#SciFri: How climate change is affecting amphibian phenology

It is no surprise to many to find out that I have a high affinity for amphibians, I have been studying them in an academic setting since 2012 but my love for them spans much further back than that. During my life time I have noticed a few patterns which are quite alarming and have recently caught the eye of the scientific community. Amphibians use a number of environmental cues to time their breeding cycle, these include such things as day length, the lunar cycle and night time temperature. As I’m sure you’ve noticed, this year so far it has been very mild – the leaves on the trees outside my office have only just turned yellow this week and started to fall – something that should have happened a month or so ago. These changes in phenology are largely driven by changes in climate, changes that could have drastic consequences for our wildlife.

Common frogs (Rana temporaria) at a breeding pond in Cambridge surrounded by spawn

Mild autumns/winters pose a risk to both reptiles and amphibians as its the time of yeah when they are usually undergoing brumation (a hibernation like state) when they conserve energy and get ready for the coming breeding season. If for some reason that this hibernation is disrupted due to the weather, then it could have detrimental effects on both individuals and population alike. Wildlife doesn’t have a calendar or a watch and so they rely on the environment to provide the cues they need to tell them what time of year it is (for more information on biological clocks/rhythms please visit Curious clocks). With the mild winters we’ve been having in recent years amphibians have been appearing back at their breeding ponds earlier and earlier, my own personal experience from Cambridgeshire is that the 14th February is a prime date to start looking for amphibians (to the disdain of many a girlfriend). This is shifting and frogs and toads tend to turn up and breed first with newts appearing later to do the same, but this isn’t always the case.

I’m sure that many of you will be familiar with the cold weather we had this Spring due to the ‘Beast from the East’ – before this weather front many frogs came out to breed and unfortunately presided in the cold. The cold temperatures caused a number of garden ponds (and other larger bodies of water to freeze) meaning that any wildlife in them would quickly use up the oxygen held in the water or freeze solid. This is known as ‘winterkill’ and this year there was a spike in reports across the country, I responded to a few to find previously productive ponds reduced to a what can only be described as a dead-frog soup. Winterkill isn’t the only threat, if amphibians (or reptiles) don’t enter an aestivation state then they risk using up value energy reserves that will be hard to replace due to both a lack of prey and low metabolism. This of course only applies to a temperate climate and has been observed in both Europe and the US.

There is some winners though, newts tend to arrive to ponds after frogs have spawned, giving them plenty of opportunity to consume either their eggs or their tadpoles. Newts then lay their eggs and feed whilst the going is good before leaving the ponds to live a terrestrial life for the rest of the year (mostly). However, if amphibians (such as frogs) lay their eggs and retreat to a safe distance before cold snaps there is the risk of their spawn perishing in the cold. Spawn is somewhat frost-resistant for short durations, but it has limits. Newts and toads don’t have this issue as they lay their spawn below the surface of the water and unless the pond freezes solid, it should be fine.  As crazy at it sounds, some amphibians don’t wait until Spring to breed if the weather is mild enough. I’ve seen frogspawn in Cambridge in December but reports from the south-west and Ireland report is as early as mid-November.

A male smooth newt (Lissotrion vulgaris) consuming frogspawn at a pond in Cambridge

A change in amphibian breeding phenology is certainly something that everyone should be aware of, hopefully due to their obvious flexibility that both amphibians and reptiles will be able to adapt to climate change. For the most part, a changing climate with milder, wetter winters may lead to population declines in amphibian and reptile species across the temperate world. A number of studies have already looked at the effects across a number of species but more long-term studies are needed for both a knowledge side of things but also for potential mitigation.

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