For many North American birdwatchers, mixed-species flocks are a familiar sight in winter—flocks of chickadees, nuthatches and woodpeckers moving together through leafless woods. In tropical forests, however, mixed-species foraging is even more ecologically important. The Cachar Bulbul (Iole cacharensis), a quiet, forest-dwelling species found in north-east India and western Myanmar, regularly participates in these complex avian alliances.
Understanding why this bulbul joins other species while feeding sheds light on risk management, information sharing and survival in dense forests.
What Is a Mixed-Species Foraging Flock?
A mixed-species foraging flock is a loosely coordinated group of different bird species that move together while feeding. Unlike true flocks of a single species, these groups form because each participant gains specific benefits without direct cooperation.
In tropical forests, such flocks can include bulbuls, babblers, drongos, flycatchers, and leaf-warblers—each exploiting a slightly different foraging niche.
According to HBW Alive and broader tropical ecology literature, the Cachar Bulbul is most often observed within these mixed groups rather than leading them, suggesting a follower or opportunistic role.
Safety in the Forest Midstory
Predation pressure in tropical forests is intense. Raptors, snakes, and arboreal mammals all pose risks, especially in the forest midstory, where visibility is limited.
By joining mixed-species flocks, Cachar Bulbuls benefit from:
Many eyes scanning for danger
Early alarm calls from more vigilant species
Reduced individual vigilance, allowing more time to feed
BirdLife International notes that forest-dependent species with subdued vocalizations—like the Cachar Bulbul—are particularly reliant on external warning systems provided by flock mates.
Information Sharing: Finding Food Faster
Food in tropical forests is abundant but unpredictable. Insects move, fruiting trees are scattered, and profitable patches may be short-lived.
Mixed-species flocks act as information networks. When one species locates a rich food source or flushes insects from foliage, others quickly benefit.
For the Cachar Bulbul, which feeds on both fruit and insects, this means:
Access to disturbed insects stirred up by more active foragers
Visual cues about fruiting shrubs worth investigating
Rather than searching alone, the bird uses the collective movement of the flock to optimize foraging efficiency.
Niche Partitioning Reduces Competition
One reason mixed-species flocks remain stable is niche partitioning. Each species feeds in a slightly different way or at a different height.
The Cachar Bulbul typically:
Forages in the midstory to lower canopy
Gleans insects from leaves
Plucks small fruits while perched
Meanwhile, other flock members may probe bark, hover for insects, or forage closer to the ground. This reduces direct competition and allows multiple species to exploit the same area simultaneously.
Social Flexibility Without Strong Bonds
Importantly, mixed-species flocks are not social groups in the emotional sense. The Cachar Bulbul does not form lasting bonds with other species; participation is fluid and conditional.
If a flock moves into unsuitable habitat or becomes too exposed, individuals may quietly drop out. This flexibility is key in environments where conditions change rapidly.
From a birding perspective, this explains why the Cachar Bulbul may appear briefly within a moving flock and then vanish into foliage moments later.
Seasonal Patterns in Flock Participation
Participation in mixed-species flocks may increase during:
Non-breeding periods
Times of lower food availability
During the breeding season, birds often become more territorial and less socially flexible. However, even breeding Cachar Bulbuls may still associate loosely with passing flocks when feeding away from the nest.
This balance between territoriality and social foraging reflects a cost–benefit calculation shaped by season and life stage.
Implications for Conservation
Mixed-species flocking depends on intact forest structure and species diversity. When forests are fragmented, flocks become smaller, less stable, or disappear entirely.
For species like the Cachar Bulbul, the loss of flocking opportunities can mean:
Increased predation risk
Reduced foraging efficiency
Higher energetic stress
BirdLife International identifies habitat degradation as a major concern precisely because it disrupts these subtle social systems—not just individual species.
Why Birders Should Care
For birders, mixed-species flocks are often the best chance to encounter elusive forest birds. Learning to recognize flock dynamics—listening for alarm calls, watching movement patterns—can dramatically improve detection.
The Cachar Bulbul reminds us that some birds survive not by standing out, but by blending in socially. In the dense tropical forest, cooperation without commitment can be the most effective survival strategy of all.
