Often I have watched two, sometimes three, male Boat-tailed Grackles (Quiscalus major) standing side by side, vigorously displaying to one another for minutes at a time. Eventually, they would peacefully part, leaving me to wonder what had just taken place. Were the males arguing, albeit in a ritualized manner, over the location of a shared territorial boundary?
According to published studies, males fight over patches of real estate where groups of females decide to build their nests, usually over water among a bed of reeds. Such circumstances promote a reproductive strategy called “harem defense polygyny” whereby a dominant male tries to monopolize the majority of matings within a nesting group. However, on average, he may sire only 25 percent of the young raised by the females. This is because females travel some distance from the nest area to gather food, etc., and while they are away, they copulate with other males. In other words, no one male can control the sexual behavior of any of the females, which begs the question: How should a male behave to maximize his chances of copulating with as many females as possible?
When breeding is in full swing, a male is obligated to fight off rivals, a feat that obviously taxes his energy reserves. One way to lower the cost of defense would be to form alliances with other males. Could this be the reason why males come together and posture to one another as shown in the videotape? If two males learn to accept one another, they could combine efforts in repelling rivals from the nesting sites in the reeds as well take turns following individual females to feeding sites, etc.
In addition to confronting rivals, males spend a lot time displaying to females. It is interesting to note that males adopt a different posture when trying to get the attention of a female while the pair is away from the nesting site. Instead of pointing the beak skyward, a male walks behind the female while bowing and raising the feathers on the back of his head and neck. The tone of the male’s vocalizations is also more subdued.
Females are also approached by males when en route to their nests. In this scenario, a male flies in front of the female as he fluffs out his body feathers, opens his long tail, and sings. Typically, the male overshoots the female’s nest, but he quickly doubles back to land next to her and continues his courtship overtures by bowing and rapidly fluttering his wings. Not once have I seen a male copulate with a female near her nest. Perhaps his efforts are rewarded when the female is away collecting nest material.