Unique mating system

No fair looking at the pictures yet. Now, what would you guess to be the most abundant bird in North America? And the male of which species has the most females within the care of its territory? If you hadn’t looked at the picture, would you have guessed that both of these would be the red-winged blackbird?

It would have been on my list for the territory question, but I would have had a lot of other candidates for most abundant species. I wonder if these two issues go hand in hand. Are there lots of red-winged blackbirds because it only takes a few males to breed, feed and protect a lot of females? Or is there simply a surplus of females such that you have the situation Jan and Dean dreamed of in the phrase from their ‘60s hit “Surf City” – “Two girls for every boy?”

Studying the breeding section of bird biology, one sees that there are almost as many different mating strategies as there are species. This is especially true of the group we refer to as the blackbirds. The blackbirds include a number of species of black birds. As a group, they are a part of the family of icterids, which actually means “yellow birds,” and includes the orioles, the meadowlarks, the bobolink and the blackbirds. There are 10 species of blackbirds that breed in North America of which three are grackles, two are cowbirds and five are blackbirds.

Did you notice that “blackbird” doesn’t tell you much? The 10 blackbirds include five blackbirds, but all 10 blackbirds are black birds. And in Europe their closest equivalent to our robin is their blackbird. But I’m getting off the point.

Among the 10 blackbirds, we see species that breed strictly in solitary pairs. There are some that live in colonies but breed as couples. There are other species that function as a harem with one male breeding with and defending from other males numerous females. And then there is the red-winged blackbird.

This blackbird, by the way, is only black in the male version. Females are smaller and more sparrowlike in that they are brown and streaky rather than black and glossy. Admit it, no matter how good a birder you are, you have from time to time pondered the identity of a female red-wing whose wings are not red and whose body is not black. It happens all the time. In fact, it’s one of those sad lessons that needs to be relearned each year by some of us.

But again, I’m off the point. The point is that red-winged blackbirds, both the black birds with the red wing patches and the brown birds with the rusty streaks, have a unique mating system that is badly misunderstood by most bird enthusiasts. I, at least, have been told many times that the blackbird male with the biggest and showiest red shoulder patches, his epaulets according to the field guides, attracts the most females to his love nest – or in biological terms, his breeding territory.

I’m sorry, but once again I must make a side point. In truth, the male red-winged blackbird does not have red wings. Only a small portion of the wing is red. And it’s not even the shoulder portion. I know, the dictionary definition of an epaulet is a shoulder decoration, but the red feathers are not on his shoulder. Besides, the dictionary states that the epaulet is to be of silver or gold, not red.

The red feathers are actually on the blackbird’s wrist. Yes, birds have wrists. They even have fingers, but you can’t see them for all the feathers attached to them. They have a thumb and its name is alula. They only have three fingers, but who needs them? The feathers get in the way of picking things up anyway.

Back to the point. While it is true that red-wings, both with and without red wrists, breed in a territory governed by one male – with giant red epaulets, on his wrists – a territory containing up to 15 females - each without epaulets, anywhere – the females don’t actually care in the least for the size of the male’s big red markings. It’s a myth – a blackbird urban legend.

The females come for the great territory and breed with the male simply because he’s there. DNA studies have even shown that females often mate with some guy just outside the territory, even if his red markings are smaller. And the territory owner doesn’t seem to care, as long as it all takes place off his territory.

It turns out that what actually turns on the male red-winged blackbird is defending his territory from males that lack a territory. The special posture, the exaggerated display of his epaulets, even his singing, which is really wonderful and exciting to hear, is all an effort to discourage other males from coveting the real estate. He’s not waving his big red markings for the benefit or enjoyment of the female.

This is really unique. Grouse strut and croak and carry on to be the most attractive and get the most mates, much like cowboys in a bar on Friday night. Red-wings are more like land developers that dress up to close a deal on finishing out the last few tracts in their exclusive, gated subdivision. Breeding may be a side benefit, but it’s not the primary reason for being there.

Oh, one last thing about the red wrists of the red-winged blackbird. They are actually orange-red, with a pale yellowish lower border. So they are not a real red at all. The tricolored blackbird, however – a species found only in California, Oregon and recently in Washington – while looking overall very much like a red-winged blackbird, has wrist epaulets of a rich, beautiful, dark red with a lower border of pure white. A California subspecies of the red-winged blackbird lacks the yellow lower border and is called the bicolored blackbird. Is all that clear? Good.

So what does the species get for all this strange effort and these bizarre breeding habits? Lots of little blackbirds, that’s what. Actually, lots of little brown, stripy birds, half of which grow into black birds – but you get my point.

It turns out that there are lots of good habitat areas for red-wings throughout North and Central America. And this territory strategy is quite efficient. Several decades ago an educated estimate was made that placed the red-wing population in the United States and Canada at around 190 million blackbirds. That’s a lot of pies at four and 20 birds to the pie.

However, it’s amazing that it’s not a lot more. Here’s the math on red-wing population dynamics. Each bird has the potential to live between four and eight years. One bird is known to have survived 14 years in the wild, but let’s say a typical life span is five years.

Each female usually has two broods a year, typically with four eggs each. That’s eight young per year for five years, making 40 offspring for that one female. If half are female, those 20 birds will produce 800 offspring, 400 of which will be female. If you carry that out to five generations, that initial female will have led to the production of 6.4 million offspring in 25 years, 3.2 million of which can still go on to breed at this same rate indefinitely.

I first heard this example with robins in ecology class. It’s not too many years before the entire world is miles deep in blackbirds or robins. Well, the obvious reason that has not happened is that little of that potential is reached. A blackbird female will probably be lucky to have two or three young actually survive from each nesting season until old enough to breed. Lots will have none. Lots of adults don’t make it until their fifth birthday.

So the potential isn’t met. But even if only one female is produced per year, five generations will yield almost 4,000 blackbirds. It’s obviously an effective strategy. It doesn’t require many males either – just good, large territories governed by a male with big red markings that effectively repel territorial invaders.

OK, so what’s been my point? The point is that it’s a good family planning strategy to pick your mate not by how he looks, or moves, or sings, but by how good of a location he’s in – at least if you are a red-wing female. Location, location, location.

In fact, if you don’t care much for him personally, slip off and breed with someone else, but come back to nest in his territory. He doesn’t care. It’s really only the material things of his territory that he cares about. Go ahead, use his stuff to your family’s benefit, and in the long run, the whole species benefits.

This is, of course, blackbird morality – or ecology – and I’m not advocating it for all species. But it’s hard to argue with success.