spread out over a relatively long period, perhaps 

 as long as 4 to 5 months in Beaufort, North Caro- 

 lina. Species are moving independently and peak 

 abundances of various species are displaced in 

 time. In spring, the migratory period is greatly 

 compressed into 1 or 2 months. The shorebirds 

 move through the area much faster and peak num- 

 bers of various species tend to coincide. As a re- 

 sult, total density of shallow-probing shorebirds 

 can often be far higher during spring migration 

 than during the fall migratory period. Recher 

 (1966) has speculated that this difference may be 

 a consequence of the lower tides during the spring 

 months, which permit the birds a much greater 

 feeding time to refuel for their continued journey. 

 This tidal pattern holds true along the North 

 Carolina coast, but, in addition, the densities of 

 infaunal invertebrates on intertidal flats in North 

 Carolina are far greater in the spring than in the 

 fall (Commito 1976). Consequently, refueling can 

 be accomplished much more efficiently in a 

 shorter period of time. If this refueling need is 

 the determinant of the length of feeding delays 

 during migration, then the difference in prey 

 abundance as well as the difference in feeding 

 time because of seasonal tidal variations may be 

 causes of the short spring migratory season. This 

 argument, along with Schneider's (1978) experi- 

 mental results, helps to demonstrate the extreme 

 importance of intertidal flats as feeding grounds 

 for the migratory, shallow-probing and searching 

 shorebirds. 



5.4 DEEP-PROBING SHOREBIRDS 



The deep-probing shorebirds have been sepa- 

 rated from the shallow probers in Table 4 because 

 of Recher's (1966) and Baker and Baker's (1973) 

 analyses of feeding habits and diets among 

 probing shorebirds. These deep probers are eco- 

 logically different from the birds of the shallow- 

 probing guild. Deeper probing makes available a 

 large group of deeper-burrowing and generally 

 larger marine invertebrates. Furthermore, mem- 

 bers of this deep-probing shorebird guild arc most 

 efficient when wading in water, so that they tend 

 to forage at lower levels ahjng the shoreline than 

 the shallow probers which are largely restricted 

 (with some exceptions) to the exposed portions 

 of the flats. 



Only four species of deep probers appear reg- 

 ularly on the intertidal flats of North Carolina: 



the marbled godwit, willet, long-billed curlew, 

 and whimbrel (Table 4). Not only are there few 

 east-coast species in this guild, but also the abun- 

 dance of deep probers on North Carolina's inter- 

 tidal flats is quite low relative to similar habitats 

 (jn the west coast of North America. This geo- 

 graphic difference may be related to a large dif- 

 ference in the invertebratecommunitiesof the two 

 coasts. On North Carolina's intertidal flats, the 

 abundance of relatively large crustacean infauna 

 (such as Callianassa and Upogebia) is low (Lee 

 1974, Commito 1976, Wilson 1978). In contrast, 

 these ghost shrimp and mud shrimp are extremely 

 common in the intertidal flats of the west coast 

 (Peterson 1977). Both Callianassa and Upogebia 

 dig relatively deep burrows which protect them 

 from shallow probers but not from deep-probing 

 shorebirds. West coast abundances of other 

 infaunal invertebrates are also far higher, per- 

 mitting larger total densities of probing shore- 

 birds. These prey differences between coasts 

 probably explain why the deep-probing guild is 

 relatively underrepresented on North Carolina's 

 intertidal flats. 



When deep probers are abundant along the 

 North Carolina coast, they arc often found feed- 

 ing on ocean beaches. Willets, especially, are more 

 (jften found feeding on sandy beaches, where 

 they can gather the abundant mole crab {Emerita) 

 during the warm months, than on intertidal sand 

 and mud flats. Only during colder months when 

 Emerita has migrated off the beach into deeper 

 waters are willets likely to be found in abundance 

 on intertidal flats. Among the shallow-probing 

 guild only the sanderling seems to follow this 

 pattern of strong preference for beach habitats 

 during warm months, although it more often 

 preys upon the beach hoppers [Talorchestia and 

 Orchestia). 



It is somewhat misleading to include the wil- 

 let among the other shorebirds in the deep-probing 

 guild. Although the willet is appropriately equip- 

 ped with a comparatively long bill, it does not al- 

 ways use that bill for probing into the sediments. 

 Willets are extremely aggressive and commonly 

 follow other probing shorebirds around the flats, 

 waiting for an opportunity to attack and pirate 

 their catch before they can swallow it. Willets in 

 North Carolina often rob from marbled godwits, 

 sanderlings, and some of the smaller shallow- 

 probing shorebirds. As a result, the willet's diet 



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