There is evidence that bird species 

 differ with respect to substrate prefer- 

 ences. Sander! ings prefer sandy substrates 

 and dowitchers are more often found over 

 siltier areas (Harrington and Schneider 

 1S78) while ruddy turnstones most fre- 

 quently forage on barnacle-covered rocks 

 and in accumulations of tidal wrack 

 (Groves 1?78). Other species, such as 

 black-bellied plovers, opportunistically 

 feed in any of several habitats with no 

 noticeably strong preferences (Harrington 

 and Schneider 1978). Burger et al. (1977) 

 found that larger species prefer muddier 

 algal zones while smaller species frequent 

 drier nicrohabitats. 



Temporal segregation may occur as the 

 tides recede--when a wave of species, each 

 oriented to preferred distances from the 

 water's edge, sequentially use the same 

 areas of the tidal flat. Sanderlings and 

 semipalmated sandpipers characteristically 

 follow the water's edge as the tide ebbs 

 while semipalmated plovers restrict their 

 foraging to the middle areas of the tidal 

 flats (Harrington et al. 1974). Knots and 

 dunlins also follow the receding tide and 



although they occur together, both spa- 

 tially and temporally, competition is 

 avoided since knots prefer molluscs while 

 dunlins eat polychaetes (Evans et al. 

 1979). Dowitchers also follow the tide 

 but feed deeper in the sediments. The form 

 of the bill and leg length influence the 

 type of potential prey items available to 

 a species (Figure 15). 



Ten;poral segregation may occur on a 

 broader, seasonal scale. As shorebirds 

 arrive in fall or spring, peak densities 

 of different species may be staggered in 

 time, reducing competition, particularly 

 between ecologically similar species 

 (Recher 1966). Even subtle differences in 

 migration schedules may have profound ef- 

 fects on resource availability. Harrington 

 and Schneider (1978) mention that shrimp 

 that feed on the juveniles of infaunal 

 invertebrates may not arrive on the flats 

 until late in the shorebird migratory sea- 

 son. Shorebirds that prey on crustaceans, 

 such as black-bellied plovers and sander- 

 lings, are later fall migrants than short- 

 billed dowitchers and semipalmated sand- 

 pipers that consume infaunal prey. 



VERTICAL FEEDING RANGE 

 B C 



SEDIMENT 

 SURFACH 



BILL LENGTH 

 o Cinches) 



14 



Figure 15. Vertical feeding depths of some comnon New England shorebirds (modified 

 from Recher 1966). Bill lengths are an average of the ranges given by Palmer (1967). 

 A = species foraging between the water and sediment surface (heights of bars refer to 

 water depths); B = species primarily feeding on the sediment surface; C = species 

 mainly feeding below the sediment-water interface (the willet feeds below the sediment 

 surface as well as in shallow water). 



52 



