Is the Cape Weaver population on Robben Island isolated?
Vegetation of Robben Island
The natural vegetation on Robben Island is Strandveld. After European occupancy of Robben Island in the 17th century, Eucalypyus and other exotic trees were introduced. Some of these were planted to provide shade for leper patients (1846-1931). Cape Weavers now breed in the exotics. Unfortunately no one seems to have recorded when Cape Weavers first started breeding here.
Bird movements between the mainland and the island
The extent to which Cape Weavers and other passerines move between the mainland and Robben Island is not known. The initial population must have been established through weavers flying the 8 km stretch across the ocean. There has been one recovery of a Cape Weaver ringed on the mainland and recovered on Robben Island.
CC27773 was ringed on 20/08/1997 in Protea Valley, Tygerberg, as an immature male by Margaret McCall. It was found a little over a year later as a skeleton on Robben Island by Mr J Kieser. He found the ring on 02/12/1998 and sent it to SAFRING. The distance between ringing and recovery sites is 22 km. This is the only non-seabird recovery on Robben Island (only seabirds had been ringed on the island).
To discover if there are regular, or only occasional, movements between the mainland and the island, I started to ring weavers on Robben Island in 2000. The weaver population is small, resulting in small numbers being ringed. Large numbers are ringed on the mainland around Durbanville by the Tygerberg ringers. I decided to ring once annually on the island during the breeding season, and did so in 2000 and 2001. At the time I thought that the weavers went to the mainland during winter where there would be more feeding opportunities. In early May 2002 I visited the island to ring Swift Terns and discovered that there were lots of weavers. Thus I now also want to ring once every winter.
38 Cape Weavers have been ringed on Robben Island to date. Many hundreds have been ringed around Durbanville over the last two years but there have been no retraps yet showing movement between mainland and island.
Ringing totals of Cape Weavers on Robben Island:
|16-17 October 2000 || 11
|6-7 November 2001 || 16
|17-18 May 2002 || 11
Male Cape Weaver at nests in Eucalypt on Robben Island
Cape Weaver colonies on Robben Island
|Workshop colony||Eucalypt||33°48.441'S 18°22.638'E||16 m|
|Church colony||Cedar||33°48.342'S 18°22.603'E||25 m|
|MCM house colony||Cedar||33°48.'S 18°22.'E|| m|
Map of Robben Island showing the Workshop and Church colonies
Read more about Robben Island
Contact: H Dieter Oschadleus, weavers4africa [at] gmail.com