An appraisal of seed enumeration and videographic techniques for determining seed removal rates by birds
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We examined the efficacy of seed enumeration and videographic techniques for determining seed removal by birds from indigenous (Chrysanthemoides monilifera and Olea europaea subsp africana) and alien (Lantana camara and Solanum mauritianum) shrubs at different study sites in the Cape Floristic Region. The seed enumeration technique involved counting the numbers of fruits and associated seeds removed monthly by birds, excluding those naturally abscised, from the shrub canopy. The videographic technique involved visual counts from images of the numbers of fruits and associated seeds consumed by birds over specific time intervals captured by a digital camcorder. Daily seed removal rates by all birds, irrespective of species, measured by both techniques were similar with no significant interactions evident between measuring techniques, site and shrub species. Both techniques displayed higher seed removal from tiny-seeded S. mauritianum than other shrub species; this was also evident among individual bird species. However, the seed enumeration technique was unable to discriminate between foraging organisms, contamination of traps by wind-blown fruits abscised from neighbouring branches and fruit theft from the canopy and the traps. In contrast, the videographic technique provided permanent visual and time-lapse records for individual foraging bird species allowing greater measurement precision and interpretation of fruit removal behaviour by birds. We recommend use of the videographic technique over the seed enumeration technique for studying vertebrates’ seed removal in a detailed manner.
- RESEARCH: Esler K