How many bats are there?
By Tim Lucas
Knowing whether bat populations are growing or shrinking tells us about the health of the bat population (see Dr Kate Barlow’s blog). It also gives us information about the health of the ecosystem in general, as discussed by Dr Robin Freeman. However, these are relative measures; are there more bats this year than last year? Sometimes we want to know an actual number. Are there a thousand bats? Ten thousand? A million?
For example, if we are trying to conserve a rare bat species we need to estimate the actual number of bats. At very low population sizes inbreeding starts to become a significant problem for conservation. Ten percent fewer bats than last year could mean a decrease from 100,000 bats to 90,000 bats or it could mean a decrease from 1,000 to 900 bats. While both situations are worrying, only in the later case do we need to start considering genetic inbreeding.
So how do we estimate the size of a bat population from our acoustic surveys? This is not a simple problem. If I go out with my bat detector and count 200 bats, what does this mean? Maybe I actually detected every single bat making the population size only 200. Maybe I detected one percent of all bats making the population size 20,000.
In essence the problem is to work out how many bats you expect to detect per hour of surveying. This depends on a number of factors. The flight speed of a species is important. You are more likely to come into contact with bats that fly quickly. If you sit by a motorway you will see more cars than if you sat by a country lane even if the total number of cars is the same on each road.
Secondly the actual area of land that you are surveying is clearly important and this depends on the distance within which you can detect a bat. Louder bats can be detected from further away, just as larger animals can be seen from further away. This means you are surveying a larger area if you are looking for loud species than if you were looking for quiet species.
The frequency of the bat call also matters as high frequency sounds travel less far than low frequency sounds.
As an example, the spectrogram shown has a loud ‘hockey stick’ call at about 25kHz but also a quieter harmonic above it, at about 60 kHz. Even without considering through use of seo services that the harmonic is quieter (it is less bright on the spectrogram) it will travel about half the distance of the lower frequency call. The maths to work out these distances is long and boring so I hope you don’t mind me not showing my working!
So, if we can make a good guess of how large an area we are actually surveying we can work out what proportion of the bat population we saw. Did we survey 1% of land in Europe, or 0.001% and so did we see 1% of the bat population, or 0.001%. Using this information and information about how fast bats fly we can try to work out how many bats there are in total and use this information to conserve them as best we can.
The importance of bat base-lines
By Dr. Elizabeth Boakes
If you were to look in a mammal field guide you might think we already know where different bat species can be found. However, our knowledge of species distributions is often behind times. Information on changes in a species’ range is usually of higher quality in species with small ranges, simply because these species are easier to monitor. There is therefore a real risk that declines in more widespread species may be overlooked, particularly if these declines occur in the middle rather than the edge, of a species’ range. Indeed, a species range size, as measured by its borders, may remain constant for a long period of time even if local extinctions are occurring throughout its centre, a process known as fragmentation. The species final collapse toward extinction may be so rapid that sufficient conservation intervention cannot be made in time to save the species (see figure).
Widespread species also tend to be overlooked by scientists who, with limited time and funds, necessarily have to focus attention on species already known to be threatened. In the last 30 years this has led to a real dearth of data on more common species. This is extremely worrying since it means that without these ‘biodiversity base-lines’, ecologists will struggle to map declines in previously widespread species and hence may not be able to find their underlying causes. If we do not knowwy a species is declining it makes it far harder, if not impossible, to reverse that decline.
With the help of volunteers, monitoring widespread species across their range becomes much more tractable and means that a better understanding of species ranges over time can be constructed which will prove invaluable in the future should that species start to decline. Volunteer records are as essential to conservation management as museum collections and I like to think of volunteers as curators of nature. In our rapidly changing world it is hard to predict what species will become threatened next but if we are armed with a repository of distribution data we can hope to notice and respond to these changes as quickly as possible. The Bat Detective project, and your key contributions to unlocking the data wtihin it, are therefore a fantastic conservation resource, not just for today but for decades of future bat custodians.
Indicator species and trends
Bats are often referred to as ‘indicator species’ this signifies that a species is considered indicative of some underlying environmental characteristic. As Kate discussed last week, not only do Bats provide us with essential services (such as pest control and pollination), they also indicate how the nocturnal ecosystems they inhabit are faring. A healthy ecosystem should be able to support bats and changes in bat abundance and distribution may indicate underlying changes to that ecosystem (thus ‘indicator’). Bats are also known to be particular sensitive to such changes and thus may make a more effective indicator than other species.
The Joint Nature Conservation Committee has adopted six widespread bat species as an indicator of mammals in the wider countryside (see ‘Indicators in your pocket’: http://jncc.defra.gov.uk/page-4229). Since 1978, records indicate that populations have declined dramatically, but more recent conservation efforts and monitoring programs have helped to produce more positive recent trends. However, in the context of the longer term declines, much more needs to be done to help bat species maintain these gains, and hopefully increase further.
How does this relate to the Bat Detective project? Well, much of these data are from well-established UK monitoring programs, and we have a less clear picture of how bats are faring across Europe and worldwide. The identification of bat calls that you’re providing through batdetective.org will allow us to then identify the species that make these calls and then develop a much clearer picture of the distribution and abundance of these species throughout Europe (and eventually the world!).
So keep up the amazing work! Your wonderful efforts will help us to identify species that are at risk and areas that need better conservation and management!
Why do we need to monitor bats?
Dr Kate Barlow, Head of Monitoring, Bat Conservation Trust
For one we need our bats! Bats are an important part of our ecosystems not least because they provide us with all sorts of useful services around the world, including pest control and pollination. And if we know we need bats surely it is a good idea to see how they are doing?
Over the last century bat populations suffered severe declines, both in the UK and across Europe. A combination of different pressures on bats including agricultural intensification, increasing building and development, direct persecution and use of pesticides including timber treatments which severely affected some bats resulted in significant losses of bats over a number of decades. Today all bats and their roosts are protected by law both in the UK and across Europe. To ensure that protection is effective, to find out how well we are doing at preventing further declines in bat populations, and to attempt to improve habitats for bats so that numbers can recover, we need to know how well our bat populations are doing, and this is where monitoring comes in. The Bat Conservation Trust runs a National Bat Monitoring Programme which relies on an army of dedicated bat volunteers spread across the UK who go out in force every year carrying out our bat surveys and sending us data on bats in their areas. We can then put all of this information together to see how well bat populations are faring at the UK level and use the results to ensure conservation work is focused where it is needed. But if that wasn’t reason enough to monitor bat populations, there is more….
What surprises a lot people is the diversity of bat species around the world, from fruit bats in Australia to tiny pipistrelles in the UK. In fact bats account for about a fifth of the world’s mammal species, that’s well over a 1000 different species of bats! In the UK we have 17 different breeding species of bat. They all are active at night, flying around our cities and countryside searching for and catching their insect prey. Each species has different needs, some roost in buildings others in trees, different bats spend their time foraging in different habitats and eat different insects. The common pipistrelle, one of our smallest and most widespread bats, can be seen busily flitting about around dusk in many gardens and parks across the country, feed on tiny flies, hoovering up thousands of midges and mosquitoes every night. Some of our bigger bats like the noctule need a bigger meal to keep them going and will eat larger insects like beetles, and some bat species have very particular needs and will only be found in the best areas of old woodlands where their favourite moth food can also be found. Different bats, in different habitats eating lots of different insects means that bats can tell us a lot about habitats and ecosystems. And as bats are found across the world and sensitive to change we can try to use bats to track global change. In short if we know how bats are doing we know more about the state of our planet.
Bat monitoring can be done in a number of different ways and keen bat workers can be found carrying out bat surveys at all times of year – standing outside buildings on summer evenings carefully counting bats as they head out from their roosts to feed; clambering around winter bat sites peering into cracks and crevices to search for hibernating bats; or wandering around the countryside armed with bat detectors looking for bats in different habitats. All these different monitoring methods produce a lot of data, and the data needs to be entered, stored, processed and analysed. The Bat Detective website will help us to analyse bat data and develop more efficient methods to process the vast amount of data our monitoring produces.
So going back to my question on why it is important to monitor bats, I could simply say because it keeps me in work! Or because I love bats. But there are so many better reasons for us to know how our fascinating and furry friends of the night are faring, from assessing the health of habitats to monitoring global change, there is still so much to learn from bats.
I’ve Found a Bat … Now What?
As you know, we have a huge number of audio snippets and we want to know what’s in them! We would certainly never be able to find the bats all by ourselves — There are just that many recordings.
This is where the Bat Detective project steps in. We’re really hoping that citizen scientists will help us to locate and identify bat tweets and insect clicks that have been captured across the globe by the lovely volunteers.
Once we gather your votes on the contents of a snippet, this will highlight the recordings of interest and provide us with labels. On top of hunting for the bats, your labelled sequences of searching, feeding and social tweets will also allow us to analyse the different sounds.
As the number of your identifications grows, the more information we will have; it doesn’t even matter if a recording is given a range of different labels! By pointing out the controversial sounds, we can gain an insight into the calls that are hard to distinguish.
If the majority of your votes on a snippet’s contents agree, then this recording can be compared to other snippets that have been similarly labelled. By finding the features they have in common, and what sets them apart from other sounds, we can begin to automate our quest for interesting sounds.
To help us decide on useful identifying features as an seo company for bats, which could be wildly obvious or devilishly subtle, we can use machine learning. This involves designing a computer program that we can hand our snippets and your voted labels to, for it to then return different ways the sounds can be grouped together. Analysing these resulting clusters will then pave the way for automatically detecting the different bat tweets (and insect buzzes) within any number of snippets!
So many files!
All the data that goes into Bat Detective has been collected by many wonderful volunteers around the world as a series of individual recordings, each 90 minutes long. Each of these recordings contains thousands of the individual snippets that you see on bat detective. As the bat calls are ultrasonic, we use time-expansion to record them. A specialised microphone records ultrasonic information for a short period (320 ms) and then slows that sound down and plays it into a recorder (slowed by 10x, giving a 3.2 second recording). This results in a long recording that contains thousands of small 3.2 second snippets of audio.
Chopping all this data up has really tested some of our desktop computers. Once you consider that we have 1000s of events, each containing thousands of snippets (and each snippets has a sound file and a spectrogram image), you can see that we very quickly have a lot of files! I recently discovered that copying 4.5 million tiny files to a usb disk can take a while!
We’re really excited about getting people involved in Bat Detective, because many of these snippets contain calls from individuals bats, and individual researchers finding them manually would be impossible! Having everyone help us find these calls not only allows us to try and identify the species making those calls, but will also allow us to try and generate methods to automatically detect bats, insects and other noises in these data.
Welcome to Bat Detective!
Bat Detective is an online citizen science project where the public can help to monitor bats across Europe and track changes in the environment by listening to the weirdly wonderful ultrasonic tweets of bats.
Bat Detective project allows visitors to take part in conservation by listening out for bat tweets in recordings collected over 80,000 km of roads across Europe by thousands of volunteers from the iBats program, including bat recordings from the heart of Transylvania.
By sorting the sounds in the recordings into insect and bat calls, bat detectives will help the Bat Detective team learn how to reliably distinguish bat tweets to develop new automatic identification tools.
Bats use lots of different types of sounds, from singing to each other to find a mate, to using the echoes from their tweets to find their way around. Usually bat sounds are inaudible to humans as they are too high for us to hear, but special ‘time expansion’ ultrasonic detectors convert these sounds to a lower frequency, and visitors to Bat Detective can listen to these unique recordings and help the Bat Detective team distinguish different sounds.
One out of every five species of bats is threatened with extinction and better automatic identification tools are desperately needed to quickly process vast amounts of sound data collected by volunteers from bat monitoring programs who survey bat populations each year.
Bats are found all over the world from local parks to pristine rainforests and monitoring their population trends provides an important indicator of healthy ecosystems. Developing new tools that allow the Bat Detective team to interpret population trends from sound will allow bats’ tweets to act as a way to track environmental change.
Bat Detective has been developed by the science team at University College London and Bat Conservation Trust with the development team at Citizen Science Alliance, which runs Zooniverse.org with funding from the Alfred P. Sloan foundation.