There is a season — Tern! Tern! Tern!

Seasons, breeding and juveniles reveal slightly altered looks but in the same “color” palate. Winter is the only time I see royal terns on the sandy beach at La Jolla Shores, and during this time, the bird’s crown is almost entirely white with just some inconspicuous black spotting forward of the black crest. During February, the onset of breeding season, royala acquire a black skullcap of plumage that covers the rear half of the crown and extends forward to completely envelop the eye area. Breeding birds of both sexes share this inscrutable look. As for nesting, it won’t happen in La Jolla because tern couples prefer an estuary to an open coast. Even so, they have no history of nesting in any significant numbers in San Diego’s inland waterways, preferring to deal with their broods in the southern latitudes of Mexico’s estuaries. Though out of my sight, by late June, the birds’ black caps have receded, revealing their typical white forehead with black stubble near the crest. Juvenile royal terns look similar to nonbreeding adults but youngsters have black-splotched wings and an orangey bill that may lean more toward yellow instead of red.

Sources suggest a royal tern does not have a strong seasonal pattern, being found along San Diego County’s coast year round. Maybe so, but whenever a royal is seen, count on it being near seawater — a commitment likely connected to its favored prey choice, small fish like anchovies and sardines. The mercurial movements — and booms and busts — of these fish species are one reason the status of royal terns has been poorly understood throughout the 20th century. We are only beginning to document changes in behavior of seabirds and correlate them with their prey (in terms of numbers and distribution fish). The point is to understand how the changes relate to fishing pressures on these important prey and global climate change. Since seabirds that nest with success can expect to be widely distributed across their range, decreases in their numbers or change in their expected range provide quick and visible proof. Though the royal tern is no canary and it lives by the ocean instead of in a coal mine, it is one of the seabird species on the front lines responding to global environmental change. In other words, the royal is more than an arbiter of sartorial taste.

In my speck of range that intersects with that of the royal tern, I will enjoy observing these birds as long as they choose to stay. Somehow, it always happens that one morning, just as I discovered they are here, I discover they’ve gone. Then after nine or 10 months, they just as abruptly return from points south to again adorn our seashore.