Summer World_ A Season of Bounty - Bernd Heinrich [14]
Fig. 9. Male wood frog with neck lock on a female, who will swim with him to the spawning place.
It is almost impossible for one male to pry another off, and the males stay attached to their prospective mates for hours and potentially days (if one were to remove them from the pool). A female, even if she is dead, can have a dozen suitors attached to her on various appendages and in various positions. Half a dozen or more males may simultaneously try to lock onto a single live female, but only one of them will achieve the one sure position—a solid neck lock as he perches on her back. He won’t let go, and the resulting twosome may look like a two-headed, four-legged mutation; at least one such coupled pair was claimed as such, by a woman who excitedly brought it to my office.
The female then takes the locked-on male for a ride. She swims to the one spot in the pool where all the other frogs will also deposit their eggs. He will not release her until she has laid her walnut-size lump of several hundred eggs, and he then releases his sperm onto them and also releases his grip around her neck. She will then almost immediately leave the pool. This is probably the last time in their lives that either will ever have contact with open water again, except for those rare and lucky individuals who manage to survive another year. If they do survive, then they unerringly return to the same pool they left the year before. Much has been found out and there is still much to ponder about these fascinating animals, but several questions jumped into my mind.
Where and Why Do Wood Frogs “Nest” Communally?
Much about the unique behavior of wood frogs, whose breeding and larval life are strictly dependent on water, can probably be understood from the standpoint of a highly evolved lifestyle that is suited for breeding in temporary pools—those that are subject to drying out early in the summer. As many as twenty frogs spawned in a tire-track depression behind our house, and this depression usually dried out even before the eggs hatched. However, the frogs have no prescience of how long the water in any pool will last. Thousands of them breed in a beaver pond along our road. A year after the beavers made it, this pond was populated by frogs. On the other hand, another beaver pond near our house has never attracted a wood frog chorus in the twenty-five years that I have been watching and listening. It is, however, an ancient (i.e., “permanent”) pond, one that is populated not only by all the other local frog species, but—more significantly for the wood frogs—also by minnows, sunfish, and catfish. Wood frogs even breed every year in a washtub-size pool formed in a rock depression on a hill at my camp in Maine. This particular pool is not subject to dropping groundwater levels, and I’ve never seen it dry out, but fish have never reached it. In short, wood frogs avoid breeding in water that contains fish; and the smaller the pool, the more likely it is to dry out at some time during the summer and therefore to be fishless. Pool size, permanence, and impermanence, as such, make no difference. Apparently, adult wood frogs have an aversion to fish, and for good reason. Wood frog tadpoles have the bad habit (relative to other frog tadpoles) of swimming around conspicuously near the water surface and feeding there on algae, rather than hiding on the bottom like most other tadpoles. I released a handful of wood frog tadpoles into an