Here is a nice article written for Vermont Ebird about Lincoln's Sparrows:

In my experience they are often, but not always in mixed species sparrow flocks, and rarely, if ever singing in the fall. 

Spencer Hardy, 

On Sep 18, 2013, at 5:42 PM, Martha Pfeiffer wrote:

> Does the Lincoln's sparrow mix with Fall Song Sparrows - or is it a solitary bird?  Is it singing in the Fall?
> Would appreciate any info anyone can give.
> Martha Pfeiffer
> Dorset