Sorry for the delay getting this post out. It was a busy week at home and at the office.
A couple weeks ago millions of wood frogs and spotted salamanders converged on pools of water in the woods for what are basically amphibian orgies. Some animals stretch their breeding season out over weeks or even months (or in rare cases such as humans, for decades), but explosive breeders like wood frogs and spotted salamanders have only a few rainy nights in early spring. Anyone who is anybody shows up all at once. There is a mad scramble for males to find females, they do their thing, and then they crawl/hop back to their wooded territories for the rest of the year, leaving behind oodles of eggs.
Those eggs, in turn, don’t take their time either. These two species breed in temporary bodies of water (a.k.a. vernal or ephemeral pools) that will be gone by summer. At that point the larvae had better be able to survive on land.
The advantage of using temporary bodies of water is that they generally don’t have fish. Although there are other predators that will dine on amphibian eggs and larvae*, such as red-spotted newts, various birds, and even the larvae of other amphibians that get there earlier (marbled salamanders in our region), that lack of fish is still a major plus.
For herpers like me these mass breeding events are the kickoff to spring, albeit in late winter. In years past I’d drive out on rainy nights in late February or early March to witness the gamete-swollen (the females in particular look like they’re about to pop with eggs) critters waddle towards their breeding pools.
At the pools themselves you can see tons of male frogs calling and then latching onto the females’ waists with a grip called amplexus. They fertilize eggs externally, so it puts the males in position to douse the eggs emerging from the female with sperm.
Salamanders fertilize internally but do the sperm transfer externally. Males deposit little packets of sperm called spermatophores on the bottom of the pool, and the females then pick those up with their cloacas. Salamander sex is thus a lot more graceful than frog sex; males and females try to coordinate in a dance that aligns the female with spermatophore at just the right moment. A few dozen (or even hundreds) of them going at it at once looks like a sinuous rave.
This year I didn’t get out, and it’s been a few since I have. Dropping everything and heading out for an unschedulable late night in the woods about an hour from home is hard to pull off with work and parenting obligations waiting the next morning, but I do scout around for what remains the morning after: the egg masses.
If there were vernal pools closer, it would be a lot easier to visit them, but I have to leave the city to do this since there are no vernal pools here anymore.
Wind the clock back a couple hundred years to when most of Philadelphia was still a mix of farmland, woods, and wetlands, and there would have been plenty. In the floodplains of our creeks you probably would have found vernal pools, which would also have been true in low-lying woods along the Delaware River. I once gave a talk about Philadelphia reptiles and amphibians at which an older attendee told me about catching spotted salamanders as a boy in a vernal pool near Cobbs Creek, a pool that is no longer there.
Not all that far away from the now-dead pool there’s another that I think should have amphibians. It forms at the base of a quarry every fall and winter. By summer it’s mostly gone. If any spotted salamanders or wood frogs were in those woods, they would happily breed in it.
Every winter I think, “What if I just gathered up a bucket of frog and salamander eggs and dropped them in that pool?” Would that be enough to restore populations of the critters in the park?
Every winter I don’t, and for a few good reasons. First, I am a rule follower by nature, and moving buckets of wild animals around (including their eggs) is definitely not legal, at least without some serious permits that I don’t have.
It also turns out to be more difficult than I had thought. When I looked it up, I discovered that amphibian eggs consume way more oxygen than I had realized, meaning that you don’t have much time (50 eggs in a gallon of water at 50 degrees have one hour of oxygen) to get them from where they were laid to the target pond, and this would necessarily consume more time (an hour drive in the middle sandwiched by short hikes between parking and pools) than it would likely take for the eggs to consume the oxygen in the water. Of course you can buy more time by cutting the volume of eggs compared to the volume of water, but I think you’d need a lot of eggs to get a population going. Remember the core population ecology truth that in a stable population every breeding female leaves behind an average of two surviving offspring. Turn that around for critters that lay dozens to hundreds of eggs each spring, and the odds aren’t great for a jar’s worth of eggs.
Reintroduction efforts are not usually easy, and the agencies that handle them save their resources for species that really need it, the ones at risk of extinction. You also have to take care not to spread illnesses from population to population along with the animals (though I can’t imagine an illness that rural amphibians upstream would have that urban amphibians downstream from them in the watershed wouldn’t have already been exposed to). Spotted salamanders and wood frogs are common throughout most of their range - indeed throughout most of Pennsylvania - so I’m pretty sure no one is going through all the effort simply to restore them to marginal habitat because the local humans might like having them around.
But maybe that’s enough of a reason. Another way to put it is that we deserve access to our native, natural suite of species, amphibians included, even if we live in a city. We do this kind of thing for plants all the time; we plant seeds or plugs of native species that are generally common but locally scarce in the city. It doesn’t benefit them as a species, but it benefits us and arguably the rest of the ecosystem. I think giving our amphibians a shot might be worth it.
*I’d rather use the less-technical term “tadpole,” that usually refers to tailed, legless larvae of frogs and toads but it usually isn’t taken to include salamander larvae, which have legs from the get-go.