Woodland Bird Flocks

Woodland Flocks

A large flock of Fish Crows (at least 200), a single-species flock

Flocks are groups of birds that remain together as they forage or travel. While flocking is a behavior associated with migration, it is exhibited year round by many species of birds. Most flocks consist of just one species of bird, although it is common for multiple species to form an association with each other. This is known as as a mixed flock, mixed guild, or even a bird wave depending on the literature. Mixed flocks are commonly seen with shorebirds, seagulls, and most of the smaller bird species such as songbirds or woodpeckers. In the breeding season, mixed species aggregations may be associated with nest colonies such as how terns, shorebirds, seagulls, and in the northern regions of Europe and North American, Auks share on nest area. Swallow species such as the colonial Sand Martin (or Bank Swallow), and the more solitary Rough Winged Swallow may associate with each other when nesting in riverbanks (a habitat that is limited in distribution). Mixed flocks are primarily  seen during the nonbreeding season when food is less abundant and birds are no longer defending nesting territories or raising young.

In the Carolinas, the most common types of mixed flocks include those made up of woodland birds, blackbirds and starlings, fruit eating birds (frugivorous) like waxwings or thrushes, and seed eating birds (sparrows, finches etc). These flocks are a good opportunity to see different bird species in the field or around the garden. A group mostly made up of common species like chickadees might contain migratory warblers or vireos during the autumn, different woodpeckers, or even a rare visitor. Take a close look at any group of songbirds from late summer through spring as you might be surprised what could waiting around the corner

Autumn and Winter Flocks

Chickadee with oriole in background, a winter flock. There were a dozen or more birds in this grouping during this December morning in 2018.

Mixed feeding flocks are most likely to be encountered from the mid-summer (as early as July) through early spring (April) when most birds are not defending breeding territories. During these seasons songbirds and other birds will follow chickadees, titmice, or other resident birds as they forage, roost, or migrate southward. You will also see this with seagulls, sandpipers and plovers, as well as other types of songbirds. The woodland bird flocks are interesting because they can contain dozens of species of birds, and can benefit individuals that associate with them. These flocks also have an establish social and hierarchal structure and are an example of complex social behavior that is exhibited in many intelligent species. 

Role: The role of mixed feeding flocks in woodland or meadowland species is still being studied although there are several theories on their purpose. The most common theory is that mixed flocks can offer more protection to birds and increase their productivity during times of scarcity. This means more eyes and ears to detect potential threats such as predators, and an increased likelihood that the birds will find food and water. In the case of woodland birds, chickadees and other birds will sound an alarm if a hawk, cat, or snake is in the area, causing the other birds to take cover or begin mobbing. These benefits extend beyond the flock as mobbing birds can also alert other species of bird, as well as mammals (squirrels, deer, etc) of a  potential danger.

Structure: While most flocks are just aggregations of birds that form near food or water sources, or at roosts, mixed flocks contain complex social mechanisms to maintain their structure. With woodland birds, chickadees, titmice, or in some cases nuthatches usually lead the flock. These birds are known as a nuclear or nucleus species as they serve as the center or core of the flock. Chickadees, titmice, and Brown Headed Nuthatches maintain complex social hierarchies amongst their own species with dominant individual serving as a leader. The birds that associate with the flock are known as attendants and join the flock only when it enters its territory. Some birds however, will follow the fringes of a flock or switch between multiple flocks in an area. For the purposes of this article I will call these birds followers (to distinguish them from attendants). 

• Nuclear Species: Carolina Chickadee, Tufted Titmouse, Brown Headed Nuthatch, other species like Pine Warbler

• Attendants: Birds such as Downy or Hairy Woodpeckers, Carolina Wren,  and White Breasted Nuthatch

• Followers: Examples include flocks of Eastern Bluebirds or wintering Juncos of Chipping Sparrows, also treecreepers, kinglets, flickers, migrating warblers, vireos, and flycatchers

Nucleus: Titmice and Chickadees typically lead Mixed Flocks

Attendant: Wrens like this House Wren only loosely associate with flocks

Follower: Nuthatches often stay with mixed flocks across multiple teritories  

Niches: Woodland flocks can contain dozens of species of birds that range from mostly terrestrial species like the Ovenbird, Waterthrush, Carolina or Winter Wren, to canopy dwellers like tanagers, vireos, and Crested Flycatchers. During migration or winter, insectivorous birds other gravitate towards resident chickadees, or titmice to find reliable food or safety from predators. In such groups, birds are more likely to find food but there is also the potential of competition. Mixed flocks avoid issues with interspecies competition because most of the birds have different techniques, and diets. Chickadees, titmice, and Pine Warblers are generalists and can feed on a variety of prey as well as seed/fruits on all levels of the forest and its edges. Wrens, sparrows, and thrushes stay near the ground or in the latter case near fruits, while a Wood Pewee or Scarlet Tanager may stick to the treetops to catch insects. 

Pileated Woodpeckers open up food sources for smaller birds

Interspecies Benefits: Some birds such as woodpeckers, or nuthatches can provide opportunities for other birds. When there is a Red Bellied or Pileated Woodpecker with the flock, the other bird species may gain access to food that would be otherwise inaccessible. When one of the woodpeckers drills into a decaying limb for termites, beetles, or ants, smaller woodpeckers like the Downy may come in later to excavate further. Chickadees, titmice, wrens, warblers, and other birds that are unable to excavate into trees will also benefit by eating whatever insects that are exposed or knocked to the ground. Another example of a benefit of mixed flocks can include predator warning. Chickadees, wrens, and jays are very alert and can serve as lookouts for the entire group. If a Sparrowhawk species such as a Cooper's Hawk is detected, chickadees and titmice will produce a high pitched "seeeese" whistle, causing the other birds to freeze or dive for cover. Other calls such as the chickadee's  "Deee deee" call or the scold of wren can trigger mobbing behavior.

Sparrowhawks (Accipiter sp.) are bird specialists, mixed flocks serve as an early warning system for both avian and terrestrial predators. 

  

Range: Most mixed feeding flocks cover a fairly small area although these groups cover more territory than a typical nesting territory. By comparison, nomadic flocks of waxwings, American Robins, blackbirds, and most of the finch or Chipping Sparrow/Junco flocks may cover many miles or travel between abundant food sources. On the other end of the scale, flocks of "Hedge Sparrows" like White Throated, White Crowned, Song, and Fox Sparrows rarely leave stray far from hedgerow or field they are living in (same is true for flocks of cardinals). Chickadees and woodland birds are in the middle as they can cover some great distances within a forest and circulate through dozens of gardens and several bird tables, but rarely travel long distances for food. 

You can learn more about flocking behavior at these two Wikipedia Articles which are a good starting point for beginners (with references at the bottom of each entry). The articles are Mixed Species Flock and Flock.

Finding Woodland Flocks 

This park is ideal habitat for both woodland and meadowland birds

Woodland flocks can be found in almost any forest, woodland, or hedgerow in the Carolinas and most birds that visit your bird table or garden are woodland species. Look or listen for chickadees, titmice, or other recognizable species and keep an eye out for anything different. If chickadees or titmice come to the birdfeeder, look in nearby trees, and shrubs for other birds that may be associated with them. Depending on the season, there may be dozens of songbird species associated with a flock (with some flocks exceeding 100 individuals). These groups are the best way to find autumn or early spring migrants as warblers, vireos, flycatchers, and gnatcatchers usually attend or follow flocks when they are feeding or resting between jumps. Even in the summer, you can still find flocks as chickadees and Brown Headed Nuthatches, immediately reform their flocks after completing their brood, while juvenile and nonbreeding warblers, vireos, and gnatcatchers will stick around woodland birds when they are no longer on their territory. I divide woodland flocks into two categories, the traditional chickadee/titmouse-led guilds, and the flocks made up of pine specialists and birds commonly associated with open areas. I will go into non-woodland flocks in another article as they have similar structures and can lead birders to unusual or unexpected species. 

Kinglets are commonly found in "standard flocks" also look for treecreepers, vireos, and warblers

Standard Woodland Flocks: Flocks that are typically led by chickadees, or titmice and usually contain forest or forest edge species. These are what I consider "traditional" mixed feeding flocks and are the kind that contain nuthatches, woodpeckers, warblers, vireos, treecreepers, and kinglets. Flock make up can differ by habitat, season, or available food sources. 

Pine Warblers may take the place of chickadees as the leader of flocks in pine-dominated landscapes  

Pinewood Flock: A slight variation of the standard flock that may be led by Brown Headed Nuthatches or Pine Warblers, although there are often chickadees as well. These groups may contain the same species as above but frequently include meadowland or open country species such as Common Flickers,  Red Headed Woodpeckers, Chipping Sparrows, Juncos, Goldfinches, Siskins, or House Finches. These groups are often seen in open stands of pines, woodland openings, or in many parks. 

In the Garden

 A garden with trees and shrubs are can to host mixed flocks as well

Woodland flocks often visit adjacent residential areas and chances are there is at least one mixed feeding guild within your neighborhood or in a nearby woodland. While chickadees, titmice, and nuthatches (as well as Red Bellied Woodpeckers) are very adaptable and outgoing, most of the forest species are overlooked because they do not come to bird tables, or gardens. Autumn and winter flocks can bring many opportunities to find shier species of birds, migrating species, and even a rare or vagrant species. Additionally, when flocks of chickadees, or titmice come to the feeder, the rest of the flock is not far behind. 

Attraction: You can attract woodland flocks to your garden by providing food, water, and suitable roosting spots. Any garden or community that has good habitat for chickadees, titmice, woodpeckers, or nuthatches will likely host flocks in the winter. Deciduous trees and shrubs are good for attracting most warblers, vireos, and flycatchers, while evergreens like junipers, hollies, wax myrtle, arborvitae can provide dense cover for roosting birds. Pines are important for many species of birds and are a prerequisite for Brown Headed, or Red Breasted Nuthatches and Pine Warblers. Open areas, flowerbeds, meadows, rain  gardens, and riparian vegetation can add additional habitat for sparrows, buntings, flycatchers, and other species not associated with forests. Really, almost any garden can host woodland flocks with little to no improvement although native plants, winter flowering plants like Camellia (which kinglets, Orange Crowned Warblers and orioles love the nectar from) and fruit bearing plants add to the food value. 

Feeders: Woodland flocks often come to gardens with bird tables and other sources of food. Chickadees, titmice, nuthatches, Pine Warblers, Downy/Hairy Woodpeckers, and Red Bellied Woodpeckers all visit bird tables on a regular basis, often throughout the year. In the autumn and winter, these "ordinary" species come with new surprises. While many of the flock followers will stay in the trees or hedges, some of the bolder species might check out a bird feeder or suet cage, or land on railings or nearby shrubs. Kinglets, many warbler species, and Winter Wrens will sometimes come to porches or dooryards with chickadees, even if they do not use the feeder. During snowy conditions or when it is cold, a treecreeper, Yellow Throated Warbler or someone else might try out suet or mealworms, while the very sight of chickadees and cardinals could draw in a nearby Baltimore Oriole or overwintering tanager. 

Rarities: One of the best things about mixed flocks is the chance that you may get lucky and find something unusual, rare, or out of season. Autumn flocks can bring almost anything imaginable. A cluster full of American Redstarts, Parulas, or Cape May Warblers (not to mention chickadees and titmice) might contain a overlooked or uncommon Nashville or Wilson's Warbler. Overwintering warblers, tanagers, and other summer or transient residents will gravitate towards chickadees in order to survive. A Summer or Western Tanager, or the odd gnatcatcher might spend the winter in a garden or park by staying close to chickadees, cardinals and other gregarious species.   

Other Flocks to Scan: While I will mainly be focusing on woodland flocks in this article, it is still a good idea to investigate any flock of birds that visits your garden or you come across in a woodland, park, or shoreline. 

Flock of shorebirds at Shackleford Banks in 2010, this group has godwits and oystercatchers 

• A large "swarm" of blackbirds or starlings (typically made up overwhelmingly of wintering Red Winged Blackbirds, Common Grackles and Common Starlings) might contain meadowlarks, Rusty Blackbirds, or a Brewer's Blackbird. 

• The same is true for the massive flocks of Cedar Waxwings or American Robins that descend on fruit-laden shrubs from December to early March as they begin their slow journey north. 

• A flock of House Sparrows or native White Throated/Crowned Sparrows could hide a Dickcissel, Bobolink, or Indigo Bunting during migration, or a Fox Sparrow in the winter. 

• Goldfinch, House Finch and Siskin flocks might include Evening Grosbeaks, Purple Finches or a Crossbill during irruption years (not to mention any combination of escaped finches from captivity). 

• As a rule, shorebird and seagull flocks never just contain contain Laughing or Ring Billed Gull or Sanderlings/Willets. There could be anything from Iceland Gulls to Golden Plovers mixed in (both vagrants from the Old World), along with more common species. (hence photo above)