Evidence for pre-dispersal predation of seeds of Tithonia diversifolia by the black-faced canary (Serinus capistratus)

Abstract

Pre-dispersal predation of seeds of exotic Asteraceae by foraging birds is understudied. Using phenological records and photo-assisted analysis of damages made to seed heads, this paper provides evidence that the black-faced canary Serinus capistratus Finsch and Hartlaub feeds on immature achenes of Tithonia diversifolia (Hemsley) A. Gray and may control its propagule pressure up to 18% of the total number of achenes aged between 20–30 days counted from petal fall.

Keywords:

• invasive
• Mexican sunflower
• seed predation
• black-faced canary

Acknowledgments

The study was conducted with academic support from Dr Beth A. Kaplin (Antioch University New England), Dr Elias Bizuru (University of Rwanda), and Dr Edward N. Mwavu (University of Makerere). Mrs Theodette Gatesire, Research Assistant at the Dian Fossey Gorilla Fund International, offered field assistance throughout the study period and was resourceful in bird identification.

Notes

1. By seed head we refer to a type infrutescence that results from a fertilized flower head (typical inflorescence in the Compositae family in which flowers are grouped together to form a single flower-like structure; Imbert & Ronce 2001), which in reality should be referred to as a ‘fruit head’ because the achenes it carries are not seeds but fruits. However, for the purpose of this study, the terms ‘seed head’ and ‘fruit head’ are used interchangeably because predation took place when the achenes were still immature and, consequently, the seeds they contained would not be viable should they manage to survive food grinding in the bird’s digestive tractus.

2. TD seed set in tropical and subtropical environment was estimated at 70% or more by Wang et al. (2004).