Holy Bat Detector! Ecologists Develop First Europe-Wide Bat ID Tool

ScienceDaily (Aug. 3, 2012) — Just as differences in song can be used to distinguish one bird species from another, the pips and squeaks bats use to find prey can be used to identify different species of bat. Now, for the first time, ecologists have developed a Europe-wide tool capable of identifying bats from their echolocation calls.

Grey Long-Eared bat. (Credit: copyright Hugh Clark / Bat Conservation Trust)


The new free online tool — iBatsID — will be a major boost to conserving bats, whose numbers have declined significantly across Europe over the past 50 years. Details are published August 7 in the British Ecological Society’s Journal of Applied Ecology.

Working with an international team of ecologists, lead author and PhD student Charlotte Walters from the Zoological Society of London (ZSL) selected 1,350 calls of 34 different European bat species from EchoBank, a global echolocation library of more than 200,000 bat calls.

The calls were then analysed to find out which characteristics were most useful in distinguishing different bat species. According to Walters: “Lots of different measurements can be taken from an echolocation call, such as its maximum and minimum frequency, how quickly the frequency changes during the call, and how long the call lasts, but we didn’t know which of these measurements are most useful for telling different species’ calls apart.”

The 12 most useful call parameters were then used to train artificial neural networks to produce the new identification tool, iBatsID, which can identify 34 different bat species across the whole of Europe. Most species can be identified correctly more than 80% of the time, although accuracy varies because some species are much harder to identify than others.

“iBatsID can identify 83-98% of calls from pipistrelle species correctly, but some species such as those in the Myotis genus are really hard to tell apart and even with iBatsID we can still only identify 49-81% of Myotis calls correctly,” she explains.

iBatsID should have a major impact on European bat conservation, which until now has been hampered by the absence of a standardised, objective and continent-scale identification tool.

According to Professor Kate Jones, another of the paper’s authors and chair of the Bat Conservation Trust: “Acoustic methods are really useful for surveying and monitoring bats, but without using the same identification methods everywhere, we can’t form reliable conclusions about how bat populations are doing and whether their distributions are changing. Because many bats migrate between different European countries, we need to monitor bats at a European, as well as at country, scale. In iBatsID, we now have a free, online tool that works anywhere in Europe.”

Bat populations have declined significantly across Europe since the middle of the 20th century. As a result, all bats are now protected through the EU Habitats Directive. Bats face many pressures, including loss of roosting sites in trees and buildings; loss of feeding habitats in woodlands, meadows, parks and gardens; falling insect numbers; and habitat fragmentation resulting in the loss of green corridors such as hedges that provide connectivity in the landscape.

As well as providing vital ecosystem services, such as pollinating plants and controlling insect pests, bats are important indicators of biodiversity. “Bats are very sensitive to changes in their environment, so if bat populations are declining, we know that something bad is going on in their environment. Monitoring bats can therefore give us a good idea of what is going on with biodiversity in general,” Walters adds.

 

Link:

http://www.alphagalileo.org/ViewItem.aspx?ItemId=122962&CultureCode=en

Journal Reference:

  1. Charlotte L Walters et al. A continental-scale tool for acoustic identification of European bats. Journal of Applied Ecology, 7 August 2012 DOI: 10.1111/j.1365-2664.2012.02182.x

Citation:

British Ecological Society (BES) (2012, August 3). Holy bat detector! Ecologists develop first Europe-wide bat ID tool. ScienceDaily. Retrieved August 9, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120807101243.htm

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Birds That Live With Varying Weather Sing More Versatile Songs

ScienceDaily (Aug. 3, 2012) — A new study of North American songbirds reveals that birds that live with fluctuating weather are more flexible singers.

Northern oriole. Researchers analyzed song recordings from more than 400 male birds spanning 44 species of North American songbirds — a data set that included orioles, blackbirds, warblers, sparrows, cardinals, finches, chickadees and thrushes. (Credit: © Richard L. Carlson / Fotolia)


Mixing it up helps birds ensure that their songs are heard no matter what the habitat, say researchers at Australian National University and the National Evolutionary Synthesis Center.

To test the idea, the researchers analyzed song recordings from more than 400 male birds spanning 44 species of North American songbirds — a data set that included orioles, blackbirds, warblers, sparrows, cardinals, finches, chickadees and thrushes.

They used computer software to convert each sound recording — a medley of whistles, warbles, cheeps, chirps, trills and twitters — into a spectrogram, or sound graph. Like a musical score, the complex pattern of lines and streaks in a spectrogram enable scientists to see and visually analyze each snippet of sound.

For each bird in their data set, they measured song characteristics such as length, highest and lowest notes, number of notes, and the spacing between them.

When they combined this data with temperature and precipitation records and other information such as habitat and latitude, they found a surprising pattern — males that experience more dramatic seasonal swings between wet and dry sing more variable songs.

“They may sing certain notes really low, or really high, or they may adjust the loudness or tempo,” said co-author Clinton Francis of the National Evolutionary Synthesis Center.

The Pyrrhuloxia or desert cardinal from the American southwest and northern Mexico and Lawrence’s goldfinch from California are two examples.

In addition to variation in weather across the seasons, the researchers also looked at geographic variation and found a similar pattern. Namely, species that experience more extreme differences in precipitation from one location to the next across their range sing more complex tunes. House finches and plumbeous vireos are two examples, Francis said.

Why might this be?

“Precipitation is closely related to how densely vegetated the habitat is,” said co-author Iliana Medina of Australian National University. Changing vegetation means changing acoustic conditions.

“Sound transmits differently through different vegetation types,” Francis explained. “Often when birds arrive at their breeding grounds in the spring, for example, there are hardly any leaves on the trees. Over the course of just a couple of weeks, the sound transmission changes drastically as the leaves come in.”

“Birds that have more flexibility in their songs may be better able to cope with the different acoustic environments they experience throughout the year,” Medina added.

A separate team reported similar links between environment and birdsong in mockingbirds in 2009, but this is the first study to show that the pattern holds up across dozens of species.

Interestingly, Francis and Medina found that species with striking color differences between males and females also sing more variable songs, which means that environmental variation isn’t the only factor, the researchers say.

 

Link:

http://www.eurekalert.org/pub_releases/2012-08/nesc-btl080312.php

Journal Reference:

  1. I. Medina, C. D. Francis. Environmental variability and acoustic signals: a multi-level approach in songbirds. Biology Letters, 2012; DOI: 10.1098/rsbl.2012.0522

Citation:

National Evolutionary Synthesis Center (NESCent) (2012, August 3). Birds that live with varying weather sing more versatile songs. ScienceDaily. Retrieved August 5, 2012, from http://www.sciencedaily.com­ /releases/2012/08/120803131930.htm