Archive by Author | robfreeman

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).

Range declines can appear stable over time, making possible declines towards the centre of the range.

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.

Figure 1 – Estimates for the abundance of pipistrelle species 1978 – 1992. Source Bat Conservation Trust, via JNCC (

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’: 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 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!).

Figure 2 – Trends in widespread bat populations, 1999 to 2011. Source Bat Conservation Trust, via JNCC (


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!

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.