Evolution of embryonic developmental period in the marine bird families Alcidae and Spheniscidae: roles for nutrition and predation?

Background: Nutrition and predation have been considered two primary agents of selection important in theevolution of avian life history traits. The relative importance of these natural selective forces in the evolution of avianembryonic developmental period (EDP) remain poorly resolved, perhaps in part because research has tended to focuson a single, high taxonomic-level group of birds: Order Passeriformes. The marine bird families Alcidae (auks) andSpheniscidae (penguins) exhibit marked variation in EDP, as well as behavioural and ecological traits ultimately linkedto EDP. Therefore, auks and penguins provide a unique opportunity to assess the natural selective basis of variation in akey life-history trait at a low taxonomic-level. We used phylogenetic comparative methods to investigate the relativeimportance of behavioural and ecological factors related to nutrition and predation in the evolution of avian EDP.Results: Three behavioural and ecological variables related to nutrition and predation risk (i.e., clutch size, activitypattern, and nesting habits) were significant predictors of residual variation in auk and penguin EDP based on modelspredicting EDP from egg mass. Species with larger clutch sizes, diurnal activity patterns, and open nests hadsignificantly shorter EDPs. Further, EDP was found to be longer among birds which forage in distant offshore waters,relative to those that foraged in near shore waters, in line with our predictions, but not significantly so.Conclusion: Current debate has emphasized predation as the primary agent of selection driving avian life historydiversification. Our results suggest that both nutrition and predation have been important selective forces in theevolution of auk and penguin EDP, and highlight the importance of considering these questions at lower taxonomicscales. We suggest that further comparative studies on lower taxonomic-level groups will continue to constructivelyinform the debate on evolutionary determinants of avian EDP, as well as other life history parameters

Trends in Forage Fish Populations in Northern Hudson Bay since 1981, as Determined from the Diet of Nestling Thick-billed Murres Uria lomvia

Trends in the composition of nestling thick-billed murre diets were analyzed for the period 1980-2002 on the basis of observations of food delivered to nestlings at two breeding colonies in northern Hudson Bay. The incidence of arctic cod, sculpins, and benthic Zoarcidae decreased and the incidence of capelin and sandlance increased over the period considered. Arctic cod fell from a mean of 43% of deliveries in the mid-1980s to 15% in the late 1990s; benthic species (zoarcids and sculpins) fell from 36% to 15%, while capelin increased from 15% to 50% over the same period. July ice cover in Hudson Bay approximately halved during 1981-99. We suggest that the observed changes in diet composition reflect changes in the relative abundance of the fish species involved and that the decline in arctic cod and increase in capelin and sandlance were associated with a general warming of Hudson Bay waters, the result of ongoing climate change in the region.On a analysé les tendances dans la composition du régime alimentaire des oisillons du guillemot de Brünnich au cours de la période allant de 1980 à 2002, d'après les observations de l'apport de nourriture aux oisillons à deux colonies de nidification dans le nord de la baie d'Hudson. On a assisté, au cours de cette période, à une baisse de la fréquence de la morue polaire, du chabot et des zoarcidés benthiques, et à une augmentation de celle du capelan et du lançon. La morue polaire a chuté d'une moyenne représentant 43 % de l'apport au milieu des années 1980 à 15 % à la fin des années 1990; les espèces benthiques (zoarcidés et chabots) ont chuté de 36 à 15 %, tandis que le capelan a augmenté de 15 à 50 % au cours de la même période. En juillet, le manteau glaciel dans la baie d'Hudson a diminué de moitié environ entre 1981 et 1999. On suggère que les changements observés dans la composition du régime alimentaire sont un reflet des changements dans l'abondance relative des espèces de poissons concernées et que le déclin de la morue polaire et l'augmentation du capelan et du lançon étaient associés à un réchauffement général des eaux de la baie d'Hudson, réchauffement qui résulte du changement climatique que connaît actuellement la région

Egg production in the thick-billed murre (Uria lomvia) and razorbill (Alca torda) - a life-history perspective

A key tenet of life-history theory is that costs of reproduction lead to physiological and evolutionary trade-offs among fitness components. Although avian egg production was a key topic in the development of life-history theory, the significance of egg production costs within the life histories of birds remains poorly understood. Two aspects of egg production that have received considerable attention are variation among females in their capacity to renest following clutch loss, and variation in the size of egg they lay. I examined these aspects of egg production in two pelagic seabirds, Thick- billed Murres Uria lomvia and Razorbills Alca torda. It is generally thought that egg production costs are relatively low in pelagic seabirds that lay single-egg clutches, but age- and date-specific patterns in renesting capacity and egg size suggest that significant constraints on egg production operate in these birds. -- The proportion of Thick-billed Murres that renests following egg loss declines with the date of loss. However, early-laying females that had their eggs removed continued to renest until late in the laying period. First and replacement eggs were similar in crude composition, but replacement eggs had low protein content. Despite this, replacement eggs were no less likely to hatch than were first eggs, and chicks from replacement eggs were no less likely to survive to nest departure, and to recruitment age (4-5 years). I conclude that variation in the egg-production capacity of females that lose their eggs early and late (probably age/experience effects) drives the seasonal declines in renesting rates. Capable females will relay until late in the laying period because, for these birds, the potential fitness payoff from a replacement egg is similar to that from a first egg. It remains to be determined whether there are survival costs associated with the production of replacement eggs for female Thick-billed Murres. -- Thick-billed Murre eggs vary considerably in size, and egg size affects offspring performance: chicks from large eggs have their wing feathers grow more quickly than do those from small eggs. One hypothesis often invoked to explain the existence of variation in egg size in the face of expected directional selection for large eggs is that the optimal egg size varies with environmental conditions; this hypothesis predicts that benefits of hatching from a large egg will be magnified when feeding conditions are unfavourable. I tested this by comparing between colonies that experience favourable (Coats Island) and unfavourable (Digges Island) conditions, using an experimental egg-switching protocol. Contrary to prediction, the effect of egg size on wing feather growth was no greater at Digges Island than at Coats Island. -- This effect of egg size on wing-feather growthhas not been detected in other birds, suggesting that it might reflect adaptations to the unique intermediate developmental strategy employed by murres and Razorbills. To test this hypothesis, I examined the effect of egg size on post-hatching development in the Razorbill using the same egg-switching protocol. Results clearly supported the hypothesis: as in Thick-billed Murres, large-egg Razorbills experienced enhanced early wing-feather growth. There are a number of adaptations in the development of intermediate alcids that might explain why this egg-size effect is readily detectable in these birds. As there was no evidence for a trade-off between egg size and provisioning in either Thick-billed Murres or Razorbills, the existence of considerable female-specific variation in egg size remains unexplained

Diet of the Pacific Sand Lance (Ammodytes hexapterus) in the Salish Sea, British Columbia, in the 1960s

The diet of the Pacific Sand Lance (Ammodytes hexapterus) was quantified from the stomach contents of 115 Pacific Sand Lance caught in the Strait of Georgia and Saanich Inlet (Vancouver Island) in the Salish Sea, British Columbia, in the spring and summer of 1966, in the Strait of Georgia in the spring and summer of 1967, and in the Strait of Georgia and Saanich Inlet in the spring and summer of 1968. There were 12 major taxa of prey in diets, 8 of which were Crustacea. Based on an index of relative importance, copepods were the dominant prey in 1966 and 1968, but not in 1967, when cladocerans, larvaceans, and teleosts also were common. The copepods Pseudocalanus spp. and Calanus marshallae were the only taxa to appear in diets in all three years. Pseudocalanus dominated the copepod component of diets in 1966, when sampling occurred in July; unspecified copepod nauplii (an early larval stage) were dominant in 1967 and 1968, when sampling occurred earlier (April to June). With the profound changes that have occurred in the Salish Sea over recent decades, these data can serve as a baseline for comparison

Data from: Limited consequences of infestation with a blood-feeding ectoparasite for the nestlings of two North Pacific seabirds

The seabird tick (Ixodes uriae) parasitizes over 60 host species in the circumpolar regions of both hemispheres, and acts as a vector for a number of potentially virulent pathogens. On Triangle Island, British Columbia, Canada, the nestlings of Cassin’s Auklet (Ptychoramphus aleuticus) and Rhinoceros Auklet (Cerorhinca monocerata) are often parasitized by seabird ticks, which may affect their growth and survival in the nest. We used a logistic growth model to interpolate between successive measures of mass (g) and wing chord (mm) for 558 Cassin’s Auklet and 344 Rhinoceros Auklet chicks over 11 years from 1996 to 2007. From the model, we estimated the asymptotic measure and the age at inflection point for each chick’s growth trajectory, and assessed the effect of tick load relative to other sources of annual and seasonal variation in growth. Most chicks (72.4% of Cassin’s Auklets, and 62.2% of Rhinoceros Auklets) hosted ≥1 ticks at least once while in the nest, and the median tick load was two in both species. The probability of hosting a tick declined strongly with chick age, such that by day 40 after hatching less than 1% hosted ticks. We found evidence that tick load had a negative effect on asymptotic weights and wing lengths of both species, but the effect was minor relative to that of other sources of annual and seasonal variation. Only at very high loads – which were rare – did ticks have effects on growth that were likely to be biologically relevant. Tick load had little effect on survival to fledging in either species.We argue that these mild effects of ticks on their hosts are consistent with a co-evolutionary process that results in intermediate virulence when parasite transmission is linked to host recovery

VARIATION IN EGG SIZE AND LAYING DATE IN THICK-BILLED MURRE POPULATIONS BREEDING IN THE LOW ARCTIC AND HIGH ARCTIC

Abstract. We used data collected across 28 years to compare how timing of laying and egg size respond to environmental variability in two low-arctic and two higharctic Thick-billed Murre (Uria lomvia) populations. Ice conditions strongly affect food availability to marine birds in the Arctic, and the percentage of the sea's surface covered by ice within 300 km of the breeding colony varied more among years near the start of laying at our high-arctic study colonies (Prince Leopold and Coburg Islands, Nunavut, Canada) than at our low-arctic study colonies (Coats and Digges Islands, Nunavut). However, mean values differed little. These results indicate that Thick-billed Murres breeding in the High Arctic experience more variable ice conditions, but not necessarily more severe ice conditions, during the period of egg formation. In response, both median laying date and mean egg size varied more among years at high-arctic than at low-arctic colonies. Several lines of evidence suggested that the variation was a result of within-female effects, i.e., phenotypic plasticity rather than different individuals breeding in years in which environmental conditions differed. Previous studies have shown that Thick-billed Murres lay eggs later in years of heavier ice coverage, especially in the High Arctic where ice conditions can be severe, and only in the High Arctic was later laying associated with reduced egg size. The relationship tended towards a negative asymptote suggesting that each female may have her own minimum egg size. Our results show that Thick-billed Murres that inhabit a more variable environment display greater variability in life-history traits. More generally, they offer insight into mechanisms linking environmental heterogeneity to phenotypic variation in life-history traits. Key words: egg size, environmental conditions, laying date, plasticity, Thick-billed Murre, Uria lomvia. Variación en el Tamaño del Huevo y la Fecha de Puesta en Poblaciones Reproductivas de Uria lomvia en el Á rtico Bajo y el Á rtico Alto Resumen. Empleamos datos colectados a lo largo de 28 años (1975-2002) para determinar cómo el ajuste temporal de la puesta y del tamaño del huevo responde a la variabilidad ambiental en dos poblaciones del Á rtico bajo y dos poblaciones del Á rtico alto de Uria lomvia. Las condiciones del hielo afectaron fuertemente la disponibilidad de alimentos para las aves marinas en el Á rtico. El porcentaje de la superficie del mar cubierta por hielo a menos de 300 km de la colonia reproductiva varió más entre años cerca del inicio de la puesta en nuestras colonias de estudio del Á rtico alto (Islas Prince Leopold y Coburg, Nunavut, Canadá) que en nuestras colonias de estudio del Á rtico bajo (Islas Coats and Digges, Nunavut). Sin embargo, los valores medios difirieron poco. Estos resultados indican que los individuos de Uria lomvia que crían en el Á rtico alto experimentan condiciones de hielo más variables, pero no necesariamente más severas, durante el período de la formación del huevo. Como respuesta, tanto la fecha mediana de puesta y la media del tamaño del huevo variaron más entre años en las colonias del Á rtico alto que en las del Á rtico bajo. Varias líneas de evidencia sugirieron que esta variación fue el resultado de variaciones propias de las hembras (i.e., plasticidad fenotípica) y no de variación entre individuos diferentes que criaron en años en los cuales las condiciones ambientales difirieron. Estudios previos han mostrado que Uria lomvia realiza su puesta más tarde en los años de mucha cobertura de hielo, especialmente en el Á rtico alto, donde las condiciones de hielo pueden ser severas, y sólo en el Á rtico alto la demora de la puesta se asoció con una reducción del tamaño del huevo. La relación tendió hacia una asíntota negativa, sugiriendo que cada hembra podría tener su propio tamaño mínimo del huevo. Nuestros resultados muestran que los individuos de Uria lomvia que habitan un ambiente más variable muestran mayor variabilidad en los rasgos de historia de vida. De modo más general, nuestros resultados ofrecen información sobre los mecanismos que vinculan la heterogeneidad ambiental con la variación fenotípica en los rasgos de historia de vida

Sex allocation in a monomorphic seabird with a single-egg clutch : test of the environment, mate quality, and female condition hypotheses

Sex allocation theory posits that mothers should preferentially invest in sons when environmental conditions are favorable for breeding, their mates are of high quality, or they are in good body condition. We tested these three hypotheses in rhinoceros auklets (Cerorhinca monocerata), monomorphic seabirds that lay a single-egg clutch, in 2 years that differed in environmental conditions for breeding. Results supported the environment and mate quality hypotheses, but these effects were interactive: offspring sex was independent of paternal traits in the poor year for breeding, while females mated to larger and more ornamented males reared more sons in the better year. Conversely, offspring sex was unrelated to female condition, as indexed by hatching date. We propose that good rearing conditions enable females to rear sons possessing the desirable phenotypic attributes of their mates. Results also supported two critical assumptions of sex allocation theory: (1) dimorphism in offspring condition at independence: daughters fledged with higher baseline levels of corticosterone than sons and (2) differential costs of rearing sons versus daughters: mothers rearing sons when environmental conditions were poor completed parental care in poorer condition than mothers rearing daughters in the same year and mothers rearing either sex when conditions were better. These novel results may help to explain the disparate results of previous studies of avian sex allocation

Dietary segregation between two cohabiting species of sparrows revealed with stable isotope analysis

Fox Sparrows (Passerella iliaca (Merrem, 1786)) and Song Sparrows (Melospiza melodia (A. Wilson, 1810)) cohabit on many islands along the Pacific coast of North America, and previous studies suggest that they rely on similar prey types. We used δ13C and δ15N stable isotope analysis on blood collected from breeding adults of both species in each of two habitats on Triangle Island, British Columbia, Canada, to test the hypothesis that the two species exhibit a consistent pattern (direction) of dietary segregation in different habitat types. Both δ13C and especially δ15N values differed between habitats, indicating that the two habitats were isotopically distinct. As predicted, δ15N values differed consistently between the two species in the two habitats, averaging ~ 1.5‰ higher in the smaller Song Sparrow than in the larger Fox Sparrow in both. We infer that Song Sparrows included more animal matter and less plant matter in their diets than Fox Sparrows, and suggest that fixed traits related to body size might underlie the dietary (trophic) differences. In contrast, δ13C values did not differ between species. We conclude that dietary segregation could help to facilitate the widespread cohabitation of these two species of sparrows