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Marco Island’s population – on land – doubles during the winter season. Under the surface of the surrounding waters, though, the local population of bottlenose dolphins is year-round, with several hundred, in distinct groups, living, feeding – and breeding.

The breeding activities of dolphins, and the new babies born, were the subject of a talk Monday evening by naturalist Bob McConville at the Rose Historical Auditorium. As well as being a Florida Master Naturalist, McConville is a nature photographer, the author of books on Southwest Florida’s ecology, and part owner and tour operator aboard the “Dolphin Explorer,” offering boat excursions that get visitors up close to marine mammals and even let them participate in research.

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His work as a tour guide informs his speaking style, as on Monday he made sure to intersperse the biological information about dolphins with jokes and schtick to keep the audience laughing and engaged. Along with dolphins, he touched briefly on the bird life around the island, showing photos of species including pelicans, snowy egrets, red shouldered hawks, peregrine falcons, oyster catchers, and “snowbirds” who were illustrated with photos of Hawaiian shirt-clad, camera-toting specimens.

“Don’t feed them,” he warned, “they’ll follow you home.”

But the talk focused primarily on dolphins, the subject of a decade-plus long study McConville has carried out, giving him time to map out the family trees of several of the lines, with calves now being born the grandchildren of female dolphins still active in local waters. Individuals are identified primarily by striations or notches on their dorsal fins, which other dolphins rub against or nip during social interactions.

The calves nurse for up to two years, and stay very close to their mothers, so that relationship is easy to establish, but ascertaining the male parent is problematic, he said “There are no wedding rings among dolphins. The females are very promiscuous,” and will mate with several males during a given season. Unlike many species, dolphins do not pair off in long term couples relationships, but often, two males will establish a “male pair bond,” which enables them to fend off other suitors for the favors of females they are pursuing.

Dolphin mothers are protective toward their calves, who sometimes fall victim to predation by hammerhead or bull sharks. While in the oceans generally, only 30 percent of dolphins survive to their third birthday, in local waters the figure is 80 percent. After sharks, said McConville, the biggest threat to young dolphins still under their mothers’ care is male dolphins, who will sometimes grab them and hold them underwater to drown, so that the female will be available for mating activities.

Birthing season for dolphins varies widely with small differences in location, and while some authorities announced the season was done, it runs from August through October for the Marco River dolphins, a population of around 110, said McConville. The 100 dolphins in the Caxambas area give birth in spring and early summer.

Babies are born tail-first, generally in shallow water, keeping their blowhole inside the mother’s body so they don’t drown during the birthing process. Last year, reported McConville, the population gave birth to 10 babies, and nine survived. The local population is healthy and stable, he said, and hasn’t suffered overly from red tide, which did kill hundreds of dolphins in the wider Gulf coast area during previous years’ outbreaks.

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The Marco Island Historical Society, which sponsored Monday’s lecture, free to society members and $10 for non-members, has over two dozen programs lined up during the coming season. Next up is Theresa Schober speaking on “Wild, Wild South: the History of Florida’s Cattle Industry” on Tuesday, Nov. 5. For more information, contact MIHS at the Marco Island Historical Museum, 180 S. Heathwood Drive, call 239-389-6447, or go online to themihs.info.

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