Birds Do It

Boat-tailed Grackles displaying

“Maybe I’m a prude,” she said to me, “but it seems that you write a lot about sex.”

Well, yes. Sex, and reproduction, dominates the life and activity of birds for a few months during the year. We are currently into those months, and the drive to breed and reproduce is what makes birding so great in the Spring and Summer.

During the most of the year, the main activity is to survive. Sex cannot get in the way. The gonads (ovaries and testes) are not needed. It costs energy to carry them around, so they shrink almost to nothing.

When the time approaches that conditions are optimal for the survival of young, the gonads  increase in size by a hundred fold. The testes of the male American Goldfinch, a late nesting songbird, are largest in mid-July when their nesting peaks.

All of this is complex and there are many variables. Exceptions are rampant. Even so, here is a brief overgeneralized description of what happens: As the length of the day increases, the gonads also increase many fold and send hormones flooding into the system. Studies of songbirds have shown that the region in the brain that controls singing behavior also undergoes large scale change in volume and neuron number, stimulated by the hormones.

Ovenbird singing on his territory

With the brain stimulated, off they go - on migration, territorial defense, courtship, and mating. Bird reproduction takes place when the environmental conditions are most favorable to the successful raising of young. In our temperate northern climes, longer day length (Spring and Summer) also means abundant protein resources essential to raising young. In different climates, the time of the year will be different. Young birds have to be fed by their parents (altricial - e.g. songbirds) or they have to be able to forage and feed themselves soon after hatching (precocial - e.g. waterfowl and shorebirds), with parents teaching and protecting.

For mammals, it is very different. The female nurses her young. The male is only needed for one thing, and once he has made his contribution, he is superfluous. A mother bear with fat reserves can give birth in the middle of winter, nurse her newborn in her den while the snows fly, and emerge in Spring with her offspring ready to learn how to feed itself.


Many mammals have evolved particular seasonal breeding patterns. In others, females are receptive (in heat) at variable times. Years ago we had a male mongrel mutt. Several times during the year, he went berserk when one or the other of the neighborhood females was in heat, even if she was blocks away. Crack a storm door with a lapse in attention, and he was through it and gone. Hours later he would return and spend a day sleeping off his adventures. When we had him neutered, it calmed his response, but did not entirely rewire his brain. A year after he was neutered, a neighbor called, threatening him with a paternity suit.


You’ve heard the old expression, “In Spring, a young man’s fancy turns to love.” It is true for birds; it is not true for a young man. His fancy can turn that way any time of the year. Humans are unique in that - using the biological terms - sexual receptivity, mating, and breeding can occur at any time and in any season. There may be spikes in the fertility rate during power outages, but those outages are random in nature. Sex does not depend upon any season. Whenever the power goes off, and we can’t watch television, we find something else to do. Our sexual uniqueness in the animal world means that we can be thinking about sex at any time on any day.

Male Chestnut-sided Warbler singing on territory

Our birds think about sex seasonally, and when they do, they are totally consumed by sex and its consequences. They are not distracted by television. Their attention may waiver in the presence of a predator, but that distraction is related to their purpose. Survive to breed. Protect your young, but not at your own fatal expense.

Among the birds, sex has little to do with pleasure. They have no external sex organs. There is a single opening, the cloaca, which serves the intestinal, urinary, and reproductive systems. When mating, most birds touch this organ in what is known as the cloacal kiss. During the touch, semen is transferred from the male to the female. The cloacal kiss is brief, lasting mere seconds, if that long.

Chipping Sparrow

I am certainly guilty of occasionally projecting our unique human approach and cultural attitudes about sex on the birds. But frankly, our cultural attitudes about sex do not apply to the birds. Sex among the birds has to do with each individual being driven by the encoded need to reproduce its genetic heritage. When the Chipping Sparrow male establishes his territory, attracts a female, and drives off intruding males, he is driven by internal wiring to pass along his genes. When he dashes off for a quickie with a neighboring female (and it is literally very quick) he does so in the encoded drive to produce more offspring, more genetic descendants. When his mated female slips away for a quickie with a neighboring male, she is hedging her bets. Just in case her mate is not quite the man she thought he was, she gathers genetic material from a second male; if his genes prove the better genes, then there is a greater possibility for her genes to be extended.

Red-winged Blackbird

The manner in which birds assess who will make the best mate is elaborate and complicated. Prove you can feed my young by bringing food to me, says a female tern to a male tern, or a female kestrel to a male kestrel, or a female Blue Jay to a male Blue Jay. Prove you can find nutritious food by being redder than your neighbor, says a female House Finch to a male House Finch. Prove you can protect me from raccoons by defending a cattail territory far from the muddy shore says a female Red-winged Blackbird to a male Red-winged Blackbird. Sing better, flutter wings better, flash a wider fan tail, be more colorful. The variations are as many as the species. What the subtle distinctions are which lead to the mate choice are imperceptible to us. Something that a male bird does triggers something in the brain of a female bird that leads her to say, that is the one I should choose.


What we see among the birds during the Spring and Summer is not really about sex. It is about individuals prolonging their genetic life. We get to watch it. We see their colors. We hear their songs. We watch the frenetic activity. And by gosh, it is fun. And if once in while we project our human sexual culture onto the birds by offering up a salacious snicker ... I say, so what. That is part of the fun of good birding.