FIG. 13-1 Adaptations in the bills of birds, (a) 



(b) an insect-eating warbler; (c) a plant-eating duck; 

 (e) a predaceous hawk; (f) an aerial 



(d) a fish-eating heron 

 insect-eating whippoorwi 



Many species eat both plant and animal matter, 

 on occasion, or at particular seasons, but animals are 

 considered to be truly omnivorous only if they feed 

 on plants and animals in nearly equal amounts or in- 

 discriminately. Omnivores occasionally also consume 

 dead organic matter. Some aquatic organisms are 

 filter-feeders and may consume everything within a 

 particular size range that passes through their feeding 

 apparatus (Jorgensen 1955). However, filter-feeders 

 may demonstrate selectivity by feeding in neighbor- 

 hoods where certain species predominate. Some 

 copepods select particles of a particular size, reject- 

 ing larger ones, by regulating the distance between 

 the maxillae in the filter mechanism (Hutchinson 

 1951). 



Probably most, if not all, animals have chemore- 

 ceptors of some sort, either to discriminate chemical 

 substances dissolved in drinking water or food 

 (taste), or chemical substances that are water- or 

 air-borne (smell). Essential oils and alkaloids in 

 plants are important as conditions of acceptability to 

 insects. Hairiness, other surface features, or the 

 visual stimuli that plants present are also conditions 

 of attractiveness or acceptability of a food item. 



The food preference of any species depends on 

 chromosomal inheritance, parental training, and per- 

 sonal experience of that species, but the relative sig- 

 nificance of each of these factors has not been evalu- 

 ated for most animals. Young birds and mammals, in 

 their first experiences at independent feeding, may 

 pick up a variety of material but reject those items 

 that are distasteful or indigestible ; they soon learn to 

 distinguish acceptable substances. This process is 

 established as the parents feed offspring only those 

 things traditional to the species, or so direct the feed- 

 ing movements that untraditional food is excluded. 

 Some adult insects lay their eggs on material that 

 will serve the larvae as food. The larvae acquire the 

 habit of feeding on that material, and do not readily 



change to something else as adults (Brues 1924, 

 Thorpe 1939). 



FEEDING ADAPTATIONS 



Among kinds of mammals, teeth show con- 

 siderable adaptive radiation, correlation with type of 

 food consumed. The molar and premolar teeth of in- 

 sectivorous species, such as shrews and bats, are low 

 and have sharp-pointed cusps for crushing weak- 

 bodied prey. The piscivorous toothed whales have 

 largely lost all differentiation in their teeth, which 

 are simple, conical, grasping structures. The teeth of 

 the carnivorous dogs and cats are high-crowned and 

 tubercular, well fitted for shearing flesh. Herbivor- 

 ous ungulates and rodents have teeth that are flat- 

 crowned, suited to grinding harsh grasses and other 

 vegetation. Their jaws are capable of considerable 

 lateral motion. Omnivores may have both grinding 

 and pointed teeth. Saprovores have rather blunt 

 teeth. The ant-eating sloths and their relatives have 

 no teeth, and the mouth is almost tubular in shape. 

 The tongue has become long and prehensile for lap- 

 ping up tiny ants. 



The bills of birds display great variety in shape 

 and size, adaptations to feeding in numerous quite 

 specialized niches in the environment. The tongues 

 of birds are variously modified to serve as long 

 probes or spears (woodpeckers and nuthatches), as 

 a strainer (ducks), as a long capillary tube for ob- 

 taining nectar from flowers (hummingbirds), as a 

 rasp (hawks and owls), as a finger for manipulating 

 the food in the mouth (parrots and sparrows), and 

 as a tactile organ (sandpipers and herons) (Gardner 

 1925). 



The mouth parts of insects are adapted primarily 

 either for biting and chewing or for piercing and 

 sucking. Among marine invertebrates, adaptations 

 for feeding on detritus (Blegvad 1914) include 

 pseudopodia (Foraminifera) ; ciliated epithelium that 

 maintains a flow of water through the animal 

 (sponges, clams) ; prehensile, often ciliated arms 

 (various polychaetes ; holothuroideans) ; and soft 

 eversible gullets (various polychaetes, sipunculids). 

 Those that are herbivorous or carnivorous, as well 

 as detritus feeders, have prehensile tentacles armed 

 with nematocysts (hydroids, actinians), radulae in 

 the mouth (mollusks), eversible stomachs (starfish), 

 and masticatory structures in the mouth or stomach 

 (crustacea, diptera larvae). 



In addition to mouth part adaptations, there are 

 many modifications in other parts of the digestive 

 tract for handling particular types of food. These 

 adaptations occur throughout the animal kingdom, 

 but are especially evident in birds. A crop is present 



Ecological processes and dynamics 



