Biology of Marine Birds - Chapter 18 pptx

Three of these are of particular significance to this discussion: the Scolopacidae sandpipers, snipes, and phalaropes and Charadriidae plovers which include 71% of all shorebird species,

Environment

Nils Warnock, Chris Elphick, and Margaret A Rubega

CONTENTS

18.1 Introduction 582

18.2 General Features of Shorebird Biology 582

18.2.1 Foraging 582

18.2.2 Sociality 588

18.2.3 Breeding Systems 588

18.2.4 Nests, Eggs, and Young 588

18.2.5 Survival and Longevity 590

18.3 Shorebirds at the Ocean–Continent Interface 590

18.3.1 Coastal Habitats 590

18.3.1.1 Coastal Wetlands 590

18.3.1.2 Beaches 591

18.3.1.3 Rocky Shores and Coral Reefs 592

18.3.2 Influence of Tides 592

18.3.3 Influence of Oceanography and Climate 593

18.4 Shorebirds on Islands 594

18.4.1 Endemism 594

18.4.2 Visitors 594

18.5 Shorebirds at Sea: Phalaropes 595

18.5.1 Morphological Adaptations of Phalaropes to Life at Sea 595

18.5.2 Pelagic Feeding Biology of Phalaropes 595

18.5.3 Distribution of Phalaropes at Sea 596

18.6 Shorebird Migration across the Marine Environment 596

18.6.1 Common Overwater Migration Routes 597

18.6.1.1 Arctic Ocean 597

18.6.1.2 Pacific Ocean 598

18.6.1.3 Gulf of Mexico and the Caribbean Sea 599

18.6.1.4 Atlantic Ocean 599

18.6.1.5 Indian Ocean 599

18.6.2 Behavior While Migrating 600

18.6.2.1 Orientation and Timing 600

18.6.2.2 Flock Size, Flight Speed, and Altitude 600

18.7 Conservation of Marine Shorebirds 601

18.7.1 Problems at the Ocean–Continent Interface 601

18.7.1.1 Commercial Harvesting of Shorebird Prey 602

18.7.1.2 Hunting 602

18.7.1.3 Pollution 602

18.7.1.4 Coastal Development 604 18

18.7.2 Problems at Sea: Phalaropes 604

18.7.3 Influence of Climate Change and Sea-Level Rise 605

18.7.4 Future Shorebird Protection in Marine Environments 605

Acknowledgments 606

Literature Cited 606

18.1 INTRODUCTION

The purpose of this chapter is to review the ecology of shorebirds in the context of their relationship

to the marine environment The shorebirds are a group of families usually placed in the order Charadriiformes along with gulls, skuas, terns, skimmers, and auks (e.g., del Hoyo et al 1996, American Ornithologists’ Union 1998) An alternative view, based on studies of DNA-DNA hybrid-ization, is to treat this entire group as a suborder within the order Ciconiiformes (Sibley and Monroe 1990) The shorebirds are traditionally thought of as a monophyletic group, although this may not

be the case and the relationships among the families within the order remain uncertain (American Ornithologists’ Union 1998) Depending on taxonomic source, shorebirds are variously divided into about a dozen families Three of these are of particular significance to this discussion: the Scolopacidae (sandpipers, snipes, and phalaropes) and Charadriidae (plovers) which include 71%

of all shorebird species, and the Haematopodidae (oystercatchers), with 11 species found largely

in marine environments (Table 18.1) Even though their name conveys an affinity to water, shore-birds are not traditionally considered marine shore-birds (Burger 1984a) However, the taxonomic, ecological, and behavioral characteristics of the two groups indicate much in common, and shore-birds (especially the phalaropes) have many traits that suit them for a life on or near salt water Overall, 58% of shorebird species are known to use marine habitats regularly, either during breeding or nonbreeding seasons (Table 18.1) Thirty-nine percent of breeding shorebirds sometimes

or always nest along the coast, while 66% of nonbreeding shorebirds use the coast for stopovers

or nonbreeding grounds (Burger 1984a) The majority of shorebirds migrate (62%, Table 18.1), and most of these birds cross marine bodies Two shorebird species, the Red-necked Phalarope

(Phalaropus lobatus) and the Red Phalarope (P fulicaria), spend up to 75% of their time directly

on the open ocean, more than many species traditionally referred to as seabirds

18.2 GENERAL FEATURES OF SHOREBIRD BIOLOGY

On land and at sea, shorebirds tend to be omnivorous, although invertebrates are their dominant prey In a survey of shorebird diets in the Western Hemisphere, the most common taxonomic classes

of invertebrate prey eaten were the Insecta, Malacostraca, Gastropoda, Polychaeta, and Bivalvia (Skagen and Oman 1996), but other important prey for shorebirds include small amphibians, fishes, seeds, and fruit The four species of seedsnipes apparently only eat plant matter (Fjeldså 1996), while at the other extreme sheathbills often eat carrion and small penguin chicks (Burger 1996) Shorebirds typically obtain their prey by locating it visually and plucking it from the water column, ground, or other surfaces, or by probing in mud There is considerable interspecific and occasional intraspecific variability in bill morphology (Burton 1974, Sutherland et al 1996, Rubega 1997) that results in a wide variety of feeding habits Many species have straight bills for making rapid thrusts through soft substrates or firm soils or for picking prey off the water’s surface (see also Pelagic Feeding Biology of Phalaropes) The curved bills of species like the Long-billed Curlew

(Numenius americanus) and the Whimbrel (N phaeopus) are similar in shape to the burrows of invertebrates such as ghost shrimps (Callianassa californiensis) and probably facilitate capture of

these prey species Many scolopacids have bills with tactile and chemosensitive receptors at their

Grey-breasted Seedsnipe Thinocorus orbignyianus Unknown No

Pedionomidae

Scolopacidae

Far Eastern Curlew N madagascariensis Yes Yes

Nordmann's Greenshank T guttifer Yes Yes

Grey-tailed Tattler Heteroscelus brevipes Yes Yes

Tuamotu Sandpiper Prosobonia cancellata No Yes

Short-billed Dowitcher Limnodromus griseus Yes Yes

Buff-breasted Sandpiper Tryngites subruficollis Yes No

Spoon-billed Sandpiper Eurynorhynchus pygmeus Yes Yes

Broad-billed Sandpiper Limicola falcinellus Yes Yes

Ruff Philomachus pugnax Yes Yes

Rostratulidae

Greater Painted-snipe Rostratula benghalensis Yes Unknown

South American Painted-snipe Nycticryphes semicollaris Unknown No

Madagascar Jacana A albinucha No No

Comb-crested Jacana Irediparra gallinacea Unknown No

Pheasant-tailed Jacana Hydrophasianus chirurgus Yes No

Chionidae

Burhinidae

Haematopodidae

Eurasian Oystercatcher Haematopus ostralegus Yes Yes

Canarian Black Oystercatcher H meadewaldoi Unknown Yes

American Black Oystercatcher H bachmani Yes Yes

Australian Pied Oystercatcher H longirostris No Yes

Magellanic Oystercatcher H leucopodus Unknown Yes

Ibidorhynchidae

Recurvirostridae

Black-winged Stilt Himantopus himantopus Yes Yes

Banded Stilt Cladorhynchus leucocephalus Yes Yes

Charadriidae

Eurasian Golden Plover Pluvialis apricaria Yes Yes

Grey (Black-bellied) Plover P squatarola Yes Yes

Red-breasted Plover Charadrius obscurus Yes Yes

Three-banded Plover C tricollaris Unknown Yes

Kentish (Snowy) Plover C alexandrinus Yes Yes

Red-kneed Dotterel Erythrogonys cinctus Unknown No

Tawny-throated Dotterel Oreopholus ruficollis Yes Unknown

Diademed Plover Phegornis mitchellii Unknown No

Inland Dotterel Peltohyas australis Unknown Unknown

Black-fronted Dotterel Elseyornis melanops Unknown No

Magellanic Plover Pluvianellus socialis Yes Yes

Javanese Wattled Lapwing V macropterus Unknown No

Grey-headed Lapwing V cinereus Yes No

African Wattled Lapwing V senegallus Unknown No

Lesser Black-winged Lapwing V lugubris Yes No

Greater Black-winged Lapwing V melanopterus Yes Yes

Dromadidae

Glareolidae

Double-banded Courser Smutsornis africanus No No

Bronze-winged Courser Rhinoptilus chalcopterus Yes No

Collared Pratincole Glareola pratincola Yes Yes

Australian Pratincole Stiltia isabella Yes Yes

Note: Under Migrate, Yes = species known to migrate regularly (note that if part of a species

migrates and part does not, the species would be listed under Yes), No = species known not

to migrate, and Unknown = species for which it is unclear if the species is migratory Under

Marine, Yes = species known to use marine habitat regularly (marine habitat defined as

beginning with coastal estuaries, mudflats, and other types of marine shoreline extending into

the pelagic zone), No = species not known to use marine habitat regularly, and Unknown =

species for which it is unclear if the species regularly uses marine habitat.

Information summarized from del Hoyo et al (1996) including accounts by Baker-Gabb (1996),

Burger (1996), Fjeldså (1996), Hockey (1996), Hume (1996), Jenni (1996), Kirwan (1996),

Knystautas (1996), Maclean (1996), Pierce (1996), Rands (1996), van Gils and Wiersma (1996),

tips — thus prey can be found by touch and smell (von Bolze 1968, Heezik et al 1983), and evenpressure gradients (Piersma et al 1998) Species with these adaptations tend to feed both duringthe day and at night (Warnock and Gill 1996, van Gils and Piersma 1999).

18.2.2 S OCIALITY

Generally, shorebirds are gregarious when not breeding and territorial during the breeding season.However, gregarious nonbreeding shorebirds will often vigorously defend small feeding territories,abandoning them to rejoin flocks when tides cover feeding areas or predators appear (Myers et al.1979) Some species are colonial breeders, especially members of the Recurvirostridae (avocetsand stilts), Dromadidae (crab-plovers), Chionidae (sheathbills), and Glareolidae (coursers andpratincoles) families (Burger 1996, Maclean 1996, Pierce 1996, Rands 1996) In an extreme

example, perhaps the entire population of Banded Stilts (Cladorhynchus leucocephalus) in eastern

Australia, up to 100,000 birds, will attempt to breed at one inland lake (Alcorn and Alcorn 2000).This event happens when the normally dry interior alkali lakes of the region receive rain, creatingbreeding habitat and stimulating blooms of invertebrates

18.2.3 B REEDING S YSTEMS

Breeding systems vary considerably among shorebird species Most shorebirds are monogamous,with individuals forming a pair bond with just one individual each breeding season and both parentscaring for the young (Emlen and Oring 1977, Oring and Lank 1984) In many monogamous species,

pair bonds are strong and often persist from year to year (e.g., Eurasian Oystercatchers Haematopus

ostralegus, Ens et al 1996; Semipalmated Sandpipers Calidris pusilla, Sandercock 1997).

Polygyny, in which some males mate with more than one female within a single breedingseason, is found in at least 25 species, most of which are sandpipers, snipes, and woodcocks (Emlenand Oring 1977, Oring and Lank 1984) In a few of these species, birds gather at leks, where malesdisplay to females from small, vigorously defended territories (Hoglünd and Alatalo 1995) Cop-ulation does not involve pair-bonding and males play no role in parental care Of shorebirds with

lek behavior, the best known are the Buff-breasted Sandpiper (Tryngites subruficollis, Lanctot and Laredo 1994), the Great Snipe (Gallinago media, Hoglünd and Alatalo 1995), and the Ruff (Philo-

machus pugnax, Van Rhijn 1991), all northern latitude breeders.

Polyandry, in which a female mates with multiple males (Emlen and Oring 1977), occurs in

the phalaropes, all jacanas except for the Lesser Jacana (Microparra capensis), and in some plovers,

painted-snipes, and sandpipers (Baker-Gabb 1996, Jenni 1996, van Gils and Wiersma 1996,Wiersma 1996) The males of these species generally incubate the eggs and raise the young A fewspecies practice rapid multiple clutch polygamy in which males and females have access to multiplemates within a season, and each may simultaneously incubate separate clutches Perhaps the best-

documented case of this occurs with the Temminck’s Stint (Calidris temminckii), where both males

and females exhibit multiclutch behavior with multiple mates within the breeding season (Hildén

1975, Breiehagen 1989) Often the breeding system varies among individuals within a species Forexample, many individuals of nominally “polygamous” species may mate monogamously, andpolygamy may occur in some species that are generally monogamous Males and females of themonogamous Eurasian Oystercatcher often engage in extra-pair copulations, although DNA fin-gerprinting has shown that few chicks (1 of 65 chicks) are not actually fathered by the dominantmale partner (Heg et al 1993, in Ens et al 1996)

18.2.4 N ESTS , E GGS , AND Y OUNG

The typical shorebird nest is a bowl-like scrape in the ground (often near water) that is lined with

pebbles, shells, grasses, or leaves A few species, such as the Solitary Sandpiper (Tringa solitaria)

in North America and the Wood Sandpiper (T glareola) in Eurasia, are tree-nesters These birds

do not build nests, but instead use abandoned nests of passerines Some species of plovers that

breed in hot environments such as Africa’s White-fronted Plover (Charadrius marginatus) and Australia’s Inland Dotterel (Peltohyas australis) cover their nests with sand, probably to regulate

temperatures and hide them from predators (Wiersma 1996) Sheathbills also often lay nests incaves, crevices, and petrel burrows to avoid having their nests depredated by skuas or trampled

(Pluvianellus socialis) is unique among shorebirds in that parents apparently regurgitate food from

their crop to chicks until after the chicks fledge (Jehl 1975) The Burhinidae (thick-knees, Hume1996), Glareolidae (coursers and pratincoles, MacLean 1996), Dromadidae (crab plovers, Rands1996), and some species — snipes and woodcocks — of Scolopacidae (sandpipers, snipes, andphalaropes, Piersma 1996b) provide food for their young for about the first week of life

As with incubation, the timing of fledging varies among shorebird species Smaller sandpipersand plovers fledge at 14 to 26 days; larger sandpipers and plovers fledge at 28 to 45 days, whilesome jacanas, oystercatchers, thick-knees, and stilts may take 50 days or more (del Hoyo et al.1996) Many species breed in their first spring (at approximately 1 year of age); some (especiallylarger species) do not mature sexually until 2 to 5 years of age In species where nesting habitat

is limited, individuals may have to wait several years before acquiring high-quality breeding sites

In some Eurasian Oystercatchers, it may take up to 10 years before a bird is able to successfullyget a mate and a breeding territory (Ens et al 1996)

FIGURE 18.1 An adult American Oystercatcher pries a limpet off a rock while its chick waits to be fed.

Note, the oystercatcher has broken a piece off the limpet shell to insert the blade-like, laterally flattened bill tip (Drawing by J Zickefoose.)

18.2.5 S URVIVAL AND L ONGEVITY

Annual adult survival rates of shorebirds typically range from 60 to 70% in small species and 85

to 95% in larger species; survivorship of shorebirds in their first year is often less than 50% (Evansand Pienkowski 1984, Evans 1991, Jackson 1994, Sandercock and Gratto-Trevor 1997, Warnock

et al 1997, Reed et al 1998) Shorebirds are relatively long lived at 4 to 10 years, with someindividuals surviving for 20 years or more In one amazing example, a Eurasian Oystercatcher that

was banded as a nestling in 1949 was killed by a Eurasian Sparrowhawk (Accipiter nisus) in 1992

at the age of 43 years and 6 months (Exo 1993) Even small sandpipers can be long lived as

evidenced by a female Least Sandpiper (Calidris minutilla, the world’s smallest shorebird with a

mass of 19 to 25 g) that was observed breeding at a minimum age of 16 years (Miller and McNeil

1988, Cooper 1994)

18.3 SHOREBIRDS AT THE OCEAN–CONTINENT INTERFACE

The lives of many shorebird species are intimately connected to the ocean, especially at theboundary between land and sea Shorebirds use a wide variety of coastal habitats, ranging fromrocky surf-battered shorelines, to mangrove swamps and sheltered coastal bays Some speciesbreed in coastal areas, but the majority use these habitats primarily during the nonbreeding season.Because of the relatively low freezing point of salt water, littoral environments often provideaccessible food despite cold weather Also, ambient temperatures in coastal areas frequently arewarmer than sites farther inland Consequently, coastal wetlands and the ocean shore continue to

be desirable wintering grounds long after interior wetlands at similar latitudes have becomeunsuitable for foraging shorebirds

18.3.1 C OASTAL H ABITATS

18.3.1.1 Coastal Wetlands

Coastal wetlands include some of the most productive habitats in the world, and shorebirds arefound in virtually every kind of coastal wetland The nontidal portions of saltmarshes and coastallagoons provide breeding and foraging habitat for many species Tidal mudflats are home to foragingflocks, which can number into the hundreds of thousands of birds Tidal marsh breeders include a

few species of oystercatchers and some tringine sandpipers, such as Common Redshank (Tringa

totanus) and Willet (Catoptrophorus semipalmatus) Coastal lagoons support a wider variety of

breeding species, including avocets, stilts, phalaropes, and plovers

Shorebirds commonly interact with the marine environment on estuarine mudflats, where vastnumbers gather during migration and winter in some parts of the world For example, 3 to 4

million Western Sandpipers (Calidris mauri) may stop at the Copper River Delta in Alaska during

a 4-week period in early spring (Bishop et al 2000) These birds are en route to their tundranesting grounds and join millions of other shorebirds also stopping at the delta (Isleib 1979).During the winter, over 2 million shorebirds use the vast tidal flats of the Banc d’Arguin inMauritania, western Africa (Wolff and Smit 1990) In Asia, West Africa, Central and SouthAmerica, and other tropical areas, mangroves and their associated mudflats are important habitatsfor shorebirds (Hepburn 1987, Parish et al 1987, Morrison et al 1998) Estuaries are highlyproductive and shorebirds take advantage of the abundance of soft sediment invertebrate prey thatthey can find by probing in the mud

Different shorebird species can be found in subtly different parts of marshes Larger species,such as curlews and godwits, with their long legs and bills, are capable of feeding in deeper waterthan small sandpipers and plovers Some species tend to feed in small flocks at the edge of a marshwhere they can pick at the base of small clumps of vegetation, whereas others are found in larger

flocks on exposed mudflats Despite these differences, there is much overlap in habitat use andmany birds form mixed species foraging flocks Birds of different species also come together athigh-tide roosts The latter are often located within the marsh or in nearby adjacent agriculturalfields or wetland lagoons Large foraging and roosting flocks are vulnerable to avian predators,such as falcons, accipiters, and owls (Page and Whiteacre 1975, Cresswell 1996) The amazing

sight of a tightly bunched, wheeling flock of Calidris sandpipers attempting to evade a hunting Peregrine Falcon (Falco peregrinus) can been seen on estuaries throughout the world.

18.3.1.2 Beaches

Sandy beaches provide important breeding habitats for certain Charadrius plovers in many areas

of the world The most ubiquitous species, the Snowy Plover (Charadrius alexandrinus, known as

Kentish Plover outside the Americas), will lay its eggs in little more than a shallow depression inthe sand, perhaps lined with a few pebbles, bits of shells, or pieces of vegetation (Page et al 1995).These nests are exceptionally vulnerable (see Conservation of Marine Shorebirds, below) A number

of closely related species, including Wilson’s Plover (C wilsonia) in the Americas, White-fronted Plover in Africa, and Malaysian Plover (C peronii) in Southeast Asia, also nest on sandy beaches

(Wiersma 1996)

Pebble beaches are used as nesting habitat by Common Ringed Plovers (C hiaticula) in Eurasia and Semipalmated Plovers (C semipalmatus) in North America (Cramp and Simmons 1983, Nol and Blanken 1999) Several oystercatcher species, such as Blackish Oystercatchers (Haematopus

ater) of South America, will also nest in this habitat (Hockey 1996).

Many beach-nesting species regularly place nests near seaweed, driftwood, or other beach

debris (e.g., Piping Plover Charadrius melodus, Haig 1990) In this respect, they are similar to

some tundra- and taiga-nesting shorebirds, which often build nests near a small tree or shrub (e.g.,

Greater Yellowlegs Tringa melanoleuca, Elphick and Tibbitts 1998) Such locations may provide

partial protection from predators by placing the nests in an area with some visual variation, or theymay simply serve to help the parents find their nest in a relatively featureless landscape

Various shorebird species will nest close to colonies of beach-nesting seabirds (usually smallterns), sometimes even placing nests amidst the colony (Burger 1987, Burger and Gochfeld 1990,Alleng and Whyte-Alleng 1993) This behavior may offer protection in that terns mob potentialpredators (Burger 1987) Individuals may gain indirect benefits from nesting in a colony: if theirnest is surrounded by other nests there is a higher probability that a predator will encounter adifferent bird’s nest first and become satiated than if their nest were isolated (also see J C Coulson,

Chapter 4, this book) Colonial nesting, however, is not without disadvantages Groups typicallyare more conspicuous than singletons, making them vulnerable to predators Raising the stakesfurther, gulls, which often nest near terns, will prey upon shorebird eggs Some shorebirds turn thetables and prey on the eggs of colonial larids (Crossin and Huber 1970, Burger and Gochfeld 1990,

Alberico et al 1991); Ruddy Turnstones (Arenaria interpres) can destroy entire colonies (Loftin and Sutton 1979) and will even steal fish brought in to young Arctic Terns (Sterna paradisaea) by

their parents (Brearey and Hildén 1985)

Other beach-nesting shorebirds include the Beach Thick-knee (Esacus magnirostris) of

Aus-tralia and Southeast Asia, which feeds by stalking crabs like a heron (Hume 1996), and the unusual

Crab Plover (Dromas ardeola) of the Middle East Crab Plovers are the only shorebird to dig nest

burrows, which they build in coastal sand dunes (Rands 1996) Presumably, burrowing offersprotection from predators and the sun This species, which is unrelated to other plovers and placed

in a monotypic family (Dromadidae), breeds colonially and lays white eggs just like many otherhole-nesting birds (Rands 1996)

During the nonbreeding season, various inland-breeding shorebirds occur in beach habitats.These are often tundra-nesting birds, and most do not use beaches in large numbers Sanderlings

(Calidris alba) are one exception and are usually found in small groups at the water’s edge where

they move back and forth with the wave front as they feed on small invertebrates (Cramp andSimmons 1983).

18.3.1.3 Rocky Shores and Coral Reefs

Rocky-shore specialists are particularly concentrated along the highly productive Pacific coast of

northwestern North America This group consists of the American Black Oystercatcher

(Haemato-pus bachmani), Rock Sandpiper (Calidris ptilocnemis), Wandering Tattler (Heteroscelus incanus),

Black Turnstone (Arenaria melanocephala), and Surfbird (Aphriza virgata) Tattlers also are found

on tropical islands throughout the Pacific, where they frequent coral reefs and the shores of volcanicislands, and Surfbirds range to southern Chile (van Gils and Wiersma 1996) These species rarely

wander away from rocky coastal substrate Purple Sandpipers (Calidris maritima) are a North

Atlantic counterpart to Rock Sandpipers, which they resemble closely (Paulson 1993), and rockyshorelines are an important habitat for several oystercatcher species in the Southern Hemisphere(Hockey 1996)

Other species that regularly use rocky shores during the nonbreeding season, but which are by

no means restricted to them, include Whimbrel, Ruddy Turnstone, and Grey-tailed Tattler

(Het-eroscelus brevipes, van Gils and Wiersma 1996) In many areas, rocky promontories and islands

are used as roosting areas by shorebirds that feed on estuarine mudflats that become inundated athigh tide

In New Zealand, the endangered Shore Plover (Charadrius novaeseelandiae) is restricted to

rocky shores where it nests in dense vegetation or occasionally in crevices among the boulders(Davis 1994) Several species of oystercatchers also use rocky shores for nesting, and some, such

as the American Black Oystercatcher (Andres and Falxa 1995), rarely breed elsewhere catchers come in two main color types: species that are predominantly black and species that havebold black-and-white plumage patterning Where both types co-occur, the species that is predom-inantly black in color tends to be found in rocky shore habitats, whereas the pied species usuallyfeeds in soft substrates (Hockey 1996) This pattern suggests that all-dark plumages, which arethought to be a derived characteristic (Hockey 1996), might confer an advantage in rocky shorehabitats, and dark plumages certainly make oystercatchers difficult to see against basaltic, seaweed-covered rocks Despite different phylogenetic affinities, many of the other rocky-shore specialistsalso have dark upperparts during the times of year when they use this habitat, supporting the ideathat this coloration might provide benefits There also are morphological similarities among speciesfound on rocky shores

Oyster-18.3.2 I NFLUENCE OF T IDES

For many coastal shorebirds, the greatest single influence on their local distribution and behavior

is the state of the tide, since water above certain levels covers feeding habitat and alters preyavailability (Burger 1984b) Since many shorebirds feed on mudflats that get covered during hightides, habitat use between high and low tides is frequently different For example, Western Sand-pipers at San Francisco Bay primarily use mudflats on low tides and move to seasonal wetlands

and salt ponds on high tides (Warnock and Takekawa 1995) Similarly, Northern Lapwing (Vanellus

vanellus) chicks in Sweden use mudflats at low tides and pastures next to the mudflats on high

tides (Johansson and Blomqvist 1996) Many other studies from around the world have noted thesame pattern: mudflats are used on low tides; pastures, marshes, mangrove, sand beaches, etc onhigh tides (see Burger 1984b for list) In some areas with low tidal amplitude such as the southernBaltic Sea in Germany and Poland and coastal lagoons in southern Brazil, shorebirds rely on wind

to expose mudflats (Piersma 1996b)

Foraging behavior is significantly influenced by tides In Australia, calidridine sandpipers spend

a greater proportion of their time feeding in months when mudflat exposure is higher

(December–March, Dann 1999) Prey choice can also change for shorebirds through the tide cycle.

At the Dutch Wadden Sea, the bivalve Macoma predominated in the diet of Eurasian Oystercatchers during high-falling and high-rising tides, while Nereis worms predominated during low tides (De

Vlas et al 1996) Feeding rates of some species can also change during the tide cycle, undoubtedlydue to changes in invertebrate behavior (Pienkowski 1981) For instance, feeding rates of Black-

bellied Plovers (Pluvialis squatarola; also called Grey Plover) increased as the tide fell and then

decreased abruptly about 2 h after low tide (Baker 1974) In contrast, no significant differenceswere detected in foraging rates of Common Redshanks on rising or falling tides (Goss-Custard1977)

Depending on the timing of the tides, birds may be faced with little daylight during which theycan feed on mudflats This problem is especially acute at high latitudes where days are short Ifthere is insufficient time to find enough food to survive, these birds must either find alternativeforaging sites during high tide, or feed at night when the tide is low Nocturnal feeding is commonamong shorebirds and some species switch from visual foraging to tactile methods at night, whileothers appear capable of visual hunting in the dark (McNeil et al 1992)

Because of their propensity to nest at the tidal interface, plovers and oystercatchers are apt tohave nests destroyed by tides, especially during storms (Burger 1984b) Up to 10% of AmericanBlack Oystercatcher nests may be lost to storm surges (Andres and Falxa 1995) and high tideswere responsible for 78% of 27 nest failures during a 3-year study of American Oystercatchers

(Haematopus palliatus, Nol 1989) In Russia, almost half of 40 Common Ringed Plover nests at

Kandalaksha Bay were destroyed by tides (Bianki 1967 in Burger 1984b), while over 3% of Snowy

Plover nests (n = 901 nests) around Monterey Bay, CA were lost due to high tides between

1984–1989 (L Stenzel and G Page unpublished data)

18.3.3 I NFLUENCE OF O CEANOGRAPHY AND C LIMATE

It is well known that seabird distributions are influenced by particular water masses and currents(see this volume), but how these factors influence shorebird distributions is less understood Severalstudies have suggested that shorebirds are more abundant along coasts near marine upwelling than

in adjacent areas without upwelling All large concentrations of coastal shorebirds in the neotropicscoincide with areas of upwelling (Duffy et al 1981, Schneider 1981) Similar relationships betweenupwelling and bird abundance have been noted along the Atlantic coast of Africa (Tye 1987,Alerstam 1990) and in the Bay of Panama (Butler et al 1997) The abundance of winteringSanderlings is correlated with major coastal upwellings, presumably because the higher productivitytranslates into greater food supplies on beaches where they feed (Morrison 1984)

Interannual variation in the marine environment brought on by climatic conditions has a documented, profound effect on marine birds (Duffy et al 1988, Ainley 1990; E A Schreiber,

well-Chapter 7, this volume) El Niño–Southern Oscillation (ENSO) events are perhaps the best studied

of these phenomena, yet little is known of how they affect shorebird populations Since ENSOevents cause shifts in ocean currents, upwelling, and weather patterns, all variables that impact thedistribution and abundance of the marine prey of shorebirds, it is probable that these periodic eventshave profound impacts on shorebird populations Briggs et al (1987) noted that in the fall of 1982,phalarope densities off the coast of California were almost a quarter of their normal level, andattributed this decline to the ENSO event of 1982–1983 During this same ENSO event, Red-neckedPhalaropes were absent from the waters around the Galapagos Islands (Duffy 1986), a site wherethey are common in normal years (Rubega et al 2000) Displacement of shorebird species otherthan phalaropes by ENSO events is not uncommon In 1998, an unprecedented number of Bristle-

thighed Curlews (Numenius tahitiensis), as well as Grey-tailed Tattlers, Eurasian Whimbrel (N.

phaeopus variegatus or N p phaeopus), and Bar-tailed Godwits (Limosa lapponica), occurred

along the northwest coast of North America, far outside their normal range These vagrants wereapparently displaced while migrating by the climatic conditions associated with the 1997–1998

El Niño and the Western Pacific Oscillation (Mlodinow et al 1999) To what degree these climaticevents also result in significant mortality of shorebird populations is unknown.

18.4 SHOREBIRDS ON ISLANDS

Biologists often think of islands as important sites for evolutionary differentiation of terrestrialspecies Seabirds as a group do not seem to be obvious candidates for isolation in an oceanic setting,but high rates of breeding site fidelity have resulted in considerable differentiation and speciationamong Procellariiformes and Pelecaniformes on different island groups (e.g., Siegel-Causey 1988,Warham 1996) Shorebirds also have evolved a number of distinct species and subspecies that areconfined to oceanic islands, many of which are among the most endangered shorebirds in the world

These include the St Helena Plover (Charadrius sanctaehelenae), Chatham Snipe (Coenocorypha

pusilla), and Tuamotu Sandpiper (Prosobonia cancellata), each restricted to the islands after which

they are named and each with populations of only a few hundred birds (Piersma 1996a, b, Wiersma

1996) Even more threatened are the Black Stilt (Himantopus novaezelandiae) and the Chatham Oystercatcher (Haematopus chathamensis) of New Zealand, with populations of 100 birds or fewer

(Hockey 1996, Pierce 1996) Three of the few shorebird species that have become extinct within

recent centuries were oceanic island species: White-winged and Ellis’s sandpipers (Prosobonia

leucoptera and P ellisi) of the Society Islands went extinct in the late 1800s (Piersma 1996b), and

Canarian Black Oystercatcher (Himantopus meadewaldoi) of the Canary Islands disappeared early

in the 20th century (Hockey 1996) The Shore Plover is largely restricted to rocky shores on onesmall island in the South Pacific, having been extirpated from the rest of New Zealand ShorePlovers breed, feed, and roost along the shoreline Foods include gastropods, bivalves, polychaetes,and various crustaceans, and much foraging occurs on large wave-cut platforms where they searchamong the seaweed and at the edges of tide pools (Marchant and Higgins 1993)

18.4.2 V ISITORS

Oceanic islands provide vital nonbreeding habitat for a number of shorebird species The insularPacific hosts the world’s population of Bristle-thighed Curlews, plus large numbers of Pacific

Golden Plovers (Pluvialis fulva), Wandering Tattlers, and Ruddy Turnstones (Figure 18.2) The

annual transoceanic migrations of these birds often involve nonstop flights of several thousandkilometers Bristle-thighed Curlews travel overwater from their western Alaska breeding grounds

FIGURE 18.2 Ruddy Turnstone turns over a rock while looking for invertebrates to eat (Drawing by

J Zickefoose.)

to spend the winter on atolls and small islands in the tropical Pacific Ocean (Marks and Redmond1994), where they occasionally prey upon seabird eggs (Marks and Hall 1992) These migrationsare even more remarkable in that birds like Bristle-thighed Curlews and Pacific Golden Ploversshow strong interyear fidelity to wintering sites (Johnson and Connors 1996, Marks and Redmond1996) On Laysan Island, of 16 marked adult Bristle-thighed Curlews, only one bird changed itsnonbreeding home range area in 3 years of study, and that bird only moved 1 km after storm wavesswept over its home range (Marks and Redmond 1996).

Lengthy overwater flights are unusual among birds in general, so why do some shorebirds makejourneys to remote islands? One likely reason is that remote islands offer a safe environment.Wintering Bristle-thighed Curlews even undergo a simultaneous molt of their primary feathers,which leaves many birds flightless and vulnerable for short periods (Marks 1993), a trait that would

be unimaginable for most shorebirds Other advantages of wintering on distant oceanic islands mayinclude reduced competition for space (Marks and Redmond 1996), and moderate temperatureswhich are energetically less expensive than colder climates (Kersten and Piersma 1987, Piersma

et al 1995) Conditions on islands are changing, however, with detrimental effects to shorebirds.These effects include increased urbanization spurred by human population growth and the intro-duction of mammalian predators As this happens these sites become much less suitable for birdsthat have adapted to a predator- and human-free environment (see Conservation of Marine Shore-birds, below; J C Coulson, Chapter 4, this volume)

18.5 SHOREBIRDS AT SEA: PHALAROPES

While the majority of shorebirds interact with the marine environment during at least some part

of their annual cycle, phalaropes are the only shorebirds that inhabit oceanic waters for much oftheir lives Red and Red-necked phalaropes spend up to 9 months of the year swimming on the

open ocean Wilson’s Phalarope (Phalaropus tricolor), the only other species in the genus, is not

marine in life history or distribution However, it is similarly aquatic and spends the nonbreedingseason on saline lakes in the interior of North and South America (Colwell and Jehl 1994) Unlessotherwise stated, “phalaropes” hereafter refers to Red and Red-necked phalaropes

18.5.1 M ORPHOLOGICAL A DAPTATIONS OF P HALAROPES TO L IFE AT S EA

As pelagic birds go, phalaropes are small (~20 cm long and weighing no more than 45 g; Crampand Simmons 1983, Rubega et al 2000) and brightly colored during the breeding season While

at sea, they wear the countershaded coloring so common to seabirds (Bretagnolle 1993), with whiteunderparts, tail, neck, and face, gray mantle, and black eyepatches They look like tiny gulls Closeexamination of phalaropes reveals a combination of morphological adaptations for an aquatic lifenot seen in any other shorebirds, including modified legs, feet, and plumage

Phalaropes are surface swimmers, which propel themselves by paddling, and their feet and legsreflect this Their legs are laterally flattened to minimize drag and their toes are lobed, like those

of loons and grebes, rather than webbed like most seabirds The lobes fold behind the toe on theupstroke through the water, again reducing drag, and open on the backstroke to increase thrust(Obst et al 1996) All shorebirds have plumage that is waterproof to some degree, but phalaropesare exceptionally waterproofed, with strikingly heavy belly and breast plumage (M Rubega personalobservation)

18.5.2 P ELAGIC F EEDING B IOLOGY OF P HALAROPES

Confined to surface waters by their buoyancy, phalaropes will eat almost anything that floats and

is small enough to ingest (including crustaceans, hydrozoans, molluscs, polychaetes, gastropods,insects, small fish, fish eggs, seeds, sand, and plastic particles), but they are first and foremostplanktivores (see Cramp and Simmons 1983, Rubega et al 2000, and references therein) While at

sea they specialize on copepods, euphausiids, and amphipods, apparently rejecting plankters largerthan about 6 mm by 3 mm (Baker 1977, Mercier and Gaskin 1985).

They locate prey by swimming along, looking into the water, and pecking at prey spotted on

or near the surface Where prey densities are high, peck rates as high as 180/min have been reported(Mercier and Gaskin 1985) A feeding phalarope uses the water clinging to prey to suspend a dropbetween its jaws; the prey ends up suspended in the drop Spreading its jaws stretches the drop,and the surface tension drives the drop to the back of the bill where drop volume is minimized,and the prey can be swallowed; this whole process can take as little as 0.01 sec (Rubega and Obst1993) To feed, phalaropes take advantage of the surface tension of water, a measure of the attraction

of water molecules to one another, and the property which causes water drops to assume shapeswith the smallest possible volume (Rubega and Obst 1993, Rubega 1997)

Phalaropes are well known for drawing prey to the surface using a feverish, toy-like spinningbehavior Historically, spinning has been explained as a way of “stirring up” prey from the bottom

of pools or ponds (e.g., Tinbergen 1935) It is now known that spinning does generate water flowthat lifts prey to the surface, although not in the manner originally thought Instead, phalaropescreate miniature upwellings by kicking surface water away from the center of the loop that theirspin inscribes This deflection of surface water causes water to flow up from beneath to replacethe water at the surface (Obst et al 1996) Spinning can draw water to the surface from as deep

as 0.5 m in the water column Per unit of water inspected for prey, this Herculean effort is nearlytwice as expensive energetically as swimming in a straight line (B Obst unpublished data)

18.5.3 D ISTRIBUTION OF P HALAROPES AT S EA

Both marine phalaropes have circumpolar breeding distributions in the subarctic and Arctic, andessentially only come ashore to breed (Cramp and Simmons 1983, Rubega et al 2000) In thenonbreeding season, like any good seabird they congregate in waters that are productive, and theirat-sea distributions are largely tied to areas of upwelling where surface productivity is increased

or food is brought to the surface Thus, the California Current off western North America (Briggs

et al 1984, 1987), the Humboldt Current off western South America (Murphy 1936), and theBenguela Current off West Africa (Stanford 1953) are important foraging areas

At smaller spatial scales, phalaropes feed at physical features in the ocean They are a familiarcomponent of the marine avifauna at convergences, drift lines, fronts, slicks, thermal gradients, andupwellings where food is concentrated and brought to the surface (Briggs et al 1984, Brown andGaskin 1988, Tyler et al 1993, Wahl et al 1993; see D A Shealer, Chapter 6, this volume) Thesize of phalarope flocks at predictable prey patches caused by these kinds of oceanographic featurescan reach staggering proportions; a single upwelling near Mount Desert Rock off the Maine coast

in the northwest Atlantic is reported to have attracted an estimated two to three million migratoryphalaropes (Finch et al 1978, Vickery 1978, Mercier and Gaskin 1985)

Biotic factors that concentrate prey can also affect distributions In the Gulf Stream, off theeast coast of North America, small numbers of phalaropes have been found at floating mats of the

marine alga Sargassum These birds presumably feed on zooplankton associated with the mats,

which are themselves often concentrated by various oceanographic features (Haney 1986) Red

Phalaropes also feed in the muddy surface slicks created by Gray Whales (Eschrichtius robustus)

feeding on the ocean floor (Harrison 1979, Obst and Hunt 1990, Elphick and Hunt 1993)

18.6 SHOREBIRD MIGRATION ACROSS THE MARINE

ENVIRONMENT

One of the most spectacular yet poorly understood aspects of shorebirds is their biology duringpassage over large bodies of water With the exception of phalaropes, shorebirds rarely touch thewater during migration Well over half of all shorebird species are migratory (Table 18.1), and many

species undertake significant passages over large marine water bodies (Figure 18.3) These migrationsare generally associated with favorable wind patterns (Alerstam 1990) where overwater routes provideenergetic savings compared to migrating along coastal paths (Williams and Williams 1990) Trans-oceanic migrants commonly embark on journeys of 3,000 to 5,000 km (McNeil and Burton 1977,Alerstam et al 1990, Piersma and Davidson 1992); others appear to be capable of flights from 5,000

to 10,000 km (Thompson 1973, Tulp et al 1994, Johnson and Connors 1996) or further (Williamsand Williams in press) Notable long-distant transoceanic migrants include the Pacific Golden Plover,

Ruddy Turnstone, Red Knot (Calidris canutus), the phalaropes, Bar-tailed Godwit, Hudsonian Godwit (Limosa haemastica), and the Far Eastern Curlew (Numenius madagascariensis) Transoceanic flights

are not limited to the larger shorebirds, however, as evidenced by flights of Semipalmated Sandpipersand Least Sandpipers across large sections of the Atlantic Ocean from northern North America to

South America (McNeil and Burton 1977), and flights of the Red-necked Stint (Calidris ruficollis)

across large sections of the Pacific Ocean to and from Australia (Minton 1996)

18.6.1 C OMMON O VERWATER M IGRATION R OUTES

18.6.1.1 Arctic Ocean

Shorebirds regularly migrate along the shores of the Arctic to access either breeding grounds ormigration corridors heading south (Johnson and Herter 1990) Radar studies have revealed that some

FIGURE 18.3 Major marine migration routes of shorebirds and known wintering areas of Red-necked and

Red phalaropes Data sources include Thompson 1973, McNeil and Burton 1977, Summers et al 1989, Alerstam 1990, Alerstam et al 1990, Myers et al 1990, Williams and Williams 1990, Summers 1994, Burger

1996, Wiersma 1996, Riegen 1999, Alerstam and Gudmundsson 1999, Underhill et al 1999, and Williams and Williams in press.

shorebirds fly from central Siberia, east over the Arctic Ocean, to reach migration corridors in northernNorth America that take them to wintering grounds in the Americas (Alerstam and Gudmundsson1999a, b) Red Knots breeding in northeast Ellesmere Island, Canada, may fly over parts of the ArcticOcean north of Greenland, then down to Iceland before continuing on to sites in Europe (Davidsonand Wilson 1992) Some shorebirds occasionally pass near the North Pole (Vuilleumier 1996).

18.6.1.2 Pacific Ocean

The longest transoceanic flights by shorebirds occur in the Pacific region (Williams and Williams

in press) A fat female Bar-tailed Godwit appears to be capable of flying directly from southeasternAustralia to South Korea (9200 km) on its way to breed in northern Russia or Alaska (Barter 1989),while Pacific Golden Plovers, Bristle-thighed Curlews, and other shorebirds commonly fly trans-oceanic routes from islands in the Central and South Pacific to tundra breeding grounds (Thompson

1973, Marks and Redmond 1994, Johnson et al 1997; see Islands: Visitors, above) The majorshorebird routes in the western Pacific go from New Zealand and Australia to the island regions

of Malaysia, Indonesia, the Philippines, and Papua New Guinea to Korea, China, and Japan(especially the Yellow Sea region) and then northward (Figure 18.3), crossing stretches of ocean

up to 6000 km long (McClure 1974, Tulp et al 1994, Wilson and Barter 1998, Riegen 1999)

Along the eastern Pacific Ocean, shorebirds such as Dunlin (C alpina) and Wandering Tattlers

fly from the Alaska Peninsula and elsewhere in western Alaska across the Gulf of Alaska to winteringsites from British Columbia to Mexico (Warnock and Gill 1996; Figure 18.4) Red-necked andWilson’s phalaropes follow inland routes southward through central Canada and the western UnitedStates, heading west and southwest to reach the Pacific, where they join Red Phalaropes movingsouth offshore from British Columbia to South America (Cramp and Simmons 1983, Colwell andJehl 1994, Rubega et al 2000) Red Phalaropes are numerous in the California Current off thewestern coast of the United States from May to March These birds are joined by migrating Red-necked Phalaropes from July to November (Briggs et al 1984, Tyler et al 1993, Wahl et al 1993).Red and Red-necked phalaropes winter off the western coast of South America; most in this sector

of the Pacific are found in or near the Humboldt Current Red Phalaropes wintering in the HumboldtCurrent come from breeding populations in North America, and possibly the Siberian Arctic Redand Red-necked phalaropes are also consistently found around the Galapagos Islands (R Pittman,

FIGURE 18.4 Wandering Tattlers migrate from their breeding grounds in Alaska to along the American

Pacific coast sites as far south as the coast of Peru, and to islands throughout the Central Pacific (Photo by

J R Jehl, Jr.)