Green’s Dictionary of Slang

pecker n.1

[peck v.1 (1) ]

1. the head in the context of eating.

[UK]R.S. Surtees Young Tom Hall (1926) 59: [of a horse] He’d be constantly having his pecker in the manger, and peckers in mangers cost money.
[Aus]Bell’s Life in Sydney 4 Sept. 3/1: The said bonnet being perched over her pecker.
[UK]R.S. Surtees Mr Sponge’s Sporting Tour 166: When I saw the critter’s great pecker steadily down in his plate, I thought I would try and steal a march upon him.

2. an eater.

[UK]C.C. Robinson Dial. Leeds n.p.: He’s a rare pecker [EDD].
[UK]Sl. Dict. 249: Peck, A hearty eater is generally called ‘a rare pecker’.
[UK]Leeds Times 19 Nov. 7/6: He’s known to be a rare pecker at summat to heyt.
[UK]Farmer & Henley Sl. and Its Analogues.

3. the appetite [B&L suggest -er sfx].

[UK]Barrère & Leland Dict. of Sl., Jargon and Cant.
[UK]Farmer & Henley Sl. and Its Analogues.