Posted on: April 16th, 2015
I became smitten with toads when I spent a week at Easter in 1982 collecting them nightly, every two hours from bucket traps surrounding a small pond in mid Wales. As a student, I had the enormous good luck to work with one of the most able zoologists of his era.
Paul Gittins had been brought up in Pontypridd, studied zoology at Cambridge and then did a PhD on gibbons in (I recall) Malaysia. Returning home to the job centre in Pontypridd when unemployment was 3 million he jokingly asked whether there were any jobs for population biologists. ‘Yes’, they said , ‘the University of Wales are looking for someone to study toads in Llandrindod Wells’.
Paul joined Field Centre Director Fred Slater and for 5 years undertook some of the best natural history science on common toads ever, good basic studies of a common British species. As a student, I helped some of Paul’s fieldwork and learned to love toads and to understand something about animal population dynamics. Sadly Paul died young of multiple sclerosis, a great talent lost. But I think of Paul each spring as the toads return to our village pond.
The toads come back around the end of March. Studies have shown they’re just over a week later than when Paul Gittins was studying them. In a Polish study between the 1978 and 2002, the delay was 8 days, probably caused by milder winters and so a reduced period of hibernation.
Paul and his colleagues in mid Wales measured the population of the toads of Llandrindod Wells Lake (or Llandod Lake as we knew it). They estimated the population by mark recapture techniques as a pretty consistent 5-6000 males and around 2000 females over several years. They estimated that around 3000 males joined the population each year and about 1400 females. The difference was due to females returning to breed a year later and greater mortality.
The mid Wales studies showed that males arrive earlier than females and smaller males before larger males. In our village pond last week, I loved showing my teenage son the mating orgies of males clasping in ‘amplexus’ to the females in the desperate hope of fertilising her string of eggs. He thought this was ‘cool’ and so do I.
We looked at the horny (sorry for the pun) rough edge on the male's forearm that he uses to clasp the female. When we picked one out of the water, its grip on to my thumb was just as tight as on the poor females. The croaking that males do – one of their most endearing habits – is probably a mechanism for warding off other males and certainly when you pick a male up, he’ll chirrup away with a sound, to me, better than any canary.
Toads migrate to their ponds in ‘waves’ with males arriving up to a month before the larger females. Toads are very site-faithful, with only one in five venturing to other ponds. They appear to be able to locate their precise pond, even when they are translocated to another catchment, they probably do this by smell and perhaps (as birds) by magnetic cues. In the Llandrindod Wells Lake study, the catchment was estimated at 340 ha and this to have a density outside the breeding season of 23 toads per hectare.
Toads are pretty prodigious egg-layers and although they don’t spawn in a big blob, as frogs do, their string of eggs that they wrap around pond leaves might contain as many as 6000 eggs. This very extensive egg laying probably explains why toads go for larger ponds and frogs will happily lay their spawn in small ponds (like our garden pond) shallows and even puddles.
Toads are, sadly under assault from all sorts of quarters, from agricultural intensification, drying out, silting and neglect of ponds, climate change, diseases and water pollution.
But one of the most obvious threats is by being run over by cars. Mercifully this is thought not to be a serious threat to populations and in many cases, those kind-hearted wonders who volunteer for Wildlife Trusts and local amphibian groups can save them from being squashed through their regular nightly toad patrols.
I just like toads, they are nature's good guys.
A few references
Population Characteristics of the Common Toad (Bufo bufo) Visiting a Breeding Site in Mid-Wales S. P. Gittins, A. G. Parker and F. M. Slater Journal of Animal Ecology Vol. 49, No. 1 (Feb., 1980), pp. 161-173
Population Dynamics of the Common Toad (Bufo bufo) at a Lake in Mid-Wales S. P. Gittins Journal of Animal Ecology Vol. 52, No. 3 (Oct., 1983), pp. 981-988
Changes in the first spawning dates of common frogs and common toads in western Poland in 1978—2002 Piotr Tryjanowski, Mariusz Rybacki and Tim Sparks Annales Zoologici Fennici Vol. 40, No. 5 (2003), pp. 459-464
Assessing Landscape Connectivity with Calibrated Cost-Distance Modelling: Predicting Common Toad Distribution in a Context of Spreading Agriculture Agnès Janin, Jean-Paul Léna, Nicolas Ray, Christophe Delacourt, Pascal Allemand and Pierre Joly Journal of Applied Ecology Vol. 46, No. 4 (Aug., 2009), pp. 833-84
Amphibian Phenology and Climate Change Trevor J. C. Beebee, Andrew R. Blaustein, Terry L. Root, Joseph M. Kiesecker, Lisa K. Belden, Deanna H. Olson and David M. Green Conservation Biology Vol. 16, No. 6 (Dec., 2002), pp. 1454-1455
Long-Term United Kingdom Trends in the Breeding Phenology of the Common Frog, Rana temporaria W. Andrew Scott, David Pithart and John K. Adamson Journal of Herpetology Vol. 42, No. 1 (Mar., 2008), pp. 89-96