When we put in our pond (50x 75 ft) several years ago, we had lots of
frogs coming to it for two years.  The sound was delightfully loud on
summer nights.  Now we don't have any.  What happened to them?  We
have seen some black snakes in the pond.  There's also a bull frog
left.  Could they be the culprits? M. Shaw

the dingo ate your frogs

Or not...
http://www.ecokidsonline.com/pub/eco_info/topics/frogs/intro/images/frog_ufo.gif

Is that what they are teaching the kids these days?

Hmmm, something about a big frog in a small pond.  Maybe the little
squeakers found a smaller pond where they  - or their chief -  could
be the big frog.

why do you comment if you don't know the answer??  There are frogs
that will eat other frogs and so do most snakes you must also remember
that the frogs don't always stay when introduced to an environment.
Some have hopped on, some eaten and some maybe have died. Please
remember survival of the fittest.

Global amphibian population declines are still somewhat of a mystery
to scientists. Although we have identified several factors that will
increase mortality and decrease reproduction, we have yet to identify
which of these are currently exerting the strongest influence on
global populations. Moreover, multiple causes can interact at multiple
scales, complicating the matter even further. In short, depending on
your location, your culprit could be anything ranging from a random
localised phenomenon (e.g. a neighbours new cat may have eaten them)
to a regional exotic species invasion (which bullfrogs are in many
regions) to a global phenomenon such as climate change (which may
disrupt mating cycles and introduce harsher weather conditions that
stress susceptible populations) or ozone depletion (UVB radiation has
been demonstrated to trigger deformities in developing embryos when
eggs are near the surface of the water body). Of course, the true
culprit is probably the interactions between several of these and
other factors. If you really miss the frogs, try introducing a few
individuals from a nearby pond or lake (do not introduce store-bought
pets- you don?t want to risk a major dieoff in your pond by
introducing individuals with new biological contaminants or be
responsible for introducing yet another invasive exotic species). For
more information, Alford and Richards provide a rather thorough
examination of some of the factors (and the effects of their
interactions) responsible for global amphibian declines in their 1999
paper in Annual Review of Ecology and Systematics
(http://www.jstor.org/view/00664162/ap010002/01a00060/0).

Regards,
	-Calico Jack