Wicked Big Puddles: What an Odd Spring

The strange spring and how it impacting vernal pools and amphibians is noticed in other parts of the country: Wicked Big Puddles: What an Odd Spring

FROM WICKED BIG PUDDLES: Dry pool in Stoneham, MA, 26 March, 2012

Wood frogs still calling

Wood frog adults and eggs appear to have survived the freezing temperatures last week. This frog species is well adapted to cold (it is the only amphibian in Alaska) and has started calling again after a break during the cold weather over the last week or so.

On Friday afternoon last week there were many frogs calling in Duluth parks and backyards. In a pond in Hartley Park, the wood frogs were making a huge racket (along with one spring peeper).

Wood Frog eggs in Hartley Park (about 2 weeks old)

Some wood frogs laid eggs 2 weeks ago, and many of these eggs are developing well. The small black embryos are elongated with visible heads and tails. In some locations they have started to emerge from the gelatinous envelopes of the eggs, but are not yet free-swimming. In the egg masses that I have been following, there are also many that are not developing due to the cold temperatures or other causes.

Developing wood frog embryos (black) in egg masses turned green from symbiotic algae (notice the dead eggs, which have almost entirely white centers)

 

 

How are frogs impacted by the early spring?

The early spring could benefit or harm the frogs. We have several frog species that start calling (and breeding) as soon as the ice-melts in wetlands and small ponds.

The earliest breeder of these is the wood frog (Rana sylvatica), which sounds like quark-quark. This species emerges from hibernation as soon as the small wetlands they breed in have open water. Wood frogs can benefit from the early spring by breeding earlier, which gives their tadpoles longer time to grow over spring and summer. Bigger tadpoles turn into bigger froglets, which increases their likelihood of survival through the fall and following winter.

Adult wood frog

HOWEVER, early springs are often associated with low snow pack, which means that these small, usually temporary, ponds start the season with much lower water levels than in a typical spring. As these ponds are generally fed by snowmelt and precipitation (no, or little, connection to groundwater), the water levels at wood frog breeding time are directly tied to snowmelt, and maintaining adequate water levels for tadpoles to develop depends on spring and early summer rains. If the ponds dry up in June (even for just a few days), before the tadpoles metamorphose into frogs, the entire generation of frogs from the pond is lost.

Another impact of the early spring is the possibility of extended calling for wood frogs (who usually just call for a few days to a week) which could greatly exhaust the males as they wait for females to arrive in the ponds to lay eggs. Male frogs arrive in ponds first and beginning calling individually or in groups. Females arrive later, select a mate (based on factors we don't fully understand) and lay eggs. In an early spring, male wood frogs can start calling WEEKS before the eggs are laid - especially if the weather shifts between warm and cold several times a week. Frog calling is very energetically demanding activity, and male wood frogs complete breeding before foraging for food on the forest floor. If the warm spring weather starts and stops (as it has this year), the male wood frogs could get really worn out and deplete their energy reserves while calling on and off for multiple weeks while they wait for the weather to be consistently warm enough for the females to arrive and be ready to lay eggs.

(as posted on Ask NRRI)

Wood frog eggs - April 6, 2012

Reports of frog calls have been coming in for 2 weeks. First reports were on Friday March 23, 2012 from Hartley Park - the earliest date since I've been keeping track. Most likely these were all wood frogs.

Last week, frogs started and stopped calling a few times. Now I can say it is spring because the wood frogs have started laying eggs! I found my first wood frog eggs this afternoon, amidst a full chorus of calling wood frogs.
 

Example of wood frog eggs (freshly laid)

Lots of egg masses in one pond, but only a few in another - I expect egg laying will continue over the next few days.

Wood frogs are explosive breeders, meaning that they lay all their eggs during the same short stretch of days (usually in one central location per pond).


I will continue to follow the development of eggs and tadpoles in these and other ponds through the spring and summer.

Early Spring in Duluth!

Reports of wood frogs calling are coming in weeks earlier than last year.

All you need to do to see the early spring is look out the window and remember what it looked like last year.

Wood frog breeding habitat - April 2011

In case you need more than your own eyes:

Scenes from an Early Spring - MPR report from last week

Sign of a Healthy Lawn

I never thought about our city lawn as good frog habitat, but it must be a good location for hunting after some rain (and when the lawn is left a little longer).  This week there were two HUGE adult wood frogs hopping around in the lawn - the bigger one got away before I got to see it, but the smaller one was almost as wide as it was long. 

Seeing this frog, presumably gorging on the abundant insect life in our sunny lawn, reminded me why we don't use any chemicals on the lawn and try to limit chemical use on our property.  

Amphibians are very sensitive to chemicals released in the environment. 

Unfortunately, lawn care practices could be detrimental to the survival of urban frogs, toads, and salamanders due to the fact that homeowners use many times more pesticides per acre than applied in agricultural areas.

The most important things that you can do to protect amphibians in your yard are:

1) Choose non-chemical weed controls

2) Minimize fertilizer use

3) Minimize pesticide use

4) Provide natural habitat for foraging and corridors

More details can be found in the U.S. Fish and Wildlife Service's Homeowner's Guide to Protecting Frogs: Lawn and Garden Care or on the USFWS website.

Wood Froglets

Less than three months after the eggs were laid, young wood frogs are emerging from ponds and wetlands around Duluth.  Wood frog metamorphosis occurs fairly quickly and can be easily observed in pond edges.  

Over the last two weeks wood frogs in Hartley Park transformed from 2 inch long tadpoles into froglets about 3/4" long. 

The rainstorms that have rolled through Duluth this week likely encouraged wood frogs to emerge from the wetlands. There are many froglets hopping along the wet forest floor - watch for them on the trails and your lawn. 

Wood frog at Gosner stage 40/41. Hindlimbs are fully developed, forelimbs are about to emerge from under skin.

Wood frog at Gosner stage 42. Forelimb just emerged, full tail remains.

 

Wood frog at Gosner stage 43. Tail somewhat reduced.

Wood frog at Gosner stage 44. Tail greatly reduced.

Wood frog at Gosner stage 45. Only small tail stub remains.

Another wood frog at Gosner stage 45.

Amphibian growth and development is dependent on many factors, including temperature, availability of food, water depth, and photoperiod (the amount of daylight).  Many amphibian species can accelerate or delay larval (tadpole) development and metamorphosis based on quality of their aquatic habitat. Although most wood frogs in a pond transform into froglets at approximately the same time (calling synchronous metamorphosis), multiple stages can usually be found during a visit.

 

Wood frogs resting on a floating board.  Top at Gosner stage 44 or 45, bottom at Gosner stage 42.

*The Gosner staging system was developed for Northern Leopard Frog (Rana pipiens) to identify key points in developmental progress from embryo through metamorphosis, also used for other Ranid species such as the wood frog (Rana sylvatica). citation: Gosner KL. 1960. A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16:183-90.