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Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds

Breeding Biology, Life Histories, and Life History–Environment Interactions in Seabirds

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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 performance 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



Spheniscidae, penguins

Diomedeidae, albatross

Procellariidae, shearwaters

Pelecanoididae, diving petrels

Hydrobatidae, storm-petrels

Phaethontidae, tropicbirds

Pelecanidae, pelicans

Fregatidae, frigatebirds

Sulidae, boobies

Phalacrocoracidae, cormorants

Stercorariidae, skuas

Laridae, gulls

Laridae, terns

Rhynchopidae, skimmers

Alcidae, auks, murres (total)

Synthliboramphus sp.,

Endomychura sp.

Alca torda, Uria sp.



Sphenisciformes

Procellariiformes



1–2

1

1

1

1

1

2–3

1

1–3

2–4

2

1–3

1–2

1–5

1–2

2

1



17

21

79

4

21

3

7

5

10

36

7

50

45

3

23

4

3



Avg.

Clutch

Size



A



A–B

A–B

A–B

A

A

A

A

A–B

A

A

A

A

A

A

A

A



Breeding

Cycle



4–5



2–5

5–9

2–8

2

2–3

2–5

2–3

5–8

2–5

2–4

3–7

2–4

2–4

3

2–5

2–4



Age 1st

Breed

(yr)



33–35



33–63

62–79

43–62

42–58

38–55

39–51

28–32

52–60

41–58

27–35

24–32

24–30

22–37

21–24

28–46

31–36



Incubation

Period



20



54–170

115–280

45–130

42–75

55–75

72–90

71–88

150–170

78–139

38–80

24–50

32–60

20–67

28–30

26–50

2–4



Chick

Period

(d)



long



0–50

0–44

0–?

0–?

0–?

0

7–20

30–200

0–200

20–65

14–24

7–45

5–30

14–20

0–?

long



PostFledging

Care (d)



Bu,Cr



O-Bu

O

Bu(O)

Bu

Cr,Bu

Un,Cr

O,Tr

Tr

O,Tr

O,Tr

O

O

O(Tr)

O

Cr,Bu,O

Bu,Cr



Nest

Location



SP



SA

SP

SP

SP

SP

SP

A

A

A

A

SP

SP

SP

SP

SP

P



Hatch

Type



P-Tm



STr-P

Tr-P

STr-Tm

STr-Tm

STr-P

STr-Tr

STr-Tr

Tr

STr-Tr

Tm-STr

P-Tm

Tm-Tr

Tm-Tr

Tm-STr

P-Tm

Tm-STr



Breeding

Region



NS,OS



NS,OS

OS,NS+

OS

OS

OS

OS

NS,NS+

OS

NS,OS

NS

NS,NS+

NS,OS

NS,OS

NS

NS,OS

OS,NS



Forage

Distance



75



62–95

91–96

72–96

75–87

79–93

90

?

?

83–96

80–91

90–98

74–97

75–93

?

75–95

77



Annual

Survival

(%)



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 offshore, 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.)



Charadriiformes



Pelecaniformes



Family



Order



No. of

Species



TABLE 8.1

Range of Demographic Parameters Observed in the Families of Seabirds



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Biology of Marine Birds



FIGURE 8.1 Grey-backed Storm-petrels, like all members of the Order Procellariiformes, lay one egg. (Photo

by H. Weimerskirch.)



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. Temperature 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.



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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.)



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 Thickbilled 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 rubricauda), 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.



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8.2.3 EFFECTS



Biology of Marine Birds



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 BIENNIAL BREEDING

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.)



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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 NESTING



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



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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 Whitethroated 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



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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. Razorbilled Auks nest toward the bottom of the cliff in the rock rubble. (Drawn by J. Zickefoose.)



Red-tailed Tropicbird



Wedge-tailed Shearwater



Black Noddy



Christmas Shearwater



226



FIGURE 8.5 Typical nesting habitat for tropical Pacific Ocean seabirds. While all species are colonial, nesting densities vary by species and with habitat. Masked

Boobies nest on open ground, building no nest, though they may collect a few 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) building 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 structure). 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).



Masked Booby



White Tern



Red-footed Booby



Great Frigatebird (()



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TABLE 8.2

Number of Species in Each Family of

Seabird Breeding at Different Latitudes



Sphenisciformes

Penguins

Procellariiformes

Albatrosses

Shearwaters

Diving-petrels

Storm-petrels

Pelecaniformes

Tropicbirds

Pelicans

Frigatebirds

Boobies

Cormorants

Charadriiformes

Skuas

Gulls and terns

Skimmers

Auks



Tropical



Temperate



Polar



1



11



5



1

21

0

8



20

46

4

11



0

7

0

1



3

3

5

7

5



0

4

0

3

28



0

0

0

0

1



0

28

3

0



2

50

0

17



5

7

0

3



Note: Tropical (between the Tropic of Cancer and

Tropic of Capricorn); Temperate (Tropic of Cancer to

Arctic Circle [66.3oN] and Tropic of Capricorn to 60oS).

Where species breed in more than one zone, that given

is where the majority of individuals breed.



Shearwaters and Brown Boobies choose areas of highest wind levels, while Great Frigatebirds tend

to nest in areas of lowest wind levels in the lee of the island (Schreiber 1999). The frigatebird

choice of nest sites may relate to wing loading and body mass, since a black bird might not be

expected to nest in a windless area if avoiding heat stress was its main consideration. High winds

may make it difficult for frigatebirds to remain on their nests, given their light weight and extremely

long wings (they have the lowest wing loading of any flying bird; Diamond and Schreiber in press).

In all habitats there is the opportunity for both species preferences and competition to influence

nest-site selection (see below). In some cases, larger species may obtain breeding sites by virtue

of their size and ability to defend these sites. However, where there is great heterogeneity, there

can be separation by habitat type. As early as the 1950s, Fisher and Lockley (1954) noted differences

in habitat use by a range of species nesting on rocky cliff faces.



8.3.3 HIGH-LATITUDE



VS.



LOW-LATITUDE SPECIES



All four orders of seabirds breed over a wide range of latitudes from tropical to polar environments,

although all four do not have species equally distributed across all latitudes (Table 8.2). Species

particularly associated with high latitudes and cold water include penguins, most albatrosses, diving

petrels, skuas, some gulls and terns, and auks. Those nesting in warm water areas include one

penguin, one albatross, some petrels and shearwaters, frigatebirds, boobies, tropicbirds, and some

gulls and terns. These environments affect the choice of both nesting and foraging habitat. Some

habitat choices faced by seabirds are a function of the habitats available within these regions. For

example, in high-latitude environments, there are no trees. Temperate region birds may have



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Biology of Marine Birds



marshes, trees, rocky or grassy slopes, and rocky islands, giving way at lower latitudes to salt

marshes, sandy beaches, coral rubble, and bushes. At high latitudes, cold temperatures influence

nest-site locations, while in tropical regions, heat stress may play a more critical role.



8.3.4 HABITAT USE



VS.



HABITAT SELECTION



The fact that seabirds forage in marine habitats, often pelagically, defines their habitat use to some

extent. The factors that affect foraging habitat selection are complex, and include fish and invertebrate distribution, weather patterns and ocean currents, and upwellings. These factors are discussed

in Chapter 6. Choice of breeding habitat for seabirds is somewhat constrained by their foraging

behavior (type of foraging habitat, daily flight distances, and other energetic considerations).

However, within these constraints, the question of habitat use vs. habitat selection is critical. Do

seabirds use the nearest available habitat to breed or are they selecting specific habitats from the

range available? Additionally, are their breeding habitat preferences influencing their choice of

foraging habitats?

Habitat selection can be defined as the choice of a place to live (Partridge 1978), and it implies

selection from a range of available characteristics (Burger 1985). Selection of breeding habitat,

however, includes at least two distinct choices: colony site location and nest site location. In the

few solitary-nesting seabird species, the two are functionally the same, but in most seabirds, the

two types of selection are distinct. Colony-site selection generally occurs when the colony is first

established, and subsequent birds simply nest within the colony. It is difficult to examine colonysite selection in species that use the same nesting place for many years, although frequently,

scientists can measure microclimate of nest sites to determine what birds are selecting, such as sun

exposure, wind level, or temperature. A new colony may form from a roost (birds loafing in areas

other than their nesting colony; Brown Pelicans, Schreiber and Schreiber 1982; Red-footed Boobies,

Schreiber 1999). There are not good data on why this happens or what causes these birds not to

return to their natal colony.

For some species, environmental conditions vary from year to year altering the habitat of the

colony and making colony-site selection more frequent. Heavy rains during ENSO events cause

dense vegetation growth in Sooty Tern colony sites on Christmas Island, making them unsuitable

for nesting (Schreiber and Schreiber 1989). During the following breeding cycle, birds select an

area of less-dense vegetation in which to lay. Franklin’s Gulls and Forster’s Terns (Sterna forsterii)

that nest in marshes frequently change sites from year to year (McNicholl 1975, Burger 1974;

Figure 8.6). Black-billed Gulls (Larus bulleri) that nest in braided rivers shift colony sites annually

(Beer 1966), and skimmers and terns nesting on sand bars in tributaries of the Amazon shift sites

as new islands are created following floods (Krannitz 1989).

Seabirds select specific colony sites based on a range of abiotic and biotic characteristics

(Buckley and Buckley 1980). While many studies describe the nesting habitat of seabirds, implying

that the birds have selected these sites, in order to demonstrate habitat selection it is necessary to

compare the habitat characteristics used by the species with the characteristics that are available,

such as substrate, wind levels, and vegetation density. Burger and Lesser (1978) compared the

characteristics of 34 Common Tern colonies in Barnegat Bay, New Jersey, with those of 225 other

salt marsh islands. They found that the nesting islands differed significantly from the 225 other

islands in size, distance to nearest other island and to shore, exposure to open water, and vegetation

characteristics. The characteristics that terns selected were islands that were sufficiently high to

avoid tidal flooding during the nesting season, but sufficiently low to lack mammalian predators

(such as rats and foxes; Burger and Lesser 1978).

Similar selection of colony sites occurs in places with numerous potential nesting islands, such

as in the Caribbean (Schreiber and Lee 2000) and in the Galapagos Islands (Cepeda and Cruz

1984). However, for some species that nest on isolated oceanic islands, there may be no other

available island nearby and these birds tend to exhibit high philopatry (Great Frigatebirds, Schreiber



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