Depends on how you define "remains"
Basically the big pieces wash or are blown off
What remain days later in some cases are goop streaks of dry blood and tissue in dead air zones. ultra-violet light reflects back as yellow-green. After a scrape and a filtration wash of what looks like a finger-nail scraping a puff of down feather may pop out and presto the bird species and maturity is confirmed. Works for other foreign material like, dirt or blue-ice as well.