The Houston Zoo has many beautiful species held in captivity, including Phoenicopterus ruber, commonly referred to as the American flamingo. I observed a flock of thirty flamingos for foraging behavior on Saturday, February 1st, at 11:30 am. Flamingos are well cited as filter feeders, using their bills and tongue movements to pump water containing food through structures in the beak that allow for filtering (Jenkin 1957). I observed similar feeding behaviors in both juvenile and adult flamingos. The flamingos placed their beaks in the water and created a vibration, which allows the flamingos to sift through the water. Water waves could be seen as the birds peripherally placed their beaks on the water surface. Occasionally, I observed that a bird would put its head under water and move it in a circular formation around a central point. This behavior has been described previously as “jig movements” (Jenkins 1957). Based on my observations, this flamingo behavior is a method by which to disturb the bed of the pond. Members of the flamingo flock surprisingly demonstrated minimal variation in their feeding styles. However, I noticed that the juvenile grey flamingos spent much less time foraging for food in comparison to the adult flamingos within the thirty minutes of observation. Instead, the juvenile birds spent more time on land observing and standing next to the adult flamingos. This observation is supported by a study concluding that most flamingo species feed in large flocks (Bildstein et al., 1991).
The flamingos I observed were kept in captivity, so the feeding behavior noted may have been different from what would be observed in the wild. One reason for this may be that the space provided for the flock in captivity is limited. They are confined to one area which may cause these birds to be more aggressive and compete for resources. For example, there were times when I observed two birds quarreling and demonstrating what seemed to be territoriality for their feeding location. These behaviors may be characterized as territoriality because each individual spent a majority of its time in a particular domain and aggressively approached intruding flamingos. Additionally, the lack of predators for the flock is unlike natural environment. Although these variables may cause difficulty in making generalizations about flamingo feeding behavior, previous studies done to observe foraging in flamingos in the wild had findings similar to my own at the Houston Zoo (e.g., Jenkins 1957).
Whether in captivity or in the wild, all water-feeding birds have needed to adapt properly to the challenges of gathering food from a water source (Rubega et al., 1993). Examples of difficulties for a subset of water-feeders include isolating small organisms from the water (Rubega et al., 1993). Filter-feeding is an evolutionary adaptation that aids in the consumption of such small prey.
One adaptation flamingos have to filter-feeding is a highly specialized beak. The positioning of the jaw and tongue of the flamingo provides for the filter mechanism that allows for efficient acquisition of small organisms from the water (Jenkin,1957). Flamingos also have specialized behavior for filter-feeding. In one study, the specialization of filter-feeding behavior in the relatives of flamingos was traced in parallel to the specialization of their beaks. The study demonstrated that structural changes of the flamingo anatomy greatly influenced modification of flamingo feeding behavior from pecking mechanisms to filter-feeding (Zweerz et al., 1995). Although much is known regarding the mechanisms of flamingo feeding, it is still unclear whether filter-feeding in flamingos is learned or innate (i.e., genetically determined). Through morphological analysis of other filter-feeding species, it seems true that the adaptation of a highly specialized beak has enhanced the use of filter-feeding in flamingos but more research must be conducted to determine whether filter-feeding and secondary foraging behaviors are learned or if they have a full or partial genetic basis (Zweerz et al., 1995).
References:
Bildstein, Keith L., Peter C. Frederick and Marilyn G. Spalding. Feeding Patterns and Aggressive Behavior in Juvenile and Adult American Flamingos. The Condor. Vol. 93, No. 4 (Nov., 1991), pp. 916-925.
Jenkin, Penelope M. The Filter-Feeding and Food of Flamingoes (Phoenicopteri). Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 240, No. 674 (May 9, 1957), pp. 401-493.
Rubega, Margaret A. and Bryan S. Obst. Surface-Tension Feeding in Phalaropes: Discovery of a Novel Feeding Mechanism. The Auk, Vol. 110, No. 2 (Apr., 1993) , pp. 169-178.
Zweers, G., F. de Jong, H. Berkhoudt and J. C. Vanden Berge. Filter Feeding in Flamingos (Phoenicopterus ruber). The Condor , Vol. 97, No. 2 (May, 1995) , pp. 297-324.
Tags: birds, foraging, group behavior, learning