By Michael DeLea
What adjectives come to mind when
you hear the word crocodilian? Ancient? Monster? Man-eater? Perhaps you think
of one of the 23 species that inhabit the world today, two of which can be found
here in the United States. How about attentive parents? Crocodilians exhibit
complex social behaviors, none perhaps more interesting than those demonstrated
during reproduction. Not only do members of the order Crocodylia outclass the
remainder of their reptilian relatives, they rank among nature’s elite when it
comes to caring for their young.
Hungry Crocodile? Or attentive parent? |
As observed in many reptiles, nest
construction can be a complicated and time-consuming endeavor. For example, it
has been documented that female American Alligators (Alligator mississippiensis) will make frequent trips to the nest
site adding materials and reshaping the nest prior to egg deposition. The design
of the nest plays an even more important role when you consider the fact that
sex determination is a function of temperature in at least half of the extant
species of crocodilians.
Juvenile Alligator mississippiensis I encountered in Southwestern Florida |
During the incubation period,
crocodilians have been observed demonstrating various degrees of nest
attendance and defense. This behavior is in stark contrast to that of other noncrocodilian
reptiles that typically lay their eggs and leave the unborn young to fend for
themselves. As to be expected, it has been shown that increased attendance of a
parent leads to an increased nest success rate. In addition to maintenance, the
presence of a watchful parent is a very powerful predator deterrent. In a study
of American Alligator nest attendance, the defensive behaviors of the
alligators were broken down into a 10-step response sequence that increased in aggressiveness,
depending on the perceived threat of the intruder. Protective parents therefore
give their offspring a greater chance of survival by fending off predators such
as raccoons, bears, and even humans.
Female American Alligator in a typical defensive posture, preparing to defend her nest from intruders. |
After
what can amount to months of incubation, the eggs will begin to hatch. Even
before the newborns emerge from their shells, they begin calling out to an
adult. Upon hearing the calls emanating from the nest, the adult will approach
and begin excavating very carefully. The babies will continue to call out to
alert the adult to their location until they are unearthed. The task of the
parent is not completed once the young are freed from the nest, however. To
avoid having the nest flood due to natural conditions that affect water levels,
there is usually an expanse of land to be traversed before the newborns can
safely reach the nearest body of water. At this point, the parent will pick up
their young with their powerful jaws and transport them to the water that will
serve as the nursery.
Clutched between jaws that generate the largest bite force ever recorded for living animals (3,700 psi), this crocodile transports her young to safety. |
The
extent to which juvenile crocodilians will be cared for varies between species.
In some cases the parental care will cease shortly after transportation to the
nursery, when they are left to fend for themselves. In other cases, such as the
care demonstrated by the spectacled caiman (Caiman
crocodilus crocodilus), females occupying nearby habitats have been known
to take turns watching over each other’s offspring.
The
ancestors of today’s modern crocodilians have been traced back over 65 million
years ago. During that time they have adapted well to life on earth, outlasting
the dinosaurs and many other species. When you look at certain aspects of their
behavior, paternal care for example, it is obvious that these creatures have evolved
to be successful in an ever-changing environment and will continue to do so.
References:
Deitz, D.C. and T.C. Hines. 1980. Alligator nesting in North-Central
Florida. Copeia, 2: 348-258.
Hunt, R.H. 1987. Nest excavation and neonate transport in wild
Alligator mississippiensis. Journal
of Herpetology 21(4): 348-350.
Kushlan, J.A. and M.S. Kushlan. 1980. Function of nest
attendance in the American Alligator. Herpetologica 36(1): 27-32.
Somaweera, R. and R. Shine. 2012. Australian Freshwater Crocodiles (Crocodylus johnstoni) transport
their hatchlings to the water. Journal of Herpetology 46(3): 407-411.
I'm surprised mothers invest a lot of energy in parental care while nesting, and then pass their babies off to another mother when they enter the water. How might this "community watch" be a benefit to crocodiles?
ReplyDeleteThat is such an interesting method for sex determination. I wonder if most broods hatch as a single sex, or if the parent makes conscious alterations to the nest to have them come out close to equal. It must make it pretty easy for animal breeders to control the outcome of the offspring.
ReplyDeleteWay to paint cold-blooded crocodilians as warm and fuzzy! Do any other reptiles exhibit this degree of assistance with their young? It's interesting how parental assistance can be quite variable as an evolutionary adaptation for fitness.
ReplyDeleteSeems you've used my photo and information without credit.
ReplyDeletehttp://www.alligatorfarm.com/blog-item/crocodiles-as-parents/
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