Social Dynamics and Foraging Strategies of Woodpeckers in Mixed-Species Flocks of Birds in Subtropical Forests

Woodpeckers represent a frequent component of mixed-species flocks in subtropical forests but have received less attention in mixed flock research than Passeriformes and other bird taxa. To understand when and how woodpeckers join this type of association and their role within them, we surveyed mixed flocks for 388hs over three years in Argentina's Yungas foothill forest. We studied the association frequency and foraging behavior inside and outside mixed flocks of the four woodpecker species present in the study area: Cream-backed Woodpecker Campephilus leucopogon, Golden-olive Woodpecker Colaptes rubiginosus, Dot-fronted Woodpecker Veniliornis frontalis, and White-barred Piculet Picumnus cirratus. Woodpeckers were present in 26% of the 206 recorded mixed flocks, with a higher frequency during dry seasons. They joined mixed flocks with twice as many species as the average flock in the area and shared the flock with other non-woodpecker bark-forager species in 88% of cases. The largest species, Cream-backed Woodpecker, joined flocks less often than smaller species but frequently participated in flocks composed mainly of other large-sized bird species. We recorded the foraging behavior of 52 woodpecker individuals for durations ranging from 11 to 449 seconds: 24 within mixed flocks and 28 outside. Some woodpecker species were found to mimic other bark-forager species' foraging sites in an exact manner. Medium-sized species foraged higher when inside mixed flocks, whereas the largest and smallest species did not alter their foraging height. Only the smallest species, White-barred Piculet, increased its foraging efficiency within mixed flocks and was recorded as a leader in understory flocks. Further insights are needed into the disadvantages and/or benefits of woodpecker species joining mixed flocks. However, our results indicate that woodpecker participation in mixed-species flocks is primarily influenced by higher flock diversity and the presence of other non-woodpecker bark-foragers, the latter also playing a key role in enhancing their foraging success.