Definition of "birdsmouth"

Support the veneer stack on a ¾-in.-thick board with a narrow V notch cut into one edge. This board is called a birds-mouth, and the V notch provides clearance for the blade while the work is supported for cutting.

1994 July, Rosario Capotosto, “Inlay: How to Add Understated Elegance to any Woodworking Project”, in Popular Mechanics‎, page 68

After the wall and ceiling framing has been completed the erection of the roof takes place. Nail the four straight rafters selected as the first and last into position at the birdsmouth.

1995, Charles Simpson with Barry Hodgson, Building a House: Framing Practices, South Melbourne: Macmillan Education Australia, page 160

birdsmouth, sally; in timber frame construction, a notch cut into the end of an inclined timber to receive a horizontal timber running perpendicular to it; used for the housing of rafters; other similar notches in other components: birdsmouth brick a special brick manufactured with an indented end, designed for use in decorative brickwork and at an internal obtuse corner in a brick wall. […] birdsmouth joint, birdsmouthed notched joint; in timber roof construction, a joint formed by notching the extremity of a rafter with a birdsmouth and fastening it to a wall plate; any joint similar to this.

2011, Nikolas Davies with Erkki Jokiniemi, Architect's Illustrated Pocket Dictionary, Kidlington, Oxford, Burlington, Mass.: Architectural Press, pages 44–45

There are various ways of tying rafters to sidewalls, and the choices may vary depending on roof pitch. One of the most common is the use of “birdsmouths” cut into the rafter. A notch is cut into the rafter so that the rafter bears down flat upon the doubled top plate of stick framing, or upon the girt in heavy timber framing.

2013, Rob Roy, “Basic Timber Frame Structure”, in Timber Framing for the Rest of Us: A Guide to Contemporary Post and Beam Construction, Gabriola Island, B.C.: New Society Publishers

A birdsmouth is a notch cut into the underside of a roof rafter to enable it to sit tightly and securely on the timber wallplate that runs across the top of a wall. It's so called because it resembles the wide-open mouth of a baby bird wanting to be fed.

2014 November 8, Jeff Howell, “The value of keeping the pressure up”, in The Daily Telegraph‎, London, archived from the original on 7 May 2015, page P13