FILTER-FEEDING IN FLAMINGOS (PHOENICOPTERUS-RUBER)

We propose a model of filter feeding in Caribbean (Phoenicopterus r. ruber) and Greater Flamingos (P. r. roseus) that is based on a description of the oropharyngeal integument, using SEM and radiography, and analysis of kinematics and performances. Our model extends that of Jenkin (1957). We propose a lingual back-and-forth pump, that causes a lateral in- and outflow of water. Outflow of water is manipulated by directing water more distally to pass somewhat larger lamellar meshes, or more proximally to pass slightly smaller meshes. Performance analysis of filtering monotypic suspensions of seeds ranging from 0.1 to 10.0 mm cross-section shows peak performances at 2-4 mm. Sizes smaller than 0.5 mm and larger than 6.0 mm are not altered Performance analysis of filtering suspensions of two seed types shows that discrimination capacity, though not perfect, is accurate if food of preferred size is offered. In addition to touch, taste also controls discrimination. We present a provisional morphospace of avian filter feeding mechanisms derived by nomological deduction from an initial pecking mechanism and develop in this domain preliminar historical-narrative hypotheses of the evolution of avian filter mechanisms. The morphospace connects chicken-like pecking, considered as the initial type of feeding, through initial probing, to five categories of filtering. These categories are: accidental filtering (as in Phalaropus), ram filtering (as in Pachyptila, grasp-pump filtering fas in Anser), (inverted) back-and-forth pump filtering, causing a lateral in- and outflow (as in Phoenicopterus), and through-pump filtering, causing distal inflow and proximal outflow (as in Anas). The evolutionary hypotheses consider probing as developed from ancestral pecking, and filter feeding as branching early from that route.