7.5 As larks sing songs, researchers hear population health
http://arstechnica.com/journals/science.ars/2008/10/22/what-can-we-learn-from-a-birdsong
As
larks sing songs, researchers hear population health
By Yun Xie | Published:
October 22, 2008 - 11:35AM CT
Biologists and ecologists
have long known that animal behavior reflects environmental factors like
habitat loss. For example, disruption in the populations of wild dogs in Africa
negatively affected cooperative behavior in the packs, causing problems with
defense, pup rearing, and hunting. Habitat destruction also influences the
repertoire of bird songs. Paola Laiolo, a conservation biologist from Spain,
and her colleagues have seen that Dupont's lark had less variation in its songs
when populations decreased because there were fewer birds from which to learn
new notes. This loss of musical range was detrimental to the sexual appeal of
male larks.
Dupont's Lark: SEO/BirdLife.
From a conservation
perspective, Laiolo proposes that valuable information can be gathered by
quantifying the behavioral processes of animals. Research groups have tried to
measure animal behavior in the past with variable degrees of success—it can be
tricky to create statistical tools to account for behavioral patterns.
Laiolo chose to work with the
songs of Dupont's lark, as they are well understood. By using computer software
to differentiate songs and fitting the song variations to a piecewise and
exponential model, she hoped to correlate song diversity and population
viability. In essence, she wanted to see if it was possible to use the song
repertoire of individual birds as an indicator of population problems. She was
also interested to find a minimum threshold of habitat size.
From 2004 to 2007, Laiolo
recorded songs from 385 male larks in 51 steppe patches across Spain. The
patches were anywhere from 20 to over 5000 ha in size, and some patches
contained as few as one male lark, while others had over 250. According to
Laiolo, the variability in patches "is largely due to human-driven habitat
transformations, which is threatening the species’ persistence in many small
and isolated areas." During the course of her study, three out of the 51
Dupont’s lark populations went extinct.
Laiolo ended up isolating 253
different songs and found that at least two lark populations shared 169 songs.
Well situated larks would sing as many as 12 types of songs. She discovered
that "individual song diversity is linked to population viability because
of its positive association with population size." Average repertoires of
less than five songs indicated populations that were at risk. It also appeared
that a minimum threshold size of 100 ha is necessary for population
sustainability, as habitats smaller than that contained larks that sang only a
few songs.
Laiolo suggests that we can
do more than simply enjoy the beauty of a lark’s song. Carefully listening to
the full repertoire of individual larks might clue us in on their viability in
a particular habitat.
Ecological
Applications, 2008. DOI: 10.1890/07-1433.1
