Almond blossoms and their avian nectar feeders

Abstract

The behaviour of birds visiting Almond trees for nectar was observed and quantified. The adaptations of Almond trees to cope with and attract the attention of birds were examined. Nectar production was correlated with the colour of the filaments of the stamens. Flowers with red filaments produced little nectar whereas nectar was generally plentiful in flowers whose filaments were light pink or white. Almond trees differ from other species of Prunus in that their blossoms are more robust and well able to withstand the attentions of sparrows without falling off the tree. Almond trees are polymorphic and only a small minority of trees (1-5%) attracted many birds. Most of the trees that were examined were used by the resident pair of Sardinian Warblers. The following species of birds were observed taking nectar: Sylvia melanocephala, Sylvia atricapil/a, Phyl/oscopus col/ybita, Passer hispaniolensis and Remiz pendulinus. The length of time spent varied from a few seconds to 23 min. Means varied between 1. 18 min (S. atricapilla) and 5. 13 min (S. melanocephala). The warblers searched the flowers visually before selecting a flower to probe with the bill. Hovering was observed only once, the birds probed the flowers while perching nearby. Passer hispaniofensis tore flowers open or perforated flowers at one side in order to get at the nectar. Only 26. 7% of the flowers on one study tree remained intact; sparrows had torn open all the rest. Most of the flowers with red filaments developed further despite having been tom open by sparrows. At another study site, Sylvia melanocephala was observed to jab into or tear flowers in order to get at insect larvae inside the flower. Pollen stains were observed on the birds' heads frequently. A hypothesis is presented which attributes the rarity of avian nectarivory in the Mediterranean to the low species diversity of plants there by comparison to the tropics.