217 Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds Keith C. Hamer, E. A. Schreiber, and Joanna Burger CONTENTS 8.1 Introduction 218 8.2 Breeding Phenology 218 8.2.1 Effects of Age on Breeding Phenology 220 8.2.2 Effects of Weather 220 8.2.3 Effects of Food Availability 222 8.2.4 Biennial Breeding 222 8.2.5 Aseasonal Breeding 223 8.3 Breeding Habitat 223 8.3.1 Nesting and Foraging Habitats 223 8.3.2 Colony and Nesting Habitats Used 224 8.3.3 High-Latitude vs. Low-Latitude Species 227 8.3.4 Habitat Use vs. Habitat Selection 228 8.3.5 Competition for Habitat: Is There Competitive Exclusion? 229 8.3.6 Role of Predation, Weather, and Other Factors 230 8.3.6.1 Predators 230 8.3.6.2 Weather 230 8.3.6.3 Other Factors Affecting Nest-Site Selection 230 8.3.7 Nest-Site Selection and Reproductive Success 231 8.4 Breeding Systems and Social Organization 231 8.4.1 Coloniality and Dispersal 231 8.4.2 Mating Systems 232 8.4.3 Obtaining a Mate 232 8.4.4 Duration of Pair Bonds 233 8.5 Breeding Biology and Life Histories 234 8.5.1 Eggs 234 8.5.2 Incubation 235 8.5.3 Chicks and Chick-Rearing 238 8.5.4 Postfledging Care 243 8.5.5 Survival 245 8.5.6 Age at First Breeding 245 8.5.7 Relationships among Life History Traits 247 8 © 2002 by CRC Press LLC 218 Biology of Marine Birds 8.6 Breeding Performance and Life History–Environment Interactions 248 8.6.1 Age-Specific Survival and Fecundity 248 8.6.2 Breeding Frequency 249 8.6.3 Adult Quality 249 8.7 Postbreeding Biology 250 8.8 The Evolution of Seabird Life Histories 251 Literature Cited 253 8.1 INTRODUCTION Seabirds comprise about 328 species in four orders, the Spenisciformes (penguins; 17 species in one family), Procellariiformes (albatrosses, shearwaters, petrels, diving petrels, storm-petrels; 125 species in four families, here termed petrels), Pelecaniformes (pelicans, tropicbirds, frigatebirds, gannets, and cormorants; 61 species in five families), and Charadriiformes (gulls, terns, skuas, skimmers, and auks; 128 species in four families: see Appendix 1 for a complete list of species). Seabirds range in size from the Least Storm-petrel (Halocyptena microsoma; body mass = 20 g) to the Emperor Penguin (Aptenodytes forsteri; body mass = 30 kg). They exploit a broad spectrum of marine habitats, from littoral to pelagic and from tropical to polar, breeding at higher latitudes and in colder environments than any other vertebrate on earth. The general characteristics of the different families of seabirds are summarized in Table 8.1 (Family Sternidae is included in the Family Laridae following Croxall et al. 1984, Nelson 1979, Croxall 1991). Seabirds can all be broadly categorized as long-lived species with delayed sexual maturation and breeding and low annual reproductive rates. Many species have a lifespan well in excess of 30 years with fewer than 10% of adults dying each year, and most do not commence breeding until age 3 years or older (over 10 years in some albatrosses; see Appendix 2). Most species lay only one to three eggs per clutch and in some cases rearing offspring takes so long (e.g., 380 days in Wandering Albatrosses, Diomedea exulans) that successful parents breed only every second year. These life history traits are adaptive evolutionary responses to conditions of living in the marine and maritime environment, both at sea and on land. They have been generally assumed to reflect the patchy and unpredictable distribution of marine food resources, although there are additional explanations that have not received sufficient recognition (see Chapter 1 and conclusions below). Some confusion has arisen in the literature because of a failure to distinguish between life histories (comprising sets of evolved traits) and life-table variables such as age-specific fecundity and mortality (that indicate an individual’s performance and are the consequence of how life history traits interact with the environment; Charnov 1993, Ricklefs 2000). For instance, all petrels are constrained by their life history evolution to lay a single-egg clutch, no matter how favorable the environment (Figure 8.1). Some other species have the potential to lay larger clutches, with the number of eggs laid varying from one individual to another, and between years within individuals. Life history adaptations determine the potential limits to this variation within each population, whereas variation within individuals is better expressed in life-table variables. This chapter explores the variation in breeding biology and nesting ecology among seabirds. It examines breeding phenology and habitat in different species and environments, breeding systems and social organization, life history traits (including analysis of comparative data for different species from Appendix 2), the relationships between different life history traits, breeding perfor- mance and life history–environment interactions, and postbreeding biology, focusing in particular on postbreeding migration and dispersal. 8.2 BREEDING PHENOLOGY About 98% of seabirds are colonial and have synchronously timed breeding cycles within colonies. The benefits and costs of breeding synchronously are discussed in Chapter 4. At the beginning of © 2002 by CRC Press LLC Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds 219 TABLE 8.1 Range of Demographic Parameters Observed in the Families of Seabirds Order Family No. of Species Avg. Clutch Size Breeding Cycle Age 1st Breed (yr) Incubation Period Chick Period (d) Post- Fledging Care (d) Nest Location Hatch Type Breeding Region Forage Distance Annual Survival (%) Sphenisciformes Spheniscidae, penguins 17 1–2 A–B 2–5 33–63 54–170 0–50 O-Bu SA STr-P NS,OS 62–95 Procellariiformes Diomedeidae, albatross 21 1 A–B 5–9 62–79 115–280 0–44 O SP Tr-P OS,NS+ 91–96 Procellariidae, shearwaters 79 1 A–B 2–8 43–62 45–130 0–? Bu(O) SP STr-Tm OS 72–96 Pelecanoididae, diving petrels 4 1 A 2 42–58 42–75 0–? Bu SP STr-Tm OS 75–87 Hydrobatidae, storm-petrels 21 1 A 2–3 38–55 55–75 0–? Cr,Bu SP STr-P OS 79–93 Pelecaniformes Phaethontidae, tropicbirds 3 1 A 2–5 39–51 72–90 0 Un,Cr SP STr-Tr OS 90 Pelecanidae, pelicans 7 2–3 A 2–3 28–32 71–88 7–20 O,Tr A STr-Tr NS,NS+ ? Fregatidae, frigatebirds 5 1 A–B 5–8 52–60 150–170 30–200 Tr A Tr OS ? Sulidae, boobies 10 1–3 A 2–5 41–58 78–139 0–200 O,Tr A STr-Tr NS,OS 83–96 Phalacrocoracidae, cormorants 36 2–4 A 2–4 27–35 38–80 20–65 O,Tr A Tm-STr NS 80–91 Charadriiformes Stercorariidae, skuas 7 2 A 3–7 24–32 24–50 14–24 O SP P-Tm NS,NS+ 90–98 Laridae, gulls 50 1–3 A 2–4 24–30 32–60 7–45 O SP Tm-Tr NS,OS 74–97 Laridae, terns 45 1–2 A 2–4 22–37 20–67 5–30 O(Tr) SP Tm-Tr NS,OS 75–93 Rhynchopidae, skimmers 3 1–5 A 3 21–24 28–30 14–20 O SP Tm-STr NS ? Alcidae, auks, murres (total) 23 1–2 A 2–5 28–46 26–50 0–? Cr,Bu,O SP P-Tm NS,OS 75–95 Synthliboramphus sp., Endomychura sp. 4 2 A 2–4 31–36 2–4 long Bu,Cr P Tm-STr OS,NS 77 Alca torda, Uria sp. 3 1 A 4–5 33–35 20 long Bu,Cr SP P-Tm NS,OS 75 Note: Breeding cycle: A = annual breeder, B = biennial breeder. Hatchling type: SA = semialtricial, SP = semiprecocial, A = altricial, P = precocial. Breeding region: P = polar, SP = subpolar, Tm = temperate, STr = subtropical, Tr = tropical. Foraging distance: OS = feeds of fshore, NS = feeds nearshore, + indicates feeding at a slightly greater distance than nearshore. Phalacrocoracidae includes only subfamily Phalacrocoracinae (cormorants). The four genera of Alcids that have chicks that fledge (leave the nest) before they can fly are listed separately. (See further explanation of codes in Appendix 2.) © 2002 by CRC Press LLC 220 Biology of Marine Birds the breeding season, birds generally arrive back at the colony site over a short period of time, moving into the colony and establishing nesting territories. The majority breed on an annual cycle, although there may be small fluctuations in the commencement of nesting that are related to weather variations and/or food availability. Some albatrosses and petrels, and probably at least female frigatebirds, breed biennially (every other year) due to the length of time it takes chicks to become independent (Appendix 2). Several factors play a role in setting the timing of the breeding cycle: temperature, food availability, age, experience, and length of daylight, and probably others. Tem- perature is very important in polar, subpolar, and temperate breeding seabirds, while it is probably unimportant in subtropical and tropical areas. Seabird food (fish, squid, krill, etc.) is not uniformly available in space or time in the oceans and fluctuations in it undoubtedly play a significant role in setting the timing of breeding in all areas of the world (see Chapters 1 and 6). 8.2.1 EFFECTS OF AGE ON BREEDING PHENOLOGY Older breeders are commonly the first ones to return to the breeding colony at the beginning of the season and have the highest nesting success, suggesting that experience may have an important influence on timing of breeding (Adelie Penguins, Pygoscelis adeliae, Ainley et al. 1983; Wandering Albatrosses, Pickering 1989; Northern Fulmars, Fulmarus glacialis, Weimerskirch 1990; Manx Shearwaters, Puffinus puffinus, Brooke 1990; Northern Gannets, Morus bassanus, Nelson 1964; Black-legged Kittiwakes, Rissa tridactyla, Coulson and Porter 1985). Young birds may spend one to several seasons around the colony learning how to court and claim a territory before they begin breeding (Fisher and Fisher 1969, Harrington 1974, Nelson 1978, Hudson 1985, Schreiber and Schreiber 1993; Chapter 10). There are some data to indicate that there is an optimum age for first breeding and that birds beginning earlier may have a shorter life span (Ollason and Dunnet 1978, Croxall 1981). This implies a cost to the bird of breeding so that beginning at a younger age does not necessarily mean the pair will raise more offspring in their lifetime. 8.2.2 EFFECTS OF WEATHER Seabirds are well adapted to their surrounding climate. They have a good insulation of feathers, are endothermic, and have a suite of behaviors that allow further adjustment to local weather patterns. However, any extremes of climate or unusual climatic events can affect the nesting cycle of seabirds and their breeding success. These effects may be due directly to the weather itself, or indirectly to changes in food availability. Direct effects of weather on nesting are discussed in detail in Chapter 7 and only a brief overview is presented here. FIGURE 8.1 Grey-backed Storm-petrels, like all members of the Order Procellariiformes, lay one egg. (Photo by H. Weimerskirch.) © 2002 by CRC Press LLC Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds 221 Polar and subpolar seabirds may have the greatest energetic constraints imposed on them by climate. They have a short time available for breeding, they must cope with low air temperatures (Figure 8.2), prey are available only during a restricted season, and the length of the nesting period approaches the limit of available time. Since they need to begin their breeding season as soon as possible each year, they may arrive on the colony to find snow and ice inhibiting access to burrows or nesting areas, thus late season storms can delay nesting (Procellariiformes, Warham 1990; Adelie Penguins, Ainley and Le Resche 1973; Gentoo Penguins, P. papua, and Chinstrap Penguins, P. Antarctica, in Antarctica, Williams 1995). The effects of different weather variables in temperate breeding species are less clear. Wind speed is inversely correlated with site attendance in the early stages of the breeding season in Thick- billed Murres (Uria lomvia; Gaston and Nettleship 1981). Several species delay nesting during cold weather, including Brown Pelicans (Pelecanus occidentalis; Schreiber 1976), Black Skimmers (Rynchops niger), Common Terns (Sterna hirundo; Burger and Gochfeld 1990, 1991), and many other species. Subtropical and tropical species are less confined to a season by weather patterns, but food availability is still generally seasonal (see Chapter 6) and most species nest seasonally, although the season is less constricted than in most higher latitude species. For instance, on Johnston Atoll (central Pacific Ocean) Wedge-tailed Shearwaters (Puffinus pacificus), Christmas Shearwaters (Puffinus nativitatus), Brown Boobies (Sula leucogaster), Brown Noddies (Anous stolidus), and Grey-backed Terns (Sterna lunata) lay in a strictly confined season over 1 to 2 months. Masked Boobies (S. dactylatra), Red-footed Boobies (S. sula), Red-tailed Tropicbirds (Phaethon rubri- cauda), and White Terns (Gygis alba) lay in most months of the year, although a definite laying peak occurs in the spring (Schreiber 1999). The reasons for these differences among species have not been determined. It could be that social facilitation is more important in some species, resulting in a short laying period. Seasonal changes in food availability may also affect the energetic expenditures of some species more than others. El Niño–Southern Oscillation (ENSO) events have dramatic effects on breeding cycles for species in the tropical Pacific (Schreiber and Schreiber 1984, Duffy 1990; Chapter 7). The ultimate reason for their effect on breeding cycles is probably related to food availability. FIGURE 8.2 Adelie Penguin chicks in Antarctica wait for their parents to return from sea and feed them. Polar nesting species must have enough thermal insulation to survive cold temperatures. (Photo by P. D. Boersma.) © 2002 by CRC Press LLC 222 Biology of Marine Birds 8.2.3 EFFECTS OF FOOD AVAILABILITY Seabirds tolerate almost any degree of cold and heat but are highly sensitive to changes in food availability as documented by their responses to ENSO events (Schreiber and Schreiber 1989, Duffy 1990; Chapter 7). Birds may not attempt to nest at all during such events, or initiation of nesting may be delayed until food supplies increase (Ainley and Boekelheide 1990, Schreiber 1999). Food availability fluctuates seasonally on a global scale (Chapter 6) and therefore it is not equally available throughout the prolonged reproductive periods of seabirds. Even in the tropics, which we associate with a uniform climate, there are seasonal changes that affect the abundance and distribution of food, and these play a regulatory role in seabird nesting cycles (Chapter 6). The highest seasonality of food availability occurs in polar areas, where some species commence nesting before the great flushes of summer oceanic productivity. Given that adults are more adept foragers than immature birds (Chapter 6), young birds should fledge during the period of highest food availability to help ensure their survival while they learn to feed themselves. Emperor Penguins lay during the Antarctic winter and their chicks fledge 7 to 8 months later during the summer, when food availability is highest (Williams 1995). Wandering Albatrosses also time their nesting season so that chicks fledge when food is most available (Salamolard and Weimerskirch 1993). We know little about food availability to seabirds, making it difficult to determine why nesting cycles are timed the way they are, or why cycles are altered in some years. In some cases, ornithologists roughly determine changes in food availability by weighing adults, measuring growth rates in chicks, monitoring provisioning rates of chicks, or measuring nest success (Jarvis 1974, Gaston 1985, Chastel et al. 1993, Schreiber 1994, 1996, Phillips and Hamer 2000a). 8.2.4 B IENNIAL B REEDING Some species with extended nesting seasons are able to breed only every second year (e.g., King Penguins, Aptenodytes patagonicus; several of the albatrosses; White-headed Petrels, Pterodroma lessoni, of which 13% are annual breeders; Carboneras 1992, Chastel et al. 1995, Williams 1995). Some frigatebirds (Fregata sp.) may also breed biennially, particularly females, which continue to feed fledglings for 30 to about 180 days after they fledge, by which time they are 8 to 12 months old or more (Figure 8.3; Diamond 1975, Diamond and Schreiber in press; Appendix 2). The complete nesting cycle in King Penguins takes about 400 days, the longest of all seabirds. FIGURE 8.3 A female Lesser Frigatebird broods her single small chick on Christmas Island (central Pacific). Chicks hatch naked and take 5 to 6 months to fledge, after which they return to the nest for another 2 to 5 months to be fed. (Photo by R. W. and E. A. Schreiber.) © 2002 by CRC Press LLC Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds 223 Biennial breeding in species with a nesting cycle lasting less than a complete year has been attributed to birds being unable to breed and molt at the same time, owing to the energy requirements of each. White-headed Petrels, for instance, breed biennially even though they need only 160 to 180 days for a breeding cycle (seemingly allowing enough time to molt and breed annually, and similar to the breeding period of Great-winged Petrels, Pterodroma macroptera, that breed annually). Chastel (1995) suggests they breed biennially because they fledge their young at the end of summer and must molt during the winter when food availability is low, which slows the molt process. 8.2.5 ASEASONAL BREEDING There are some reports of subannual breeding by seabirds (a cycle of fewer than 12 months; Ashmole 1962, Dorward 1963, Harris 1970, Nelson 1977, 1978, King et al. 1992). Some of these studies were conducted during ENSO events that we now know cause changes in the timing of the nesting season due to changes in food availability (Schreiber 1999; Chapter 7). For some purported aseasonal breeders, breeding is probably annual with some adjustment according to food supply. Among the best-known reports of subannual breeding are those from the British Ornithologists’ Union Centenary Expedition to Ascension Island from October 1957 through May 1959 (see Ibis 103b, 1962, 1963). During this period, one of the most pronounced ENSO ever recorded was underway (Glynn 1990). Reports of subannual breeding in several species may have represented delayed breeding in one year because of unusual changes in food availability, and this needs further investigation. Sooty Terns (Sterna fuscata) may apparently lay every 10 months (Ashmole 1963), but there are not good data that it is the same birds breeding each time. Snow and Snow (1967) and Harris (1970) reported a 9- to 10-month cycle in Swallow-tailed Gulls (Creagrus furcatus) in the Galapagos, but both studies were during ENSO events. Earlier, Murphy (1936) had found them to breed in all months of the year, although this also was during an ENSO event in 1925. This species may actually have a true subannual cycle. Perhaps because these birds nest in an area of abundant food associated with the Humboldt Current, they are not constrained to an annual cycle by seasonal food availability. They may also have the ability to alter their diet during the year to adjust to seasonality of food resources. King et al. (1992) documented both annual and subannual breeding in seven seabird species in a 6-year study on Michaelmas Cay (16°S, 145°E), during which two ENSO events occurred (1986–1987, 1990–1994). Interestingly, the two pelagic feeders, Sooty Terns and Brown Noddies, remained at the island year round and experienced the greatest nesting failures and desertions. Diet was not studied in this population, but food was most likely the factor controlling timing of nesting and presence on the island. On Johnston Atoll (central Pacific), Sooty Terns breed in all months of the year during ENSO events, when they have repeated failures and relayings (Schreiber 1999), leading one to wonder if this was the reason they were breeding in all months on Michaelmas Cay. On Christmas Island (central Pacific Ocean) some White Terns are reported to breed on a subannual cycle (Ashmole 1968), although this has not been studied over a multiyear period. Some seabirds are actually double-brooded and able to raise two broods in a year: Brown Noddies, Black Noddies (Anous minutus), White Terns, Cassin’s Auklets (Ptchoramphus aleuticus; Manuwal and Thoresen 1993, E. A. Schreiber unpublished; Appendix 2). It is interesting that three of these species nest in the supposed “depauperate” tropical waters. 8.3 BREEDING HABITAT 8.3.1 N ESTING AND FORAGING HABITATS Habitat use in seabirds can be divided into nesting habitat and foraging habitat. While many land birds, such as passerines, often use the same habitat for both of these functions, seabirds do not. Instead seabirds nest on land and forage in estuarine or oceanic waters, often far from their nest © 2002 by CRC Press LLC 224 Biology of Marine Birds sites. Further, since many seabirds have delayed breeding, they may spend years at sea, coming to land only occasionally until they begin breeding Species in the four orders of marine birds fall into three main habitat categories as a broad generalization: (1) species that feed pelagically and nest mainly on oceanic islands, such as albatrosses, petrels, frigatebirds, tropicbirds, boobies, and some terns; (2) species that nest along the coasts and feed in nearshore environments, such as some pelicans, cormorants, gulls, some terns, and alcids; (3) those few species that nest and forage in inland habitats, and come to the coasts during the nonbreeding season (such as some skuas and jaegers, Franklin’s Gull (Larus pipixcan), Bonaparte’s Gull (L. philadelphia), Ring-billed Gull (L. delawarensis), and Black Tern (Chlidonias niger). Grey Gull (L. modestus) is unusual in that it breeds in the interior deserts of Chile, but feeds coastally even during the breeding season (Howell et al. 1974). There are several important issues with habitat use in marine birds: (1) colony and nesting habitats used; (2) habitat selection in high-latitude and low-latitude species; (3) habitat use vs. habitat selection; (4) competition for habitat use and the role of competitive exclusion; and (5) the roles of predation, weather, and other factors in habitat selection. 8.3.2 COLONY AND NESTING HABITATS USED Seabirds nest in a great variety of habitats from steep cliffs to flat ground, laying their eggs in trees or bushes, in burrows, in crevices, or in the open (Appendix 2; Figures 8.4 and 8.5). They nest on the mainland, in marshes, or on coastal or oceanic islands. Some even nest on roofs (Vermeer et al. 1988). A typical cliff habitat in eastern Canada illustrates habitat use by some species of breeding seabirds (Figure 8.4), from the large surface-nesting Northern Gannets at the top of the cliff to the smaller Black Guillemots (Cephus grylle) in crevices in the middle areas of a cliff. The habitat is partitioned to some extent by the size of the birds, with larger birds nesting in the open and toward the top, and smaller birds on ledges and in crevices lower down. In a crowded area, the species on the cliff face tend to be in small subcolony units of their own species, and during courtship there is much competition both between and within species for nesting sites. A typical tropical coral atoll may have 14 to 18 nesting species of seabirds (Figure 8.5). Some of the largest species nest in the open on the ground, such as Masked and Brown Boobies, although some nest in bushes and trees (Red-footed Boobies and Great Frigatebirds, Fregata minor). Terns may nest in bushes or trees (White Terns, Brown and Black Noddies), or on the ground (Sooty and Grey-backed Terns, Brown Noddies). Burrow-nesting birds may include Wedge-tailed Shearwaters and Audubon’s Shearwaters (Puffinus lherminieri), while crevice-nesting species include White- throated Storm-petrels (Nesofregatta fuliginosa). Christmas Shearwaters nest under bunches of grass or other vegetation. There are species-specific preferences for the various available breeding areas, which in some cases overlap and there is competition for nest sites. This occurs more on smaller atolls with less habitat available. Within each order there is wide diversity of habitat use, and this variability may extend to within some species as well. For instance, Red-footed Boobies nest in trees or on the ground (Schreiber et al. 1996); Sooty Terns nest in the open at some colonies, while in other places they nest under bushes (Schreiber et al. in preparation); and Herring Gulls (Larus argentatus) nest in nearly all habitats from flat ground to cliffs and trees (Pierotti and Good 1994). Some species, however, nest in only one habitat; most albatrosses, skuas, and most gulls nest only on the ground in the open. Franklin’s Gulls build floating nests in marshes and nest in no other habitat (Burger and Gochfeld 1994a). Many seabird species can be adaptable in the habitat they use, and given varying conditions, may change habitats. The type of available habitat influences competition for nest sites, both within and between species. The greater the diversity in spatial heterogeneity, the greater niche diversification is possible. Even on an apparently uniform sandy atoll in the tropics, there can be great diversification of nesting sites and birds can make choices about which areas to use. On Johnston Atoll, Christmas © 2002 by CRC Press LLC Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds 225 FIGURE 8.4 Typical nesting habitat and location of each species for a colony of seabirds along the coast of eastern Canada. Northern Gannets nest mostly on the flatter areas toward the top of the cliff, building mounded nests of rock or turf. Northern Fulmars nest toward the top of the cliff under dense grasses or vegetation, in crevices or shallow burrows. Black-legged Kittiwakes nest over a broad range of heights along the cliff face on narrow ledges, mounding nest material to hold their eggs. Thick-billed and Common Murres also nest over a broad range of heights on the cliff face. They build no nest laying their single egg on a narrow ledge. Razor- billed Auks nest toward the bottom of the cliff in the rock rubble. (Drawn by J. Zickefoose.) © 2002 by CRC Press LLC 226 Biology of Marine Birds FIGURE 8.5 Typical nesting habitat for tropical Pacific Ocean seabirds. While all species are colonial, nesting densities v ary by species and with habitat. Masked Boobies nest on open ground, building no nest, though they may collect a fe w small pebbles (nests tend to be widely dispersed and rarely occur singly). Red-footed Boobies nest near the tops of trees or bushes (nests from about 0.5 to 10 m apart) b uilding a nest of twigs lined with some vegetation. Great Frigatebirds nest in the tops of bushes, or in or near the tops of trees (nests tend to be quite close together). They build a similar but less substantial and smaller nest than Red-footed Boobies. Black Noddies nest in trees, generally under leafy cover when possible (nests about 0.5 to 1.5 m apart depending on tree struct ure). Christmas Shearwaters nest under grasses or other vegetation, in crevices or short burrows (about 1 to 8 m apart). Wedge-tailed Shearwaters nest in burrows (0.5 to 3.0 m long and about 1 to 10 m apart, partly depending on substrate). Red-tailed Tropicbirds nest under bushes or other vegetation providing shade and some movement space (individuals are grouped by availability of vegetation, desired space between nests, and desired isolation from neighbor; from 0.5 to 10 m apart). Red-tailed Tropicbird Wedge-tailed Shearwater White Tern Masked Booby Christmas Shearwater Black Noddy Great Frigatebird (() Red-footed Booby © 2002 by CRC Press LLC [...]... (Schreiber and Schreiber 1 983 ) The causes and consequences of divorce in seabirds are discussed in more detail by Bried and Jouventin (Chapter 9) 8. 5 BREEDING BIOLOGY AND LIFE HISTORIES 8. 5.1 EGGS The sizes of eggs laid by seabirds are discussed in Chapter 12 by Whittow The majority of seabirds lay clutches of one to two eggs, and 54% of species lay single-egg clutches Some species of cormorant lay up to... (Figure 8. 16; Pearson correlation of arcsine and log-transformed data; r = 0.57, n = 68, p . Traits 247 8 © 2002 by CRC Press LLC 2 18 Biology of Marine Birds 8. 6 Breeding Performance and Life History–Environment Interactions 2 48 8.6.1 Age-Specific Survival and Fecundity 2 48 8.6.2 Breeding. Jouventin (Chapter 9). 8. 5 BREEDING BIOLOGY AND LIFE HISTORIES 8. 5.1 E GGS The sizes of eggs laid by seabirds are discussed in Chapter 12 by Whittow. The majority of seabirds lay clutches of one. Effects of Age on Breeding Phenology 220 8. 2.2 Effects of Weather 220 8. 2.3 Effects of Food Availability 222 8. 2.4 Biennial Breeding 222 8. 2.5 Aseasonal Breeding 223 8. 3 Breeding Habitat 223 8. 3.1