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Archives for October 2019

Autumn Advice for Amphibians & Reptiles

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As the days begin to shorten and night time temperatures fall, amphibians and reptiles will start to look for places to spend the winter. Amphibians, such as common toads, frogs and newts will seek out secluded places to spend the colder months. They will often enter gardens and find their way into piles of leaves, loose soil, areas of long grass and other dense scrub or vegetation. Amphibians will commonly enter gardens in the autumn even if there is not a pond nearby. Most species will move several hundred metres from their breeding ponds in search of suitable terrestrial habitats. Therefore, if you come across an amphibian whilst tidying up your garden in the autumn, do not be concerned.

Loose soil is ideal for common toads, frogs and newts which will bury themselves up to a depth of 30 cm beneath the surface.

By early October most of our reptile species will have entered their winter hibernation. The majority of the UKs reptile species will have favoured hibernating sites but some, particularly slow-worms, common lizards and grass snakes, will make use of piles of dead logs, leaves or compost for the winter. It is important that reptiles are not disturbed during their hibernation period since it takes them longer to recover if they have to become active.

Long grass and dense scrub is ideal for hibernating common lizards.

 Here are some actions you can take this autumn to help amphibians and reptiles in your garden:

  • Leave piles of leaves in a secluded area of your garden for amphibians, grass snakes and slow-worms to seek refuge and hibernate.
  • Avoid burning and disturbing piles of dead leaves and other vegetation – these are ideal habitat for amphibians and reptiles to spend the winter months.
  • Provide areas of loose soil which amphibians will bury into and spend the winter. Being able to bury beneath the frost zone is important for their winter survival.
  • Leave some dense long grass or shrubs in your garden for amphibians and common lizards to seek refuge.
  • Loose paving slabs and wooden boards are ideal for amphibians – leave these on top of loose soil to provide the best habitat.
  • Avoid too much tidying up of your garden – some wilder areas will provide very suitable habitats for amphibians and reptiles.
  • Try building a hibernacula: pile up logs and stones, then add soil to fill in the gaps (see below). You can even bury these into the ground and plant flowers in the soil on top. Click here to find our activity sheet on how to do this. 

Remember to visit our FAQ’s pages and our Info & Advice pages for even more information about our native species and their habitats. 

This hibernacula will be very suitable for a range of amphibian and reptile species including common frogs, toads, newts and grass snakes.

 

What our animals are doing this month… November 2019 Edition

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By November all of our amphibian species in Scotland should be overwintering as temperatures drop.  However this doesn’t mean all of our amphibians are necessarily doing the same thing.  Milder patches of winter will see amphibians become active again, but here we explore amphibian whereabouts should the cold persist….

Amphibians on land – Our frogs, toads and newts will seek out suitable areas of stable humidity and temperature safe from predators to spend the winter months.  These may be under rocks, in compost heaps, amongst piles of deadwood, amongst loose earth or old burrows, in piles of rubble and stone or under sheds and greenhouses.  There is a huge variety of places they may use but do be careful before lighting any bonfires of logs and leaves that it isn’t an amphibian’s home!

Amphibians in the water – What can be overlooked though are the amphibians spending winter in the water.  Male common frogs in particular are known to spend colder months dormant at the bottom of the pond as they shut down and breathe through their skin.  Larvae that failed to develop in the spring and summer will also be spending their winter in the water too.  Provided a pond doesn’t completely freeze and still has suitable oxygen levels the larvae can survive and complete metamorphosis in early spring.  This may ultimately give them a size advantage over the larvae that developed within the previous summer.

You may see tadpoles in a pond over winter as they wait for next spring to develop!

Remember, for any further information on reptiles, amphibians and their habitats, visit our FAQ’s pages or our Info & Advice pages. 

Croaking Science: Spadefoot toads- unique life-histories and evolution

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Spadefoot toads are one of the best known examples of fossorial frogs. They gained their name because three of the genera have a specially adapted hind foot which enables effective burrowing. Many spadefoot toads live in arid habitats and they are uniquely adapted to harsh, dry environments. The adults are highly secretive, often spending most of the year buried underground. Individuals of some species may burrow to depths of two metres below the surface (AmphibiaWeb, 2008). North American spadefoot toads typically have a highly explosive breeding strategy, often emerging after heavy rains to breed (Figure 1). The adults are able to burrow into sand to avoid hot summer temperatures, while the larvae have an extremely rapid development, enabling some species to metamorphose into terrestrial juveniles within just 30 days (Pfenning, 1992). However, European spadefoot toads have a different life history with a prolonged breeding period of several months and having large larvae which take several months to metamorphose (Degani, 2015).

Figure 1. Spadefoot toads, like the Couch’s spadefoot toad (Scaphiopus couchii) from Texas, are highly adapted to living in harsh, dry environments. [Photo credit: Howcheng, https://commons.wikimedia.org/wiki/File:Scaphiopus_couchii_ANRA.jpg]

Spadefoot toads are spread widely across the whole of the northern Hemisphere from eastern Russia to western United States. Most, but not all, spadefoot toads possess an adapted hind foot (Figure 2) and it was assumed that it was only the species which lived in arid environments which possessed this feature. However, recent evolutionary research by Chen et al. (2016) has suggested that this may not be the case. Chen et al. (2016) report on a new spade-foot bearing fossil toad from eastern Mongolia. The fossil, Prospea holoserisca, is estimated to be 56 million years old and resembles modern spadefoot toads. It is the earliest definite fossil frog with an enlarged hind limb which was used for effective burrowing (Chen et al., 2016). Analysis by Chen et al. (2016) has shown that this fossil is the ancestor of both the living spadefoots which possess the specially adapted hind foot and those which do not. The anatomy of the fossil spadefoot toad suggests that it could burrow, but analysis of the environment at the time indicates that it did not live in an arid environment, like modern spadefoot toads. This has led Chen et al. (2016) to the conclusion that burrowing in an arid environment is an exaptation instead of an adaptation. In other words, burrowing behaviour did not evolve in response to an arid environment, but instead the frogs already had the hind foot morphology which enabled the frogs to burrow in sand when the environment subsequently became arid (Chen et al., 2016). Indeed, another study has suggested that the rapid larval development often observed in North American spadefoot toads did not evolve in response to an increasingly arid environment but relates instead to the size of the frogs’ genome and evolutionary history (Zeng et al. 2014). These studies show that amphibian species may utilise morphology and behaviour which they already possess when environmental conditions change.

Figure 2. The underside of a male spadefoot toad (Pelobates fuscus). Note the spade-like legs on the back legs marked by the red arrows. [Photo credit: Christian Fischer, https://commons.wikimedia.org/wiki/File:PelobatesFuscusVentraltagged.JPG]

There are six species of spadefoot toad belonging to the genus Pelobates which are distributed across Europe, Western Asia and North Africa. Due to their fossorial existence for most of the year, information on their behaviour is generally lacking. The common spadefoot toad, Pelobates fuscus, has a prolonged breeding period lasting from April to June during which time the males defend territories around the pond and, unlike many breeding toads, call underwater (AmphibiaWeb, 2008) (Figure 3). Eggert & Guyétant (2003) carried out a study of calling males in northeast France and found that males with a lower body condition arrived later than males with higher body condition. Males arriving early at the breeding pond experienced high competition for females and it is risky for males in low body condition as they are unlikely to be successful in mating. Therefore, Eggert & Guyétant (2003) propose that males optimise their breeding migration by arriving earlier or later, depending on their body condition. In addition, older (and more experienced) males tended to stay for less time at breeding ponds, presumably because they were able to obtain a mate more quickly (Eggert et al., 2003). Unlike species of toad which have an explosive breeding strategy where males have little time to secure a mate, species with a longer breeding season like the common spadefoot toad have the opportunity to utilise different mating tactics to ensure greater chances of successfully mating.

Figure 3. Male common spadefoot toads (Pelobates fuscus) have alternative breeding tactics. [Photo credit: Bearbeitung von deBild, https://commons.wikimedia.org/wiki/File:Knoblauchkroete_IMGP4749.jpg]

The common spadefoot toad (P. fuscus) and eastern spadefoot toad (P. syriacus) overlap in parts of their range. Both species have highly similar ecology and life history: both burrow underground, are nocturnal, reproduce at the same period of the year, use similar aquatic habitats for reproduction and forage in the same terrestrial habitats (Cogălniceanu et al., 2014). Therefore, there is a high potential for niche overlap and competition between species. In their recent research, Székely et al. (2017) found that each species had different foraging patterns which avoided competition. The eastern spadefoot toad emerged from the soil less often than the common spadefoot toad but was active for much longer and moved over twice the distance. These differences in movement patterns are likely to allow the different species to exploit different prey types which would allow coexistence and reduce competition (Székely et al., 2017). Since the eastern spadefoot toad is a widely foraging species it is likely to encounter more sedentary prey species that are clumped and unpredictable. However, this is likely to be costly in terms of energetic expenditure. The common spadefoot toad is less active, but will be able to exploit larger, faster moving and active prey. However, these are generally fewer in number (Székely et al., 2017). Therefore, each species exploits a different foraging strategy, each with its own advantages and disadvantages. Although these behavioural differences are relatively small, they allow each species to exploit different prey species and coexist in the same habitats. 

References

AmphibiaWeb (2008) Pelobates fuscus: Common spadefoot <http://amphibiaweb.org/species/5270> University of California, Berkeley, CA, USA. Accessed Oct 25, 2019.

Chen, J., Bever, G.S., Yi, H. & Norell, M.A. (2016) A burrowing frog from the late Paleocene of Mongolia uncovers a deep history of spadefoot toads (Pelobatoidea) in East Asia. Nature Scientific Reports, 6: 19209. doi 10.1038/srep19209.

Cogălniceanu, D., Roşioru, D., Székely, P., Székely, D., Buhaciuc, E., Stănescu, F. & Miaud, C.

(2014). Age and body size in populations of two syntopic spadefoot toads (genus Pelobates) at the limit of their ranges. Journal of Herpetology, 48: 537-545.

Degani, G. (2015) The habitats, burrowing behavior, physiology, adaptation and life cycle of spadefoot toads (Pelobates syriacus, Boettger, 1869) at the southern limit of its distribution in Israel. Open Journal of Animal Sciences, 5: 249-257.

Eggert, C. & Guyétant, R. (2003) Reproductive behaviour of spadefoot toads (Pelobates fuscus): daily sex ratios and males’ tactics, ages and physical condition. Canadian Journal of Zoology, 81: 46-51.

Pfenning, D.W. (1992) Polyphenism in spadefoot toads tadpoles as a locally adjusted evolutionarily stable strategy. Evolution, 46 (5): 1408-1420.

Székely, D., Cogălniceanu, D., Székely, P. & Denoël, M. (2017) Out of the ground: coexisting fossorial species differ in their emergence and movement patterns. Zoology, 121: 49-55.

Zeng, C., Gomez-Mestre, I. & Wiens, J.J. (2014) Evolution of rapid development in spadefoot toads is unrelated to arid environments. PLOS ONE, 9: e96637, doi: 10.1371/journal.pone.0096637.