Cobb's Wren (Troglodytes cobbi) is a fairly small (12-13.5 cm) wren which is endemic to the Falkland Islands. It was formerly classified as a subspecies of the House Wren (Troglodytes aedon) but is now commonly considered to be a separate species due to differences in plumage, voice, ecology and morphology.
The plumage is brown, greyer on the head and breast and more rufous on the tail. There are dark bars on the flight feathers and tail. The bill is long, blackish and slightly curved. The main confusion species is the Grass Wren which is smaller with a shorter bill, buff eyestripe and dark streaks on the back and head. Cobb's Wrens have a number of buzzing calls and their song is a series of jumbled trills and whistles. The song can be heard from August to February and varies between individuals with different males having different song patterns.
The birds typically inhabit dense stands of tussac grass near the coast. They are often found on beaches searching among kelp and debris to find small invertebrates such as insects and amphipods. They are tame and can often be approached closely. When disturbed they prefer to slip away like a mouse between boulders or tussac clumps rather than fly.
The nest is a ball of grass lined with feathers and tussac root fibres. It is built on or near the ground among tussac or in a rock crevice. The eggs are pinkish with small reddish spots, three or four are laid in a clutch. The eggs are laid from early October to December and two broods are probably raised during the breeding season.
This wren is restricted to small rat-free islands with a population of only 4,500-8000 pairs (1997/1998 estimate). The species is considered to be vulnerable to extinction as it is fragmented into small populations which could disappear if their islands were colonized by rats or cats. The birds habit of feeding and breeding at ground level makes them very vulnerable to predation unlike the Grass Wren which lives higher up and can coexist with predators.
The plight of the Cobb's Wren was recently brought to broader attention by being featured as Canon's endangered species of the month for the February 2009 issue of National Geographic Magazine.