By Obaka Torto, Tue, 28/04/2015 – 14:13
Over the last year, intensive effort has been under way to survey and monitor the Critically Endangered Long-billed Tailorbird, in the East Usambara Mountains in Tanzania, to provide information on the species’ distribution and habitat requirements.
The Long-billed Tailorbird Artisornis moreaui occurs at only two locations: the Njesi plateau in northern Mozambique; and the East Usambara Mountains in northern Tanzania, which holds the majority of the population. These sites are separated by almost 1000 km and, despite much searching, the species has not been observed elsewhere. The bird’s known range is just a few hundred square kilometers, an area substantially smaller than cities such as Nairobi or Dar es Salaam.
The Long-billed Tailorbird has an unusual ecology. It is strongly forest dependent, not occurring outside of the forest, or in forest fragments smaller than 300 ha. Moreover, the bird is restricted to relatively open parts of the forest, such as canopy gaps, stream lines and forest edges. Unfortunately, its habitat requirements and distribution coincides with the places where humans are also active, such as along streams and areas bordering the forest. Thus, habitat disturbance by humans often threatens this tailorbird.
Smallholder, subsistence agriculture as well as commercial crops have replaced over 60% of the indigenous forest. What remains is often heavily disturbed, severely fragmented, and degraded by numerous invasive plants, introduced to the Tanzania site via the development of the Amani Botanical Garden. Nesting sites are often destroyed due to bush clearance for agriculture or thatching. The frequency of observation along forest edges is about 30% lower than in forest interior, and edge territories tend to be occupied for shorter time spans, suggesting that birds often abandon their nesting sites due to higher levels of disturbance.
The BirdLife International project office in Tanzania, in collaboration with the RSPB, has initiated a multi-year project to conserve the endemic and threatened biodiversity of the East Usambaras, with a focus on the Long-billed Tailorbird. Over the last year, a top priority has been to carry out intensive field work to draw a high resolution map of the distribution of this species. A field team of local ornithologists have been trained to recognise the species: a small, skulking and often unobtrusive bird, which is well known for being difficult to observe.
Armed with GPS, binoculars, laser rangefinders and aerial photos, the local team have been combing an area of more than 200 km², recording all the observations with a resolution of a few metres. The resulting maps show a cluster of points that correspond to an estimate of 80-120 territories, some of which have been continuously occupied for about eight years. The map shows sites that have the highest concentration of observations, as well as where human activities are more likely to cause the highest levels of disturbance. This intensive fieldwork has resulted in the discovery of 17 new territories of this Critically Endangered bird: this is a fantastic breakthrough which will enable project staff to target conservation efforts and to provide more information on the status of the species.
Story by Dr Norbert Cordeiro, Dr Luca Borghesio, Alice Ward-Francis (RSPB) and Festo Semanini (BirdLife International)