439 Chick Growth and Development in Seabirds G. Henk Visser CONTENTS 13.1 Introduction 439 13.2 Growth Patterns of Seabird Chicks in Relation to Taxon and Parental Feeding Strategy 442 13.2.1 Interspecific Variation in Growth Rates 442 13.2.2 Intraspecific Variation in Growth Rates 443 13.3 Energetics of Growth 444 13.3.1 Introduction 444 13.3.2 Components of the Chicks’ Energy Budget 444 13.3.3 Methods to Determine Energy Budgets in Free-Living Chicks 446 13.3.3.1 Periodic Chick Weighing 446 13.3.3.2 The Time-Energy Budget 447 13.3.3.3 The Measurement of Water Influx Rates and Subsequent Conversion to Energy Intake 450 13.3.3.3.1 The Doubly Labeled Water Method: Some General Principles 450 13.3.3.3.2 Applications of the DLW Method in Adult Seabirds: The Need for Standardization 451 13.3.3.3.3 Applications of the DLW Method in Seabird Chicks 452 13.3.4 Energy Budgets of Growing Seabird Chicks: The Importance of Asymptotic Body Mass, Duration of the Nestling Period, and Latitude 452 13.4 Development of Temperature Regulation 455 13.5 Physiological Effects of Food Restriction 457 13.6 Toward the Construction of Energy Budgets of Entire Family Units during the Peak Demand of the Brood 458 Acknowledgments 459 Literature Cited 459 13.1 INTRODUCTION Chicks of most seabird species grow up on land situated in close proximity to the sea. It is presumed that the nature of their food supply has not allowed the evolution of the self-feeding precocial mode of development in seabirds (Lack 1968). Although there are marked interspecific differences with respect to developmental mode, in the majority of seabird species, chicks stay in or close to their nest until fledging, being parentally fed and brooded. For example, chicks of pelicans, frigatebirds, gannets, and boobies are born naked with their eyes closed, being totally dependent on parental food and warmth (Figure 13.1). Chicks that hatch in this developmental state have been classified 13 © 2002 by CRC Press LLC 440 Biology of Marine Birds as being altricial by Nice (1962; see Table 13.1). Chicks of tropicbirds (Figure 13.2) hatch with their eyes closed, but are covered in down (being classified as being semialtricial-2; Nice 1962), whereas tern, auk, murre, and jaeger chicks hatch with a downy plumage with their eyes open, and are able to walk (semiprecocial: Figure 13.3). In contrast, chicks of some murrelet species (Synth- liboramphus spp. and Brachyrhamphus spp.) leave the nest shortly after hatching, being fed at sea by their parent (precocial-4; Nice 1962, Eppley 1984, Gaston 1992, Starck and Ricklefs 1998a). Chicks of Common Murre (Uria aalge), Thick-billed Murre (Uria lomvia), and Razor-billed Auk (Alca torda) do so after having attained about 25% of adult body mass (Daan and Tinbergen 1979, Gaston 1985, Starck and Ricklefs 1998a). Obviously, early nest desertion by the chick potentially reduces parental traveling time and enables exploitation of remote feeding areas (Ydenberg 1989). However, this strategy can only be achieved with the co-evolution of some specific physiological adaptations of the chick to minimize and compensate for its heat loss (e.g., Eppley 1984). FIGURE 13.1 A newly hatched altricial Lesser Frigatebird chick (Fregata ariel). (Photo by R. W. and E. A. Schreiber.) TABLE 13.1 Criteria for Classification of Neonates Type of Neonate Plumage Eyes Nest Attendance Parental Brooding Parental Feeding Precocial-1 Contour feathers Open Leave nest None None Precocial-2 Down Open Leave nest Yes None Precocial-3 Down Open Leave nest Yes Showing food Precocial-4 Down Open Leave nest Yes Yes Semiprecocial Down Open Around nest Yes Yes Semialtricial-1 Down Open In nest Yes Yes Semialtricial-2 Down Closed In nest Yes Yes Altricial None Closed In nest Yes Yes From Nice 1962. © 2002 by CRC Press LLC Chick Growth and Development in Seabirds 441 Seabirds have developed different feeding strategies, ranging from in-shore feeding to off-shore feeding (see Chapter 6). In species that feed in-shore (e.g., some pelicans, cormorants, gulls, and some terns), the chick can be fed several times a day and one parent can remain at the nest to brood it. This foraging mode may not necessitate chicks developing homeothermy at an early age (Klaassen 1994). Small seabird chicks frequently receive food as whole particles, such as fish (e.g., in most tern species), or as a predigested food mash (e.g., in young chicks of the Black-legged Kittiwake [Rissa tridactyla], cormorants, boobies). In pelagic seabirds (e.g., albatrosses, petrels, fulmars, boobies, and some terns), however, due to the long travel distances to their food source, parents are often gone for one or more days on a foraging trip. Therefore, until the achievement of homeothermy by the chick, feeding rates of the chick may be somewhat reduced over those of near-shore feeding birds. After the chick(s) achievement of homeothermy, both parents can leave the nest, potentially resulting in a doubling of the amount of food brought to the brood (Ricklefs and Roby 1983). While foraging, most pelagic seabirds store the food in their stomach to carry it back to the colony, although a few species carry fish in the bill (e.g., White Terns, Gygis alba; puffins). Procellariiform birds are unique in the sense that parents partly concentrate the food caught FIGURE 13.2 A 1-day-old Red-tailed Tropicbird chick. They are the only Pelecaniform chicks to hatch with a full coat of down. (Photo by E. A. Schreiber.) FIGURE 13.3 A Sooty Tern chick hatches with its eyes open and able to walk. The down on this just-hatched chick has not dried out yet. (Photo by E. A. Schreiber.) © 2002 by CRC Press LLC 442 Biology of Marine Birds into stomach oil. This substance mainly consists of wax esters with a very high energy density, and stomach oil formation has been interpreted as a strategy to increase the amount of energy per feeding trip (Ricklefs et al. 1985, Roby 1991, Roby et al. 1997). This physiological development has enabled procellariiform birds to exploit more remote feeding areas. Recent reviews in the literature include growth patterns of birds in general (Starck and Ricklefs 1998b), developmental plasticity (Schew and Ricklefs 1998), energy budgets during growth (Weath- ers 1992, 1996), and development of temperature regulation (Visser 1998). It is the aim of this chapter to partly update the information presented in these reviews with special emphasis on seabird chicks. In addition, current knowledge of several aspects of postnatal development on seabird chicks is integrated into the text to provide insight into patterns of evolutionary and geographical diver- sification. Some recent methodological developments are evaluated in an attempt to provide guide- lines for the standardization of future work on the construction of energy budgets in seabird chicks and adults. 13.2 GROWTH PATTERNS OF SEABIRD CHICKS IN RELATION TO TAXON AND PARENTAL FEEDING STRATEGY 13.2.1 I NTERSPECIFIC VARIATION IN GROWTH RATES Starck and Ricklefs (1998b) present growth parameter estimates based on logistic growth curves for a mixed data set of altricial and precocial land and seabird species (n = 557 species). The logistic growth curve, which has a sigmoid shape, enables the description of the development of body masses (M, g) of chicks as a function of age (t, d): M = A/(1 + exp(–k l (t – t i ))) (13.1) where A represents the asymptotic body mass of chicks (g), t i the time of inflection point of the curve (d), and k l the logistic growth rate constant (d –1 ). For the seabird subset (Figure 13.4), FIGURE 13.4 Relationship between the logistic growth constant (k l , d –1 ) and asymptotic body mass (A, g) in seabird chicks. Drawn diagonal line represents the general relationship between A and k l in birds (Equation 13.2 of this chapter, Starck and Ricklefs 1998b). © 2002 by CRC Press LLC Chick Growth and Development in Seabirds 443 asymptotic body masses range between 38.5 g for the Least Tern (Sterna antillarum, Schew 1990) and 15,500 g for the Emperor Penguin (Aptenodytes forsteri, Stonehouse 1953), and the logistic growth constants range between 0.019 d –1 for the Amsterdam Albatross (Diomedea amsterdamensis, Jouventin et al. 1989) and 0.38 d –1 for the fastest growing species, the Black Tern (Chlidonias niger, Schew 1990). Assuming independence of the data points for all 557 species, the relationship between both parameters was described by: k l = 0.962A –0.31 (13.2) (Figure 13.4; Starck and Ricklefs 1998b). Equation 13.2 was used to predict k l for each seabird species listed by Starck and Ricklefs (1998b). Next, its residual value was calculated with the general equation: Residual value = 100 · (observed value – predicted value)/predicted value (13.3) The analysis revealed that, after correction for differences in asymptotic body masses, most seabird families exhibit relatively low growth rate constants, which is particularly the case for the Fregatidae (average level relative to prediction: –58.0%, which differs significantly from zero, after comparison of the standard error of the residuals, t 3 = –14.4; p <0.001), Hydrobatidae (–56.9%; t 4 = –19.0; p <0.0001), Diomedeidae (–28.3%; t 9 = –2.81; p <0.02), Phaethontidae (–4.2%; t 2 = –6.1; p <0.03), and Procellariidae (–20.9%; t 17 = –3.0; p <0.01). In the Spheniscidae, average relative growth rates were significantly above prediction (+32%; t 10 = 2.5; p <0.03); and in the Sulidae (+2.9%; t 4 = 0.18; p = 0.86), Alcidae (+6.9%; t 11 = 1.0; p = 0.33), and Laridae (+8.2%; t 31 = 1.4; p = 0.16), residual values were higher than prediction, but these differences were not significant. These values indicate that growth rates are particularly low for many pelagic seabird species, and tend to be higher in species that feed in-shore such as the Laridae. Highest relative growth rates are observed in the Spheniscidae. This has been interpreted to be an adaptation to the short Antarctic summer enabling the chicks to leave the colony before the onset of the winter (Volkman and Trivelpiece 1980). In Section 13.3.4 we explore the energetic consequences of variations in growth rate for free-living chicks and their parents. 13.2.2 INTRASPECIFIC VARIATION IN GROWTH RATES Chicks of most seabird species are generally fed a high-quality diet rich in protein and energy, with the possible exception of chicks of some petrel and albatross species that are mainly fed squid with a relatively low energy content (Prince and Ricketts 1981, see also Section 13.3.2). However, the quantity of food delivered by parents can be less predictable (see Chapters 6 and 7). In some species there is tremendous variation in postnatal growth rates owing to changes in the available food supply. For example, residual values for the logistic growth constants of Wedge-tailed Shear- waters (Puffinus pacificus) range between –72 and –9% (n = 13 studies), Black-legged Kittiwakes between –6 and +52%, Common Terns (Sterna hirundo) between –27 and + 74% (n = 21 studies), and Atlantic Puffins (Fratercula arctica) between –45 and +22% (n = 27 studies). In addition, these four species exhibit marked intraspecific differences in calculated asymptotic body mass values which vary between 424 and 750 g, 335 and 421 g, 100 and 133 g, and 265 and 400 g, respectively. These large differences may reflect differences in body condition of the fledglings at this stage. There is considerable evidence that growth retardation results from reduced food availability. For example, in a year with poor food availability, parental foraging trips of the Magellanic Penguin (Spheniscus magellanicus) lasted 20% longer than normal, chick feeding rates were reduced, and average body mass in 5-day-old chicks was 30% lower than in years with normal food availability (Boersma et al. 1990). Consequently, there were large differences between years with respect to the number of chicks fledged per nest, and in a 5-year study values ranged from 0.02 chicks per © 2002 by CRC Press LLC 444 Biology of Marine Birds nest to 0.60 (Boersma et al. 1990). In some cases, variation in food availability is related to El Niño–Southern Oscillation (ENSO) events (e.g., Schreiber and Schreiber 1993, Schreiber 1994). In other cases, intraspecific variations in chick growth and nesting success have been attributed to individual differences in timing of egg laying within a particular year (Brooke 1986, Catry et al. 1998), age and breeding experience of the parents (Brooke 1986, Coulson and Porter 1985), individual quality, genetically determined (Brooke 1986), weather conditions (especially wind speed; Konarzewski and Taylor 1989), differences in food availability between colonies within a season (Frank 1992, Frank and Becker 1992), and between years (Boersma et al. 1990, Danchin 1992, Crawford and Dyer 1995). One of the key parameters for the interpretation of inter- and intraspecific variations in growth rates in seabird chicks seems to be the amount of energy collected by parents during chick rearing per unit of energy spent (see Section 13.6). On the longer term, food restrictions and the subsequent growth retardation can potentially result in reduced survival (e.g., in the Common Murre, Harris et al. 1992), tolerance to starvation (e.g., in the Lesser Black-backed Gull [Larus fuscus], Griffiths 1992), and reduced recruitment rate (e.g., in the Black-legged Kittiwake, Coulson and Porter 1985). 13.3 ENERGETICS OF GROWTH 13.3.1 I NTRODUCTION One of the key factors needed for interpreting seabird life histories is the construction of energy budgets of free-living chicks and their parents (Drent et al. 1992). It is assumed that during the evolution of avian life histories, chicks have developed an array of adaptive responses, for instance: 1. In single-chick broods, the total amount of food required until independence (TME, kJ). However, in multi-chick broods, sibling competition may select for rapid growth and active food solicitation, potentially resulting in an increase of the TME. 2. Peak level of daily metabolized energy (peak-DME, kJ d –1 ). 3. Duration of the growth period (t fl , d) in order to reduce the risk of predation (Lack 1968), and (in polar environments) to complete the reproductive cycle before the onset of winter (Obst and Nagy 1993). It has to be noted that minimizing the duration of the development period may require increasing growth rate and therefore daily energy requirement (Weathers 1992, and Section 13.3.4). These adaptations may enable parents to maximize their lifetime reproductive output. 13.3.2 COMPONENTS OF THE CHICKS’ ENERGY BUDGET Of all energy ingested by a chick (gross energy intake: GEI, kJ d –1 ) only a part can be metabolized (metabolizable energy intake: MEI, kJ d –1 ); the remainder is excreted in the form of feces and urine (FU, kJ d –1 ). The assimilation coefficient (Q, dimensionless) is defined as: Q = (GEI – FU)/GEI (13.4) Once gross energy intake and assimilation coefficient are known, metabolizable energy intake can be calculated by MEI = Q · GEI (13.5) The gross energy content of chick food varies with the type of diet, and is reported to be about 2.9 to 4.5 kJ g –1 fresh mass for krill (depending on its reproductive status; Clarke and Prince 1980, © 2002 by CRC Press LLC Chick Growth and Development in Seabirds 445 Davis et al. 1989), 2.9 to 4.9 kJ g –1 for zooplankton (Clarke and Prince 1980, Montevecchi et al. 1984, Simons and Whittow 1984, Clarke et al. 1985), 4.2 to 10.3 kJ g –1 for fish (depending on its fat content; Montevecchi et al. 1984), and 39 to 41.7 kJ g –1 for the oil component of procellariiform diets (Warham et al. 1976, Simons and Whittow 1984, Obst and Nagy 1993). Some seabird species are known for having highly specialized diets (e.g., feeding exclusively on fish [terns] or krill [some penguins]), whereas other species (like most Procellariiformes) exhibit a nonspecialized aquatic diet (squid and other zooplankton, krill, fish, and trawler offal). Assimilation coefficients have been determined in seabird chicks of several species and for different diets (Table 13.2). Average values for fish, krill, and zooplankton diets are 0.80 (SD = 0.035, n = 10), 0.75 (SD = 0.014, n = 2), and 0.75 (SD = 0.040, n = 3), respectively. It is interesting to note that the measured values in chicks are in close agreement with those reported for adult birds fed fish or invertebrates (0.77 and 0.74, respectively; Castro et al. 1989), which suggests that digestion efficiency in seabird chicks is high. Little information is available on the development of the assimilation efficiency as a function of the chicks’ ages. An increase in assimilation coefficient from 0.8 at 11 to 12 days of age to a value of 0.88 at 20 to 21 days of age was reported in Double- crested Cormorant (Hypoleucos auritus) chicks (Dunn 1975). A similar trend with age was found in Jackass Penguin (Spheniscus demersus) chicks (Heath and Randall 1985), but not in chicks of the Cape Gannet (Morus capensis, Cooper 1978) and Common and Sandwich Tern (Sterna sand- vicensis, Klaassen et al. 1992). TABLE 13.2 Assimilation Coefficients for Seabird Chicks in Relation to Food Type Family/Species Food Type Coefficient Source Spheniscidae Jackass Penguin (Spheniscus demersus) Fish 0.76 Cooper 1978 Jackass Penguin (S. demersus) Fish 0.83 Heath and Randall 1985 Jackass Penguin (S. demersus) Zooplankton 0.71 Heath and Randall 1985 Gentoo Penguin (Pygoscelis papua) Krill 0.74 Davis et al. 1989 Procellariidae White-chinned Petrel (Procellaria aequinoctialis) Fish 0.78 Jackson 1986 White-chinned Petrel (P. aequinoctialis) Zooplankton 0.74 Jackson 1986 White-chinned Petrel (P. aequinoctialis) Krill 0.76 Jackson 1986 Sulidae Cape Gannet (Morus capensis) Fish 0.74 Batchelor 1982 Cape Gannet (M. capensis) Fish 0.76 Cooper 1978 Phalacrocoracidae Double-crested Cormorant (Hypoleucos auritus) Fish 0.85 Dunn 1975 Laridae Common Tern (Sterna hirundo) Fish 0.81 Klaassen et al. 1992 Arctic Tern (S. paradisaea) Fish 0.80 Drent et al. 1992 Sandwich Tern (S. sandvicensis) Fish 0.82 Klaassen et al. 1992 Black-legged Kittiwake (Rissa tridactyla) Fish 0.80 Gabrielsen et al. 1992 Alcidae Dovekie (Alle alle) Zooplankton 0.79 Taylor and Konarzewski 1992 Note: In chicks of some diving petrels, prions, and storm petrels, the digestion efficiencies of the dietary wax component was near 0.99 (Roby et al. 1986). © 2002 by CRC Press LLC 446 Biology of Marine Birds It appears as if there are marked differences between species with respect to assimilation efficiency as a function of diet type. For example, assimilation coefficients in White-chinned Petrel (Procellaria aequinoctialis) chicks were relatively insensitive to diet type, and values ranged from 0.74 for a squid diet to 0.78 for a fish diet (Jackson 1986). In contrast, assimilation coefficients of Jackass Penguin chicks varied from 0.68 and 0.87 for these two diets (Heath and Randall 1985). The high flexibility of the digestive system of White-chinned Petrel chicks is interpreted to be an adaptation to their nonspecialized diets (squid, krill, fish, and trawler offal; Jackson 1986; see also Brown 1988). Metabolized energy can be allocated to the following components of the chicks’ energy budget: (1) resting metabolism at thermoneutrality (i.e., the energy required for maintaining some basal physiological functions within the chicks’ body; RMR, units kJ d –1 ), (2) heat increment of feeding (i.e., the energy required to warm and digest the food; HIF [also referred to as specific dynamic action of food; SDA], units kJ d –1 ), (3) temperature regulation (to compensate for heat losses from the chick to its environment: TR, units kJ d –1 ), (4) activity (e.g., walking, preening, calling, and begging; A, units kJ d –1 ), (5) biosynthesis-related heat production (the energy required for synthe- sizing new tissue such as fat and protein; S, units kJ d –1 ), and (6) tissue energy (energy deposited as protein and fat; TE, units kJ d –1 ): MEI = RMR + HIF + TR + A + S + TE (13.6) At a given level of metabolizable energy intake of a chick (e.g., the maximum level that can be provided by the parents), growth is highest at low levels of energy expenditure. Growth is zero if MEI equals energy expenditure, and growth is negative if MEI is lower than the level of energy expenditure. Under the latter conditions, body tissue (e.g., fat or protein) is used to produce energy for supporting other physiological functions. 13.3.3 METHODS TO DETERMINE ENERGY BUDGETS IN FREE-LIVING CHICKS Four different methods have been used to determine the chick’s level of MEI under free-living conditions: 1. Determination of gross energy intake based on periodic weighing of the chick in the field (e.g., Prince and Walton 1984, Ricklefs et al. 1985, Obst and Nagy 1993) 2. Determination of energy expenditure of the chick based on the extrapolation of laboratory measurements to field conditions, with an added component for energy deposited in tissues (see Ricklefs and White 1981) 3. Measurement of water influx rates and subsequent conversion to gross energy intake (Gabrielsen et al. 1992, Konarzewski et al. 1993) 4. Measurement of the level of energy expenditure directly in the field with doubly labeled water method, with an added component for growth energy (see Klaassen et al. 1989, Klaassen 1994, Visser and Schekkerman 1999) 13.3.3.1 Periodic Chick Weighing A method used frequently to assess levels of food intake in seabird chicks is based on periodic chick weighing (expressed in grams per unit of time; e.g., Ricklefs 1984, Ricklefs et al. 1985, Schreiber 1994, 1996, Philips and Hamer 2000). Chicks are weighed regularly (e.g., at 2- to 12-h intervals) to monitor changes in their body mass. It is assumed that body mass decreases with time, a process that can be approached mathematically (e.g., by taking initial body mass, age, body size index, and time into account; Philips and Hamer 2000). If the chick exhibits a positive change in body mass, it is assumed that it was fed exactly between two weighings. The food intake level at © 2002 by CRC Press LLC Chick Growth and Development in Seabirds 447 the assumed feeding time is calculated as the difference between backward and forward extrapo- lation of the mass loss curves of a recently fed and fasting chick, respectively. The value obtained represents the amount of food eaten by the chick (in grams per unit of time). Next, to convert this value to gross energy intake (GEI), an assumption must be made with respect to the mass-specific energy content of the food (see Section 13.3.2). Finally, MEI can be calculated on the basis of Equation 13.5, after assuming a specific value for the assimilation coefficient of the diet (see Section 13.3.2 and Table 13.2). Although this method is very easy to apply, it can only be used in chicks that are fed meals that are heavy relative to their body mass. In addition, apart from weighing and extrapolation errors, the calculated MEI level is subject to several other accumulating methodological errors. The first potential error is caused by the uncertainty with respect to the exact feeding time. This error is larger if weighings are done with a lower frequency. However, a high weighing frequency may, in some cases, interfere with chick begging, or parental feeding behavior, although some species are not bothered by it. In some sedentary seabird chicks, this problem can be circumvented by contin- uous weighing on an electronic balance, as employed in albatross chicks (Prince and Walton 1984, Huin et al. 2000). The second potential error relates to the conversion of mass change to GEI. This error is probably smallest in species with a specialized diet, facilitating accurate estimation of the mass- specific energy content of the diet. The error is probably largest in procellariiform chicks because of the large difference in energy density of separate components of their diet, which ranges from about 4 kJ g –1 for predigested food to about 40 kJ g –1 for the stomach-oil component (see Section 13.3.2). Another complication is the large variation in the relative quantity of the oil component between meals within a species (e.g., values determined for different birds from the same colony during one observation day ranged between 20 and 83% in Wilson’s Storm-Petrel [Oceanites oceanicus]; Obst and Nagy 1993), between species (e.g., see Roby 1991), and the relative difficulty to estimate the fraction of the oil component in a chick’s diet (Roby et al. 1997). The third potential error of this method is the conversion of GEI to MEI (Equation 13.5), after assuming a specific value for the assimilation coefficient. As discussed in Section 13.3.2, these average values range from 0.77 for krill and zooplankton to about 0.99 for stomach oil (Roby et al. 1986). Because of its high mass-specific gross energy content and its high assimilation coeffi- cient, stomach oil is the most important component in energy budgets of procellariiform chicks, and it may contribute up to about 80% of their energy budgets (Roby 1991, Obst and Nagy 1993). The overall error of using the “chick weighing” method to estimate MEI can be as high as about 25%, depending on the number of assumptions made (Weathers 1992, 1996). 13.3.3.2 The Time-Energy Budget The “time energy budget” method differs fundamentally from the “chick weighing” method in the sense that in the former method, metabolizable energy intake is estimated on the basis of measure- ments on energy expenditure (the components RMR, HIF, TR, A, and S; Equation 13.6) with an added component of the tissue energy (TE; Equation 13.6). As a first step, levels of oxygen consumption (and carbon dioxide production) are determined in resting chicks while housed in a small respiration chamber (indirect calorimetry; Weathers 1996). Next, metabolic rate (MR) can be calculated after assuming a specific energy equivalent per unit oxygen consumed or carbon dioxide produced. Typically, levels of energy expenditure are determined at different ambient temperatures to reveal the lowest level of energy expenditure at thermoneutrality (RMR), and the thermoregulatory costs (TR) at temperatures below the lower critical temperature (LCT, units °C). At each temperature, thermal conductance can be calculated being the metabolic level per degree temperature difference between the chick’s body and its environment (see Visser 1998). The thermal conductance is assumed to be minimal at ambient temperatures below LCT. © 2002 by CRC Press LLC 448 Biology of Marine Birds To facilitate extrapolation of laboratory measurements to field conditions, the thermal environ- ment of a chick must be characterized in its habitat (Bakken 1976, Klaassen 1994). This is most easily accomplished in chicks that live in deep burrows (e.g., procellariiform chicks, by measuring burrow-air temperatures), and it is most difficult in mobile chicks that live in sparsely vegetated colonies. When fully exposed, a chick experiences cooling effects of wind, compensated for by the chick elevating its metabolism. These effects can be strongly diminished by the chick positioning itself in vegetation (i.e., an energy-saving mechanism). In contrast, when fully exposed, a chick may experience the heating effects of solar radiation (enabling the chick to reduce thermoregulatory costs). Both effects can be integrated when employing heated taxidermic mounts, or (partly) with temperature measurements using black spheres (Gabrielsen et al. 1992, Klaassen 1994). To estimate the tissue energy component of the energy budget in relation to the chicks’ age, it is necessary to determine their growth curve in the field (see Section 13.2.1), as well as their mass- specific energy content of the body. The latter component is often estimated with the general equation: E = a + b · (M/A) (13.7) where E represents the mass-specific energy density of the whole body (kJ g –1 ); a the intercept value at zero body mass (g); b the slope of the relationship; M the body mass (g) of the chick at a particular stage; and A its asymptotic body mass (g; Ricklefs 1974, Weathers 1996). The mass- specific energy density increases from about 3 to 4 kJ g –1 in young Double-crested Cormorant chicks (Ricklefs 1974) to about 22 kJ g –1 in heavy Wilson’s Storm-Petrel chicks 1 week prior to fledging (Obst and Nagy 1993). For some species-specific estimates, see Table 13.3 (Note: a steeper slope indicates that as birds get heavier, they have a higher energy density per gram of body mass). As can be seen, seabirds exhibit large differences in developmental patterns, and energy densities are particularly high in some pelagic seabird species (Ricklefs et al. 1980, Obst and Nagy 1993, Ricklefs and Schew 1994). Therefore, the use of group-specific estimates of the regressions to estimate energy accumulation is suggested, instead of the use of Weathers’ (1996) Equation 13.10 for birds in general. To estimate the biosynthesis-related heat production in chicks, a synthesis efficiency value of 0.75 has traditionally been assumed (Ricklefs 1974), which has been used for the construction of energy budgets of most species listed in Table 13.3. More recently, Weathers (1996) advocated the separation of tissue growth into a fat component (with high synthesis effi- ciency) and a protein component (with low synthesis efficiency). Although this approach is more correct, it appears as if little error is made when employing a value of 0.75 (Konarzewski 1994, Ricklefs et al. 1998). There are a number of potential methodological errors involved in this time energy budget method that merit attention. First, it is virtually impossible to account for the costs associated with locomotion or activity of the chick (e.g., see Dunn 1980). Probably these costs are lowest in individual procellariiform chicks that spend “about 90% of their time resting and sleeping” (Simons and Whittow 1984, Brown 1988), but the costs can be much higher for chicks growing up in dense colonies where frequent social interactions occur (Figure 13.5). Second, the extrapolation of laboratory measurements to field conditions for estimating the costs for temperature regulation is relatively difficult, especially because of the difficulty in accounting quantitatively for energy-saving mechanisms such as huddling, sheltering, or exposure to solar radiation. Third, poikilothermic chicks are frequently brooded by a parent, which considerably reduces its energy expenditure level (Klaassen 1994). Fourth, the extrapolation procedure is very sensitive to the assumed body tem- perature of the chick under field conditions. Although chicks of most species tend to keep up a body temperature of about 40°C, chicks of some species enter into torpor periodically between feeding bouts (Pettit et al. 1982, Boersma 1986). Occurrence of torpor has been interpreted to be an energy-saving mechanism to minimize costs of temperature regulation. © 2002 by CRC Press LLC [...]... that the production of 1 l of carbon-dioxide per hour is equivalent to a level of energy expenditure of 27.3 kJ h–1 (see Gessaman and Nagy 1988) Concentrations of the heavy isotopes 2H and 18O in the body-water pool of animals are often determined on the basis of three blood samples, stored in flame-sealed capillaries or vacutainers The first sample is taken prior to administration of the dose, to determine... adult seabirds, with a fractional evaporative water loss value of 0.25 © 2002 by CRC Press LLC 452 Biology of Marine Birds 13. 3.3.3.3 Applications of the DLW Method in Seabird Chicks Application of the DLW method in growing chicks has been hampered by uncertainties with respect to the routes of 2H (or 3H) and 18O loss from the chick’s body-water pool Both isotopes may not leave from the body-water pool... 135 204 178 398 277 284 239 199 233 176 97 217 © 2002 by CRC Press LLC 453 Note: A: Asymptotic body mass (g); Tfl: duration of the fledging period (d); TME: total amount of energy metabolized until fledging (kJ); Peak-DME: peak level of daily metabolized energy during the growth period (kJ d–1) Chick Growth and Development in Seabirds TABLE 13. 4 Energy Budgets of Seabird Chicks 454 Biology of Marine Birds. .. predictive equations for TME and peak-DME in seabirds: TME = 11.09 A0.771 · tfl0.747 (13. 12) (F2, 25 = 211, r2 = 0.939, p . (Figure 13. 1). Chicks that hatch in this developmental state have been classified 13 © 2002 by CRC Press LLC 440 Biology of Marine Birds as being altricial by Nice (1962; see Table 13. 1). Chicks of. possibly raising the energy budget of birds in these colonies. (Photo by R. W. Schreiber.) © 2002 by CRC Press LLC 450 Biology of Marine Birds 13. 3.3.3 The Measurement of Water Influx Rates and Subsequent. is this 3 1/2-week-old chick. Brooding still may offer some energetic savings to the chick. (Photo by E. A. Schreiber.) © 2002 by CRC Press LLC 458 Biology of Marine Birds species), none of these