Available now - Wilson Ornithological Society

WOS 2010 ~ ABSTRACTS p. 10
ABSTRACTS – PLENARY & SYMPOSIUM PRESENTATIONS
Presenting authors are indicated by bold type. Symposium talks are arranged by presentation number.
Margaret Morse Nice Lecture
Brood parasitism in cuckoos, cowbirds, and African finches. Robert B. Payne and Laura Payne, Museum of
Zoology, Univ. Michigan, Ann Arbor, MI 48109
Margaret Nice studied cowbirds and their effects on song sparrows. We draw on her work to ask some general
questions about brood parasitism in birds: what is the impact of brood parasitism on the nesting hosts Are the brood
parasites generalists or specialists on their hosts How has their specialization affected their evolution and
speciation How did brood parasitism evolve We briefly consider the cowbirds and cuckoos, and then we describe
our studies of the African brood-parasitic finches, especially the indigobirds. The brood-parasitic finches have less
effect on their host brood than cowbirds (cuckoos have the greatest impact) and the young finches grow up and
fledge with the host nestlings. Most Vidua finches are species-specific on certain estrildid finches, the males mimic
the songs of their host species, and the nestlings mimic the host nestlings. In the field the females are attracted to
mate with a male indigobird that mimics her host species. We used molecular methods to discriminate between two
hypotheses of the origin of specific associations of brood parasite and host: (1) co-speciation of parasite and host,
and (2) later colonization and host switch by the parasite. We report a natural population of an indigobird that has
switched to a new host species. We used experimental cross-fostering tests to find the basis of learning and
imprinting in the indigobirds in male song mimicry, in female choice of males that mimicked their own host species,
and in female choice of species nests to parasitize. We also cross-fostered between the estrildid finches to find
whether the hosts could raise young that did not match the host young, as expected if the indigobirds have shifted to
new host species they did not mimic. Field observations, molecular studies and behavior experiments all indicate
most of the 20 species of brood-parasitic finches are the result of host switch and later mimetic adaptation. Finally,
we briefly consider a test of Darwin's explanation for the origin of brood parasitism.
Symposium 1: New perspectives in migratory physiology and energetics
S01 The fat of the matter: how dietary fatty acid composition affects energy expenditure of birds during migration.
Scott R. McWilliams, Dept. Natural Resources Science, Univ. Rhode Island, Kingston, RI 02881, and Barbara
Pierce, Dept. Biology, Sacred Heart Univ., Fairfield, CT 06825
Birds use primarily fat stores to fuel migratory flights, but few studies have focused on the causes and consequences
of observed seasonal changes in fatty acid composition of fat stores in birds. We tested two hypotheses that address
the causes of these seasonal changes in composition of fat stores: (1) diet composition determines fatty acid
composition of fat stores, and (2) birds selectively metabolize and store certain fatty acids during migration in lieu of
changing their diet. Red-eyed Vireos (Vireo olivaceous) consistently chose diets with more triolein over diets with
more tristearin and tripalmitin, and these preferences were similar between seasons. When we maintained vireos for
two years on different semisynthetic diets, the fatty acid composition of their body fat was similar to that of their
diet, and any changes over time were not consistent with the selective-metabolism hypothesis. Thus, fatty acid
composition of stored fat was primarily a product of diet composition; selective metabolism possibly played a
minor, but important, role. Given recent evidence that fatty acid composition of birds affects their energy
expenditure during intense exercise, the implication is that birds during migration can influence the fatty acid
composition of their body fat by selective feeding, and this can significantly affect the energetic cost of migration.
S02 Towards a theoretical framework for avian fat storage. Edwin Price, Dept. Biology, Univ. Western Ontario,
London, ON N6A 5B7
It is well documented that birds primarily use fat to fuel their long-distance migrations. Fat, however, is a complex
mixture of many different fatty acids that have the potential to affect flight in different ways. Nonetheless, there is
little existing theory as to which fatty acids or types of fatty acids birds should store in preparation for migration. I
will review recent work on the physiological effects and properties of various fatty acids in their roles as energy,
structural, and signaling molecules. In particular, fatty acids are mobilized from adipose tissue at varying rates;
mobilization decreases with chain length and increases with the number of double bonds. Similarly, fatty acids with
more double bonds are more quickly oxidized by muscles, a pattern that may be driven in part by selectivity of the
fatty acid transporter carnitine palmitoyl transferase. Dietary fatty acids can also be incorporated into muscle
membranes, where they have to potential to affect membrane properties, thereby affecting exercise. I will examine
the evidence for this mechanism and its relative importance for affecting flight performance. Using these recent
studies as a guide, I will develop a framework for predicting which fatty acids birds should store during migration,
focusing on the tradeoffs between energy storage, mobilization, and stopover refueling.