Waiting Impatiently for “Spring” in SW Florida

February 25, 2015

Nature Notes by Bill Dunson

A recent family visitor asked me when Spring starts in SW FL. A cogent question which I answered by saying it depends on how you define “Spring,” by planetary motion (March 20) or by ecology, and then which natural signs you choose. Certainly based on ecology there is no single start to spring but many different ones. My primary definition of Spring based on amphibian breeding was partially fulfilled on Feb. 12 when I heard the first chorus frog calling.

In our yard at present we have mainly zebra heliconian butterflies which are long-lived and resistant to cold. Their caterpillars feed on corky stem passionvine which is abundant in our yard. The butterflies can fly on days when other lepidopterans are immobile and I noticed that this individual was sunning itself in a spot protected from the wing by holding its wings open perpendicular to the sun. This type of behavioral thermoregulation allows for activity on sunny days with cool air temperatures.

I found some Cuban tree frogs hunkered down inside a leaf of cabbage palm and they may also benefit from some solar heating on cool days. But they are mainly waiting for the summer rains which are still far away before they can breed. Night time dews provide the moisture they need in the interim. Brown anoles are abundant and active even in February and are masters of finding a sunny spot to bask. This large male was doing pushups to assert his dominance and even extended his bright dewlap which likely deters rival males and attracts females.

In the avian world migrations will soon begin for most species. I found a banded snowy plover on Palm Island that will likely be returning to the FL Panhandle to breed. It was banded in St Joseph State Park in July and the pattern of colorful “bling” on its legs identify it positively. Many snowy plovers migrate only a relatively short distance compared to the Arctic breeders such as sanderlings, red knots and turnstones that are now still common on our beaches.

Just beyond the plover I sighted a spectacular Caribbean resident the reddish egret, and by coincidence there was a rare whimbrel nearby. The whimbrel will soon be heading to the arctic. I noticed a Bonaparte’s gull which has been present in abnormally large numbers in FL this winter. It lacks the dark hood which will soon develop during the breeding season. Such periodic occurrences of northern birds may indicate unusual circumstances in their normal wintering grounds. Several years ago razorbill auks migrated south to FL and then disappeared. These atypical movements may be the result of climate change or just be caused by natural fluctuations in food supply.

Overhead I saw an adult bald eagle which was soaring on thermal air currents. They are winter breeders in FL so their presence tells us nothing about the beginning of Spring. An adult yellow crowned night heron in our yard had a distinctive reddish eye; changes in leg color and plumes accompany the onset of breeding season. But the surest sign of the continuing winter season is the presence of large numbers of yellow-rumped warblers which are winter residents only. They will soon be winging their way to their far northern breeding territories.

So here in late February I conclude that true “Spring” is yet to come, although there are early signs that it is near.

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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