Red-knobbed Coot

Nest: Built by both sexes, occasionally with help of juvs⁴⁰. Usually floating mound of sedge stems, grasses, leaves and stems of Bulrushes Typha capensis, weed stems or reeds. Has ramp on 1 side, and a deep open cup on top, lined with finer material⁴⁰. On shallow (but > 1 m) to deep water, out in open or among emergent vegetation, sometimes on water lily leaves or mat of reeds³⁶. If within emergent vegetation, may be built on a base of bent and trampled stems, site allowing quick and easy access to open water³⁶. Material added during incubation; off-duty bird brings material that is incorporated into nest by incubating bird³⁶. Builds 'false nests' and rafts as resting platforms⁴⁰. Usurped Whiskered Tern nests¹².

Laying dates: Botswana Jul (1), Aug (6), Sept (7), Oct (18), Nov (5), Dec (4), Jan (6), Feb (3), Mar (10), Apr (15), May (3), Jun (7)²⁹; Zimbabwe Jul (10), Aug (15), Sept (3), Oct (2), Dec (1), Jan (7), Feb (8), Mar (13), Apr (23), May (44), Jun (21)¹⁴; ne S Africa Jul (55), Aug (15), Sept (31), Oct (10), Nov (13), Dec (34), Jan (32), Feb (55), Mar (50), Apr (24), May (11), Jun (27)³⁴; KwaZulu-Natal Jul (7), Aug (2), Sept (6), Nov (5), Jan (3), Mar (1), Jun (1)⁷; W Cape Jul (245), Aug (649), Sept (927), Oct (471), Nov (93), Dec (42), Jan (21), Feb (5), Mar (12), Apr (2), May (7), Jun (14)²¹.

Eggs: Usually 2-6 (4.4, n = 82), rarely up to 10^6,10,22 or 11¹⁸. Oval. Bu ff or yellowish stone, with small purplish-brown dots³². Size (n = 243) 49.0-61.1 x 32.8-42.0 mm (53.6 x 37.7 mm)¹⁸. Mass (n = 3) 45-46 g (45.3 g)⁶.

Incubation: Period 18-25 d; by both sexes, with frequent changeovers. Incubating bird sits tight⁴⁰.

Development & care of young: Newly hatched young mostly covered with ashy to grey-black down above, longest filaments on back and mantle tipped white. Also with bare pink and blue spot on crown, and golden hair-like down on neck and collar. Underparts paler grey, tinged silvery or blue-grey. Bill red, tipped orange-pink (extreme tip black, with narrow subterminal white band). Eyes brown. Legs and feet pale grey-green, tinged pink³⁶. Breast feathers emerge first, flight feathers last³⁶. Newly hatched young gives peeping calls⁴⁴. Precocial, able to leave nest at 1 d and to dive soon after hatching³⁶. Fed and cared for by both ads, sometimes with help of juvs from earlier brood³⁶. Fledging period probably 55-60 d³⁶. Broods often divided unequally among ads and helpers, and remain separated at least until fledged; little intra-family hostility shown by divided broods^8,36.

Breeding success: In W Cape, 175 of 504 eggs hatched (n = 109 nests); 56 nests failed through predation (20), wave action (18) and rising water level (18); Grey Heron the only identified predator⁴⁸. Mayfield nesting success 49.8% for nests, and 56.9% for eggs, giving overall br success of 29.3%⁴⁸. In Namibia, 43-75% of nests parasitised by conspecifics; hosts rejected 69% of parasite eggs¹⁵. In Gauteng, eggs contained high levels of heavy metals⁴², very likely leading to poor hatching success and early chick mortality.

Author:WRJ Dean