Host suitability in the Diderik cuckoo Chrysococcyx caprius - ploceid brood parasitism breeding system.
Loading...
Date
2003
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Host suitability is critically important to the success of brood parasitism. Parasites must
select a host that not only accepts its egg but also is capable of successfully rearing the
parasite to fledging. Nearly all brood-parasites appear to avoid low-quality hosts that are
likely to reject their eggs, that are of inappropriate size, or that feed their nestlings
nutritionally inadequate or insufficient food. The diderik cuckoo, (Chrysococcyx caprius),
is an obligate brood parasite known to parasitise a wide spectrum of ploceids, including the
yellow weaver (Ploceus subaureus) and the southern red bishop (Euplectes orix). Theory
predicts that brood parasites should exploit insectivorous passerines of similar adult size to
themselves that provision large quantities of high protein food to their young. However,
the relatively smaller granivorous red bishop is the most heavily parasitised host species of
the diderik cuckoo in southern Africa. To investigate why an apparently unsuitable host
species was so heavily parasitized several populations of parasitised red bishops and
yellow weavers (omnivores) were studied in the Pietermaritzburg region, KwaZulu-Natal,
South Africa. Host suitability was assessed by examining diet quality, host-provisioning
rates, cuckoo nestling growth and cuckoo fledging success. Diderik cuckoo nestlings were
provisioned the same diet as the host nestlings in red bishop and yellow weaver nests.
However, cuckoos in bishop nests received a protein-deficient seed diet from as early as
six days following hatching. In contrast, weaver-cuckoo faeces contained 1~ times more
insect than their bishop counterparts throughout their nestling period. Provisioning rates by
bishop females were significantly slower than by yellow weavers, and neither bishop nor
weaver hosts showed any 'supernormal' effort when feeding a young cuckoo. Both host
species provisioned cuckoo nestlings at a similar rate and with a similar food mass as their
own nestlings. Diderik cuckoos in bishop nests grew at a slower rate and fledged in a
poorer condition than their yellow weaver counterparts. Red bishops are likely the most
exploited host of the diderik cuckoo because i) cuckoo eggs are more readily accepted by
the less discriminating bishop and ii) the bishop-breeding season coincides more closely
with that ofthe diderik cuckoo than the yellow weaver. Thus, diderik cuckoos may
preferentially exploit bishop hosts because of the low frequency of cuckoo egg rejection,
which ultimately results in many cuckoos fledging from bishop nests despite the lowquality
diet provisioned and 53% (n = 53) fledging success in nests of this species. In the
yellow weaver system, the protein-rich diet and the greater probability of cuckoo nestling
survival (80%, n = 5) may compensate for the high rejection rate of cuckoo eggs by this
host. Thus, both host systems seem to represent evolutionary compromises for the diderik
cuckoo, with neither red bishops nor yellow weavers being entirely ideal as host species.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.
Keywords
Chrysococcyx., Ploceidae--South Africa., Cuckoos., Birds--Parasites., Weaverbirds., Theses--Zoology.