Magella Guillemette

FLIGHTLESSNESS AND THE ENERGETIC COST OF WING MOLT IN A LARGE SEA DUCK

Although the replacement of feathers apparently represents the major event of somatic production in the annual cycle of wild birds, knowledge about the energetics of molt has always been hampered by logistical and technical difficulties, which are exacerbated by the fact that birds are able to compensate behaviorally to buffer any variation in energy demand. During wing molt, sea ducks (Mergini) and other diving birds lose all of their wing feathers at once, leading to a period of temporary flightlessness of variable duration, a condition that considerably restricts their movements and increases the probability of predation. In the present study, we present the first results aimed at quantifying the duration of flightlessness, energy expenditure, and foraging effort during molt of a wing-propelled diving bird, the Common Eider (Somateria mollissima). Data loggers were implanted in the body cavity of 13 females to record heart rate and hydrostatic pressure (depth) every two seconds for a period of 220 days. Flight frequency and duration were assessed from elevated and constant heart rate, and the absence of flight was used to quantify the duration of flightlessness, which lasted, on average, 36 +/- 8 days (mean +/- SD). Using a period of four weeks before and four weeks after the flightless period, we found that dive depth (ranging from 1 to 2 m, on average) and daily diving time did not vary during the course of the study. Daily metabolic rate increased by 9%, and resting metabolic rate by 12% from the pre-molt period to the flightless period and remained high during the post-molt period. This study indicates that the energetic costs of replacing flight remiges in female eiders are substantial, although this is not associated with any change in foraging effort, which suggests that female Common Eiders lose mass during wing molt. Finally, estimates of energy savings associated with the total absence of flights during wing molt represent 6% of daily metabolic rate or 14% of resting metabolic rate. This finding contrasts with the classical view that little or no benefit is associated with a flightless condition. We suggest that such energy savings may have favored the evolution of temporary flightlessness in diving birds.

EFFECTS OF DATA-LOGGERS IMPLANTED FOR A FULL YEAR IN FEMALE COMMON EIDERS

Abstract Data-loggers can be implanted into the body cavities of birds to monitor their physiology and behavior. This technology opens the potential for year-round monitoring, as long as data-loggers can be retrieved one year later and the implantation does not alter the birds health or behavior. We tested the impact of carrying data-loggers on reproductive parameters of nine female Common Eiders breeding in the Baltic Sea. We minimized disturbance and maximized return rates of experimental females by implanting data-loggers during the second half of the incubation period and by choosing early breeders, which were presumably high quality individuals. All experimental females came back to the study plot the year following implantation. Using a before-after approach applied to an experimental and a control group, we found no evidence that carrying data-loggers had any harmful effect on laying dates, clutch sizes, or hatching success of experimental females. It appears that data-loggers implanted in the body cavities of female Common Eiders do not interfere with their reproductive activities. Explanations for this result are that data-loggers are small compared to body mass (<1%), and their implantation into the body cavity does not alter the hydrodynamic or aerodynamic properties of these diving birds. Efectos de Medidores Implantados por un Año Completo en Hembras de Somateria mollissima Resumen. Pequeños medidores (i.e., “data-loggers”) pueden ser implantados en las cavidades corporales de las aves para monitorear su fisiología y comportamiento. Esta tecnología abre el potencial para realizar monitoreos a lo largo del año, siempre y cuando los medidores puedan ser recuperados un año más tarde y éstos no afecten la salud o el comportamiento de las aves. Evaluamos el impacto de llevar medidores sobre parámetros reproductivos de nueve hembras de la especie Somateria mollissima que se estaban reproduciendo en el Mar Báltico. Minimizamos el disturbio y maximizamos las tasas de retorno de las hembras experimentales implantando los medidores durante la segunda mitad del período de incubación y escogiendo aquellas que se reprodujeron al comienzo de la estación, que presumiblemente eran individuos de alta calidad. Todas las hembras experimentales regresaron al sitio de estudio al año siguiente de la implantación. Utilizando un método de antes y después aplicado a un grupo experimental y a uno de control, no encontramos evidencia de que llevar medidores tenga algún efecto negativo sobre la fecha de postura, el tamaño de la nidada o el éxito de eclosión de las hembras experimentales. Al parecer, los medidores implantados en las cavidades corporales de las hembras de S. mollissima no interfieren con sus actividades reproductivas. Las explicaciones para este resultado son que los medidores son pequeños en comparación con la masa corporal (<1%), y que su implantación en la cavidad corporal no altera las propiedades hidrodinámicas ni aerodinámicas de estas aves buceadoras.

POSTDEVELOPMENT EXPERIMENTS TO DETECT ANTHROPOGENIC DISTURBANCES: THE CASE OF SEA DUCKS AND WIND PARKS

Typically, ecological impact assessments (EIA) are conducted under time constraints, making the collection of baseline data and application of Before-After-Control-Impact (BACI) designs difficult. Here we report the results of three “postdevelopment” experiments testing the effects of a small wind park on the abundance, distribution, and behavior of wintering Common Eiders (Somateria mollissima), a large sea duck. Our approach was based on the rationale that the probability of detecting an impact should increase with decreasing distances from the wind park. Because prey abundance is likely to drive the distribution of wintering eiders, we removed that confounding variable by (1) randomizing its effect over the study area, and (2) incorporating the variable into the analysis. In the first experiment, we compared the abundance and distribution of eiders when wind turbines were switched on and off. This was complemented by investigating the escape behavior of flocks when wind turbines were switched on after ...

To fly or not to fly: high flight costs in a large sea duck do not imply an expensive lifestyle

A perennial question in ornithology is whether flight has evolved mostly to facilitate access to food or as an anti-predator strategy. However, flight is an expensive mode of locomotion and species using flight regularly are associated with an expensive lifestyle. Using heart rate (HR) data loggers implanted in 13 female common eiders (Somateria mollissima), our objective was to test the hypothesis that a high level of flight activity increases their energy budget. We used the long-term recording (seven months) of HR as an index of energy expenditure and the HR flight signature to compile all flight events. Our results indicate that the eider is one of the thriftiest volant birds with only 10 minutes of flight time per day. Consequently, we were not able to detect any effect of flight activity on their energy budget despite very high flight costs (123–149 W), suggesting that flight was controlled by energy budget limitations. However, the low flight activity of that species may also be related to their prey landscape requiring few or no large-scale movements. Nevertheless, we suggest that the (fitness) benefits of keeping flight ability in this species exceed the costs by allowing a higher survival in relation to predation and environmental harshness.

It is time to move: linking flight and foraging behaviour in a diving bird

Although the adaptive value of flight may seem obvious, it is the most difficult behaviour of birds to monitor. Here, we describe a technique to quantify the frequency and the duration of flights over several months by implanting a data logger that records heart rate (fH), hydrostatic pressure (diving depth) and the body angle of a large sea duck species, the common eider (Somateria mollissima). According to the mean fH recorded during flight and the parameters recorded to identify the fH flight signature, we were able to identify all flights performed by 13 individuals during eight months. We cumulated local flight time (outside migrations) and found that activity occurs primarily during dawn and morning and that flying activities are strongly related to diving activities (Pearsons r=0.88, permutation test p<0.001). This relationship was interpreted as a consequence of living in a dynamic environment where sea currents move the ducks away from the food patches. We believe that the technique described here will open new avenues of investigation in the adaptive value of flight.

Distribution of wintering common eiders over mussel beds : does the ideal free distribution apply ?

The preferred habitat of common eiders (Somateria mollissima) wintering in the Gulf of St. Lawrence, eastern Canada consists of submerged reefs distributed in patches of different sizes which are composed of kelp beds and urchin barrens. In this habitat, the blue mussel (Mytilus edulis), a preferred prey, is found only inside kelp beds and is considered to have a high carrying capacity to be depleted slowly over the course of the winter. We examined the effect of population density on the number of mussel patches simultaneously used by eiders. Our rationale was that if interference competition was occurring, we should observe a spacing of eiders and the number of patches used should increase with an increase in population density. We used the number of eiders counted in these patches as an index of density. The data show that the eiders crowd into one or two patches as population density increased. We thus discarded the possibility that interference competition was driving the distribution of wintering eiders. We also hypothesized that prey depletion could influence eider distribution over the winter and we predicted that patch use was correlated with food availability through time and follows a simple ideal free distribution. Our data supported this hypothesis. Although population density and prey depletion act at two different time scales and result in two contrasting distributions, we show that these two factors can play a role in determining eider distribution.

Seasonal variation in energy expenditure is not related to activity level or water temperature in a large diving bird

SUMMARY There is considerable interest in understanding how the energy budget of an endotherm is modulated from a physiological and ecological point of view. In this paper, we used daily (24 h) heart rate (fH24), as a proxy of daily energy expenditure (DEE) across seasons, to test the effect of locomotion activity and water temperature on the energy budget of a large diving bird. fH24 was monitored continuously in common eiders (Somateria mollissima) during 7 months together with measures of time spent flying and time spent feeding. fH24 varied substantially during the recording period, with numerous increases and decreases that occurred across seasons, although we did not find any relationship between fH24 and the time spent active (feeding and flying). However, inactive heart rate (fH,inactive) decreased as locomotion activity increased, suggesting that common eiders were using some form of compensation when under a high work load. We were also unable to detect a negative relationship between water temperature and resting heart rate, a proxy of resting metabolic rate. This was unexpected, based on the assumption that high thermoregulation costs would be associated with cold waters. We showed instead that a high level of energy expenditure coincided with feather moult and warm waters, which suggests that the observed variable pattern of seasonal DEE was driven by these two factors. Nevertheless, our results indicate that compensation and possibly the timing of moult may be used as mechanisms to reduce seasonal variation in energy expenditure.

Distribution, Diet and Dive Behavior of Barrow’s and Common Goldeneyes during Spring and Autumn in the St. Lawrence Estuary

Abstract Barrow’s (Bucephala islandica) and Common (B. clangula) goldeneyes winter in large numbers in the St. Lawrence estuary and little is known of their distribution and diet. The objective of the study was to characterize how these two similar species, co-existed in the St. Lawrence estuary during the non-breeding season. Their local distribution, diet, and dive efficiency were compared. There was little overlap in habitat use by both goldeneyes. Their distribution was not correlated in the autumn (r = 0.04) but was in the spring (0.68). Autumn and spring distributions were more correlated in Common Goldeneyes (r = 0.82) than in Barrow’s Goldeneyes (r = 0.49). Both species moved to the north shore of the estuary during January and February 1999 as south shore intertidal areas froze. Barrow’s Goldeneyes foraged in larger flocks than Common Goldeneyes (x̄ = 20.3 vs 9.8 birds) and flocks were larger in autumn than spring. Both species fed on amphipods but differed in their use of gastropods (Barrow’s Goldeneye) and polychaetes (Common Goldeneye). Dive duration was similar in both species but varied between areas. Pause duration was shorter in Common Goldeneyes than in Barrow’s Goldeneyes but was not affected by area. Dive efficiency was higher in Common Goldeneyes than Barrow’s Goldeneyes and varied between areas. The predominance of polychaetes in the diet of Common Goldeneyes and of amphipods in the diet of Barrow’s Goldeneyes had not been highlighted before. These species provide a good example of niche differentiation between closely related species.

Nesting success of common eiders Somateria mollissima as influenced by nest-site and female characteristics in the Gulf of the St. Lawrence

Abstract In the common eider Somateria mollissima as well as in many other bird species, nesting success has been associated with female reproductive characteristics and predator accessibility to the nest site. In this study, we tested the following predictions on nesting common eiders: 1) female and nest-site characteristics are correlated within a colony, where those with the highest ranked reproductive traits nest where the environment provides best protection, 2) females nesting on forested islands generally exhibit better reproductive traits than females nesting on open islets (hereafter habitats) because the former provide the best nest protection, and consequently, 3) colonies located on forested islands have higher nesting success than those on open islets. During the summers of 1995 and 1996, we recorded nesting success at 270 eider nests on two forested islands and four open islets. Simultaneously, we measured several variables describing nest (nest concealment, vegetation height, distance to shore and density of associated nesting gulls) and female (laying date and clutch size) characteristics. Using factor analysis to relate nest-site and female characteristics, we found a correlation between factor scores within four of the six colonies monitored. This correlation indicated that females with largest clutch size and early laying were associated with nest sites of low concealment that were close to shore. However, female score did not differ with habitat. Nesting success did not differ between habitats when controlled for female and nest scores, but was related to female score, and marginally to nest-site score. Because nesting success was principally related to female characteristics rather than to nest-site characteristics, we suggest that eiders rely on nest attendance rather than on nest concealment to protect their nests. Nesting close to shore may shorten incubation recesses and improve hatchling survival when leaving the nest.

Foraging Effort and Pre-Laying Strategy in Breeding Common Eiders

Abstract. To face energetic demands of reproduction, female birds need to build up body reserves before breeding and/or feed while producing eggs and incubating. Five female Common Eiders were implanted with data loggers that recorded flying and diving activity for a year. The pre-laying period, defined as the interval between the end of spring migration and laying of the first egg, extended over eleven to 27 days and represented a period of intense foraging activity. Daily time spent diving (DTSD) during the pre-laying period averaged 159.6 ± 16.0 min compared to an annual average of 91.4 ± 37.8 min. Diving decreased to 69.8 ± 7.4 min during laying and became almost negligible at the onset of incubation. Females showed hyperphagic behavior during follicular growth, suggesting that they may directly utilize ingested food for egg production and laying. Given the small number of instrumented females, available evidence was reviewed on foraging and time of arrival in various populations and subspecies. Despite large variations in migration distance, the pre-laying period was similar to other populations (16–28 days), as well as DTSD (160–211 min). Reduced take-off capability may constrain the timing of accumulation of body reserves and foraging effort. Further, the level of body mass required for nesting (laying and incubation) was estimated to be 543 g higher than in winter, of which about 41–72% would be accumulated on the breeding grounds. Protection of foraging areas during the pre-breeding period is important to maintain healthy populations.