The effect of bill structure on seed selection by granivorous birds
The effect of bill structure on seed preference and handling time in granivorous birds was determined for a long, slender dove bill, a conical finch bill, and a hooked parrot bill using diamond doves (Geopelia cuneata), Java sparrows (Padda oryzivora) and Fisher’s lovebirds (Agapornis fischeri). Four seed species were used during trials: white millet (Panicum miliaceum), red manna (P. maximum), canary seed (Phalaris canariensis) and Japanese millet (Echinochloa frumentacea). Diamond doves handled all seed species significantly faster than sparrows and lovebirds, as they swallow seeds whole. Java sparrows and Fischer’s lovebirds husked seeds prior to ingestion; lovebirds took significantly longer than Java sparrows in handling all seed species. Seed characteristics, size and shape affected handling time with reference to bill structure. Diamond doves took significantly longer to handle elongate seeds while Java sparrows handled round seeds slowly and Fischer’s lovebirds required similar handling times for all seed species. Java sparrows and Fischer’s lovebirds selected greater proportions of the same seed species, suggesting that birds which husk seeds prefer similar seed species. Seeds were not selected according to nutritional intake rate. Japanese millet was the preferred seed species of Fischer’s lovebirds and Java sparrows, but provided few calories and little protein per unit time. Seed selection was influenced by bill structure, as seeds were selected, amongst others, according to handling time, and handling time was dependent on bill structure.
Key words: seed selection, bill structure, granivorous birds.