[katherined]

Hope someone can help. Saw a bird yesterday I have never seen before. Closest I could find was a Black Throated Warbler. Right size and shape, except this bird was stark black with bright white under the wings and under belly. Was not a swallow, wrong tail and shape. Any ideas? Saw just off Mara Lake

[Birder2000]

Sounds like your bird is either a Yellow-rumped Warbler or a Black-throated Grey Warbler.