Kevin - two helpful hints in separating Sharp-shins from Merlins is the amount of tail extension and eye color. Accipiters have relatively longer tails and shorter rounded wings such that when viewing the perched profile of a bird the tail extends well beyond the tips of the wings...see Sibley pp. 112-113. Falcons have relatively shorter tails and longer pointed wings such that the tail extension beyond the wingtips is much shorter thasn in an Accipiter. See Sibley pp. 131-133. In some instances there is barely any tail extension beyond the tail based on birds I have held in the hand while banding them.
Eye color is also helpful in that falcons of all ages have dark brown eyes. Young Accipiter eyes are yellow and transition with age through orange to fiery red.
Just remember to look 'em in the eye.
From: Kevin Thorley <[log in to unmask]>
To: VTBIRD <[log in to unmask]>
Sent: Sat, Feb 2, 2013 2:20 pm
Subject: [VTBIRD] Identification help - Merlin in January?
I took these a few weeks ago at Colchester Bog. The quality is awful, but
I am hoping it is enough for someone to help with an ID. According to the
Sibley guide, Merlins are not likely to be seen here in the winter. My
other guess would be an accipiter. Thoughts?