From Chapter 7: Relationships with Other Species

In many avian communities a common type of feeding relationship is the mixed-species feeding flock – a loosely organized band of birds that travel and forage together for prolonged periods, moving more or less as a group while maintaining a comfortable distance between individuals. Certain species typically act as flock leaders and arefollowed by a variety of attendant species. The composition of a flock shifts and changes throughout the day as different birds join or leave.

Most woodpeckers that participate in feeding flocks do so as followers, but red-cockaded woodpeckers play a dual role. Compared to other insectivorous birds of the southern pine forests, red-cockaded woodpeckers are late risers. While these woodpeckers are still in their roost holes, a diverse group of feeding companions typically convenes in the vicinity of their cavity-tree cluster. The red-cockaded woodpeckers emerge shortly after dawn. Once they begin foraging, the assembled company moves off through the forest. These flocks usually stay relatively coherent until late morning, when the woodpeckers reduce their feeding activity.

The frequent use of cavity-tree clusters as assembly points for southern pine forest feeding flocks suggests that red-cockaded woodpeckers are important members, but the group dynamics are not yet fully understood. For the most part the woodpeckers seem to pay little attention to their flock-mates except for generally coordinating their movements with the rest of the group and reacting to alarm calls that signal a predator’s approach. Sometimes the woodpeckers lag behind, but at other times flock movements appear to be influenced by their foraging agenda.

The two species most intimately linked with red-cockaded woodpeckers in these flocks are the brown-headed nuthatch and the eastern bluebird. These birds often follow red-cockaded woodpeckers closely for prolonged periods in one-on-one pairings, with the follower consistently remaining within three feet (1 m) of the woodpecker as it progresses. This behavior is apparently motivated by the opportunity to apprehend prey that have been disturbed by the woodpecker’s foraging activities. Attendant species are often seen darting out to capture insects that take flight from sites where red-cockaded woodpeckers are working.

The main benefit of feeding-flock relationships for red-cockaded and other woodpeckers is that they provide additional eyes and ears to monitor for approaching hawks or other predators. Research on downy woodpeckers has shown that they spend less time cocking their heads and scanning their surroundings for signs of danger when they are with feeding flocks than when alone. With more time freed up for foraging, downies in feeding flocks capture prey at a faster rate than do solitary individuals.

Meanwhile there is no disadvantage to keeping company with non-woodpeckers because they are not rivals for foraging sites or food. However, competitive pressure between closer kin usually dictates that the number of woodpeckers in a feeding flock is low, except for family groups of red-cockaded woodpeckers. Participation is often circumscribed by territoriality. An individual may join a flock as it enters its home range, then drop out when the group moves beyond its familiar margins.

In the southern pine forest haunts of the red-cockaded woodpecker, feeding flocks are active throughout the year, except during the nesting period, and may have as many as 50 members. In Louisiana and eastern Texas the most common year-round species in these assemblages are brown-headed nuthatches, pine warblers and Carolina chickadees, which are often joined by red-cockaded, red-bellied and downy woodpeckers, tufted titmice and a variety of other birds. In North Carolina as many as seven woodpecker species have been seen in a single flock. During winter the ranks are swelled by various migrants such as warblers, kinglets, brown creepers and bluebirds.

This composition is characteristic of feeding flocks of arboreal insect-eating birds throughout much of North America. The species mix varies regionally, but certain families of birds are routinely represented. In temperate areas feeding flocks almost always coalesce around chickadees, titmice or both, which serve as flock leaders and sentinels. These birds are prominent as core species probablybecause they are quick to sound the alarm when predators come into view. Typical attendants besides woodpeckers include nuthatches, kinglets, bushtits, warblers, verdins and brown creepers. These flocks generally number up to about two dozen birds.

Feeding flocks are most important for woodpeckersduring the non-breeding season, when territorial instincts are muted and high energy demands coincide with food scarcity. Downy woodpeckers team up with others more readily when food is in short supply, and the incidence of hairy woodpeckers joining feeding flocks increases with decreasing temperature. Hairy woodpeckers are only occasional participants in feeding flocks and tend to remain near the periphery of these groups.

In the evergreen oak woodlands of Arizona, woodpeckers seen in mixed-species feeding flocks include ladder-backed and Arizona woodpeckers, red-naped sapsuckers and northern flickers. The core species are usually either common bushtits or bridled titmice. Northern flickers also forage with Mexican jays in the oak savannas of Arizona, though the two species eat different foods. In these flocks the flickers follow the jays and heed their warnings about approaching hawks or northern harriers. Northern flickers spend more time foraging when they are in the company of Mexican jays than in flicker-only flocks. In tropical and subtropical forests, antwrens are the most common core species in feeding flocks. Golden-olive woodpeckers are regularly seen with such groups and lineated woodpeckers are occasional joiners.