GLEANING OF MARSH TERRAPINS BY THREE DIFFERENT BIRD SPECIES

Ectoparasites that occur on both mammals and reptiles represent a significant food source that is exploited by a number of different bird species. Best known and most specialised of these are the oxpeckers Buphagus sp. and gleaning of mammals by birds is well documented (see: Dean & MacDonald, 1981; Dean & Vernon, 1988; Roche & Kilpin, 2003). Similar behaviour involving birds and reptiles is less well documented and observations of this behaviour at &Beyond Phinda Private Game Reserve are recorded here in order to add to this literature.

By the beginning of October 2005 water levels at Ximgonwe Dam, a large water body in the southern parts of Phinda, were extremely low. As a result large exposed areas without vegetation on the edge of the water were utilised by high numbers of Marsh Terrapins Pelomedusa subrufa that emerged to bask in the warm morning sun.

While birding with guests at the dam one morning at about 08h30, between eight and fifteen terrapins began to emerge from the water, scattered all along the edge of the dam. The emergence attracted the attention of a single Common Sandpiper Actitus hypoleucos foraging on the shoreline at a distance of about 50m. The sandpiper immediately hurried towards the terrapins and proceeded to pick ticks, visible through my binoculars, from first one terrapin then another.

After about 15 minutes this interaction between the two species attracted the attention of a Black Crake Amaurornis flavirostris which emerged from the reeds on the far bank of the dam. The crake also appeared to recognise the foraging opportunity and made its way hurriedly around to the terrapins where it too began to glean unidentified ticks from the reptiles. Approximately ten minutes later an African Jacana Actophilornis africanus also made its way over to the basking terrapins and began to take advantage of the food source, plucking ticks from the reptiles in the same manner as the sandpiper and crake. Although this last species was not as vigorous in its utilisation of the ectoparasites, it was clear that all three bird species eagerly took advantage of this (presumably) unusual food source. It was equally clear that the terrapins were comfortable with the attention and were even observed to adjust head and limb angles to allow the birds easier access to the ticks.

All three bird species observed in this instance have been recorded gleaning ectoparasites from Hippopotamus Hippopotamus amphibius (Pooley, 1967; Dean & MacDonald, 1981; Hockey et al, 2005) and also, in the case of the Black Crake, from Warthogs Phacochoerus africanus (Dean & MacDonald, 1981). There does not however appear to be any record of similar behaviour in these species gleaning reptiles such as terrapins. Terrapins themselves are known to feed on ticks present on wallowing White Rhinoceros Ceratotherium simum (Skinner & Chimimba,
 ), but no intraspecifi c gleaning was noted on this occasion.

References
DEAN, WRJ & MACDONALD, IAW. 1981. A review of African birds feeding in association with mammals. Ostrich 52 (3): 135-155.

VERNON, CJ & DEAN, WRJ. 1988. Further African bird-mammal feeding associations. Ostrich 59 (1): 38-39.

HOCKEY, PAR, DEAN, WRJ & RYAN, PG (eds) 2005. Roberts – Birds of Southern Africa, VIIth Edition. The Trustees of the John Voelcker Bird Book Fund, Cape Town, pp 326-327; 360-361; 382-382.

POOLEY, AC. 1967. Bird/crocodile and bird/hippopotamus commensalism in Zululand. Ostrich 38 (1): 11-12.

ROCHE & KILPIN, 2003. Mammal gleaning by the Terrestrial Brownbul and Eastern Nicator. Ecological Journal 5: 34.

SKINNER, JD & CHIMIMBA, CT. 2005. The Mammals of the Southern African Subregion. Cambridge University Press, Cape Town.

Posted: Birds by Daryl Dell, Date: 12 December 2010