Birds Active during the day

Yellow-margined Flatbill

Tolmomyias assimilis

iNaturalist eBird Wikipedia

A master of the mid-canopy, the Yellow-margined Flatbill is a stealthy insect hunter known for its distinctive pale eyes and bright wing accents. Widely distributed across the Amazon, it is a rewarding species for any backyard observer in the tropics.

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Quick Identification

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Size

13–13.5 cm (5.1–5.3 in) in length; weighs approximately 13–18 g (0.46–0.63 oz)

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Colors

Olive-green upperparts, pale yellowish-grey underparts, and distinctive yellow edges on the wing feathers. Both sexes appear similar.

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Key Features

Broad, flattened bill with a pale base
Bright yellow margins on wing coverts and secondaries
Pale, often whitish or light-grey iris
Upright, attentive flycatcher posture

When You’ll See Them

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Activity pattern Active during the day

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Peak hours 6-10 AM, 3-5 PM

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Season Year-round

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Diet Strictly insectivorous, feeding on a wide variety of beetles, flies, caterpillars, and small winged insects caught mid-flight or gleaned from foliage.

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Habitat Primary and secondary lowland humid forests, terra firme forests, and occasionally mature wooded gardens or forest edges.

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Where Does the Yellow-margined Flatbill Live?

The Yellow-margined Flatbill is a quintessential inhabitant of the South American tropics, with a vast range that covers nearly the entire Amazon Basin. It is natively found across a broad stretch of the continent, from the humid forests of Colombia, Venezuela, and the Guianas in the north, down through the lush interiors of Peru, Ecuador, and Bolivia, and across the massive forested expanses of Brazil. While it avoids the cooler southern climates of Argentina and Chile, it remains one of the most widespread tyrant flycatchers in the northern and central regions of South America.

Basemap © OpenStreetMap contributors

10 Countries

8.9M km² Range

Least Concern Conservation

BR Brazil PE Peru CO Colombia VE Venezuela BO Bolivia EC Ecuador GY Guyana SR Suriname French Guiana PA Panama

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iNaturalist / Verified observation data

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Behavior

The Yellow-margined Flatbill is a patient predator that spends much of its day perched upright in the mid-story of the forest. It employs a 'sit-and-wait' foraging strategy, staying motionless for long periods before making sudden, acrobatic sallies to snatch insects from the air or the undersides of leaves. Unlike many bold tropical birds, it is often heard before it is seen, possessing a sharp, whistled call that cuts through the forest humidity.

Socially, these birds are often found as solitary individuals or in pairs, but they frequently join mixed-species foraging flocks. By following woodcreepers and other insect-eaters, they capitalize on the insects flushed out by the movement of the group. They are also known for their remarkable architecture; they build hanging, pouch-like nests with a side entrance, often strategically placed near active wasp nests to deter potential nest predators like monkeys or snakes.

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Camera Tips

To capture the Yellow-margined Flatbill on camera, you must look higher than the typical ground-level setup. Mount your AI-powered camera on a tree trunk or a sturdy post at a height of 6 to 10 feet, aimed toward horizontal branches where the bird is likely to perch while scanning for prey. These birds prefer 'edge' environments where the forest meets a clearing, as the increased light attracts more of the flying insects they crave.

Since they do not visit traditional seed or suet feeders, the best 'bait' is a water feature. A birdbath with a solar-powered dripper or a small recirculating waterfall is highly effective. The sound of moving water is a powerful magnet for canopy-dwellers in tropical climates, often enticing them down from the high branches for a drink or a bath. Position your camera about 3 to 5 feet from the water source to ensure the AI can clearly identify the yellow wing margins and pale iris.

Lighting is your biggest challenge in the humid forest. Try to place your camera in a spot that receives filtered morning light, and set your camera to a fast trigger speed—ideally 0.2 seconds or faster. Because these flycatchers move in quick, explosive bursts, using a high-frame-rate video setting (60fps or higher) will allow you to capture the detail of their flight patterns. During the rainy season, ensure your camera housing is well-maintained, as these birds remain active even during light tropical showers.

Similar Species

Species that look similar or are commonly confused with Yellow-margined Flatbill.

Yellow-olive Flatbill

Has a darker iris and a more uniform olive-colored crown compared to the Yellow-margined.

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Frequently Asked Questions

They are most active during the first few hours of daylight (6-10 AM) when insects are most mobile. They often have a second peak of activity in the late afternoon before the sun sets.

Focus on attracting their food source by avoiding pesticides and planting native shrubs. A moving water feature, such as a dripper or misting system, is the most effective way to bring them down from the canopy.

They are insectivores that specialize in 'sallying' for flying insects or 'gleaning' larvae and beetles directly from the undersides of tropical leaves.

They are common in suburban areas only if those areas are adjacent to mature forests or contain large, old-growth trees that mimic their natural forest habitat.

Look at the eyes and the crown. The Yellow-margined Flatbill usually has a paler, whitish iris and a slightly grayer crown, whereas the Yellow-olive Flatbill has a darker eye and more uniform olive-green head.

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