Investigating a link between bill morphology, foraging ecology and kleptoparasitic behaviour in the fork-tailed drongo
Highlights
► Fork-tailed drongos kleptoparasitize pied babblers. ► We analyse bill morphology and foraging differences between drongos and babblers. ► Drongos target excavated prey when kleptoparasitizing babblers. ► Drongos possess significantly shorter, thicker bills than babblers. ► Procuring subterranean prey may partially incentivize kleptoparasitic behaviour.
Section snippets
Study Site and Field Methodology
Field work was carried out at the Kuruman River Reserve, Northern Cape Province, South Africa (26°58′S, 21°49′E) between 28 April and 28 May 2006. The study site is located in the southern Kalahari Desert and is characterized by semiarid grassland and acacia savannah, with an average rainfall of 217 mm per annum (see Ridley & Thompson 2011 for a detailed description of the habitat). All drongos and babblers in the study population were habituated to allow observation at a distance of 2–3 m
Bill Morphology
The differences between drongo and babbler museum specimens and specimens from the study site were qualitatively similar (average differences between museum specimens and between study site specimens: bill depth: 0.4 and 1.2 mm; gape width: 1.2 and 0.8 mm; bill width: 1.9 and 2.2 mm; head width: 0.4 and 1.7 mm; bill length: −2.8 and −2.9 mm; bill slope: 9.4 and 10.5°). The study site specimens were thus included in the analyses (all results were checked for qualitative differences by running the
Discussion
Our results show that drongo and babbler bill morphology is significantly different, with drongos possessing shorter, stouter bills and wider gapes and babblers possessing longer, decurved and thinner bills. By combining morphometric data with detailed foraging observations we have demonstrated that pied babblers and fork-tailed drongos occupy considerably different foraging niches, and that this might provide an explanation for the targeted kleptoparasitic attacks on buried larvae and pupae
Acknowledgments
We thank the Northern Cape Conservation Authority for research permits. The Kalahari Research Trust, Mr and Mrs H Kotze and Mr and Mrs de Bruin kindly allowed us access to their land in the southern Kalahari. We are grateful to Denise Hamerton and Vincent Bartnik of the South African National Museum as well as Tamar Cassidy of the Transvaal Museum for their hospitality and help. We thank all researchers at the Kuruman River Reserve for support and encouragement over the duration of our study
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