The Daily Bucket is a regular series from the Backyard Science group. Here we talk about Mother Nature in all her glory, especially the parts that live nearby. So let us know (as close as you are comfortable) where you are and what's going on around you. What's the weather like? Seen any interesting plants, bugs or critters? Are there birds at your feeders? Deer, foxes or peahens in your yard? Seen any cool rocks or geological features? Post your observations and notes here. And photos. We like lots of photos. :)Florida is well-known for its population of Alligators, which thrive throughout the state. Less well-known, though, is the Alligator's close cousin, the American Crocodile. Though widespread in Central and South America, the American Crocodile is very rare in the US, extending only to the southern tip of Florida.
The American Crocodile, Crocodylus acutus, is the largest of the four crocodile species found in the tropical areas of the Western Hemisphere, and the only one found in the US. South Florida is also the only place in the world which has both alligators and crocodiles, though they are seldom found together since Alligators prefer freshwater habitats while Crocodiles like estuarine tidal salt water, especially mangrove swamps. In appearance, Alligators have a black color and a wide snout, while Crocodiles are a greenish-gray color with darker squarish markings on their back, and have narrow snouts.
Crocodiles are much less cold-tolerant than Alligators, and this is what limits their natural range within Florida to areas south of Broward County. It also limits their size--while South American populations of American Crocodiles can reach 20 feet in length, Florida Crocs only average around 12 feet. Although human attacks have occurred in South America, in Florida Crocodiles tend to be shy and retiring, and human attacks are virtually unknown, though they occasionally take dogs or other pets. In the wild, they eat mostly fish and crabs, and occasionally shorebirds or small mammals.
Like all reptiles, American Crocodiles are ectothermic ("cold-blooded") and are dependent upon outside heat sources to maintain their body temperature. They spend most of their time basking in the sun; if they begin to get too warm, they will often sit with their jaws open to allow cooling by evaporation.
Because of their limited range, Florida Crocodiles have never been very numerous, and even before Europeans arrived there were likely not more than a few thousand of them. Crocodiles were hunted for their meat and hides, and they also lost habitat as coastal areas were developed. In the early 1970's, it was estimated that fewer than 200 of them remained, and they were one of the first animals listed under the Endangered Species Act in 1975.
American Crocodiles begin breeding in February. The males will tussle with each other to establish territories, and then mate with every adult female inside their turf. The females dig nests on sandy beaches or creek banks, lay 30-50 eggs, and cover these with large piles of vegetation, which produce heat as the plant matter rots. Crocodilians are unusual in that the gender of the youngster is not determined by genetics. Instead, eggs that encounter warmer temperatures inside the nest will produce males, and cooler spots produce females. When the eggs hatch inside the nest, the youngsters make a chirping call which prompts Mommy to dig open the nest and let them out. The hatchlings will stay together for protection for several months until they are large enough to wander off on their own. The death rate for young Crocs is very high--about half of all nests are destroyed by predators or by flooding, and over 90% of the new hatchlings are dead within a year, eaten by various predators (including large shorebirds, sharks, and adult Crocodiles). If they survive, the youngsters will reach sexual maturity in ten or twelve years. In the wild they can easily live for 75-80 years.
Today, thanks to programs to protect and expand their natural habitats, the American Crocodile has made a remarkably successful comeback--it is now estimated that between 1500 and 2000 American Crocodiles live in South Florida. and individuals are being found now in areas where they had formerly been exterminated. On at least two reported occasions, American Crocodiles have been found in Tampa Bay, far north of their normal range. It is doubtful they can survive the winter temperatures here, and these are likely animals that were illegally captured and transported.
And now it is your turn--let us know what's going on in your neck of the woods. :)