Dark with White Rumps
The first Storm-petrel you will see in our waters is the Wilson's Storm-petrel and at the right time of the summer you will see thousands. The Gulf of Maine and Stellwagen Bank are probably the best places in the world to see this bird. Do not take it for granted.

Wilson's Storm-petrels or WSP are all dark underneath  with white rumps and light crescent shaped bars on upper wing.  The same describes three other storm-petrels we look for: Leach's, Band-rumped, and European Storm-petrel. A fifth storm-petrel the White-faced Storm-petrels is most distinct.  See the page devoted to this bird.

Is That Bird Different ?
Size and slightly different  flight characteristics will first draw your attention to a different bird among the many WSPs.  Look to see if the feet are visible trailing behind the tail. If they are not  your suspicions are confirmed,  stay on the bird. Please announce that you are on a small or large Storm-petrel so that others can get on the bird too. 

 If the bird is smaller than the WSP try to see the under wing.  Look for a broad, white bar indicative of a European Storm-petrel. The crescent shaped wing bars on the upper wing are faint.

If the bird is larger than the WSPs  it may be either Leach's or Band-rumped Storm-petrel.  If you are in warm water it may be Band-rumped Storm-petrel.  In cold or warm water look for the forked tail and divided white rump patch to nail Leach's.

Size & Flight - No Trailing Feet  - Water Temperature - Under wing - Rump & Tail

WSP Feet trail behind tail when flying

WSP White Rump wraps around the sides. Crescent shaped bar on upper wing does not reach leading edge

Storm-petrels all dark with  white rumps which may be found in New England waters
The following table summarizes these characteristics.  Study the page for each bird  for more pictures and information. Flight characteristics can only be learned by study at sea in different wind conditions.

Two characteristics: color of toe webs and whether the white rump wraps around the rump are not field characteristics.  They do show up in the many excellent photographs that people are sharing with us and can be used to confirm a field identification.

¹ Harrison 1983