In addition to habitat selection and 

 bill and leg morphology, variability in 

 foraging behaviors between bird species is 

 also a critical factor in determining 

 potential shorebird food resources (Baker 

 and Baker 1973). Behavioral patterns may 

 be stereotyped to the extent that not only 

 may species identifications be possible by 

 observations of behavior, but also it has 

 been suggested that behavioral as well as 

 morphological attributes may reflect 

 evolutionary relationships (Matthiessen 

 1967). The erratic run and peck foraging 

 behavior of the plovers easily distin- 

 guishes them from the slower, more method- 

 ical probing sandpipers. Pearson and 

 Parker (1973) found behavioral uniformity 

 within each group and an inverse relation- 

 ship between bill length and stepping 

 speed suggesting that birds that peck 

 the surface for prey are more active then 

 those that probe deeper in the sediments. 

 The active audio/visual hunting by plovers 

 requires increased activity, quick move- 

 ments, and intermittent pauses for search- 

 ing and stalking. The probing sandpipers 

 locate their prey primarily by tactile 

 methods, walking slowly and continually 

 thrusting their bill into the sediment. 

 These 'i/ery different hunting techniques 

 may result in the consumption of different 

 prey species or different-sized individ- 

 uals of the same species or a more effi- 

 cient prey-capture time. For example, the 

 semipalmated plovers that forage on the 

 middle regions of the tidal flats search 

 for prey in areas that have been previ- 

 ously exploited by the probing sanderlings 

 and semipalmated sandpipers. All three 

 species may consume the same species of 

 prey but the later-arriving and visually 

 hunting semipalmated plovers are more 

 successful per unit time (Harrington 

 et al. 1974). Most probing shorebirds 

 will also respond to visual cues and peck 

 at prey items. Often the pecking or prob- 

 ing alternative may be a function of habi- 

 tat type and prey availability. 



Since migrating shorebirds may often 

 occur in high densities, aggressive inter- 

 actions in the form of displays and chases 

 are quite common among many species, 

 particularly those that feed primarily 

 by visually active hunting tactics (Burger 

 et al. 1979). Probers frequently occur 

 in foraging flocks and only rarely do 

 aggressive interactions occur, as in the 



case of knots that most commonly feed in 

 tight groups (Bryant 1979). Species such 

 as the sanderling that feed by both visual 

 and tactile methods will show little 

 aggression and feed in flocks but maintain 

 intraspecif ic distances while foraging 

 solitarily (Harrington et al. 1974). In 

 general, among shorebirds, intraspecific 

 aggressions are more frequent than inter- 

 specific interactions (Burger et al. 1979) 

 and when interspecific aggression does 

 occur, it is most common among similar 

 species such as between the least and 

 semipalmated sandpipers (Recher and Recher 

 1969b) that avoid each other by marked 

 habitat segregation (i.e., mud flats vs. 

 grassy marsh and seaweeds). 



A remaining question is what role 

 shorebirds play in the New England tidal 

 flat community. Although the majority are 

 transients, their role as major consumers 

 of invertebrate production is a substan- 

 tial one during migrations. They may be 

 best described as removers. Other than 

 the nutrients in their feces, no form of 

 the energy they consume is returned to 

 the tidal flats. During the fall migra- 

 tion, in just a few weeks they may deplete 

 large portions of their prey populations. 

 Schneider (1978) found the average harvest 

 by foraging shorebirds was 5C% and 70% of 

 invertebrate populations during two suc- 

 cessive years of study. In Massachusetts, 

 dowitchers have been reported to remove 

 nearly one half of available food re- 

 sources during July and August (Harrington 

 and Schneider 1978). Wintering species 

 may have a more dramatic effect as seen in 

 a study done in England where shorebirds 

 were responsible for removing 90% of the 

 Hydrobia (snail) population and 80% of the 

 nereid polychaetes (Evans et al. 1979). 

 Stomach contents of dunlins in Sweden 

 revealed an average of 152 Nereis (poly- 

 chaete worm) jaws per individual (Bengston 

 and Svensson 1968). Site selection among 

 foraging shorebirds is not a random, pas- 

 sive process. Favorable feeding areas 

 with a high density of prey can be recog- 

 nized and exploited. Harrington and 

 Schneider (1978) found that semipalmated 

 plovers shifted their habitat usage to 

 coincide with peak densities of nereid 

 worms and that extremely high densities of 

 knots could be correlated with an unusual- 

 ly heavy set of My til us (mussels). 



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