← Back to the atlasMixed flocks · Tucumán YungasOne flock, many species.
In autumn and winter you often meet a noisy group of different small birds moving through the forest together: warblers, chlorospingus, tyrannulets, foliage-gleaners, a woodcreeper hitching up a trunk. This is a mixed flock. Each species feeds at its own height and on its own surface, and they all move as a single front.
325flocks recorded across the Argentine Yungas 72species taking part 2,480birds counted 3study sites in Tucumán How it movesA slice of forest, with the flock passing through
Each bird keeps to its own height band. Ground birds hop through the leaf litter, trunk climbers work up the bark, tyrannulets make short sallies and return. The group drifts forward a few metres a minute.
True vertical scale: 0 to 14 m. Tap a bird to see who it is. The speciesWho travels in the flock
Share of flocks in which each species turned up at the study’s three Tucumán sites. Sorted by overall presence.
Sierra de San JavierCampo de los Alisos (PN Aconquija)Higuerillas (Escaba) Buff-browed Foliage-gleanerTicotico comúnSyndactyla rufosuperciliata Feeds1–6 m Rummages in hanging dead leaves, moss and epiphytes for insects.
Sierra de San Javier47% Campo de los Alisos56% Higuerillas70% Common ChlorospingusFrutero yungueñoChlorospingus flavopectus Feeds2–8 m Picks insects and small fruit from foliage, in groups that keep calling to each other.
Sierra de San Javier53% Campo de los Alisos52% Higuerillas22% Brown-capped WhitestartArañero corona rojizaMyioborus brunniceps Feeds2–7 m Fans its tail to flash white and flush insects, then snaps them up.
Sierra de San Javier43% Campo de los Alisos26% Higuerillas46% See plate 013 →Mottle-cheeked TyrannuletMosqueta comúnPhylloscartes ventralis Feeds4–10 m Checks leaves and makes short sallies after insects, tail cocked.
Sierra de San Javier33% Campo de los Alisos26% Higuerillas54% Rufous-bellied ThrushZorzal coloradoTurdus rufiventris Feedson the ground Hops over the ground and low branches, flipping leaf litter.
Sierra de San Javier45% Campo de los Alisos19% Higuerillas35% Golden-crowned WarblerArañero coronado chicoBasileuterus culicivorus Feeds1–4 m Works the low and middle foliage very actively, calling all the time.
Sierra de San Javier53% Campo de los Alisos19% Higuerillas20% Tropical ParulaPitiayumíSetophaga pitiayumi Feeds8–13 m Gleans insects among canopy leaves, sometimes hanging upside down.
Sierra de San Javier22% Campo de los Alisos15% Higuerillas39% Saffron-billed SparrowCerquero de collarArremon flavirostris Feedson the ground Scratches through leaf litter in the understory, nearly always on the ground.
Sierra de San Javier27% Campo de los Alisos4% Higuerillas28% Rusty-browed Warbling-FinchMonterita ceja rojizaMicrospingus erythrophrys Feeds1–4 m Searches shrubs and low foliage for insects in the first few metres.
Sierra de San Javier12% Campo de los Alisos22% Higuerillas20% Yellow-striped BrushfinchCerquero amarilloAtlapetes citrinellus Feedson the ground Works the understory and forest edge close to the ground. Nearly endemic to Argentina.
Sierra de San Javier18% Campo de los Alisos22% Higuerillas13% White-throated TyrannuletPiojito gargantillaMecocerculus leucophrys Feeds5–11 m Checks twigs and leaves of the middle and upper layers; bright white throat.
Sierra de San Javier4% Campo de los Alisos7% Higuerillas30% Sayaca TanagerCelestino comúnThraupis sayaca Feeds8–13 m Eats fruit and insects high in the trees.
Sierra de San Javier24% Campo de los Alisos11% Higuerillas7% Olivaceous WoodcreeperTareferoSittasomus griseicapillus Feeds2–12 m Hitches up trunks and thick branches, propped on its tail.
Sierra de San Javier4% Campo de los Alisos7% Higuerillas22% House WrenRatona comúnTroglodytes aedon Feedson the ground Creeps through low tangles and fallen logs, tail cocked.
Sierra de San Javier8% Campo de los Alisos4% Higuerillas13% Dot-fronted WoodpeckerCarpintero yungueñoDryobates frontalis Feeds3–11 m Taps and probes the bark of trunks and branches for larvae.
Sierra de San Javier8% Campo de los Alisos– Higuerillas7% See plate 006 →The dataWhere in the forest they feed
Share of flock birds seen in each height band and on each surface, at the three Tucumán sites.
Height
Sierra de San Javier 23%34%32%11% Campo de los Alisos 15%34%22%29% Higuerillas 35%29%23%13% 0–2 m2–5 m5–10 mabove 10 m Surface
Sierra de San Javier 10%81% Campo de los Alisos 89% Higuerillas 9%13%75% Leaf litterHerbsBarkFoliage Why it worksFour rules of a mixed flock
More eyes, less risk.Mixed flocks are a strategy to forage more efficiently and to cut the risk of being caught. With many birds watching, an alarm spreads fast.
Everyone on their own floor.Almost everything happens in the foliage and below 10 m. Because each species searches at a different height and surface, they compete little with each other.
An open door.Yungas flocks have open membership: a core of frequent species, plus others that join for a while as the flock crosses their territory.
It depends on the forest.What changes flock make-up most is forest structure: how much cover each layer has and how deep the leaf litter is. If the forest is degraded, the flock changes.
SourcesFanjul, M. E. (2023). Relationship among vegetation structure and mixed-species flocks composition along the latitudinal gradient of the subtropical montane forest of the Yungas, Argentina. Phil. Trans. R. Soc. B 378: 20220107. doi.org/10.1098/rstb.2022.0107
Fanjul, M. E. (2017). Composition and structure of the mixed-species flocks along the latitudinal gradient of the subtropical montane forest of the Yungas, Argentina. XVII Reunión Argentina de Ornitología.
Feeding heights in the animation and the behaviour notes are general for each species; the percentages and proportions come from the study.