See under redstart(def 2).
Origin of American redstart
An Americanism dating back to 1800–10
any of several small, Old World thrushes, usually with reddish-brown tails, especially Phoenicurus phoenicurus (European redstart).
any of several fly-catching, New World warblers, especially Setophaga ruticilla (American redstart), having black and white plumage with reddish-orange patches.
Origin of redstart
1560–70; red1 + obsolete start tail (Middle English start, stert tail, handle, Old English steort tail; akin to Old High German sterz, Old Norse stertr)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
any European songbird of the genus Phoenicurus, esp P. phoenicurus, in which the male has a black throat, orange-brown tail and breast, and grey back: family Muscicapidae (thrushes, etc)
any North American warbler of the genus Setophaga, esp S. ruticilla
Word Origin for redstart
Old English rēad red 1 + steort tail; compare German Rotsterz
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
type of bird, 1560s, from red (adj.1) + start "tail," from Old English steort. Cf. German Rotsterz.
Online Etymology Dictionary, © 2010 Douglas Harper