Crocodilian images which reveal fascinating stories told from a visual perspective.
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The Mating Game
Crocodilians only mate at certain times of year, within a two to three month period. During this time, however, they expend a lot of time communicating with each other, defending territories, attracting or searching for mating partners, and undertaking courtship. Adult males in particular can become extremely aggressive towards other males. This aggression does not always lead to conflict, and males spend a lot of time communicating with each other. Dominant animals raise their backs out of the water to increase their visibility, which is normally enough to dissuade potential rivals. If this doesn't work, several other signals are sent: tail waving, jaw opening, geysering, head lifting, musk gland secretions, vocalisations, and infrasonic pulses which travel through the ground or water. Watching two males signalling and moving around each other is like watching a carefully choreographed ballet. The only difference is, the ballet occasionally turns violent. If the best signals don't work, males will attack each other vigorously, often slamming their heads into their rivals' bodies.
In stark contrast to all this fighting, courtship between males and females surprises many people with its tenderness. Males court females by touch, rubbing their jaws across their partner, blowing bubbles underneath their bodies, using chemical perfumes, and rumbling softly. Eventually, the female signals her willigness to mate by lifting her head high (and often vocalising). The male swims over the female from behind and then pushes her down into the water. Often mating takes place completely underwater and is impossible to see, but rarely we get a glimpse of the actual mating act.
This month's Pic of the Month comes from John White, showing two Cuban crocodiles (Crocodylus rhombifer) at the National Zoo in Washington D.C. The clear water in their enclosure enables copulation to be seen very clearly. The male hangs alongside the female in the water, bending his tail under hers so their vents are aligned. Male crocodilians do not have "hemipenes" like most othe reptiles, but a single copulatory organ. This penis has a deep groove running along its length, down which semen travel to inseminate the female. Copulation can last for several minutes, and fortunately the male can stay underwater for some considerable time if necessary! He may mate with the female several times during the breeding season, fertilizing her eggs only in the short period after she has ovulated (i.e. when the eggs pass into the oviducts from the ovaries, before the shell forms around them). Thus development of a new clutch of baby crocodiles is set in motion.
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