The Island of Florida

PUBLIC DOMAIN
About this time of year, a lot of people start to think about Florida. I have always wondered why people who spend their winters in warmer climes are called “snowbirds,” which is the nickname for dark-eyed juncos. Juncos migrate a few hundred kilometers or less and never make it as far south as Florida. Regardless, this human flock begins leaving around Thanksgiving and most of them are down in the American subtropics by the New Year.

For about a century member of my family have been drawn to Florida. My Quebecois great-great-grandmother and her third husband moved to Florida in the 1920s and built a beachfront motel with the help of her son, my great-grandfather, who was a Hartford, Conn. carpenter looking for work in the winter. In the 1970s my father’s father and stepmother retired to the Atlantic coast of the Sunshine State and lived there happily until my pale French-Canadian grandfather succumbed to skin cancer.

The peninsula of Florida extends southward from the continent from 30.5°N to 24.5°N, with the Florida Keys at the same latitude of the southern tip of Eleuthera in the Bahamas. In fact, geologically Florida is similar to the Bahamas: both are flat, limestone platforms created by carbonate-shell producing animals growing in a shallow sun-lit sea starting ~55 million years ago (mya). Florida remained submerged until between 25 and 30 mya, when sea level dropped. It has been above and below the waves repeatedly since then, accumulating sediments when there is water over it and being eroded when it is subaerial. Today the platform extends underwater 250 kilometers to the west, but during the last Ice Age, most of this was exposed and covered by a savanna, similar to what we see in East Africa today.

The peninsula is home to several bird species that are found nowhere else in the eastern United States. These populations became stranded there as sea level rose after the end of the last Ice Age (~20,000 years ago) and the open country between the Atlantic coast and the continental interior was displaced by forest across what are now the southern states and the watery Gulf of Mexico.

One of the more visible open-country birds isolated in Florida is the burrowing owl (Athene cunicularia). The main body of the North American population breeds from central Mexico north to the prairie provinces of Canada and in the winter is found as far east along the Gulf Coast as the “prairies” of southwestern Louisiana. The Florida population appears to be the northern member of an eastern group of

populations that includes Andros Island in the Bahamas, Cuba, Haiti, Aruba and part of northern South America between Colombia and Surinam.

It is more visible than most owls because it is active day and night and lives in small groups, sometimes in suburban backyards. Historically, some of these colonies were large. In the 1930s Arthur Cleveland Bent described a Florida colony that was 3 miles long and included several hundred pairs of owls. Its natural habitat is open, treeless places with low sparse vegetation, but it has adapted to live in cemeteries, fairgrounds, airports, highway medians, and other open areas with little human foot traffic for much of the year.

In the western populations the owls rely on animals like prairie dogs to excavate burrows, and the shrinking populations of such animals due to incursions by agriculture have consequently let to declines in owl populations. In the sandy soils of Florida, however, the owls are able to dig their own burrows.

Like most owls their plumage is a mottled brown and white. They have bright white throats like many owl species and bright lemon-yellow eyes. The Florida population is darker overall with brown speckling under the wings where the western birds are an uninterrupted buffy.

A. cunicularis has not differentiated into a different species but only into subspecies, with Florida having its own, distinct from the Caribbean populations. The Florida scrub-jay, however, is judged to be a separate species (Aphelocoma coerulescens) from its western counterpart. The geographic separation is greater, with the western scrub-jays reaching only central Texas. And while western burrowing owls are migratory and wander widely, all scrub-jays are resident year-round. In fact they are among the most sedentary of birds, rarely moving more than a few kilometers from their birthplace, and they may live for 10 years. It is the only bird species entirely confined to Florida.

This crestless jay is blue on the wings and tail but has a brownish gray back. In the Florida birds the plumage of the back is a pale gray, while out west it is brownish on the coastal birds and gray-blue in the interior ones. The Florida population has blue cheeks, but the cheeks are dark gray on western birds. And while the westerners have blue foreheads, those of the Floridians are white.

According to birdsoftheworld.org, “This jay lives only in oak scrub, a fire-dominated shrub community unique to Florida and found only on well-drained sandy soils. Acceptable habitat occurs as isolated patches on sandy deposits, surrounded by vast expanses of pine woodlands, hammocks, and grasslands that are not used. The Florida oak scrub, a rare and relict habitat, has been converted throughout the twentieth century into citrus groves, improved pastures, and housing developments, with a concomitant decrease in this jay. In 1987 the U.S. Fish and Wildlife Service listed the species as Threatened.”

The cave swallow is found in Central Texas and the Caribbean, with a small population at the southern tip of Florida. Painted buntings range from Mississippi westward, but there is an isolated population along the east coast from Florida to North Carolina. The reddish egret is not found between south Florida and Louisiana. The white-tailed kite lives on the west coast, in Texas and central Mexico … and south Florida.

These so-called relict populations are evidence of the geologic past, right here in the present.