Knysna warbler  (Bradypterus sylvaticus)

The Knysna warbler is classified as Vulnerable (VU) on the IUCN Red List (1).

The Knysna warbler (Bradypterus sylvaticus) is a medium-sized, brown warbler found only in coastal regions of South Africa (2). This somewhat drab bird has pale brown upperparts, with an olive coloured head, as well a grey throat and olive-brown legs (2) (3). The fine, narrowly-pointed bill is pinkish-brown, and the eyes are brown (3) (4). 

Like other warblers of the family Sylviidae, the Knysna warbler has strong feet, well suited to perching, and a long tail that provides balance as it threads its way through dense foliage (4). 

The Knysna warbler is often mistaken for the African scrub-warbler (Bradypterus barratti), but may be primarily distinguished by its shorter tail and by the lack of spotting on the throat. The Knysna warbler is also identified by its song, which is an accelerating trill (2).

Endemic to South Africa, the Knysna warbler is found in remnant forest patches in coastal regions of the Eastern and Western Cape. It has a highly fragmented distribution, with four main areas of occupancy: the coast between Port St Johns and Dwesa Nature Reserve; the Southern Cape, from Tsitsikamma to Sedgefield; the south slopes of the Langeberg Mountains, near Swellendam; and the east slopes of Table Mountain (2). 

The Knysna warbler was also once found around Durban, but is now thought to be extinct at this location (2).

Inhabiting thick, tangled vegetation, the Knysna warbler is often found along the banks of watercourses, including drainage lines in fynbos forest patches, or on the edges of montane forest. The Knysna warbler has also adapted well to thickets of non-native brambles (2).

The Knysna warbler feeds mainly on the ground, upturning leaves and stones in search of a variety of invertebrates, including butterflies, bees, wasps, locusts and ants (3) (5).

Over the last 20 years, the Knysna warbler has experienced a widespread and severe population crash. The total number of individuals of this species is now estimated at only around 2,500 (2). In the Western Cape, the Knysna warbler population has halved since the 1980s (5), and this species has disappeared from around Durban. The most likely cause of this decline is habitat loss through the clearing of coastal forests and the burning of fire-breaks at the edges of forests (2). 

The Knysna warbler is becoming increasingly rare in native woodlands and now more commonly occupies stands of non-native plants and suburban woodland (5) (6). It is possible that in native woodlands the suppression of natural fires, which are a frequent natural disturbance and help regenerate native habitats, is reducing the availability of nesting sites for this species, causing it to nest elsewhere (6). 

Additional threats to the Knysna warbler include inbreeding depression in the tiny, fragmented Eastern Cape population. The removal of brambles, which are the subject of an eradication campaign, may also remove nesting sites for this species (2).

Parts of the range of the Knysna warbler fall within protected areas. The Table Mountain population is afforded some protection by the Cape Peninsula Protected Natural Environment, while this species is also known to occur in Tsitsikamma National Park and in Dwesa and Cwebe Nature Reserves (2). 

Proposed conservation measures for the Knysna warbler include further surveys to clarify the extent of its distribution and abundance, research into its habitat preferences and biology, and investigations into the genetic diversity of small, isolated populations (2).

Find out more about the Knysna warbler:

• BirdLife International - Knysna warbler (May, 2011)
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=7560