The alligator and its allies

by A. M. Reese

Fig. 7. A Typical ’gator “Hole.”

Only a few yards across, and surrounded by a dense growth of vegetation. On the far side is seen an opening in the surrounding grass and flags where the ground is worn smooth by the alligator in crawling out of the hole. Under the bank, probably near the place where the alligator “pulls out,” is the deep cave into which the inhabitant of this hole quickly goes on the approach of danger. As this cave may be fifteen or twenty feet deep it is not an easy matter to get the animal out. When a female alligator inhabits such a hole, a nest may often be found within three or four yards of the water, though it is sometimes at a greater distance. Such a hole as this may be connected by narrow, winding “trails” with larger ponds, as noted under [Fig. 6]. (From a Photograph by the Author.)

While it is usually stated that the eggs are incubated by the heat of the sun, it is held by some observers that the necessary heat is derived not from the sun but from the decomposition of the vegetable matter of which the nest is composed. Possibly heat may be derived from both of these sources, but it seems likely that the conditions that are especially favorable to normal incubation are moisture and an even, though not necessarily an elevated, temperature. Moisture is certainly a necessary condition, as the porous shell allows such rapid evaporation that the egg is soon killed if allowed to dry. The inside of the nest is always damp, no matter how dry the outside may become under the scorching sun, so that this condition is fully met. The eggs of the Madagascar crocodile, according to Voeltzkow,[3] offer a marked contrast to those of the alligator. Instead of being laid in damp nests of decaying vegetation, they are laid in holes that are dug in the dry sand, and are very sensitive to moisture, the early stages, especially, being soon killed by the least dampness. A crocodile’s nest containing eggs is shown in [Figure 5]. In this species of crocodile, probably C. porosus, the nest resembles that of the Florida alligator. The photograph was taken by Mr. Rowley on the edge of a small lake on the Island of Palawan, P. I.

[3] Voeltzkow, A., “The Biology and Development of the Outer Form of the Madagascar Crocodile,” Abhandl. Senckberg. Gesell., Bd. 26, Hft. I.

The daily range of temperature in the Southern swamps is sometimes remarkably great, so that if the eggs were not protected in some way they would often pass through a range of temperature of possibly fifty degrees or more; while in the center of a great mass of damp vegetation they are probably kept at a fairly constant temperature. Unfortunately no thermometer was taken to the swamps, so that no records of the temperatures of alligator nests were obtained, but it was frequently noticed that when, at night or very early in the morning, the hand was thrust deep into the center of an alligator’s nest the vegetation felt decidedly warm, while in the middle of the day, when the surrounding air was, perhaps, fifty degrees (Fahrenheit) warmer than it was just before sunrise, the inside of the same nest felt quite cool. It is probable, then, that the conditions of temperature and moisture in the center of the nest are quite uniform. One lot of eggs that had been sent from Florida to Maryland continued to incubate in an apparently normal way when packed in a box of damp sawdust, the temperature of which was about 80 degrees Fahrenheit. Another lot of eggs continued to incubate, until several young alligators were hatched, in the ordinary incubator, at a temperature of about 95 degrees Fahrenheit.[4]

[4] Reese, A. M., “Artificial Incubation of Alligator Eggs,” Amer. Nat., March, 1901, pp. 193-195.

The fact that eggs taken directly from the oviducts of the cold-blooded alligator contain embryos of considerable size seems to indicate that no such elevation of temperature as is necessary with avian eggs is necessary with the eggs of the alligator.

Fig. 8. A Typical Alligator’s Nest, Made Chiefly of Grass.

The guide is feeling for eggs without disturbing the outside of the nest. Being made of the same material as the background, the nest does not stand out very sharply, though in nature the contrast is somewhat more marked, owing to the fact that the surrounding grass is green while the grass of which the nest is built is dead and brown. (From a Photograph by the Author.)