Acrocephalus palustris
Records: 75
Drafted by: Faansie Peacock
Draft Text Last Updated:
Distribution: This species was recorded from Mkhombo
Dam in the north (10 records) to Suikerbosrand Nature
Reserve (1 record). Most records seem to be concentrated to the n and e of
Gaps in Knowledge: Comparison of numbers between years will indicate if any significant level of nomadism or major numerical influxes occurs in response to specific rainfall patterns. Data is currently rather patchy, and fuller coverage will perhaps present a better picture of distribution and status and provide for more detailed and less biased population estimates. Records in early summer should be verified.
Habitat: Catholic in habitat choice. A main criterion seems to be habitat structure, and not species composition or climate. Dense, lush covered in the form of tall grass, weeds or scrub is required, often under the shady canopy of Acacia, Combretum or Ziziphus. Although not directly associated with water, often occurs in clumps of bush in a wetland situation or in taller vegetation on the edges of vleis and pans. In the highveld, they are commonly found on the edges of exotic plantations (given that suitable understorey vegetation is present). Unlike many other species in the genus, it very rarely occupies reedbeds. Sylvia and Hippolais, all of which have similar habitats and superficially similar songs, tend to occur higher up in vegetation, the Marsh Warbler restricted to the understorey, below 2m. An exception to this is the Whitethroat, Sylvia communis, which can be sympatric with the Marsh Warbler in certain situations.
Status and movements: Non-breeding, Palearctic migrant, records spanning 4 September to 18 April. This species is normally present only from late November (most arrive in December) to April. The validity of all records before December are questionable, as this species is difficult to identify (both vocally and visually), and African Reed Warblers, A. baeticatus, which arrives in early September, often atypically occupies habitat in which Marsh Warblers would be expected to occur (i.e. thickets and weeds in stead of the normal wetland habitats), especially early in the season before breeding territories are established (pers. obs). Data peaked in the first half of February when 16 birds were recorded. Calling intensity and frequency increases significantly towards the end of the non-breeding season – this is reflected in the much higher numbers recorded later in the season. Even including the dubious September and October records, only 15 birds were recorded during the period September – January, while 50 records span February – April. During the PCC period, this species was ringed at Rietvlei Dam Nature Reserve (R. Geyser).
Population: Locally very common. In the Moreleta Kloof, linear densities of 1bird / 13.3m with 15 birds / 200m of riverine woodland have been measured (pers. obs). The population in the PCC area probably exceeds 10 000 birds in late summer. Generally densities are lower on the highveld.
Conservation: Owing to its wide habitat choice, being equally at home in disturbed areas with regenerating vegetation and in natural ecosystems, this species is not threatened.