Amphibious Diurne (and a pale frog)

I found the treefrog egg clusters of last week with little difficulty. They had been jostled slightly out of position, probably during a wrestling match between males, or during the amorous embrace of a couple.

This embrace, known as amplexus, is visually suggestive of an activity we humans would blush at, but since frogs practice external fertilization, it simply serves to ensure that only one male's DNA is the sole contributor to the next generation's diversity.  Males develop horny pads (no pun intended) on their thumbs, and this enable them to tightly grasp the female until she lays her eggs. If this were not the case, I suspect it would be a free-for-all around a releasing female.

And they have grown!  Notice in the photo how they have become elongated little grubs.  Their yolk is clearly visible, between an obvious head and tail.  I expect them to be swimming free in another week.

Pacific treefrogs not only have multiple color morphs within a population, but Wente & Phillips (2003, 2005) found that certain individuals within a population of "fixed" morphs were capable of gradual color change within a season, while most of the others remained the same color pattern from the juvenile stage.   The color of these distinct morphs changed in response to the background brightness, not the hue, which they say makes it a seasonal adaptation, rather than one that might have evolved to help them when simply crossing from one background to another.

Last week's post showed a picture of the common classic bright green tree frog.  But today, my son Evan was mowing the lawn and just caught a gray morph before it hopped under the mower.  I have handled hundreds of Pacific tree frogs in northwestern Oregon, yet this is the first time I have ever seen this morph.

A little while later he brought in a dark green, but more normal striped pattern.  

While photographing it with the flash on, it began changing to a paler but still green form.  It maintained this coloration even when released into the pond.

(dark throat typical of actively singing males)

I wondered if this might be the variable morph mentioned by Wente and Phillips, although it seems to be a bit more rapid than what they described.

References:

• Wente & Phillips (2003).  Fixed Green and Brown Color Morphs and a Novel Color-changing Morph of the  of the Pacific Treefrog. The American Naturalist.
• Wente & Phillips (2005).  Seasonal Color Change in a Population of Pacific Treefrogs. Journal of Herpetology, Vol 39, No. 1.

Amphibious Nocturne (Symphony in F Major, 1st Movement)

I built a yard pond a few years ago.  Forty-four ninety pound bags of concrete mix, a few days to spare, a very sore back, and The Pond was on it's way.  It is still on its way -- I only work on it when I feel like it.  And the one thing I can't seem to complete in a timely fashion is installing the pump system for circulating flow.

But the frogs don't seem to mind that I have other priorities.  For the past couple of years, about 10 Northern Pacific treefrogs (Pseudacris regilla) have congregated here to carry out their annual reproductive symphony.  Treefrogs prefer still water for egg-laying, so if I do install the waterfall, they might not come back.

Pseudacris translates to "false cricket," and regilla means "regal" supposedly referring to the markings, though I am not sure which marking is considered regal.  They are a lot like crickets, only much louder.  At night the noise can be deafening, especially since it isn't far from our bedroom window.  But I like it. I know it is spring and longer days with more sun is on the way.

The males do the singing, and according to CaliforniaHerps.com, there are several main calls: diphasic or two-part calls, and monophasic calls, used when the lady frog is very close to committing.

Today, March 31, instead of beginning to prepare for the return to the classroom, I decided to begin documenting the development of their eggs.

Pacific treefrogs lay their eggs attached to pond bottom vegetation. Above are two clusters attached to a bit of straw that fell in the pond. Temporarily removing them gave me the closeup photo at right, then they were returned to the upper pool.

The pale areas are the yolk of what I think are fertilized eggs (I can't imagine that they wouldn't have been recipients of all that nocturnal passion).

It will take from 1-3 weeks for the tadpoles to hatch out, dependent on temperature. Right now it is about 12 degrees Celsius, but warmer temperatures should cause more rapid development.

Now if I can just find them again in a few days.





References:

• http://www.californiaherps.com/frogs/pages/p.regilla.html Retrieved 3/31/2012
• http://php.med.unsw.edu.au/embryology/index.php?title=Book_-_Text-Book_of_Embryology_5 Retrieved 3/31/2012
• http://www.jstor.org/discover/10.2307/1445724?uid=3739856&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=47698826453837 Retrieved 3/31/2012

Short-eared Owl at Trestle Bay

Short-eared Owl

Took a drive out to view the surf from the South Jetty of the Columbia River today.  It was windy, kind of cold, and basically birdless.  But driving back past Trestle Bay, I stopped to glass a Red-breasted Merganser drake way out in the bay.   A funny looking bush in the foreground tempted a closer look, and turned into this sweet find -- I haven't seen a Short-eared Owl out at Fort Stevens since October 21, 2005.

• Short-eared Owls are highly migratory (for owls), traveling up to 2000 km one-way. Breeding is in Canada, winter grounds tend to be the southern US, though we get them along the coast here occasionally
• They are perfectly adapted to hunting grasslands and marshy areas - tawny color, streaked breast feathers, and a hovering technique before dropping on prey.
• More information about Short-eared Owls can be found at The Owl Pages 

photos were digi-scoped w/ Olympus C5050 zoom
& Swift Audubon 8.5x44 binoculars

Short-eared Owl habitat (can you see the bird?)