In nature, many species benefit from social-distancing (S-D) at specific stages of their lives. Keeping others away is instinctive. Consider your own uneasy feeling when crammed into airplane seating or squeezing onto a jam-packed subway. Some mammals live in herds or colonies. Other mammals prefer to “self-isolate” and mark their S-D boundaries with scent.
For birds, S-D is a key behavior for defining and defending their breeding or feeding territories in their “essential” habitats. Although birds occupy every ecosystem on every continent, their S-D may range from inches to miles, depending on the species. Consider their variety, from hummingbirds to albatrosses, from chickadees to eagles, from loons to sparrows. For each of 10,000 bird species, their habitats, the season, and their hormones define the scale and schedule of their innate S-D. Here is a small sampling; see if you can figure the S-D of other familiar birds.
Most Great Blue Herons winter in southern coastal and estuarine habitats. There the females and juveniles show little effort to “own” feeding grounds, but the adult males maintain their aggressive, hormone-driven S-D to defend territories such as stretches of shorelines (up to 300 yards) or favored patches of fields and marshes (1-2 acres). Their male agonistic (physical aggression) behavior applies only to defending food sources such as crayfish, frogs, fish, and crabs throughout the year. But in breeding season, GBH’s share nesting sites (rookeries) where several pairs may nest side-by-side, in the same trees, and with other species of herons, egrets, and other wading birds.
Bobolinks are songbirds in the family of Icterids (Blackbirds), and they are renowned for their annual long-distance migrations from N. American summer grasslands to the pampas grasslands of S. America’s summer and back, but they breed only in the north. So, in May the Bobolink male completes a 4,000 to 8,000 m. northbound journey with no patience for S-D squabbles with other males upon arrival. Incessant songs, aggressive calls, intensive chases, and even battles face the rivals. These S-D combatants will patrol their territorial boundaries by only inches apart. But after breeding season Bobolinks migrate in huge blackbird flocks, and they “winter” in S. America summer without any S-D display of territoriality.
The tremolo of the Common Loon may awaken the attention of distant members of the species. They sound like they’re inviting a friend over despite their S-D; but, no, the voice of the loon commands territory on its chosen lake and shore. Loon nesting sites are irregularly spaced along lakeshores and define the loons’ shoreline S-D’s - their “own” breeding territories. While feeding in the lake’s waters, loons may be seen uncomfortably close. In these near encounters, they may circle one another, display subtle differences of posture, and attack to define the S-D boundaries of their aquatic resources.
Tree Swallows, outside of their summer breeding season, will roost in marsh cattails, on beaches, or swamp shrubs and trees, in flocks of hundreds, thousands, and, on the record, millions. Adults S-D themselves only 4” apart when roosting or perching on wires. Their food is not in one place as they feed exclusively on aerial insects so without S-D for food sources. But during the breeding season, Tree Swallows seek tree cavities or nesting boxes. They can be brutally active in S-D aggression to defend their nesting cavities. Physical fights in the cavity, the air, and even the water may occur before the settling “stay home” incubation of their eggs. Defending that territory leads to S-D of about a 15-yard radius.
Black-and-white Warblers, like many small birds, are pugnacious and fearless. Their habitat in the Kingdom is moist, mixed forests, where they spend much of each day in mixed flocks foraging for insects on the limbs and trunks of trees. However, these attractive striped warblers are fiercely protective of their nest sites on the forest floor. They define their S-D in territories ranging from 3 to 10 acres of woodland. So possessive is the male that he may sometimes reclaim his previous year’s territory. His S-D is displayed with song, call notes, wing fluttering, and chasing any rival, including other warblers who have violated his S-D. In autumn though, like many neotropical migratory birds, these will join large mixed foraging flocks without any S-D. But the northbound migration is urgently motivated by the same hormones that stimulate breeding in the spring and summer and may trigger S-D aggression on the long journey.
Northern Gannets would be a highly unlikely sight in Vermont, but 100,000 Gannets claim home on the small Bonaventure Island off the Gaspé Peninsula of Quebec. These are very large (3’ long) white sea birds with black wing tips; they forage only at sea and breed only on rocky islands and cliffs. The Bonaventure Island Gannets cover thousands of square miles of the North Atlantic and are often seen plunge-diving into the shallow waters of the continental shelf. Their S-D at sea is nonexistent; they share locations wherever shoaling fish are abundant. But on the rocky islands and coastal cliffs, personal nesting territory for each breeding pair confronts dense colonies, with pugnacious males claiming S-D nest sites less than 3 ft. from others in all directions, barely room for a nest for one chick and one parent, as claustrophobic as a crowded elevator!
Charles Darwin’s vision of natural selection is reflected in thousands of bird species with genes that produce hormones for each species to inherit the scale and timeliness of its Social Distancing. You, too!