Frogs and roads don’t mix (Part 3)

At last – the final installment of this intriguing trilogy!  The third reason that frogs and roads don’t mix is that the noise of road traffic (cars, trucks, motorcycles and other vehicles) can make it difficult for frogs to be heard by other frogs.  Anyone who has listened to a group of frogs calling at a pond or stream can guess that acoustic communication (communication with sound) is very important for this group of animals.  Male frogs call to attract females for mating, and also to stake a claim on a certain calling location.  The advertisement call of a male frog says two things: 1) “Hey ladies, I’m over here”; and 2) “Back off chaps, this is my space”.  Each species of frog has a unique call, so a female frog can recognise males of the correct species in the dark (although occasional mix-ups do occur).

Acoustic interference

Road-traffic noise can reduce the distance over which a male frog’s call can be heard by females of the same species by up to 90%, with bigger frogs being the biggest losers.  This is because bigger frogs have lower-pitched calls which overlap more with the pitch (frequency) of traffic noise than do the calls of smaller frogs.  The loss of communication distance in noise is known as masking or acoustic interference.  Traffic noise is more than a nuisance for urban frogs – it may be interrupting froggy loving on a grand scale.  Road-traffic noise also hinders acoustic communication in birds and insects, while boat-traffic noise interferes with acoustic communication in fish, dolphins and whales.  Traffic noise may also make some animals more vulnerable to predation (because they can’t hear their predators coming) and reduce foraging success by animals such as bats that rely on sound to detect their prey.  It’s a noisy world out there, and it’s not just humans who are experiencing the effects!

Litoria_ewingii_Burnley_cropped

The southern brown tree frog calls at a higher pitch in traffic noise

What can we do?

Some species of frogs are calling at a higher pitch in traffic noise, helping to reduce acoustic interference and get back some of the communication distance lost.  For example, the southern brown tree frog Litoria ewingii from Australia calls at a higher pitch at noisy urban sites than at quiet rural sites.  But this is not enough to overcome the effect of traffic noise completely.  In many places around the world, we use sound barriers and other structures to protect people from high levels of traffic noise – perhaps it’s time to consider protecting frogs, birds, bats and other animals from traffic noise too?

More information

Parris, K. M. (2015). Ecological impacts of road noise and options for mitigation. Pp. 151-158 in R. van der Ree, C. Grilo and D. Smith (eds), Ecology of Roads: A Practitioners’ Guide to Impacts and Mitigation (Wiley-Blackwell, Oxford).

Parris, K. M. (2013). Anthropogenic noise constrains acoustic communication in urban-dwelling frogs. Proceedings of Meetings on Acoustics 19: 010055.

Parris, K. M., Velik-Lord, M. and North, J. M. A. (2009). Frogs call at a higher pitch in traffic noise. Ecology and Society 14(1): 25. http://www.ecologyandsociety.org/vol14/iss1/art25/

Aussie frogs try new pickup line; All Things Considered, National Public Radio (USA) (11/10/2009)

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Frogs and roads don’t mix (Part 2)

Eastern_freeway

The Monash Freeway in Melbourne, Australia carries around 150,000 vehicles per day (photo by Kirsten Parris)

In Part 1 of this series, I showed how difficult it was for frogs to cross busy roads without getting run over.  The second reason that frogs and roads don’t mix flows on from the first one – if frogs can’t cross roads safely, then they can’t move safely between different areas of habitat that are separated by roads.  This leads to something ecologists call habitat isolation.

Habitat isolation – what’s so interesting about that?

Habitat isolation causes a number of problems for frogs and other living things.  Here are three of them:

1.  A group of frogs (a population) living in an isolated area of habitat can be separated from other populations of the same species.  This means that friends from elsewhere rarely – if ever – come to visit.  Over time this can lead to a loss of genetic diversity in the population, and something called inbreeding depression.  Basically, without new frogs arriving in the population, the frogs that remain become too closely related to each other.  This can reduce their fitness, making them less likely to survive and reproduce.

2.  If a population living in an isolated habitat dies out, no new animals can move in to start a new one.  So we are left with suitable – but unoccupied – habitat.  This is a common problem in urban environments for small animals that move along the ground (such as frogs, reptiles and mammals), because cities often contain small patches of habitat for wildlife that are separated by busy roads.  Animals that can fly (such as birds, bats and some insects) can cross busy roads more easily.  In a study of pond-breeding frogs in Melbourne, Australia (Parris 2006), I found that isolation by roads reduced the number of species of frogs that lived at a pond.  Statistical modelling (a nifty method of analysing field data) predicted that the most-isolated pond (that is, the one surrounded by the most roads) would have only about 1/5 of the species as the least-isolated pond.

3.  Some animals (such as the growling grass frog Litoria raniformis) need a network of populations in a network of habitat patches to survive in the long term – this is known as a metapopulation (Heard et al. 2013).  Different patches in the network are occupied at different times.  For example, some patches might be particularly good for frogs in times of drought, and others might be occupied only when conditions are very wet.  If too many habitat patches in the network become isolated by roads, animals can’t move freely between them when they need to and the metapopulation doesn’t work properly.  In some cases, metapopulations collapse and the all the populations within them die out.

GGF_Bundoora

A growling grass frog – thinking about visiting another pond, perhaps? (photo by Kirsten Parris)

What can we do?

Keeping connections between habitat patches (such as habitat corridors) will allow frogs to keep moving between them when they need to do so.  This is particularly important in places where new housing and industrial developments are being built – it’s much easier to keep existing connections in the landscape than to put them back later!

Creating new habitat corridors and building road overpasses and underpasses may also help frogs and other animals move around urban landscapes, but these measures can be very expensive.  Also, a recent study of some Australian frogs found that they weren’t very keen to use underpasses (Hamer et al. 2014).

Where some habitat patches are going to become isolated from others in a network, it may be possible to create new wetlands to make up for the ones that the frogs will no longer be able to reach safely.

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Frogs and roads don’t mix (Part 1)

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A growling grass frog – will it cross the road?  (photo by Saide Cameron)

Frogs are small animals that hop or walk along the ground.  Roads are long stretches of gravel, concrete or bitumen that allow vehicles like cars, trucks and motorbikes to go from one place to another.  These vehicles are often large and heavy, and travel very fast – much faster than frogs can hop or walk.  This means that it is very difficult for a frog to cross a busy road safely, and many thousands of frogs (maybe even millions) are run over and killed on roads around the world every year.

Why did the frog (try to) cross the road?

So why do frogs try to cross roads?  To get to the other side, of course!  Frogs are busy animals and often have places to go.  Frogs that breed in ponds may spend part of their time at a pond and part of their time in another kind of habitat.  And at certain times of the year – such as the start and end of the breeding season – they need to move between the two.  This type of movement is known as migration.  Young frogs (juveniles) may also leave the pond where they were born and move to a new one.  This type of movement is called dispersal.

Roads are a problem for frogs because they can turn a regular journey into a very dangerous one.  A number of years ago, researchers in Denmark measured how quickly amphibians (frogs and newts) moved when they crossed a road (Hels & Buchwald 2001).  The fastest species in their study was the moor frog (Rana arvalis), which moved at 2 metres per minute.  The slowest was the common newt (Triturus vulgaris), which moved at only 0.5 metres per minute.  On Danish motorways, cars and other vehicles can travel at 130 kilometres per hour, which equals 2,167 metres per minute.  That is more than 1,000 times faster than moor frogs can hop, and more than 4,000 times faster than common newts can walk!

Road kill

Tove Hels and Erik Buchwald used this information to work out the chance of a frog or newt getting safely across roads with different amounts of traffic.  The news wasn’t very good.  The moor frogs had about a 60% chance of safely crossing a road carrying 100 vehicles per hour (2,400 per day).  This means that for every 100 frogs trying to cross the road, 60 would make it and 40 would be run over.  The slower-moving newts only had about a 10% chance of crossing safely, meaning that 90 out of every 100 newts trying to cross a road with this much traffic would be run over.  On busy roads with more than 15,000 vehicles per day, the speed of the different amphibians didn’t make much difference to their chance of a safe crossing – no matter how quickly they walked or hopped, they were almost certain to be run over.

What can we do?

In Europe and North America, where lots of frogs tend to move at once, tunnels under roads have been quite useful in reducing road kill.  Fences along each side of the road direct the frogs to the tunnels, where they cross underneath the road before going on their way.  At this stage, we don’t know whether these kinds of tunnels work in other places such as Australia, where frog movements are more spread out over time.

Some conservation groups (such as Froglife in the UK) help frogs and other amphibians to cross roads – this is known as patrolling.

Otherwise, if you are driving at night – particularly if the weather is warm and wet – slow down and watch out for small animals crossing!

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It’s not easy being green… in the city

It’s not easy being a growling grass frog in Melbourne, Australia; photo by Geoff Heard

The city of Melbourne, Australia is home to about 14 species of frogs, depending on where you draw the boundaries.  And the boundaries of Melbourne are spreading outwards at a cracking pace, with new suburbs being built on its western, northern and south-eastern edges.  Melbourne is already one of the most sprawling cities in the world, which means it covers a large area of land.  At the moment, it measures about 60 km (37 miles) from east to west, and some suburbs are more than 40 km (25 miles) from the centre of the city.

The growling grass frog is the only species of frog around Melbourne to be on the national list of threatened species.  It is listed as Vulnerable to Extinction under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).  Growling grass frogs used to be common across Victoria, but their geographic range (the area of land where they might be found) has been shrinking.  Melbourne is an important place for this species, but there are fewer and fewer wetlands around the city where these frogs still live.  Research by Dr Geoff Heard and friends has found a big drop in the number of growling grass frog populations around the Merri Creek in northern Melbourne (a population is a group of animals or plants belonging to one species that live together in the same place).

Growling grass frogs are big frogs, with adults growing up to 10 cm long.  They come in many shades of green to brown, and the male frogs have a fabulous growly call.  You can click here to learn more about them and to listen to some calls.  Claire Keely also has some great photos of growling grass frogs on her website.  Claire is studying the population genetics of growling grass frogs in Melbourne for her PhD.

Growling grass frogs love wetlands with lots of plants; photo by Geoff Heard

The growth of Melbourne is a big problem for the growling grass frog, because new suburbs are being built right where it lives.  But with some careful planning, frogs and people should be able to live together.  If the new suburbs have areas of parkland next to creeks, and new wetlands are built to help replace some of those that are covered over by houses and roads, this will help growling grass frogs – and other wildlife – to survive.  Parks and wetlands will also make the new suburbs nicer places for people to live.

Property developers have complained about a draft plan to set aside areas of parkland along creeks (known as buffer zones) where houses cannot be built.  Let’s hope that the Victorian government stands up for these beautiful and important animals in its updated plan to conserve animals and plants in the growth areas of Melbourne.  This plan, called the Biodiversity Conservation Strategy, is due to be released soon.

More information:

Frogs Australia Network- fact sheet on growling grass frogs

Getting to know the frogs of Melbourne

Recent additions to Melbourne’s growth areas (“logical inclusions”)

The draft Biodiversity Conservation Strategy for Melbourne’s growth areas

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Why do flying-foxes like to live in cities?

A grey-headed flying-fox; photo by Ian Kitchen

Flying-foxes are big bats – the biggest in the world!  They belong to a group of mammals known as the Megachiroptera (pronounced “megga-kai-roptera”) or megabats.  Unlike their smaller cousins (the Microchiroptera or microbats), they like to eat fruit, pollen and nectar rather than insects.  Megabats are only found in the southern hemisphere, and they mostly live in tropical and subtropical parts of Africa, Asia and Oceania.  So flying-foxes like their food vegetarian and their weather warm and humid.

During the day, flying-foxes hang around together in big groups called camps – and I mean hang!  They sleep hanging upside down in trees, but they also spend quite a bit of time chattering to each other and jostling their neighbours to get a better position when things are a bit crowded.  Flying-foxes are very social animals!  At night time, they fly out from the camp to look for food.  This is known as foraging, and some flying-foxes can travel up to 50 km in one night to find a good dinner and then get home again.

The biggest camps of Australia’s grey-headed flying-fox can hold 200,000 animals at a time.  In the past, this species mainly camped in natural areas like sub-tropical rainforest, Eucalyptus forest and Melaleuca swamps.  But recently, more grey-headed flying-foxes have been camping in cities, bringing them into closer contact with people.  Old camps in Sydney and Melbourne have been getting larger, and new camps have appeared in cities such as Geelong, Bendigo and Adelaide.

Grey-headed flying-foxes at Yarra Bend, Melbourne; photo by Kirsten Parris

In 2003, a camp at the Royal Botanic Gardens Melbourne was moved to a new site on the Yarra River.  More flying-foxes had been arriving at the camp every year, and people were concerned that they were damaging some important trees in the Gardens.  The Royal Botanic Gardens Sydney is currently trying to move their flying-fox camp, for similar reasons (see ABC Radio National for an interesting story about the Sydney relocation).

So why do flying-foxes like to live in cities?  Wouldn’t it be nicer for them in the forest?  Well, there are a few reasons:

1.  There’s not much forest left.  Huge areas of sub-tropical rainforest, Eucalyptus forest and coastal Melaleuca swamps have been cleared since the European settlement of Australia.  One example is the Big Scrub, an area of sub-tropical rainforest in northern New South Wales that used to cover 75,000 hectares of land.  More than 99% of this forest was cleared for farming during the 1800s, and now only about 100 hectares remains (perhaps it could be renamed the Very Small Scrub).  These days, most clearing of forest and swamps along the east coast of Australia is for urban development such as new houses, roads and shopping centres.

2.  City parks and gardens provide pleasant camp sites, and the city and suburbs can supply tasty food for flying-foxes, all year round.  For example, there are more than 300,000 street trees in Melbourne that provide fruit and nectar for grey-headed flying-foxes to eat.  Many of these trees belong to species that do not naturally occur in Melbourne.

3.  In southern Australia, cities are getting warmer.  Due to something known as the urban heat-island effect, cities are often warmer than the surrounding countryside.  And as cities grow, the effect gets larger.  Temperatures in central Melbourne have been increasing since the 1950s, leading to warmer conditions (particularly at night) and fewer frosty mornings.  Also, watering of city parks and gardens – to keep them green and lush during the warmer months of the year – acts like extra rainfall.  So parts of Melbourne are now warm enough and wet enough for grey-headed flying-foxes to stay all year round.

You’ve probably noticed that all these reasons have something to do with people.  People have changed the environment for flying-foxes in Australia by clearing large areas of their natural habitat and making new habitats for them in cities.  Is it surprising that they have decided to move in with us?

Grey-headed flying fox; photo by Ian Kitchen

More information about flying foxes:

The Australasian Bat Society

DSE Victoria – Facts about bats and flying-foxes

Hall, L.S. and Richards, G. (2000). Flying Foxes: Fruit and Blossom Bats of Australia. University of New South Wales Press, Sydney.

Parris, K.M. and Hazell, D.L. (2005). Biotic effects of climate change in urban environments: the case of the grey-headed flying-fox (Pteropus poliocephalus) in Melbourne, Australia. Biological Conservation 124, 267-276.

van der Ree, R., McDonnell, M.J., Temby, I.D., Nelson, J. and Whittingham, E. (2006). The establishment and dynamics of a recently established camp of flying-foxes (Pteropus poliocephalus) outside their geographic range. Journal of Zoology 268, 177-185.

Williams, N.S.G. et al. (2006). Range expansion due to urbanization: Increased food resources attract Grey-headed Flying-foxes (Pteropus poliocephalus) to Melbourne. Austral Ecology 31, 190-198.

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Welcome!

Welcome to my blog!  I’m an ecologist at The University of Melbourne in Victoria, Australia.  An ecologist is a type of biologist who studies living things (like animals, plants and fungi) and their environment (the places where they live).  I study frogs, birds, and other animals that live in cities.  This type of research is called urban ecology.  I plan to use this blog to write stories for kids about urban ecology – so stay tuned!

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