Frugivory and factors influencing visitation by birds at ‘Balo’ (Plocama pendula Ait., Rubiaceae) plants in the Canary Islands
1999
Nogales, Manuel | Valido, Alfredo | Medina, Félix M. | Delgado, Juan D.
We present results of a three-year study on the frugivory, foraging behavior and factors influencing bird preference visits among conspecific fruiting shrubs of the ‘Balo’ (Plocama pendula), an endemic plant of low xerophytic zones in the Canary Islands. Only four bird species were recorded eating fruits of the 20 individual plants studied, including two seed disperser species, Sylvia melanocephala (frequency of visits, FV = 64.8%) and Sylvia conspicillata (FV = 20.9%), one seed predator (Serinus canarius, FV = 12.6%), and one pulp consumer (Parus caeruleus, FV = 1.7%). The number of visits/hour by the two warbler species (1.65) was significantly higher than that of the seed predator (0.28) in the three years. However, visitation rates by dispersers decreased from 1993 to 1995 while a higher visitation rate was observed in 1995 for seed predators. Foraging rates (number of fruits consumed/visit) of seed predators (=19.2) was higher than for legitimate flbirds than for seed predators. Legitimate dispersers tended to select plants in well-developed shrub cover sites, with a low crop size of neighboring conspecifics and a high individual crop size. Visitation rate by the seed predator species to the plants was significantly correlated with fruit crop size and the presence of high numbers of seeds per fruit.
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