a dozen Rusty’s, which were somewhat variable, while the Brewer’s were much more consistent. All specimens are from April-June, and I didn’t notice any differences in color related to date within this span.

Two Rusty’s on the left and a Brewer’s on the right, upperside. The head in Rusty’s is variably gray to dull purple under a bright light. The upperparts overall were also variable in Rusty’s, with these two birds being more colorful examples. Here the left bird shows a dull blue to greenish-blue on the back, while the middle bird shows a dull purple to blue throughout the back feathers that is closer to the hue on the head. Notice also the fairly glossy, greenish-blue wing feathers on the left Rusty (the center bird has very worn flight feathers). The obvious green on the Brewer’s back, which in places more approaches yellow in hue, is not something I saw on any Rusty, even in a less saturated form, nor is the more discrete border this color creates with the saturated purple head. The color in the head on Brewer’s also gets more pinkish (towards red) in places than the hues found in Rusty. So in general, the spectrum of colors shown by Brewer’s is broader as well as being more saturated. The interesting purple fringes to the mostly green feathers on the Brewer’s back, only detected up close, puts one in mind of the interference patterns created by oil on water. Indeed the colors in these species are created by the same phenomenon, known as “thin-film interference,” which is also responsible for the gloss effect itself–gloss can occur independently of saturated colors (think crows), and is probably an evolutionary intermediate between non-glossy, matte appearing feathers, and the more saturated colors created by interference in birds like Brewer’s Blackbird. Perhaps Rusty Blackbird barbules are structurally somewhere in between glossy black feathers, like those in American Crow, and those in blackbirds with more saturated colors, like Brewer’s Blackbird and grackles.

Two Rusty’s on the left and a Brewer’s on the right, underside. Here the underparts show a similar story to the upperparts, with even more dullness and lack of color on the Rusty’s. Still, a little dull blue and greenish-blue is detectable on the chest and belly in the center Rusty, but nothing like the saturated colors in the Brewer’s, with purple heads to blue and then greenish bellies.

Rusty left, Brewer’s right, tails. The saturated green on the upperside of Brewer’s, not shown in Rusty’s, continues to the rump and uppertail coverts (not shown).

Brewer’s left, Rusty right, head, nape and shoulder.

Thanks to Ben Marks and John Bates for help with the Field Museum collection, and Yasmeen Erritouni for the info on thin-film interference in bird feathers.