This is an installment of the Get to Know Your Backyard Birds series. Read part one here.
My father is a man of simple pleasures. He has an encyclopedic knowledge of 70s rock bands, possesses an engineer’s intuition for fixing anything with a motor, and considers beers after work the only vacation he needs. His idea of a thoughtful gift involves tools or, more often, a trip to the county dump to salvage used car parts. Some of our best bonding has happened over lessons in chainsaw-wielding.
But my dad has a ritual that belies his old-fashioned pragmatism. Every single evening, he comes home from work and visits the backyard to refill the bird feeder, replenishing the cylindrical feeder from a fifty-pound bag of black sunflower seeds.
He does it because of his inordinate fondness for one bird: the northern cardinal. Cardinalis cardinalis is that run-of-the-mill red bird with the cocky crest, counted on more checklists in the Great Backyard Bird Count than any other species. They’re overabundant and undiscerning, but the striking red plumage of the males has made them the official bird of seven states. They don’t migrate, so bird watchers can follow the same mating pairs season after season.
I think my father loves northern cardinals because they make him wax sentimental. Cardinals engage in a behavior called courtship feeding, in which males fetch seeds and feed them to female mates. It is a delicate act by a typically assertive bird, and it’s easy to understand why humans interpret such a gesture as motivated by love and affection. My father always mentions when he’s seen the cardinals feeding each other.
Many birds engage in variations on courtship feeding, some of which provide more dramatic examples than the cardinal. The northern shrike, for instance, is a large songbird known for its penchant for impaling mice, insects, and even other birds on sharp twigs.1 Males present the gruesome skewer to potential mates, and females select the romantic fellow who offers the largest nuptial gift (their reward: three sexy seconds of mating).
Scientists have offered three different theories to explain courtship feeding: (1) courtship feeding allows females to evaluate the kind of parent a male would make for her offspring, (2) courtship feeding strengthens the bond between mated males and females, or (3) courtship feeding provides nesting females with extra nutrition during a time when they can’t travel far to forage.
In 2011, scientists combined and analyzed the data on courtship feeding from 170 species to parse these theories.2 What they found would probably disappoint my dad–it turns out that courtship feeding is not widespread as a mechanism for reinforcing lovers’ bonds to make them better co-parents. Instead, the behavior appears to mostly be a function of nutrition. Female birds expend a great deal of their energy on reproduction, and their success rearing young can be increased by the convenience of a mate delivering food. The researchers found a higher incidence of courtship feeding in species where females shouldered a greater share of the reproductive burden–like building nests and incubating eggs alone–and thus benefited more from being fed.
Hungry pregnant females: 1
1. Tryjanowski, Piotr, and Hromada, Martin. 2004. “Do males of the great grey shrike, Lanius excubitor, trade food for extrapair copulations?” Animal Behaviour 69 (3): 529–533. doi:10.1016/j.anbehav.2004.06.009
2. Galván, Ismael, and Sanz, Juan José. 2011. “Mate-feeding has evolved as a compensatory energetic strategy that affects breeding success in birds.” Behavioral Ecology 22: 1088–1095. doi:10.1093/beheco/arr094
ERIN WEEKS is a science and nature writer from Charleston, South Carolina. She currently works for Living on Earth.