Restriction analyses were conducted on mitochondrial DNA (mtDNA) amplified by long-PCR from an endangered bird, the Cape Sable seaside sparrow. The first of several successful mtDNA amplifications was accomplished using the partially digested tissue remains of a transmitter-monitored bird retrieved from the gut of a snake. As many as 91 mtDNA restriction fragments produced by 18 endonucleases were compared in this and four other Cape Sable specimens against mtDNA similarly amplified by long-PCR from other taxonomic forms in the seaside sparrow complex. Results indicate that the Cape Sable birds belong to an 'Atlantic' matrilineal clade, and are highly divergent from other seaside sparrows along the Gulf of Mexico.