Frog Blog Week 7 – Disappearing Tadpoles
Typical April weather for England has continued over the last seven days or so, with lots and lots of showers interrupted by occasional sunny intervals. As the sun is climbing quite high in the sky at the moment heading for the Summer solstice just 7 weeks away, when the sun does shine, it is very warm, with temperatures around the pond area being recorded as high as 20 degrees Celsius.
There has been lots of activity in the pond this week, particularly amongst the invertebrate residents, snail eggs (small blobs of jelly attached to pond weeds), have been found and relatively large numbers of pond snails, including rams-horns (those that survive bird attacks – see Frog Blog week 6) have been seen. Everything Dinosaur team members observing the pond have counted at least two water boatmen that have hatched out. Undoubtedly more will be observed over the coming weeks. A careful study of the shallows reveals that quite large numbers of damsel fly nymphs can be seen.
These armoured invertebrate predators look quite prehistoric, perhaps resembling ancient Eurypterids, the savage water scorpions that dominated the Palaeozoic seas. Given the opportunity they would certainly feed on the tadpoles, as indeed would the water boatmen.
Perhaps as a result of this increased predator activity the tadpoles have all but disappeared from the pond. Over the last five days or so the number of tadpoles observed by team members has fallen dramatically. A week ago, over a ten minute period nearly 100 tadpoles were counted, now no more than 6 or 7 are seen over the same time interval.
Predation of the Tadpoles
We suspect that many of the tadpoles will get eaten, only a very few will survive to escape the pond as miniature frogs, but we did not expect to see so few only after about 14 days after hatching. Having considered this carefully we have concluded that the majority of the tadpoles are still fine, however, their survival strategy freed from the protective jelly that surrounded the developing embryo is to hide amongst the pond weed and algae, this may be why so very few can be seen by observers.
In the past, when tadpoles have been kept, these animals have always been in tanks, so it has always been easy to watch them. In the natural pond, with so much more cover it is likely that the number of tadpoles is still quite high, but we just cannot see them anymore.
We will keep up our observations to see if we can spot more of them as they grow bigger.
Two frogs have been seen in the pond over the last few days, the smaller male frog has been joined by a larger one – at least they seem to be enjoying the rain.