How to track an 'invisible' animal

A Diana monkey feeds on a leaf Diana monkeys might be shy but scientists can use insects to survey the primates

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In the ongoing battle to care for the planet's diverse life, conservationists go to great lengths.

They trek for miles through thick jungle with heavy packs of instruments to try to learn more about species before they are lost.

But when these species are rare, shy or difficult to access, biologists are forced to learn from a distance.

A fleeting glimpse on a grainy remote camera trap, a decomposed carcass or even a dung sample can reveal detailed secrets of a species. But each of these insights is hard won, with hours of humidity and anxiety often decided by one lucky encounter.

Now the scientific community is heralding essential additions to their toolkits that require far fewer crossed fingers but a lot more DNA detective skills.

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According to a review published in the journal Molecular Ecology, gathering data on species abundance and distribution is the number one priority for conservationists.

The International Union for the Conservation of Nature's infamous Red List catalogues all species that are considered to be threatened, but around 14% of the 5,400 terrestrial animals are listed as "Data Deficient".

To address these deficiencies, researchers from the Robert Koch Institute in Berlin, Germany, suggest easy-to-catch insects can inform on hidden and vulnerable vertebrates.

Gut instincts

The researchers were working to find out more about how the fatal disease anthrax spreads in Africa, when they stumbled upon a new method for measuring biodiversity.

Faced with the difficult task of finding carcasses in the impenetrable rainforest habitat, the team turned to the flies that plagued their studies.

Blow fly Calliphoridae Blow flies and other carrion eating flies could provide essential data

Under dissection, the flesh-eating carrion flies spilled their guts to reveal the bacteria they carried and clues to what they had been eating.

In addition to the anthrax bacteria, the flies carried the unique DNA samples of their meals, allowing scientists to study exactly which mammals they had been feeding from.

"We were quite surprised that no-one else had this idea but that's the way it goes with obvious ideas," Dr Fabian Leendertz, who led the research, tells BBC Nature.

In Madagascar they recorded 13% of the known mammal species present in the guts of just 40 flies. The relatively small sample studied in the Ivory Coast confirmed six of the nine local species of primate as well as the rare and endangered antelope Jentink's duiker.

Dr Leendertz suggests that simply catching flies could help conservationists answer the question: does a rare species live here?

"The most important thing to perform well-targeted conservation actions is first to actually know which mammals are in a given area," said Dr Leendertz.

Impenetrable rainforest Dense rainforests are "tricky habitats" for scientists to monitor

"In Savannah regions that may be easier because you walk there or fly over in your plane and count the giraffes. But in the rainforest it's very difficult to see anything and to know [what] is living there."

He comments that most populations are over-estimated and based on out-of-date records.

But the so-called "invertebrate DNA" method could help to update current figures and improve their accuracy.

Although researchers still need to understand the flies a little better, to determine exactly how far they travel for a mammal feast for example, they uphold the method as a relatively easy, unobtrusive way to gather data.

Secretive salamanders

But what about species that aren't targeted by blood suckers?

In the US, scientists are using environmental clues to help them track an elusive animal with a suitably mysterious name: the hellbender.

This brown salamander is the largest amphibian in North America where it lives in river drainages but is threatened by water pollution.

Dr Rod Williams and colleagues from Purdue University, Indiana, US, decided to try and track the elusive eastern subspecies just by taking a sample of its river environment.

The team began by taking water from areas with known populations of hellbenders and filtering the samples to find evidence of the amphibians.

Eastern hellbender salamander The eastern hellbender is an increasingly rare sight

Again, traces of DNA confirmed the presence of the animals. Dr Williams describes such environmental DNA techniques as "revolutionary".

Although this DNA detective work is less costly than traditional field methods, scientists insist it will complement, rather than replace, existing techniques.

Based in Tai National Park alongside leading primate scientists Dr Leendertz aims "to really compare, within a given area, environmental DNA, invertebrate DNA and then all the classic bio-monitoring tools likes camera traps, audio traps, transect walking."

"Then we will get a better picture of which are the strengths of all the methods and which are the weaknesses," he told BBC Nature.

"Based on these data [we can] create a decision tree for conservationists [indicating] which method may be the most appropriate."

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