Winter amphibians
23rd February 2010, TuesdayA visit to Dungeness to survey for amphibians at the weekend revealed surprising patches of snow still lying on the shingle. I don’t remember such a cold winter as this down on the Marsh, and this is reflected in amphibian breeding behaviour. I found great crested newt eggs in late December 2008, and have still to find any this year.
A few weeks back I speculated that early breeding by this species might lead to poor survival of the eggs, and possibly also mortality of adults trapped for prolonged periods under the ice. Since then I have read a recent paper by Griffiths, Sewell and McCrea* who have studied the survival of this species in a cluster of ponds near Canterbury over a twelve year period. Interestingly they were able to link poor annual survival of the newts to mild winters and particularly to heavy winter rainfall. They speculate that newts hibernating on land may have respiratory problems in water logged soils.
Numbers of great crested newts counted by torchlight at Dungeness and Romney Warren were lower in 2009, relative to 2008. Will this trend continues into 2010? Whilst it has been a very cold winter, it has also been very wet recently. Certainly when these amphibians return to their breeding ponds they will find them brimming full of water.
And it appears that for common frogs, at least, there is a trickle of animals back to the breeding ponds. Three males have appeared in our Northiam pond over the past week, and if the weather gets milder they are likely to be joined by more. With this species also, however, breeding is going to be later than in recent years. Our animals have tended to spawn in mid February and I suspect it will be March before we see frogspawn.
* Griffiths, R.A., Sewell, D. and McCrea, R. S. (2010) Dynamics of a declining amphibian metapopulation: Survival, dispersal and the impact of climate. Biological Conservation vol 143, (2010) pgs 485-491.