A clever piece of detective work by an international team, including aresearcher from The Australian National University (ANU), has helped solvedthe mystery of which plants a population of crows on New Caledonia use tocraft tools.
The crafty crows are well known for making their own stick tools with hookedtips to retrieve invertebrate prey from small holes and crevices.
The New Caledonian crow is the only non-human animal known to manufacturehooked tools in the wild.
“They put a lot of effort into making them. They use specific plants withforked stems, which they remove and then process into hooked tools forforaging,” study co-author Dr Linda Neaves from ANU said.
“But they remove leaves and much of the bark, making it impossible to quicklyidentify the plant species.”
While Dr Neaves’ collaborators from the University of St Andrews in Scotlandhad been able to determine what plants the crows were using to make thesetools at two of their long-term study sites, a third remained a puzzle.
“The plants used in one of the study sites is an introduced shrub, and in theother, they seem to use a variety of raw materials. But no one had ever seenthe crows make the tools at the third site, so we had no idea what species itwas,” Matthew Steele from the University of St Andrews said.
After years of trying to work it out using a range of approaches — includingbehavioural observations in the wild and in field aviaries, radio-tracking ofbirds, and working with local botanists to examine collected tools — the crowteam was at a loss.
That’s where Dr Neaves comes in
“The field team were able to collect some tools and approached myself andProfessor Peter Hollingsworth from the Royal Botanic Garden in Edinburgh,Scotland, asking if DNA could be used to work out what plant it was,” DrNeaves said.
She managed to match DNA from the tools to a large native tree, SpanishCherry, or Mimusops elengi.
“Because it’s native, this may be one of the original plants used by the crowsfor making hooked stick tools. The field team later confirmed that temporarilycaptive crows happily crafted hooked stick tools from this plant,” Mr Steeleexplained.
“It was amazing to finally work it out,” Dr Neaves said.
“It was right in front of us the whole time. When the crow researchers firstexplained this problem, it was difficult to know if we could provide ananswer. Usually you have a bit more to work with, in this case it felt likesearching for a needle in a haystack – it could’ve been a large number ofplants on New Caledonia.”
Dr Neaves says it’s a reminder of all the little things some species rely onto survive.
“Clearly these crows have adapted their remarkable tool-making abilities overtime to make use of introduced plant species, and it is exciting to find thispopulation prefers a native tree. It raises a lot of interesting questionsabout how and why crows select the plants they use and how this may beinfluenced by changes in their environment.”
Professor Hollingworth says the study “demonstrates the broad usefulness ofDNA barcoding for the essential task of separating and identifying plantspecies.”
The long-term crow study was led by Professor Christian Rutz from theUniversity of St Andrews, with expeditions for this study led by his PhDcandidate, Matthew Steele.
The study has been published in PNAS.
Image: James St Clair
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