FILTER-FEEDING IN FLAMINGOS (PHOENICOPTERUS-RUBER)

We propose a model of filter feeding in Caribbean (Phoenicopterus r. r uber) and Greater Flamingos (P. r. roseus) that is based on a descript ion of the oropharyngeal integument, using SEM and radiography, and an alysis of kinematics and performances. Our model extends that of Jenki n (1957). We propose a lingual back-and-forth pump, that causes a late ral in- and outflow of water. Outflow of water is manipulated by direc ting water more distally to pass somewhat larger lamellar meshes, or m ore proximally to pass slightly smaller meshes. Performance analysis o f 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 f iltering suspensions of two seed types shows that discrimination capac ity, though not perfect, is accurate if food of preferred size is offe red. In addition to touch, taste also controls discrimination. We pres ent a provisional morphospace of avian filter feeding mechanisms deriv ed by nomological deduction from an initial pecking mechanism and deve lop in this domain preliminar historical-narrative hypotheses of the e volution of avian filter mechanisms. The morphospace connects chicken- like pecking, considered as the initial type of feeding, through initi al probing, to five categories of filtering. These categories are: acc idental filtering (as in Phalaropus), ram filtering (as in Pachyptila, grasp-pump filtering fas in Anser), (inverted) back-and-forth pump fi ltering, causing a lateral in- and outflow (as in Phoenicopterus), and through-pump filtering, causing distal inflow and proximal outflow (a s in Anas). The evolutionary hypotheses consider probing as developed from ancestral pecking, and filter feeding as branching early from tha t route.