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.

For Father's Day: Great Frog Dads

The Giant African Bulfrog (Pyxicephalus adspersus) made #3 on Animal Planet's Top 10 Animal Dads! Like some of our local frog species, the Giant African Bulfrog lays eggs in temporary ponds - but after the eggs are laid, male frogs remain in the ponds to protect the eggs and tadpoles.

This BBC video show the bulfrog dad protecting tadpoles from predators and desiccation:

In addition to the Giant African Bulfrog, some other amphibians provide parental care for eggs and tadpoles.  For example, male midwife toads (genus Alytes) carry fertilized eggs on their backs until they are ready to hatch. A good summary of parental care in anurans (frogs and toads) can be found here.

In case you are wondering, none of the anurans that breed in Duluth exhibit parental care.  However, female Eastern red-backed salamanders (Plethodon cinereus) guard their eggs until they hatch.  More information about this entirely terrestrial salamander can be found at the University of Michigan Museum of Zoology's Animal Diversity Web.

Distracted by non-frog signs of summer

It is easy to get distracted by the non-amphibian phenology, such as the flowers blooming around Duluth.  The lilacs in my yard are just starting to open:

In addition to these signs of spring (and summer!), frog activity continues.  The early spring breeders have growing tadpoles that will begin to develop hind limbs soon, while the late season species have not yet started to breed.  Mid-season breeders, such as the gray treefrog, are just finishing up calling. Gray treefrogs generally call from trees over and around wetlands (and thus are often mistaken for birds), and lay their eggs in seasonal and temporary wetlands.

gray treefrog in a wetland - notice the large toe pads

Gray treefrogs change in color from bright green to mottled gray in seconds to aid with camouflage. The below frog does not match it's surrounding in color, but is still hard to detect!

just grass

is that a frog?

gray treefrog in grass clump in wetland

A few years ago, I was fortunate to find many gray treefrogs while sampling a wetland with students.  Check out the variation in color.

gray treefrogs can change from bright green to dark mottled gray

The Eastern gray tree frog (Hyla versicolor) and the Cope's gray tree frog (Hyla chrysoscelis) are both found in this region and there is not a reliable way to tell these species apart in the hand.  The only way to distinguish these species is the number of chromosomes (Eastern gray treefrog is tetraploid while Cope's gray treefrog is diploid) or the males' calls (see below videos).  Additionally, there are may be habitat preferences and behavior that distinguish these species - I look forward to future research revealing the similarities and differences between the Eastern gray treefrog and Cope's gray treefrog.

Toads and Friends

Before this foggy thunderstorm rolled into Duluth, the amphibians were very busy.  In the last two weeks, three species have begun calling: Northern leopard frog (Rana pipiens), American toad (Bufo americanus), and gray tree frog (Hyla versicolor).

Around Boulder Lake, the Northern leopard frogs started and finished calling in just four days. This species is considered an early breeding species, but tends to breed at few weeks after wood frogs in the northern reaches of Minnesota.

Adult Northern leopard frog

I only heard this species calling for one day and found eggs on the same day. We got a frost the night after I found these eggs, which seems to have damaged more than 50% of the embryos.  Each leopard frog lays up to 3,000 eggs, so there were plenty of tadpoles hatching late last week despite this frost damage.  

Amercian toad calling 

American toads began breeding late last week.
One day after hearing this species calling for the first time, American toads were calling in a full chorus and multiple pairs were laying eggs in the backwaters off of Boulder Lake.




Listen to this chorus of American toads heard last Friday May 20th:

Multiple pairs of American toads in amplexus (and some males)

American toads lay long double strings of eggs, which hatch in 2-8 days depending on water temperature.

Pair of american toads in amplexus (male on back of female)
-notice the strings of eggs under the pair-

American toad eggs - freshly laid

Gray treefrogs started calling last week, and Western chorus frogs and spring peepers continued to call.

Although spring peepers were in full chorus in Duluth city limits in late April, in some locations this species did not start calling until last week. A full chorus of spring peepers is so loud that it makes my ears ring after standing by the wetland for five minutes.

Spring peeper

Listen to this chorus of spring peepers heard last Wednesday May 18th:

Developing Wood Frog Eggs

Finally, the wood frog eggs are starting to develop into tadpole shaped embryos.  I expect these eggs to hatch next week.

Fresh wood frog eggs are very easy to spot......

wood frog eggs masses - freshly laid

....but are harder to find as they develop. Egg masses lose their distinct shape and symbiotic algae turns them greenish, making the eggs blend in with the general pond vegetation and organic matter.

wood frog egg masses - newly hatched

close up of wood frog egg mass - freshly laid

Due to the transparent gelatin-like coating, embryo development can be followed from fertilization through hatch. The embryo (black ball at center of egg in left photo) begins to elongate and grow into tadpoles. The eggs hatch before the tadpoles are able to swim, so they remain in or on the egg masses for several days (see below).

close up of newly hatched wood frog tadpoles

Wood frog eggs hatch 4 to 28 days after being laid.  Embryonic development is temperature dependent, so timing of hatch varies with weather conditions. 

Frozen Wetlands

Monday morning update: the wetlands appear to have iced over last night.  I will be checking the wood frog eggs later today, hopefully they were spared from freezing.

Monday afternoon update:  the wood frog eggs in the wetlands I regularly check seem to have survived the cold weekend and some have even started to develop.

Confused About the Season

Although I am a little confused about the season, I cannot imagine what it would be like to be a frog during the recent winter-to-spring-to-winter flips. By the end of last week three species were calling - chorus frogs, spring peepers, and wood frogs. On Friday afternoon, I saw (and heard) around 100 wood frogs calling in a pond in Hartley Park, along with many egg masses and several females.

Four male wood frogs calling in vicinity of multiple egg masses, with a pair in amplexus in the middle

male before calling

Wood frogs are fun to watch calling.

 

swimming while calling

after calling

female wood frog on edge of wetland

The colder weather this weekend has quieted the calling, but these three species should be out again as it warms up over the week.

Why it would be hard to be a frog in this weather:
Male wood frogs must be almost out of energy after 3 weeks of starting and stopping calling. These early season breeders emerge from winter hibernation soon after the snow melts and the males begin calling almost immediately, fueled by fat storage from last fall. Calling is the most demanding activity that many male frogs will ever do; in some species, calling is 10 times more metabolically demanding than moving at maximum speed. The trunk muscles, which power calling, can be 12% of body mass in a male frog, while only 3% in a female. Not only is calling a lot of work, males of early breeding species expend all that energy before spending much (or any) time foraging for food.

I learned most of this from a great (but heavy) book:
The Ecology and Behavior of Amphibians - Kentwood D. Wells

Spring Peepers

Spring peepers (Pseudacris crucifer) started calling today in Duluth.  Although spring peepers have a loud voice, these frogs are pretty small at full size.  

adult spring peeper in hand for size reference

adult spring peeper in wetland

 spring peeper - identifying marks: X on back, toe pads, small size, light color

These frogs are great at hiding - I rarely spot them in wetlands, but there are a lot of videos up on UTube.

 It is exciting to hear a full chorus of spring peepers - I haven't heard this large a group calling in the city since I first moved to Duluth. About 10 years ago the spring peeper population seemed to be greatly reduced (based on calling activity), likely due to a cold winter with little snow cover. Spring peeper overwinter in leaf litter or bark, but are not as freeze-tolerant as wood frogs.

I heard spring peepers in northern Wisconsin as well, but today was my first visit to that area.

Wood Frogs!

The wood frogs are calling in Duluth - Yesterday, I heard wood frogs calling in small wetlands in and near Hartley Park.  Most of the wood frog activity was in ponds that are shallow and have solar exposure.  These ponds are likely warmer than deeper or completely shaded wetlands. 

I even found wood frog eggs in two ponds.  Wood frogs are probably still in the midst of breeding as many of the ponds I visited yesterday did not have eggs. 

Wood frogs are explosive communal breeders, meaning that breeding occurs over just a few days and all (or most) of the eggs are laid in one location in a pond.  Eggs are generally attached to submerged vegetation near the water surface in open areas of a pond that are fairly shallow (1-2 feet).  When first laid, wood frog eggs are very easy to spot.

30+ wood frog egg masses (each female lays one egg mass consisting of hundreds of eggs)

Up close, it is easy to see the embryos through the clear protective gelatin-like layers.  This allows us to track development before the eggs hatch, which occurs in 4 to 28 days depending on conditions.

recently laid wood frog eggs masses

  ***Note: If you find wood frog eggs, please leave them undisturbed in the water. 

Still waiting for spring

I have not received any new reports of frogs calling in the Duluth area since Thursday, when the temperatures dropped and then a snowstorm blew in.  The birds have continued to sing, so I don't doubt that spring is truly here.  However, this weather has probably slowed the frogs down.  I don't expect any more frog activity until it warms up again, probably Thursday based on the current weather predictions.

Wood frogs (Rana sylvatica) are the first to start calling around Duluth.  The wood frog call is usually described as 'quark-quark-quark' or duck-like. Wood frogs are easily recognizable by a dark mask and white lip line.  In overall color they range from light to dark brown and sometimes are pink or reddish. 

wood frog

Within a few days, wood frogs are joined by Western Chorus Frogs (Pseudacris triseriata) and Spring Peepers (Psedacris crucifer). Both of these frogs are very small, reaching only 1 inch or 1.5 inches as adults, but make very LOUD calls. Chorus frogs sound like running your thumb over a comb and spring peepers make a really loud 'peep' over and over. Chorus frogs range in color from tan to brown to green and can be recognized by the strips on their back. Spring peepers are generally light tan with a slightly darker brown X on their back. 

chorus frog

spring peeper

To see when frogs begin to call across North America see the map at Journey North Spring 2011 - First Frogs

Next week I'll give some tips on identifying wood frog eggs (along with photos).

Waiting for Wood Frog Calls.....

Reports have come in of wood frogs (Rana sylvatica) calling south of Duluth (around Solon Springs, WI) AND north of Duluth.  So now I am waiting for them to start calling here!

One wood frog sounds like 'quark-quark-quark' and a full chorus of wood frogs make a huge racket.

Listen to this chorus of wood frogs heard about this time two years ago:


Wood frogs will call during the day as well as evening and night.  Listen for them on your next walk through the woods or local parks- pretty much anywhere that there are small to medium wetlands.

Spring is Finally Here!

That was the talk of the neighborhood this morning as we left for work in 50 degree temperatures.  Looks like tomorrow will be spring again, but the following few days may take us back to late winter.

It has only been 4 days since I visited the frozen wetlands, but I will head out again tomorrow to see if they have opened up yet.  If the vernal pools are open, we can expect the wood frogs to be calling and laying eggs in about a week!

In case you were wondering what these amazing northern frogs might be up to right now - they are probably in the process of thawing out.  Yes, wood frogs are the famous frozen frogs!  Most amphibians find more suitable habitat for winter hibernation, such as a sandy hole below frostline or the muddy bottom of a larger lake, but wood frogs spend the winter frozen in the leaf litter.

This NOVA segment is a great intro to frozen frogs

(link to higher quality video)

You can learn more at: Frozen Frog: Expert Q & A (Jon Costanzo)

Is it spring yet?

Spring comes slow to northern Minnesota - this year it seems exceptionally slow, perhaps due to the super early spring of 2010.  Although the robins and cardinals are singing in my yard, we will be waiting a few more weeks before the frogs start to call.

I visited some ponds located within city limits today - still frozen and snow covered (see below).

Quite a difference from this time last year, when the ponds were open and the wood frogs had already laid their eggs! On April 7, 2010 this same location looked something like this:

While we wait for the ponds and lakes to open up, all we can do is practice our amphibian ID skills.  The first frog to call and breed in this region is the wood frog (Rana sylvatica). I recommend the Online ID Guide from Northern Prairie Wildlife Research Center for great pictures and maps, and the Amphibians of Reptiles of Minnesota for detailed descriptions and calls.