Joseph R. Jehl

Cyclical changes in body composition in the annual cycle and migration of the Eared Grebe Podiceps nigricollis

In changes that are among the most dramatic known for birds, Eared Grebes undergo 3-6 atrophy/hypertrophy cycles in major body constituents annually. The most pronounced takes place at staging areas in fall, when grebes become flightless for up to several months. At this season they accumulate huge fat stores (to 46% of lean body mass) and more than double the mass of body, liver, stomach, and intestine; leg and heart mass also increase. Concurrrently, pectoral muscles atrophy and can shrink below the size needed for flight (11% of total body mass). Before grebes depart for wintering areas these changes are reversed. In a 2-3 week predeparture period body mass drops by one-third as birds catabolize fat and reduce viscera mass by ?50%; leg mass also declines, while pectoral muscle increases. Similar cycles, which do not involve fattening to obesity, are repeated at wintering and breeding locations and, in some birds, on additional spring staging and fall molting areas. Heavy fat deposits in fall may insure that grebes can postpone their migration to wintering areas into the months of maximum darkness, thereby minimizing the risk of predation. The extreme predeparture reductions in leg and visceral mass, which occur in all seasons, reduce flight costs by minimizing wing loading and enhancing flight speed. Why grebes allow pectoral muscles to atrophy if they must rebuild them presently remains a puzzle. Several lines of evidence suggest that grebes attain a specific (optimal?) body composition prior to migrating. Further research into changes that may take place in other species prior to migration or at different times of the annual cycle is warranted.

Adaptations of migratory shorebirds to highly saline and alkaline lakes: Wilson's Phalarope and American Avocet

Wilson’s Phalaropes (Phalaropus tricolor) and American Avocets (Recurvirostra americana) occur in large numbers at hypersaline and alkaline lakes. Comparing birds from three lakes of different salinity and alkalinity in the Great Basin of western North America, we found no evidence of salt-loading: blood hematocrit, pH, osmolality, and sodium concentration were not elevated; stomach osmolality and sodium concentration were only slightly higher than the body fluids of the birds’ hypo-osmotic prey (brine shrimp and brine flies); salt glands were not enlarged and averaged a relatively low percentage of body weight (0.02%). Through a combination of behavioral and anatomical adaptations, phalaropes and avocets evidently are able to rid their prey of most adherent lake water and thereby largely avoid the problems of salt-loading and the ingestion of harmful ions. Both species occupy hypersaline habitats for long periods and probably derive most of their water needs from the body fluids of their prey. Their use of fresh water is sporadic and may not be required for osmoregulatory balance. Alkaline and hypersaline lakes, despite being harsh physical environments, are prime habitats for a few species of resident (e.g., flamingos) and a somewhat larger number of migratory waterbirds. Mono Lake, California, a large hypersaline (2’ 12 x the concentration of sea water) and alkaline (pH x 10) lake at the eastern base of the Sierra Nevada, attracts large numbers of a few of these species each year. Approximately 45,000 California Gulls (Larus californicus) nest there; in summer and in fall, tens of thousands of Wilson’s (Phalaropus tricolor) and Red-necked (P. lobatus) phalaropes stop over on their southward migration (Jehl 198 l), and hundreds of thousands of Eared Grebes (Podiceps nigricollis) stage there (Storer and Jehl 1985). American Avocets (Recurvirostra americana) are also common at hypersaline lakes, although at Mono Lake only a few pairs breed and flocks of several hundred occur in autumn. Hypersaline lakes are attractive to these birds because they typically lack fish, which allows the few invertebrates that can occupy them to attain great abundances. These, in turn, serve as food for the birds. At Mono Lake, brine shrimp (Artemia sp.) and brine flies (Ephydru hians) become super-abundant at some seasons. Birds feeding on these invertebrates, either by pecking them from the surface of the water or by catching them while driving, might be expected to ingest large amounts of lake water and thereby incur deleterious salt loads. Yet, our previous studies of California Gulls (Mahoney and Jehl 1985a) and Eared Grebes (Mahoney and Jehl 1985b) at Mono Lake, where salinities have varied from 72 to 90 ppt (2,160-2,700 mOsm/kg) in 1982-l 984, have shown that this is not the case. These species seem to have no special anatomical or physiological adaptations for dealing with high salt loads. Instead, they largely avoid osmoregulatory problems behaviorally, by ridding their food of adherent lake water before swallowing it. Gulls and grebes differ markedly in their use of fresh water. Gulls visit freshwater streams to drink and bathe several times each day, whereas grebes, although they may remain continuously at Mono Lake for as long as six months (Jehl, unpubl. data), never visit fresh water. Wilson’s Phalaropes and American Avocets (Fig. 1) have intermediate patterns of water use; both visit fresh water regularly, though probably not daily. If phalaropes and avocets ingest large quantities of Mono Lake water and its attendant osmotic and ionic load, they could be expected to show changes in blood chemistry, hydration state, and salt gland size. In order to determine how great a salt load these birds incur while feeding at the lake, we made the following measurements: blood pH and hematocrit; serum osmolality, sodium, and potassium; composition and osmolality of stomach contents, prey body fluids, and lake water; body water content; and salt gland weights. We then compared these values from Mono Lake birds to those

Leucism in eared grebes in Western North America

Leucism is the complete loss of a particular pigment, or all pigments, in feathers but not in soft-parts. It may be as slight as a single white feather or as pervasive as an all-white bird with normal eyes, bill, and legs (Buckley 1982). The condition has been documented, usually as a curiosity and under the term albinism, in hundreds of species. Its incidence is said to differ greatly among species (e.g., Sage 1963, Gross 1965), but the data for that conclusion are unconvincing because a high percentage of reports pertain to species that associate with, or are hunted by, man. As a result, observational bias is potentially strong. For only a few species (e.g., storm-petrels; Baptista 1966) has it been possible to consider the phenomenon more broadly and to investigate the frequency of leucism in natural populations of birds. The subject is interesting because leucism, like any variable condition, may provide indirect evidence of underlying genetic variability. Furthermore, if its frequency can be measured, this may allow some inferences to be drawn about the strength of selection against abnormally-colored individuals. In this paper, I present data on leucism compiled incidental to other research during a four-year (1981-1984) study of Eared Grebe (Podiceps nigricollis) biology at Mono Lake, California. Other aspects of this research have been presented elsewhere (Mahoney and Jehl 1985; Storer and Jehl, in press).

Observations on the fall migration of eared grebes, based on evidence from a mass downing in Utah

After the breeding season in North America, most Eared Grebes (Podiceps nigricollis) migrate to highly saline lakes in the Great Basin to molt and stage for several months. During this period they molt, undergo a cycle of breast muscle atrophy and hypertropy, and accumulate huge fat deposits before flying to wintering areas (Jehl 1988, unpubl. manuscript; Gaunt et al. 1990). On 10 December 1991 thousands of grebes departed Great Salt Lake en route to the Salton Sea, California, or Gulf of California, Mexico. Their route was southwesterly, and for the first 500 km-roughly between Salt Lake City and the Arizona border-paralleled Interstate Highway 15 and the Wasatch Mountains, which are slightly to the east. Several hours into the flight, over southern and central Utah, large numbers were forced down by a snowstorm along a 180 km stretch between Holden and Cedar City; a few were also reported in the Provo/Springfield area (Fig. 1). The birds did not fall uniformly, but apparently were attracted to lights from towns and highway intersections. Many died when they crashed to earth; others were hit by cars on the highway, which they evidently mistook for open water. Thousands more were captured alive and released on whatever local water bodies remained open. Most of our current understanding about the biology of Eared Grebes in fall migration is based on studies of birds staging at Mono Lake, California (Jehl 1988). The data from this downing provided an opportunity to test and extend some earlier findings or inferences about the differential migration of age classes, duration of the flight to wintering areas, physical condition of departing and arriving migrants, the size of pectoral muscles needed for flight, and the risks of mortality along the migratory routes (Jehl 1988, Gaunt et al. 1990).

The roles of thermal environment and predation in habitat choice in the California gull

California Gulls (Larus californicus) breeding in the Great Basin may encounter diurnal temperatures sufficient to cause chick mortality. Although nesting may occur in a variety of habitats, at Mono Lake, California, and elsewhere gulls prefer fairly open areas with irregular terrain near the shore of islands. These areas are relatively cool, but their major advantages seem to be promoting the isolation from and early detection of predators, providing hiding places for small chicks, and offering escape routes for large young and adults. Predation is a continual danger, whereas periods of high temperatures sufficient to cause mortality are too brief and irregular to have a dominant influence on long-term breeding success and thus on habitat selection.

DISAPPEARANCE OF BREEDING SEMIPALMATED SANDPIPERS FROM CHURCHILL, MANITOBA: MORE THAN A LOCAL PHENOMENON

Abstract As late as the 1940s the Semipalmated Sandpiper (Calidris pusilla) was the most abundant sandpiper breeding at Churchill, Manitoba. By the 1960s it had undergone a sharp decline, and by the mid-1990s the local population consisted of 11 pairs in a single colony. Nesting was last documented in 2001. Declines had also become evident at several other breeding sites along the Hudson Bay coast of Manitoba and Ontario, as well as in the number of migrants detected on the Atlantic coast of Canada and the northern United States. Information on the biology of the Churchill population in 1993–2004 largely agreed with that gathered at La Pérouse Bay, Manitoba, in the 1980s: reproductive success was good and new birds continued to join the colony; however, the number of breeding attempts by individuals was low and decreasing. As there is no evidence that the decline was related to local factors (e.g., altered habitats, climate change), it is probably attributable to mortality in the nonbreeding season, which leaves fewer birds available to return north. Whether causality can be fully resolved is problematic. Monitoring migrants can reveal population trends and studies on the breeding grounds can help frame hypotheses, but both approaches are time-consuming and provide only partial answers. In such cases, restoration of declining species may be best served by fostering habitat conservation throughout a species range.

Fat loads and flightlessness in Wilson's Phalaropes

Fat loads of about 45% of total body mass are maximal for most shorebird migrants. In preparing to fly nonstop from staging areas in North America to South America, some late-staging adult Wilsons Phalaropes (Phalaropus tricolor) amass greater loads (to 54%) and for a brief period become too heavy to fly. This condition is associated with rapid mass gain, but may involve other factors. Despite ostensibly ideal conditions at staging areas, the phalaropes greatest rate of fat deposition (3.4-3.6% lean body mass-day -1 ) is only 60-70% of the theoretical maximum.

Body water content in marine birds

Total body water (TBW) in adult birds averages approximately 60% of body weight, regardless of bird size (Skadhauge 1981:3). Voluminous data on land and aquatic birds have been obtained using two techniques: oven drying to constant weight and isotope or dye dilution. These techniques yield similar results (Degen et al. 1981). However, Ruch and Hughes (1975) and Walter and Hughes (1978), using isotope dilution, found very high values of TBW of 79% and 88%, respectively, in age-unspecified (presumably adult) Glaucous-winged Gulls (Larus glaucescens). They postulated that the larger TBW volume may be of adaptive significance to marine birds since a larger relative volume would buffer the impact of a salt load on the concentrations of body fluids (Walter and Hughes 1978). At that time, with the exception of one tern species (see Table 1), their data were apparently the only published values of TBW for marine birds. A high proportion of body water occurs in aquatic invertebrates (Prosser 1973:7). Documenting such a similar occurrence in marine birds would be of broad interest, particularly because it would open the question of how a bird composed of 80% or more body water could remain a functional flying organism. Young birds do have TBW approximately 80%; however, this decreases with age, reaching adult levels at about fledging (e.g., Dunn 1975, Ricklefs and White 1981, Mahoney and Jehl 1982). In this note we present and synthesize data from 22 species of marine and aquatic birds to test whether high body water may be a general phenomenon among birds which live in a marine environment (Walter and Hughes 1978). A review of the published data on TBW of birds was published by Skadhauge (1981), and Williams et al. (1982) have recently provided extensive data on water content of eggs and hatchlings in a variety of seabirds. Most of our data were obtained from healthy (except where otherwise noted) adult birds that were freshly-collected over the course of a year in southern California or at Mono Lake, Mono Co., Ca., a hypersaline lake where total dissolved solids approximate 85-90%0. We also used some birds found freshly-dead because our earlier studies revealed no difference in body water content of birds freshly-dead and those collected (see data for Eared Grebe, Podiceps nigricollis, in Table 1). We weighed each bird after removing its stomach contents, opened the body cavity to insure complete desiccation and dried the carcass to constant weight in a drying oven at 800C. Determining TBW this way does not correct for differences in body fat or possible loss of volatile fats in the drying process. A high percentage of fat would tend to underestimate TBW; loss of volatile fatty acids would slightly overestimate TBW. The errors in each case are small, and tend to cancel each other.

GROWTH PATTERNS OF TWO RACES OF CALIFORNIA GULL RAISED IN A COMMON ENVIRONMENT

Chicks of two races of California Gull (Larus californicus), which differ by 27Oh in adult body mass, grew to fledging at similar rates when maintained in a common envi- ronment and provided with food ad libitum. There were sexual differences in growth rates; males, which were larger, developed more slowly than females. Racial differences in size were maintained, but appeared to be smaller in captive adults and juveniles than in wild birds, indicating that both genetic and environmental components influence body size; racial differences in plumage were maintained and seemed to be under genetic control. Growth patterns and asymptotic size of captives differed from those reported for wild birds, reflecting both captivity effects and procedural bias in determining asymptotes in field studies.

Notes on the Seabirds of Sala y Gomez

canic spire, which measures only 700 m long by 450 m wide at its greatest dimensions (Figs. 1, 2). The western half, which rises ca. 8 m above the sea, consists of rough lava interspersed with a series of small tide pools or inlets. It is connected to the eastern half by a narrow causeway, which has been tunneled through by wave action in several places. The eastern half, flatter and less rugose, is bordered on the north by a rocky beach, to the northeast by a sandy beach, and to the south by steep-sided rocks that rise to a maximum elevation of 10 m. In its west-central sector lies a sandy depression approximately 70 m in diameter; the sand is dry at the surface but gives way to water-laden sediment within several cm. Bordering this area and to the south are many boulders ranging up to 1 m in diameter. Owing to its remoteness and sometimes difficult access, the island is rarely visited. On 3 March 1985, one of us (PH) was able to land for 40 min, and on 3 March 1986 we both were ashore for 90 min. Although our observations were hurried and limited to the late morning, we were able to survey most of the island and to extend the findings of P. Scott, which were reported by Schlatter (1984), who has provided the only previous summation of the avifauna. These opportunities arose when we were serving as naturalists aboard the Society Explorer.