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.

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.