The Food, Feeding, and Development of Young Tufted and Horned Puffins in Alaska

Abstract

-Aspects of nestling Tufted Puffin (Fratercula cirrhata) and Homed Puffin (F. corniculata) feeding ecology, growth rate, and fledging success were studied on Buldir Island, Alaska, in 1975 and on Ugaiushak Island, Alaska, in 1976 and 1977. Growth rates were measured for single wild chicks given supplemental food, single chicks raised in captivity and fed ad libitum, and for artifically twinned chicks with and without supplemental food and for twinned chicks raised in captivity. Data from these colonies and years (colony years) were compared with those from other colony years for these species and for Atlantic Puffins (F. arctica). For most aspects of nestling feeding ecology that have been measured, available data are too variable (seasonally, annually, or geographically) to give a reliable correlation with feeding conditions. Growth rates equal to 1.5% of adult body weight/day or less were associated with poor feeding conditions while growth rates of 2.5% or more represented optimum feeding conditions. Nestling growth rates currently provide the best means of assessing feeding conditions. The implications of puffins' ability to raise two chicks, rather than their normal clutch of one, are also discussed. Local seabird populations in Alaska may well be affected by the development of offshore oil and gas resources. Recognizing this, the U.S. Bureau of Land Management, through interagency agreement with the National Oceanic and Atmospheric Administration (NOAA), sponsored the Outer Continental Shelf Environmental Assessment Program (OCSEAP) to obtain baseline data on the distribution and abundance, breeding biology, and feeding ecology of certain Alaskan seabird species. These data were to be used in making management decisions and as a standard against which postdevelopment data could be compared. If the consequences of petrochemical exploitation are to be predicted and safeguards established against potential problems, the ecology of the species most likely to be affected must be known (McKnight and Knoder 1979). Between 40 and 50 million seabirds of at least 35 species breed in Alaska (Sowls et al. 1978). Alcids (Family Alcidae) comprise at least 65% of these, of which approximately 20% are puffins (Sowls et al. 1978): Tufted Puffins (Fratercula cirrhata), Homed Puffins (F. corniculata), and Rhinoceros Auklets (Cerorhinca monocerata)-actually misnamed puffins (Storer 1945). Of the 176 species of birds using marine habitats in Alaska, British Columbia, and Washington, Tufted and Homed puffins rank among those most vulnerable to oil pollution (King and Sanger 1979). In addition, they may be affected by changes in the distribution and abundance of their prey caused by offshore oil and gas development. Tufted and Homed puffins are diurnal, pelagic seabirds that measure about 390 and 350 mm in length, respectively. They nest in underground burrows or rock crevices on steep sea slopes, along cliff-edges, or in talus slopes. Both sexes have two brood patches, but females typically lay only one egg, which is incubated for six to seven weeks. Puffins capture prey (primarily small fish and invertebrates) by pursuit diving, and feed whole prey to their semi-precocial young for six to seven weeks. Information on their habits is given by Dawson (1913), Willett (1915), Bent (1919), Dement'ev and Gladkov (1951), Kozlova (1957), Gabrielson and Lincoln (1959), Swartz (1966), and Sealy (1973a). My purposes here are: (1) to present the results of studies I conducted for OCSEAP on the feeding ecology (food, feeding, and development) of nestling Tufted and Homed puffins on Ugaiushak Island, Alaska, in 1976 and 1977 and from a study I conducted on Buldir Island, Al ska, in 1975; (2) to compare my results with those for these species in other colonies and years (colony years) and with those for Atlantic Puffins (F. arctica); (3) to describe and summarize the current data for the major components of nestling Tufted and Horned puffin fee ing ecology in Alaska; and (4) to identify those components of nestling feeding ecology that might best be used in future studies to de ect possible effects of offshore oil and gas development on puffin feeding conditions (e.g., availability and abundance of suitable prey). Fledging success provides the best measure of the reproductive health of a population but it is sometimes influenced by factors unrelated