Fig. 12. Energy budgets of nestling double-crested cormorants and herring gulls. Data from E. H. Dunn (1973) and Brisbin (1965).
Cost-benefit ratios of food gathering in the nestling period differ from those at other times. Besides facing increased food demands, costs of delivery to the nest, and changes in food availability, the parents' choice of foods is constrained by the need to forage within reasonable commuting distance of the nest and perhaps by concentrated competition with conspecifics and other seabird species. In addition, small nestlings are frequently unable to eat foods normally eaten by adults (Drent 1965; personal observation). In the face of these constraints, adults often shift food preferences while raising nestlings (Belopol'skii 1961). For example, female mew gulls in the Barents Sea forage in the tidal zone, eating more small invertebrates than at other times of the year, while males continue to forage at sea and consume larger quantities of fish (Fig. 13).
| Species | Age when moderate temperature control is attained (days) | Source |
|---|---|---|
| Common eider | 0.1-0.3[41] | V. V. Rolnik, in Belopol'skii (1961) |
| Herring gull | 1.5-2 | V. V. Rolnik, in Belopol'skii (1961) |
| Herring gull | 2-3 | E. H. Dunn (1976b) |
| Leach's storm-petrel | [2] | Ricklefs (1974) |
| Mew gull | 2-3 | V. V. Rolnik, in Belopol'skii (1961) |
| Lesser black-backed gull | 2-3 | E. K. Barth (in Farner and Serventy 1959) |
| Greater black-backed gull | 2-3 | E. K. Barth (in Farner and Serventy 1959) |
| Pigeon guillemot | 2-4 | Drent (1965) |
| Common tern | 3 | LeCroy and Collins (1972) |
| Roseate tern (Sterna dougallii) | 3 | LeCroy and Collins (1972) |
| Common murre | 3 | V. V. Rolnik and Yu. M. Kaftonowski (in Sealy 1973b) |
| Razorbill (Alca torda) | 3 | V. V. Rolnik and Yu. M. Kaftonowski (in Sealy 1973b) |
| Black guillemot | 3-4 | V. V. Rolnik, in Belopol'skii (1961) |
| Tufted puffin | 3.5[42] | Cody (1973) |
| Northern phalarope | 4-5[43] | Hilden and Vuolanto (1972) |
| Cassin's auklet | 5-6 | Manuwal (1974a) |
| Horned puffin (Fratercula corniculata) | 2-6 | Sealy (1973a) |
| Common puffin | 6-7 | V. V. Rolnik and Yu. M. Kaftonowski (in Sealy 1973b) |
| Black-legged kittiwake | 6-7 | V. V. Rolnik, in Belopol'skii (1961) |
| Double-crested cormorant | 14 | Dunn (1976a) |
| Shag | 12-15 | V. V. Rolnik, in Belopol'skii (1961) |
Commuting distances vary tremendously among species (Fig. 14), but the number of feeding trips to the nest per day does not correlate with foraging distance (Cody 1973; Sealy 1973a, 1973b). There is not, therefore, a simple relationship between time and energy expenditures of the adults and foraging distances. Nocturnality, on the other hand, correlates with reduced feeding rates (usually one visit to the nest each night). Seabirds feeding far from the colony tend to show adaptations for bringing larger amounts of food per visit, such as carrying more than one fish at a time, as in tufted puffins, Lunda cirrhata, and rhinoceros auklets, Cerorhinca monocerata, vs. guillemots and murres (Richardson 1961; Cody 1973; Sealy 1973a, 1973b); developing a sublingual storage pouch, as in Cassin's auklets (Speich and Manuwal 1974); or concentration of food into stomach oil, as in petrels and albatrosses (Ashmole 1971). Commuting costs are largely eliminated when the young leave the nest, but only in the alcids does nest leaving occur long before attainment of full growth. Early nest leaving may allow adults and young to disperse to better feeding areas than are exploitable from the colony site (Sealy 1973b) and probably involves a major change in optimal food size and type as well (Lind 1965).
Patterning of adult time budgets may differ between geographical regions. For example, rhinoceros auklets are nocturnal in the far north (where the summer night is particularly short), crepuscular in the Olympic Peninsula, and mainly diurnal in the Farallon Islands (Manuwal 1974a).
Fig. 13. Foraging ranges of a pair of mew gulls during the breeding season, on a Barents Sea colony. From Belopol'skii (1961).
Food demands of nestlings have a great influence on the time and energy allocation of breeding over nonbreeding seabirds. Because food is particularly abundant in the reproductive season, however, one cannot ascertain whether the vulnerability of breeding birds to time or energy crises is far different from that at other times of the year.
Post-fledging Care
Little is known about the amount of care provided by adults to young after they are fully grown. At least some species, such as gannets and procellariiformes (Ashmole 1971), are known to desert their young, whereas others are known to feed their young, at least occasionally, for some weeks or months after they can fly—e.g., terns and gulls, many alcids, and shags (Snow 1963; Vermeer 1963; Drury and Smith 1968; Ashmole and Tovar S. 1968; Potts 1968; Ashmole 1971; LeCroy 1972).