Environmental DNA of Eurasian Three-toed Woodpecker from sap rows
Sap rows on coniferous trees have long served as a practical indicator for the presence of the elusive Eurasian Three-toed Woodpecker (Picoides tridactylus) in boreal forests, influencing conservation decisions and even legal rulings in Sweden despite limited scientific validation. This study investigates whether environmental DNA (eDNA) from these peck marks can resolve the uncertainty surrounding potential behavioral overlap with other woodpecker species, such as the Great Spotted Woodpecker (Dendrocopos major). We collected 24 samples from 12 trees (4 pines and 8 spruces) across five forest stands in northern Sweden's inland in June 2025, deliberately targeting DNA from all woodpecker species to test the anecdotal assumption of exclusivity. We amplified DNA using four primer pairs targeting parts of the mitochondrial cytochrome b (cytb) region specific to Picidae. Surprisingly, all positive identifications (20 samples, 83% success rate) in the sample set matched the Eurasian Three-toed Woodpecker exclusively, with no detections of other woodpeckers despite their sympatric abundance. Results were consistent across tree types and stands, providing support that sap rows on conifers may be specific to the Eurasian Three-toed Woodpecker in Sweden. This eDNA approach transforms an "handed-down truth" into verifiable evidence, with implications for nature conservation, forestry practices, and judicial processes. We recommend future larger-scale studies with broader geographic coverage to confirm the absence of behavioral overlap in other woodpecker species on conifers.