Black Antshrike
Thamnophilus nigriceps
The black antshrike is 15 to 16 cm (5.9 to 6.3 in) long and weighs 23 to 24 g (0.81 to 0.85 oz). Members of genus Thamnophilus are largish members of the antbird family; all have stout bills with a hook like those of true shrikes. This species exhibits some sexual dimorphism. Adult males are almost entirely black. They have dark gray flanks and their underwing coverts and edges of the underside of their flight feathers are white. Adult females have a blackish gray head and upper breast with buff-white streaks. Their upperparts, wings, and tail are rufous-brown. Voice: The black antshrike's song is "a moderately long...slightly accelerating, evenly pitched series of somewhat musical yet emphatic notes". Its calls include a "hollow, nasal note sometimes repeated" and a "nasal growl".
ID text from Wikipedia, CC BY-SA 4.0
White-shouldered Antshrike
Thamnophilus aethiops
The white-shouldered antshrike is 15 to 17 cm (5.9 to 6.7 in) long and weighs 23 to 30 g (0.81 to 1.1 oz). Members of genus Thamnophilus are largish members of the antbird family; all have stout bills with a hook like those of true shrikes. This species exhibits significant sexual dimorphism. Adult males of the nominate subspecies T. a. aethiops are mostly black. They have a few white spots on their wing's lesser coverts and the bend of the wing, white underwing coverts, and a blackish gray lower belly and crissum. Adult females are entirely deep reddish brown. Voice: The male white-shouldered antshrike's song is "a short and slowly paced...series of low-pitched, complaining notes delivered at steady pace and even pitch and intensity"; female song is similar but higher-pitched. It has been written as "anh...anh...anh...anh...anh" given at about one note per second.
ID text from Wikipedia, CC BY-SA 4.0

Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Black Antshrike and White-shouldered Antshrike.