The shy Dartford warbler is one of the iconic species of the Pebblebed heaths and the existence of significant breeding populations of this species on the heaths was one of the reasons they were designated as a Special Protection Area in 1996.
Its distribution is centred on the Iberian peninsula with southern England representing is northernmost limit. Its northwards spread is limited by climate as this species barely survives temperatures below freezing, and documented crashes in its population are usually linked to severe winters (e.g. 1962-63/2010-2011).
Within England its breeding habitat is almost entirely undisturbed lowland heathland dominated by either gorse or heather, and its distribution is closely linked to the stonechat (Saxicola torquata), a species which requires a greater need for perches affording good views, but much less for concealment.
The Dartford warbler remains on the heaths all year round, with populations being largely sedentary. It feeds almost exclusively on arthropods found in gorse, with beetles and spiders being particularly favoured. During the spring and summer caterpillars are also consumed, with these preferentially fed to the young. The species is highly territorial with territories ranging considerably in size depending on the quality of the habitat and availability of food. A typically good habitat with a high abundance of gorse of the right age and with abundant food might be about one hectare. Once chosen, individuals or pairs show strong site fidelity.
The main song period is from March to late September, and when perched the singing bird tends to turn from one side to the other, with crown and throat ruffled. Their nests are positioned close to the ground and are small and compact, made from leaves and bits of heather. Typically about four eggs will be laid from the end of March, with these hatching after about 14 days, with the young reaching fledgling stage after a further two weeks. Independence is gained another two weeks after leaving the nest.
The population of Dartford warblers on the heaths are monitored annually. The population was severely impacted by the harsh winter of 2010/11 and is now in a state of recovery.
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