Monday, March 22, 2010

Woodland Pool - early spring

Our first significant rain of the spring occurred during the weekend of March 13-14.  During that period of time, many Spring peepers, Wood frogs, and  various species of salamanders emerged from their terrestrial hibernacula and migrated to ponds, wetlands, and woodland pools.  It is in these aquatic habitats where most adult amphibians lay their eggs and their offspring begin the first half of their lives.

Here at the sanctuary, our 3-acre pond (Bechtel Lake) is a great place to hear the peeping chorus of Spring peepers.  Along the north end of the pond, hidden amoung the phragmites, these thumbnail-sized tree frogs fill the air with their incredibly loud voices.  Listening closely through the din, you may hear the low, stuttering croaks of male Pickerel frogs hoping to attract a female.  Later this spring, toads, Green frogs, and Bullfrogs will be making their voices heard.

On top of a hill, east of Bechtel Lake, is a large woodland pool.  This vernal, or temporary, pool is home to a whole host of other organisms not usually found in the other bodies of water.  The temporary nature of this aquatic habitat excludes the presence of fish and creates an unusual refuge for a number of frogs, salamanders, and a whole host of invertebrates.

During the past week, we finally got a chance to hike up the hill and explore the pool for early spring residents.  The photos below illustrate a few of the highlights of our evening.

A male and female Wood frog in amplexus

Wood frogs were in full breeding behavior that evening.  Upon approaching the pool, we could hear the distinctive "quacking" call of the males.  Most of the males were busy calling and attempting to find a female to mate with, but we did find a few pairs that had already "paired up".  Basically, the male seeks out a female and latches onto her back and holds tightly to her with his muscular forelegs.  He rides around on her back defending her from other competing males and stays with her until she finally lays her eggs.  His job is to fertilize the eggs simultaneously as she lays them.

Two Wood frog egg masses attached to Catbriar

Spotted salamander - approx. 6" long

While searching through the pool we managed to find 4 Spotted salamanders.  The two we were able to scoop up in the net were males.  The two others were likely males as well.  Males migrate to these woodland pools first to deposit spermatophores (sperm packets) on the bottom of the pools.  The females migrate to the pools later to seek out the spermatophores and lay their large masses of eggs.  There were no egg masses in the pool that evening, so its likely there were no females in the pool just yet.

Marbled salamander larva and Fingernail clam

Another species of salamander had layed its eggs last fall, and now the young larvae were already swimming about the pool.  This Marbled salamander larva is quite small, but it will have a big advantage over the currently unhatched (and unlayed) Spotted salamanders living in the same pool.  It will be larger and capable of eating other salamander larvae and tadpoles that will hatch in the pool.  For purposes of scale, the Fingernail clam in the photo is about the size of a #2 pencil eraser.

Fairy shrimp

Fairy shrimp are one of the most incredible creatures of these woodland pools.  These small invertebrates (0.5 - 1.5" long) slowly swim upside-down in woodland pools filtering and eating tiny particles from the water.  They are excellent indicators of true woodland (vernal) pools because they will only be present in pools that have dried up during the previous year.  Their eggs are only viable and capable of hatching after being subjected to a period of drying out.  If the pool doesn't dry up during the previous year, the shrimp are not likely to be present.  This indicator species is indicative of the pool's overall heath as well.  Many folks miss the Fairy shrimp because they come and go rather quickly in the early spring.

Diving beetle

One final creature of interest was this diving beetle we found swimming through the pool.  The water temperature was very cold, which may have contributed to the lack of insect diversity at this time of the year.  Perhaps in another week we will be greeted by the usual abundance of various species of diving beetles, caddisfly larvae, backswimmers, waterboatmen, etc.

If you would like an opportunity to explore the pond and vernal pool with us this spring, please consider signing up to attend our Amphibian Night Hike during the evening of April 9th.  Please visit the Westmoreland Sanctuary website for more information about the event and how to register.

Finally, if you know of a woodland pool nearby, take some time to investigate who or what may be living or breeding there at this time of year.  And keep your eye out for migrating amphibians during spring rains over the next few weeks.  Often times they cross roads, so be aware and try not to smoosh them if at all possible.

-Adam Zorn, Naturalist


chuck banks said...

Adam: Great profile of vernal pool biology. Frogs are deafening this week.
Chuck Banks

Woodswalker said...

Your blog was featured in the networking post of this week's Nature Bog Network blog, as was mine, so I'm stopping by to visit my fellow New Yorkers. I'm so glad to learn about the Westmoreland Sanctuary since my grandkids live in Mt. Kisco and I'm always looking for nature spots to take them to.

Nice post about vernal pools. Before this week's rain up here in Saratoga County, I was worried that so many of these pools hadn't formed because our winter was so short of snow. I've heard that frogs and other critters need to return to their natal pools to breed. What happens if that pool is not there?

Westmoreland Sanctuary said...

@chuck...thanks for your kind comment. Enjoy the chorus while it lasts!

@Woodswalker...from what I understand, if a vernal pool disappears (usually from being drained or filled in), the frogs and salamanders are forced to move a much greater distance in search of another suitable water body the following year. Often this results in death during their migration due to predation, road crossings, or other human-caused hazards (lawns, curbs, pets, etc). Even worse, if the pool is gone, its likely that the rest of the surrounding habitat has been destroyed or severely degraded. That's why these important areas need the same legal protections as other types of wetlands!

BTW-I enjoyed visiting your blog as well!