DNA metabarcoding reveals broad woodpecker diets in fire-maintained forests

Ecological disturbance is a key agent shaping the spatial and temporal landscape of food availability. In forests of western North America, disturbance from fire can lead to resource pulses of deadwood-associated arthropods that provide important prey for woodpeckers. Although the foraging strategies among woodpecker species often demonstrate pronounced differences, little is known about the ways in which woodpeckers exploit and partition prey in disturbed areas. In this study, we employed DNA metabarcoding to characterize and compare the arthropod diets of 4 woodpecker species in Washington and California, USA-Black-backed Woodpecker (Picoides arcticus), Hairy Woodpecker (Dryobates villosus), Northern Flicker (Colaptes auratus), and White-headed Woodpecker (Dryobates albolarvatus)-primarily using nestling fecal samples from burned forests 1-13 years postfire. Successful sequencing from 78 samples revealed the presence of over 600 operational taxonomic units (OTUs) spanning 32 arthropod orders. The nestling diets of two species in particular-Northern Flicker and Black-backed Woodpecker-proved to be much broader than previous observational studies suggest. Northern Flicker nestlings demonstrated significantly higher diet diversity compared to other focal species, all of which displayed considerable overlap in diversity. Wood-boring beetles, which colonize dead and dying trees after fire, were particularly important diet items for Black-backed, Hairy, and White-headed woodpeckers. Diet composition differed among species, and diets showed limited differences between newer (<= 5 yr) and older (>5 yr) postfire forests. Our results show mixed evidence for dietary resource partitioning, with three of the four focal species exhibiting relatively high diet overlap, perhaps due to the pulsed subsidy of deadwood-associated arthropods in burned forests. Woodpeckers are frequently used as management indicator species for forest health, and our study provides one of the first applications of DNA metabarcoding to build a more complete picture of woodpecker diets. Lay Summary center dot Forest fire creates a resource pulse of arthropod prey for woodpeckers, yet little is known about the composition of woodpecker diets in postfire areas. center dot We used DNA metabarcoding to characterize and compare the diets of four woodpecker species, focusing on nestling fecal samples from burned forests in the western USA. center dot Woodpecker diets were broader than previous studies have reported. Northern Flicker samples showed especially high nestling diet diversity compared to other focal species. center dot Black-backed, White-headed, and Hairy Woodpecker nestlings showed a high prevalence of beetles in their diets. center dot Woodpeckers are frequently used as indicators to evaluate forest management activities, and detailed characterization of woodpecker diets represents an important step in understanding their resource requirements.

Automated summary

Ecological disturbance, such as forest fire, can affect food availability for woodpeckers. In this study, DNA metabarcoding was used to analyze the diets of four woodpecker species in burned forests. The diets were found to be broader than previously reported, especially for Northern Flicker. Wood-boring beetles were an important component of the diets for Black-backed, White-headed, and Hairy Woodpeckers.