617 Wading Birds in the Marine Environment Peter C. Frederick CONTENTS 19.1 Introduction 618 19.2 Reproductive Biology 618 19.2.1 Pair Bonds and Parental Care 620 19.2.2 Nests, Incubation, and Young 621 19.2.3 Reproductive Success 621 19.2.4 Prey Availability and Nesting Success 622 19.3 Foraging Ecology 623 19.3.1 Foraging Behavior 624 19.3.2 Flock-Foraging Dynamics 624 19.3.3 Solitary Foraging 628 19.3.4 Feeding from Human Sources 628 19.3.5 Conditions Affecting Foraging Success 629 19.3.6 Prey Animals 629 19.4 Life-History Characteristics 629 19.4.1 Longevity and Fecundity 629 19.4.2 Asynchronous Hatching 629 19.4.3 Breeding-Site Fidelity 629 19.4.4 Survival 632 19.4.5 Population Regulation 632 19.5 Wading Birds as Marine Animals 633 19.5.1 Effects of Wading Birds on Marine and Estuarine Ecosystems 633 19.5.2 Dependence of Wading Birds on Coastal Zone Habitats 634 19.5.3 Marine Species 635 19.5.4 Physiology and Ecology in the Coastal Zone 635 19.5.4.1 Salt Balance 635 19.5.4.2 Tidal Entrainment 636 19.5.4.3 Effects of Storms 637 19.6 Management of Wading Birds 638 19.6.1 Management of Breeding Sites 638 19.6.2 Human Disturbance Issues 639 19.6.3 Foraging Habitat 640 19.6.4 Monitoring Wading Bird Populations 641 19.7 Conservation of Wading Birds in the Coastal Zone 642 19.7.1 Freshwater Flow and Degradation of Wetland Productivity 642 19.7.2 Rising Sea Level 642 19 © 2002 by CRC Press LLC 618 Biology of Marine Birds 19.7.3 Loss of Coastal Foraging Habitat 643 19.7.4 Disease and Contamination 643 19.7.5 Human Disturbance 645 19.8 Future Research Priorities 645 Acknowledgments 646 Literature Cited 646 19.1 INTRODUCTION Many kinds of birds walk in water, or wade. This chapter is about the long-legged wading birds, which are here defined as the herons, egrets, ibises, storks, and spoonbills, all of which are in the order Ciconiiformes. Although shorebirds are referred to as “waders” in Europe and other parts of the globe, ciconiiform birds are quite distinct from shorebirds. Cranes (family Gruidae) and fla- mingos (family Phoenicopteridae) are also long-legged birds that wade, but not in the marine environment and they are not covered in this chapter. Long-legged wading birds are long in most dimensions, having long legs, toes, bills, and necks. With few exceptions, wading birds are strongly associated with shallowly flooded wetlands, in which they generally breed and feed. Long-legged wading birds are one of the largest and most diverse groups of large birds, comprised of members of three main families (Figures 19.1 and 19.2). The Ardeidae, or herons, egrets and bitterns, are the most diverse, with approximately 60 species (Hancock and Kushlan 1984). These birds have straight, harpoon-like bills, generally narrow heads, a comb-like (pecti- nate) middle toe, and a modified 6th cervical vertebrae that allows the long neck to be held in an S-shape in flight. These species range from the diminutive Least Bittern (Ixobrychus exilis, 28 cm length) to the large and stately Goliath Heron (Ardea goliath, 140 cm). The Threskiorni- thidae (ibises and spoonbills, approximately 30 species) generally are shorter-legged, with dis- tinctive down-curved or spatulate bills, grooved bill surfaces for cleaning feathers, a lack of powder down, a cupped middle toenail, and a slit-like cranial morphology (schizorhinal). Rep- resentatives include the brilliant Scarlet Ibis (Eudocimus ruber, 58 cm long), the Giant Ibis (Thaumatibis gigantea, to 103 cm), and the Roseate Spoonbill (Ajaia ajaja, 80 cm tall). The Ciconiidae, or storks (20 species), have massive straight or slightly decurved bills, and typically defecate on their legs for evaporative cooling. These are the giants of the order, including Wood Storks (Mycteria americana, 100 cm tall), the massive Marabou Stork of the African plains (Leptopilos crumeniferus, 120 cm tall), and the immense Jabiru Stork of Central and South American wetlands (Jabiru mycteria, 145 cm tall). Although it is clear that the three main families of wading birds should be grouped together taxonomically within Ciconiiformes, there is considerable debate about other groups within Cico- niiformes. DNA evidence suggests that wading birds, flamingos, and pelicans are descended from a common ancestor (Sibley and Ahlquist 1990), and possibly that new-world vultures should be included within the order. Some taxa of wading birds are known to be quite old: ibises and herons date at least to the Miocene, about 25 million years ago. Some extinct island ibises on Jamaica and the Hawaiian Islands were flightless (Hancock et al. 1992). 19.2 REPRODUCTIVE BIOLOGY Many species of long-legged wading birds are gregarious and may breed colonially in large, conspicuous, mixed-species aggregations, which can include up to 500,000 birds (Robertson and Kushlan 1974, Ogden 1994). Like many of the adaptations and life-history features of wading birds, coloniality is thought to be, in part, the result of needing to find and exploit patches of food that are unpredictable in space and time (Krebs 1974). © 2002 by CRC Press LLC Wading Birds in the Marine Environment 619 FIGURE 19.1 Schematic classification of ciconiiform birds, following Peters (1931), Hancock and K ushlan (1984), and Hancock et al. (1992). © 2002 by CRC Press LLC 620 Biology of Marine Birds 19.2.1 PAIR BONDS AND PARENTAL CARE Wading birds are socially monogamous, with pair bonds that last at least one breeding attempt. Most wading birds probably acquire new mates every season (Simpson et al. 1987), though some species of storks may remain with the same mate for many years. Pair-formation displays often are elaborate (Meyerriecks 1960, McCrimmon 1974, Wiese 1976, Mock 1980, Hancock et al. 1992) and usually are performed from small territories defended by the male near eventual nest sites. Both members of the pair typically help build the nest, incubate, and care for young. As in many socially monogamous, colonial-nesting birds (Birkhead and Moller 1992), copulations between members of different pairs can occur (Fujioka and Yamagishi 1981, Frederick 1987b), though the extent of this behavior remains poorly studied. FIGURE 19.2 Illustrations of heads and bills of representatives of the major groups of long-legged wading birds: Roseate Spoonbill (Ajaia ajaja, Threskiornithidae, top), Wood Stork (Mycteria americana, Ciconidae, right), Black-crowned Night Heron ( Nycticorax nycticorax, Ardeidae, bottom), and Waldrapp Ibis (Geronticus eremita, Threskiornithidae, left). (Drawing by J. Zickefoose.) © 2002 by CRC Press LLC Wading Birds in the Marine Environment 621 19.2.2 NESTS, INCUBATION, AND YOUNG Breeding colonies and roosts usually are formed on islands, either surrounded by water or by some vegetative buffer, or are in tall trees. These features may serve as a form of protection from terrestrial predators (Rodgers 1987). Nest substrate requirements are generally broad and well researched in this group of birds (McCrimmon 1978, Bjork 1986, Hafner 1997). Nesting wading birds are not very picky about the vegetation type in which they nest, though they may be more specific about nest height. Burger (1978) found that nest height within a colony reflected interspecies dominance hierarchies, with the most submissive species nesting closest to the ground. Nests are built of sticks and other vegetation and may or may not be re-used between years (Hancock et al. 1992). Large aggregations of nesting wading birds can have direct effects on the vegetation in and around colonies. For example, Siegfried (1971) estimated that over 1.5 million sticks weighing over 2000 kg were needed to support a Cattle Egret (Bubulcus ibis) colony of 5000 pairs. As nest densities increase and the availability of nest material decreases, the size of individual nests decreases (Arendt and Arendt 1988), making nests less sturdy and more vulnerable to adverse weather. In addition, the deposition of excreta in colonies can kill shrubs and trees through excess nutrients (Wiese 1978). Incubation begins with the laying of the first or second egg, resulting in hatching asynchrony and a size disparity between first- and last-hatched young. This pattern leads to unequal division of food resources, and often to high mortality of the smaller young (see also “Life History” below). Incubation of eggs ranges from 19 days in the smallest herons to 30 days in the largest storks. Young are semialtricial, usually hatched with some down but are unable to move much around the nest for the first couple of days. Feeding is by regurgitation of food from parents, either onto the surface of the nest or (usually later) directly into the chicks’ bills. In herons, the young “scissor” the adult’s bill by grasping on the outside of the parent’s mandibles; the parent then regurgitates through partially open bill into the gape of the chick. In ibises and spoonbills, young place their bill directly into the gape of the parents. Growth of young is rapid; legs and feet grow disproportionately faster than other body parts (McVaugh 1975), an adaptation interpreted as the need to rapidly gain locomotor abilities in order to climb away from predators (Werschkul 1979). Unlike many birds, young ciconiiform birds leave the nest some weeks in advance of the development of flight abilities, and up to half the period between hatching and leaving the colony may be spent in treetops and the vicinity of the nest (tens to >100 m from the nest site, Frederick et al. 1992). Thus in wading birds “fledging” refers to the time at which young actually fly away from the colony, rather than the departure of young from the nest. Parents also encourage young to follow them at feeding time, starting from hops between branches, to short, and then long flights in pursuit of the parent. The period from hatching to independence from the colony may take from 40 to 100 days. 19.2.3 REPRODUCTIVE SUCCESS As with most birds, success of nesting attempts varies, depending on ecological and environmental conditions. Although nesting is rarely affected directly by weather (nests blown down or nest contents scattered, but see Quay 1963 in Parnell et al. 1988, Bouton 1999), indirect effects on foraging are more widespread (see below). Wading birds do not display much in the way of individual or group nest defense, and nesting success may be strongly affected by predatory reptiles, mammals, and birds (Shields and Parnell 1986, Rodgers 1987, Burger and Hahn 1989). Although some avian and reptilian scavengers may be considered normal associates of wading bird nesting aggregations (Shields and Parnell 1986, Burger and Hahn 1989, Frederick and Collopy 1989b, Bouton 1999, see “Management” below), large mammalian predators, particularly nocturnal ones, can cause widespread abandonment of colonies (Rodgers 1987, Post 1990). Measuring the effect of predation, however, has been a challenge, since the presence of researchers in colonies can result © 2002 by CRC Press LLC 622 Biology of Marine Birds in opportunities for scavengers to rob nests. Several approaches have managed to get around this difficulty. One is to observe nests remotely (Pratt and Winkler 1985, Bouton 1999). Productivity of nests may increase with age of nesting pairs in some species. For example, Fernandez-Cruz and Campos (1993) reported that in Grey Herons (Ardea cinerea), brood size increased from 1.8 to 2.8 in nests where parents were 2 and >4 years of age, respectively. There is evidence that clutch size increases at inland compared with coastal sites, and with increasing latitude (Rudegeair 1975, Kushlan 1977, Frederick et al. 1992). Explanations for the former pattern include energetic costs of salt excretion in coastal zones and increased availability of food resources at inland sites (Rudegeair 1975). 19.2.4 PREY AVAILABILITY AND NESTING SUCCESS Access to rich food resources is probably the single most often cited factor affecting reproductive success. Annual fluctuations in availability of prey have been linked with date of nest initiation in Wood Storks (Ogden 1994) and number of nesting birds in White Ibises (Eudocimus albus, Frederick and Collopy 1989a, Bildstein et al. 1990) and Wood Storks (Ogden 1994). Similarly, events which interrupt the supply of food seem to lead to the abandonment of nesting events. These can include sharp increases in the surface water depth (Kahl 1964, Kushlan et al. 1975, Frederick and Collopy 1989a), droughts (Bancroft et al. 1994), and sudden onset of cold temperatures (Frederick and Loftus 1993). Availability of food therefore seems to be a powerful cue in the sequence leading to the instigation of nesting, as well as a direct cause of the cessation of nesting. Food availability also affects nesting productivity. Powell (1983) compared Great Blue Herons (Ardea herodias) in Florida Bay that received food supplementation via handouts from local residents, with birds foraging in the estuary. “Panhandler” birds laid larger clutches and produced more young than did unsupplemented birds, indicating a strong effect of food availability. Similarly, Hafner et al. (1993) found that productivity of Little Egrets (Egretta garzetta) in the Camargue Delta of France was linked to access to high densities of prey in particular habitats. Rainfall in the weeks or months preceding breeding has been correlated with reproductive effort and success by wading birds (Ogden et al. 1980, Maddock 1986, Bildstein et al. 1990, Hafner et al. 1994, Kingsford and Johnson 1998). This relationship appears to be related directly to the size of flooded wetland areas, and consequently to the productivity of aquatic fish and macroinvertebrates. The dynamics of aquatic prey communities may also be affected by fluctua- tions in populations of large, predatory fishes. Secondary productivity (production of fish and invertebrates that are primary grazers) may be strongly adapted to, and affected by, cycles of drought and flood. Droughts tend to result in direct mortality of wetland vegetation, either directly through desiccation or through the action of fires. These processes may lead to the release of nutrients stored in vegetation or in the surface layers of the soil and detritus. Nutrient release during re-flooding may fuel pulses of both primary and secondary productivity. An understanding of prey animal ecology remains crucial to understanding the linkage between wading birds and their wetland environments. Given the importance of food availability to wading bird reproduction, it is not surprising that colony site choice is linked with the location, quality, and size of foraging habitat (Fasola and Barbieri 1978, Moser 1984, Gibbs et al. 1987, Gibbs 1991). In Illinois, the availability of lacustrine and emergent wetland was the primary determinant for location and size of Great Blue Heron colonies, with degree of isolation from human disturbance being of secondary importance (Gibbs and Kinkel 1987; see also Grull and Ranner 1998). Ogden (1994) demonstrated that the estuarine zone of the Everglades was abandoned by wading birds in favor of inland areas between 1975 and 1992, as a result of the loss of freshwater flows due to upstream water management (Walters et al. 1992, McIvor et al. 1994). Adult wading birds often fly considerable distances from breeding colonies to foraging sites (Figure 19.3). Ogden et al. (1988) recorded Wood Storks flying up to 130 km from breeding © 2002 by CRC Press LLC Wading Birds in the Marine Environment 623 colonies to feed, and Bildstein (1993) reported cases of White Ibises regularly traveling 110 km one way. These large distances traveled may be accomplished by direct, solitary flight (Smith 1995a), or may involve energetic savings through the use of formation flights or the use of thermals (Kahl 1964). Wading birds are usually very flexible in choice of foraging sites, and foraging locations used while breeding may change frequently, both within a breeding season and between years (Custer and Osborn 1978, Hafner and Britton 1983, Bancroft et al. 1994, Frederick and Ogden 1997). It is not clear at what point distance to food has an effect on reproductive success. Certainly the large distances recorded by Ogden and Bateman (1970, above) were associated with successful breeding. Little is known of the ecology of young wading birds following departure from the colony. Many young wading birds disperse long distances shortly following fledging, and may be found hundreds of kilometers from their natal sites (Coffey 1943, 1948, Byrd 1978, P. Frederick unpublished), possibly allowing young to identify sources of food that are unpredictable in space and time (van Vessem and Draulans 1986). 19.3 FORAGING ECOLOGY The foraging ecology of wading birds has been particularly well studied. The resulting body of literature offers a fascinating variety of scientific approaches involving the fields of sensory phys- iology, social behavior, cost–benefit analysis, predator–prey relationships, energy flow, niche par- titioning, and nutrient ecology. FIGURE 19.3 Average distances flown by adult breeding wading birds from colonies to foraging sites (km, one way); maximum distances are indicated above the bars. These data are from a mix of studies that variously used radio telemetry, marked birds, or light aircraft to document foraging distances of individual birds. Note that maximum distances for most species are much larger than means — up to 110 km for White Ibises and 130 km for Wood Storks. © 2002 by CRC Press LLC 624 Biology of Marine Birds 19.3.1 FORAGING BEHAVIOR When feeding, wading birds use a variety of foraging techniques. Herons and egrets employ a range of behaviors that include slow stalking, sit-and-wait, active pursuit, and, more rarely, aerial foraging at the surface, or aerial plunges (Meyerriecks 1962, Kushlan 1976b; see Figure 19.4.). The Green-backed Heron (Butorides striatus) uses bait of various kinds to attract fish to within striking range (Higuchi 1986, 1988). Ibises and storks stalk or pursue prey, but are more likely to probe with partly open bills into soft substrate, using tactile means and sensory pits in the bill to detect prey. Both Snowy Egrets and Wood Storks frequently use their feet to stir up prey hidden in sediments or vegetation. Spoonbills swing their bills in a horizontal arc through the water, often in unison, a technique that when coupled with the unique configuration of the shape of bill, acts to pull small particles into the bill by creating an area of lower pressure in the bill opening into which small food items may be swept (Weihs and Katzir 1994). Sight-foraging birds must contend with the dual problems of surface glare and the need to correct for the refraction caused by items being underwater (Figure 19.5). Both Little Egrets and Reef Herons (Ardea gularis) are able to correct for differences in actual position of prey due to refraction (Katzir and Intrator 1987, Lotem et al. 1991). Glare may be reduced by extending one or both wings during foraging (Frederick and Bildstein 1992), or by tilting the head (Krebs and Partridge 1973). One of the most extreme foraging behaviors is “canopy feeding,” described pri- marily for Black Herons (Ardea ardesiaca), in which the wings are spread in a circle with the head and neck beneath the canopy, creating an area of darker water into which the egret looks for prey. Although many wading birds are diurnal feeders, some, like the night-herons and Boat-billed Herons (Cochlearius cochlearius), are most frequently nocturnal, foraging in the daylight only when the energetic demands of nesting require it. Many species choose to forage during crepuscular hours at both ends of the day, in some cases despite weather and tidal conditions (Draulans and Hannon 1988). Many wading birds forage early in the morning and are more likely to forage in flocks at that time. Although early-morning feeding is explained in part by the preceding nightlong fast, early feeding may also be the result of a predictable and temporary increased availability of prey. Hafner et al. (1993) found that timing of flock feeding and temporal variation in foraging success of Little Egrets in the Camargue of France were explained by low dissolved oxygen levels in water during the morning (nocturnal respiration by macrophytes depleted the water of oxygen, forcing fish to breathe in the more oxygenated layers at the surface). Soon after sunrise, dissolved oxygen increased as a result of the diurnal portion of plant respiration, and capture rates decreased rapidly. 19.3.2 FLOCK-FORAGING DYNAMICS Wading birds often feed in dense mixed-species flocks with other waterbirds (Figure 19.6). Some species, like Snowy and Little Egrets, are rarely found foraging solitarily (Hafner et al. 1982, Master et al. 1993), while others, such as Tricolored Herons (Egretta tricolor) and Goliath Herons, are typically solitary when foraging (Mock and Mock 1980, Hancock and Kushlan 1984). Many species forage solitarily and breed colonially (Marion 1989). Individuals may switch from solitary to social foraging depending on the richness, predictability, and defensibility of the food source, as well as stage of nesting (Simpson et al. 1987, Draulans and Hannon 1988, Marion 1989). In South Florida, White Ibises and Snowy Egrets tended to travel in flocks and land together or near other birds, but Great Egrets (Ardea albus) and Tricolored Herons tended to forage solitarily whether they departed the colony in a flock or not (Smith 1995b; see also Strong et al. 1997). Master et al. (1993) suggested that Snowy Egrets were obligate in their use of dense foraging aggregations because their active foraging behaviors were, for a variety of reasons, most efficient in those situations. Foraging flocks of up to several hundred individuals often are formed of several species of waterbirds. For example, Frederick and Bildstein (1992) observed foraging flocks in Venezuela containing up to seven species of ibises, five of herons, two storks, one spoonbill, two species of ducks, and three raptors. These large aggregations are a mix of conflicting pressures for individuals © 2002 by CRC Press LLC Wading Birds in the Marine Environment 625 FIGURE 19.4 Foraging behaviors displayed by Reddish Egret (Egretta rufescens), showing running (top), double-wing feeding (right), and peering into water (left). (Drawing by J. Zickefoose.) © 2002 by CRC Press LLC 626 Biology of Marine Birds (a) (b) FIGURE 19.5 (a) Disparity between the actual and apparent position of prey in water due to light refraction at the water/air interface. (b) Striking of underwater prey by a Reef Heron (Egretta garzetta gularis), showing approach and aiming (above) and prey capture (below). (From Katzir and Martin [1994], reprinted with permission.) © 2002 by CRC Press LLC [...]... period of dependence upon adult feedings at the breeding colony References: 1, Erwin et al 199 6; 2, Watts 199 5; 3, Ryder and Manry 199 4; 4, Hafner et al 199 8; 5, Davis and Kushlan 199 4; 6, Frederick 199 7; 7, Kushlan and Bildstein 199 2, Palmer 196 2, Kahl 196 3; 8, Kahl 196 3, Hancock and Kushlan 198 4, Sepulveda et al 199 9; 9, Lack 194 9, North 197 9; 10, Owen 195 9, Butler 199 7, Hancock and Kushlan 198 3;... In some of these areas, wading birds are the dominant shallow-water avian predator on small fishes and invertebrates (Bildstein et al 198 2, Berruti 198 3, Howard and Lowe 198 4, Butler 199 7), to the extent that as a group, wading birds can be important determinants of energy flow in wetland ecosystems (Berruti 198 3, Bildstein et al 198 2, Bildstein et al 199 1) 19. 5.1 EFFECTS OF WADING BIRDS ON MARINE AND... BURKHOLDER, J M 199 8 Implications of harmful microalgae and heterotrophic dinoflagellates in management of sustainable marine fisheries Ecological Applications, Supplement 8: s36–s62 © 2002 by CRC Press LLC 648 Biology of Marine Birds BUTLER, R W 198 8 Population regulation of wading ciconiiform birds Colonial Waterbirds 17: 189 199 BUTLER, R W 199 3 Time of breeding in relation to food availability of female... FIGURE 19. 7 Comparison of maximum longevity records for free-ranging wading birds (15 species, in black) and seabirds (20 species, in white) Although there have been fewer attempts to band wading birds, ciconiiform birds appear to be shorter-lived in general than are seabirds 632 Biology of Marine Birds faithful, while some ibises are nearly obligate nomads (Hancock et al 199 2, Frederick et al 199 6a,... 130–134 GONZALEZ, J A 199 6 Kleptoparasitism in mixed-species foraging flocks of wading birds during the late dry season in the Llanos of Venezuela Colonial Waterbirds 19: 226–231 GONZALEZ, J A 199 9 Effects of harvesting of waterbirds and their eggs by native people in the northeastern Peruvian Amazon Waterbirds 22: 217–224 GOTMARK, F 199 2 The effect of investigator disturbance on nesting birds Pp 63–104 in... nonbreeding season have large effects on survival of young birds (den Held 198 1, Hafner et al 199 4, North 197 9, Cezilly et al 199 6) Very little information is available on the subject of population regulation of tropical and subtropical species 19. 5 WADING BIRDS AS MARINE ANIMALS Very few wading birds are found exclusively in marine habitats These birds are typically found close to the immediate coastline... Journal of Wildlife Management 59: 667–673 DODD, M G., AND T M MURPHY 199 6 The Status and Distribution of Wading Birds in South Carolina, 198 8 199 6 Report SG9610-A, South Carolina Marine Resources, Columbia, SC, 66 pp DRAULANS, D 198 7 The effect of prey density on foraging behaviors of adult and first-year grey herons (Ardea cinerea) Journal of Animal Ecology 56: 479–493 DRAULANS, D., AND J HANNON 198 8... availability of prey (Kushlan 198 6, Frederick and Collopy 198 9a) The presence of a tidal influence in coastal areas assures coastal birds of a relatively predictable daily drying trend One of the most obvious behavioral differences between populations of inland and coastal wading birds is the entrainment of feeding cycles to the tidal pattern (Powell 198 7, Butler 199 7, Ntiamoa-Baidu et al 199 8, Draulans... W JOHNSON 199 8 Impact of water diversions on colonially-nesting waterbirds in the Macquarie marshes of arid Australia Colonial Waterbirds 21: 159–170 KLEIN, M L., S R HUMPHREY, AND H F PERCIVAL 199 5 Effects of ecotourism on distribution of waterbirds in a wildlife refuge Conservation Biology, 9: 1454–1465 KLEKOWSKI, E J., S A TEMPLE, A M SIUNG-CHANG, AND K KUMARSINGH 199 9 An association of mangrove... KUSHLAN, J A 197 7 Population energetics of the American White Ibis Auk 94: 114–122 KUSHLAN, J A 198 6 Responses of wading birds to seasonally fluctuating water levels: strategies and their limits Colonial Waterbirds 9: 155–162 KUSHLAN, J A 199 3 Colonial waterbirds as bioindicators of environmental change Colonial Waterbirds 16: 223–251 KUSHLAN, J A 199 7 The conservation of wading birds Colonial Waterbirds 20: . Asynchronous Hatching 629 19. 4.3 Breeding-Site Fidelity 629 19. 4.4 Survival 632 19. 4.5 Population Regulation 632 19. 5 Wading Birds as Marine Animals 633 19. 5.1 Effects of Wading Birds on Marine and Estuarine. Frederick 199 7; 7, Kushlan and Bildstein 199 2, Palmer 196 2, Kahl 196 3; 8, Kahl 196 3, Hancock and Kushlan 198 4, Sepulv eda et al. 199 9; 9, Lack 194 9, North 197 9; 10, Owen 195 9, Butler 199 7, Hancock. Entrainment 636 19. 5.4.3 Effects of Storms 637 19. 6 Management of Wading Birds 638 19. 6.1 Management of Breeding Sites 638 19. 6.2 Human Disturbance Issues 639 19. 6.3 Foraging Habitat 640 19. 6.4 Monitoring