The birds kept coming, swarming in numbers I had never seen, flitting around in search of food. It was so intense that I could not maintain an accurate count of the visitors for my reporting to the Cornell Lab of Ornithology via the eBird app. Having just filled the feeders that morning, it was clear that I would soon be refilling them.
The culprits were beautiful purple finches and American goldfinches, more than 25 of each species. Overwhelmed in the melee were three dark-eyed juncos, two black-capped chickadees and a tiny chipping sparrow who seemed awed by the whole shebang. The sparrow probably wondered whom was leading the flash mob and how he could get a piece of the action without getting battered.
The spectacle got me thinking about the interactions among the various species, and the dynamics within each species. Female finches are serious eaters, ready to grab a perch and chomp seeds for 10 minutes or more. When another female arrives, there is some momentary flaring of wings and near-contact of beaks, but they sort it out quickly. When a male finch flashes in, the females generally yield and find another perch. Smaller birds usually hang back, recognizing they cannot win a pushing contest.
Then the blue jays show up like teenaged boys hopped up on caffeine and sugar, raising a ruckus and bullying others. They control the feeders for a few minutes, until their squabbling takes them away. But there were a couple outliers in the battle for dominance: a lone red-bellied woodpecker and a red-winged blackbird with an obvious chip on his shoulder. The woodpecker had a heavy beak and showed no fear. The blackbird was smaller than the jays but often refused to yield, even when outnumbered. I cheered him on, interested to see how far he would push his luck.
Scientists publish endless studies about hierarchical behavior within and among species. They even have a fancy term for the field: dominance hierarchy. The father of this field was a Norwegian zoologist named Thorleif Schjelderup-Ebbe who spent years studying chickens and, in 1918, published his theories about the “pecking order” that are still respected today. The conclusion of this work is that a dominance hierarchy is essential to maintain stability and efficiency among groups. It saves time and energy, and helps reduce the risk of injuries that can doom a creature in a competitive world.
I was fascinated to learn that even in the plant world, species dominance plays a role. Scientists refer to “ecological dominance” when one or more species play a major role in an ecosystem. In temperate bogs, sphagnum moss can dominate other plants, while in tidal swamps, the kingpin might be mangrove plants. In 1918, Danish botanist Christen Raunkiaer postulated that in communities with dominant species, overall species diversity is lower. All might be well until the dominant species suffers from disease, environmental pressure or an emerging invasive competitor.
Often it seems that size is the key determinant in establishing hierarchies, but there are exceptions. Chickadees and that red-winged blackbird showed little fear when I stepped out on the deck with more food, chastising me until I retreated inside. Wolverines and fishers, two bad-tempered members of the Mustelid family, are known for their willingness to tackle much larger animals in the unending battle for food. You may have seen battles among elk and wild sheep on television, where aggression and the strength of youth can overwhelm mere size in the competition to breed.
Aggression can only carry a leader so far, of course. Among wild turkeys, if the dominant gobbler is struck down for any reason, nearby subordinate males may take the opportunity to jump on the fallen tom with fierce kicks and pecks. We recently watched on television two gigantic elephant seals fighting over a harem. If the cantankerous old male showed any weakness or fatigue, a young adversary would quickly banish the loser from the colony.
Scientists have determined that in most species, hierarchies are well respected. Constant fighting for dominance would consume a great deal of energy and increase the risk of serious injury. Wolf packs are generally led by a breeding pair, with offspring from the last year or two filling out the pack. Subordinate wolves are expected to help with hunting and the protection of the youngest members of the pack. Recent research has shown that wolf packs generally live in harmony, with their focus on survival.
