Eggs in the freezer: energetic consequences of nest site and nest design in Arctic breeding shorebirds

Birds construct nests for several reasons. For species that breed in the Arctic, the insulative properties of nests are very important. Incubation is costly there and due to an increasing surface to volume ratio, more so in smaller species. Small species are therefore more likely to place their nests in thermally favourable microhabitats and/or to invest more in nest insulation than large species. To test this hypothesis, we examined characteristics of nests of six Arctic breeding shorebird species. All species chose thermally favourable nesting sites in a higher proportion than expected on the basis of habitat availability. Site choice did not differ between species. Depth to frozen ground, measured near the nests, decreased in the course of the season at similar non-species-specific speeds, but this depth increased with species size. Nest cup depth and nest scrape depth (nest cup without the lining) were unrelated to body mass (we applied an exponent of 0.73, to account for metabolic activity of the differently sized species). Cup depth divided by diameter 2 was used as a measure of nest cup shape. Small species had narrow and deep nests, while large species had wide shallow nests. The thickness of nest lining varied between 0.1 cm and 7.6 cm, and decreased significantly with body mass. We reconstruct the combined effect of different nest properties on the egg cooling coefficient using previously published quantitative relationships. The predicted effect of nest cup depth and lining depth on heat loss to the frozen ground did not correlate with body mass, but the sheltering effect of nest cup diameter against wind and the effects of lining material on the cooling coefficient increased with body mass. Our results suggest that small arctic shorebirds invest more in the insulation of their nests than large species

Mechanisms promoting higher growth rate in arctic than in temperate shorebirds

We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.

Do Uniparental Sanderlings Calidris alba Increase Egg Heat Input to Compensate for Low Nest Attentiveness?

Birds breeding in cold environments regularly have to interrupt incubation to forage, causing a trade-off between two mutually exclusive behaviours. Earlier studies showed that uniparental Arctic sandpipers overall spend less time incubating their eggs than biparental species, but interspecific differences in size and ecology were potential confounding factors. This study reports on a within-species comparison of breeding schedules and metal egg temperatures in uni- and biparental sanderlings (Calidris alba) in Northeast Greenland in relation to ambient temperature. We recorded incubation schedules with nest temperature loggers in 34 sanderling clutches (13 uniparentals, 21 biparentals). The temperature of a metal egg placed within the clutch of 17 incubating birds (6 uniparentals, 9 biparentals) was measured as an indicator of the heat put into eggs. Recess frequency, recess duration and total recess time were higher in uniparentals than in biparentals and positively correlated with ambient temperatures in uniparentals only. Uniparental sanderlings maintained significantly higher metal egg temperatures during incubation than biparentals (1.4°C difference on average). Our results suggest that uniparental sanderlings compensate for the lower nest attendance, which may prolong the duration of the incubation period and negatively affect the condition of the hatchlings, by maintaining a higher heat flux into the eggs

A rockling's choice:The trade-off between thermal preference and physical structure in the five bearded rockling, Ciliata mustela

Changes in the environment can alter the suitability of habitats for organisms. In marine systems, fish species have their own specific requirements in terms of temperature and other habitat features. Behavioral responses such as thermoregulatory behavior in ectothermic species allow mobile organisms to respond to detrimental changes and search for more suitable habitats. However, for many species, limited information exists on the ecological requirements to help explain species abundance in a changing habitat. An example of a quickly changing habitat is the Wadden Sea, where five bearded rockling (Ciliata mustela) abundance has increased, unlike other Wadden Sea species. The increasing abundance of rockling has coincided with increasing average sea water temperatures and the recovery of mussel and Pacific oyster beds. Warming waters and increased structural habitat may have provided rockling with a more desirable habitat. Therefore, to better understand why rockling abundance is increasing within a changing Wadden Sea, a water temperature preference chamber was used to determine rockling's preferred temperature range. In addition, rockling's affinity for structural habitat and the trade-off between preferred temperature was examined by following their response to the systematic removal of artificial physical structures within the preferred temperature conditions. The preferred temperature range of rockling was found to be 10.4–15.7 °C. Following structure removals, rockling repeatedly moved away from their chosen temperatures to adjacent compartments with different temperatures but containing physical structure, indicating that the presence of physical structure was more important than preferred temperature until 18.6 °C. These novel findings provide insight and experimental support for the hypothesis explaining rockling's increase in the Wadden Sea: 1) mean annual temperatures have been steadily increasing towards rockling's preferred thermal range and 2) increasing mussel and Pacific oyster beds are plausibly providing structural habitat, an important habitat requirement for rockling. When fish display a strong association with physical structure it is necessary to link physiological and habitat preferences to better understand climate change related responses

A rockling's choice:The trade-off between thermal preference and physical structure in the five bearded rockling, Ciliata mustela

Changes in the environment can alter the suitability of habitats for organisms. In marine systems, fish species have their own specific requirements in terms of temperature and other habitat features. Behavioral responses such as thermoregulatory behavior in ectothermic species allow mobile organisms to respond to detrimental changes and search for more suitable habitats. However, for many species, limited information exists on the ecological requirements to help explain species abundance in a changing habitat. An example of a quickly changing habitat is the Wadden Sea, where five bearded rockling (Ciliata mustela) abundance has increased, unlike other Wadden Sea species. The increasing abundance of rockling has coincided with increasing average sea water temperatures and the recovery of mussel and Pacific oyster beds. Warming waters and increased structural habitat may have provided rockling with a more desirable habitat. Therefore, to better understand why rockling abundance is increasing within a changing Wadden Sea, a water temperature preference chamber was used to determine rockling's preferred temperature range. In addition, rockling's affinity for structural habitat and the trade-off between preferred temperature was examined by following their response to the systematic removal of artificial physical structures within the preferred temperature conditions. The preferred temperature range of rockling was found to be 10.4–15.7 °C. Following structure removals, rockling repeatedly moved away from their chosen temperatures to adjacent compartments with different temperatures but containing physical structure, indicating that the presence of physical structure was more important than preferred temperature until 18.6 °C. These novel findings provide insight and experimental support for the hypothesis explaining rockling's increase in the Wadden Sea: 1) mean annual temperatures have been steadily increasing towards rockling's preferred thermal range and 2) increasing mussel and Pacific oyster beds are plausibly providing structural habitat, an important habitat requirement for rockling. When fish display a strong association with physical structure it is necessary to link physiological and habitat preferences to better understand climate change related responses

First geolocator tracks of Swedish red-necked phalaropes reveal the Scandinavia-Arabian Sea connection

We studied migration and wintering patterns of a wader with a pelagic lifestyle during the non-breeding period, the rednecked phalarope Phalaropus lobatus . Using light-level geolocation, we obtained three full annual tracks and one autumn migration track of male red-necked phalaropes caught during breeding in Scandinavia. Th ese tracks confi rmed expectations that individuals from the Scandinavian population winter in the Arabian Sea. Migration was accomplished in two to four migration leaps, staging for a few days in the Gulf of Finland (autumn) or the southern Baltic Sea (spring) and for up to a month in or near the Black and Caspian Sea (autumn and spring). In addition, travel speeds suggested that only the fl ights between the Baltic and Black/Caspian Sea are non-stop, and thus the birds seem to make additional short stops during the other flights. Stopover time in the Black/Caspian Sea is only 8 – 10 d in spring but up to 36 d in autumn, which is longer than expected if only used for pre-migratory fattening to cover the ca 2000 km to the Gulf of Oman. After entering the Arabian Sea via the Gulf of Oman, birds dispersed over the entire presumed winter range. Winter movements appear to correspond to the spatio-temporal patterns in primary production linked to seasonally changing monsoon winds. Th ese are not only the first tracks of Scandinavian red-necked phalaropes, but also the fi rst seabird tracks in the Arabian Sea, one of the most productive and dynamic marine areas on the planet