Land use change is one of the greatest threats to global biodiversity, and agricultural intensification has severely affected farmland birds in Europe. As a rapidly declining long-distance migrant and obligatory brood parasite, the common cuckoo Cuculus canorus is an interesting species on which to investigate the impacts of land use on birds. My thesis focuses on understanding the causes and mechanisms behind cuckoo declines in Britain by exploring relationships between land use, cuckoos, their hosts and adult cuckoo prey. Cuckoo population trends vary between habitat types, resulting in changes to cuckoo-habitat associations. There was little evidence of preference for semi-natural or agricultural habitats where cuckoos were widespread before their declines began, but they were strongly selective of semi-natural grass, heath and woodland by the 2000s while avoiding farmland. This suggests that female cuckoos specialised in parasitizing dunnocks (Prunella modularis) are now scarce while meadow pipit (Anthus pratensis) cuckoos have been retained in semi-natural habitats. However, as habitat cover had a consistently stronger statistical effect than host abundance on the presence or retention of cuckoos, the availability of other resources may limit current cuckoo distribution. The probability of cuckoo presence increased with the abundance of known cuckoo prey, predominantly large, hairy moth caterpillars. These species have undergone greater declines than other moths and their population trends also vary by habitat: abundance has increased in semi-natural habitats but declined in improved grassland and woodland. Therefore changing prey abundance may be a key driver of cuckoo declines in farmland. Although fundamental questions on the causes of cuckoo declines remain unanswered, maintaining semi-natural habitats as a stronghold for cuckoos in Britain might be an effective conservation strategy in the immediate future. However, measures adopted under agri-environment schemes which increase moth abundance may offer long-term mitigation of cuckoo declines while benefiting other insectivorous species.

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. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

2 spread sheets included. Title from title page of PDF (University of Missouri--St. Louis, viewed February 8, 2010). Includes bibliographical references.

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