Geology topics

Anne Dekinga

Publications and source records attributed to Anne Dekinga.

9 recordsLinked to original sources

USGS2021

Central-West Siberian-breeding Bar-tailed Godwits (Limosa lapponica) segregate in two morphologically distinct flyway populations

Long-distance migratory species often include multiple breeding populations, with distinct migration routes, wintering areas and annual-cycle timing. Detailed knowledge on population structure and migratory connectivity provides the basis for studies on the evolution of migration strategies and for species conservation. Currently, five subspecies of Bar-tailed Godwits Limosa lapponica have been described. However, with two apparently separate breeding and wintering areas, the taxonomic status of the subspecies L. l . taymyrensis remains unclear. Here we compare taymyrensis Bar-tailed Godwits wintering in the Middle East and West Africa, respectively, with respect to migration behaviour, breeding area, morphology and population genetic differentation in mitochondrial DNA. By tracking 52 individuals from wintering and staging areas over multiple years, we show that Bar-tailed Godwits wintering in the Middle East bred on the northern West-Siberian Plain ( n = 19), whilst birds from West Africa bred further east, mostly on the Taimyr Peninsula ( n = 12). The two groups differed significantly in body size and shape, and also in the timing of both northward and southward migrations. However, they were not genetically differentiated, indicating that the phenotypic (i.e. geographic, morphological and phenological) differences arose either very recently or without current reproductive isolation. We conclude that the taymyrensis taxon consists of two distinct populations with mostly non-overlapping flyways, which warrant treatment as separate taxonomic units. We thus propose to distinguish a more narrowly defined taymyrensis subspecies (i.e. the Bar-tailed Godwits wintering in West Africa and breeding on Taimyr), from a new yamalensis subspecies (i.e. the birds wintering in the Middle East and breeding on the northern West-Siberian Plain).

Ibis↗

USGS2020

A red knot as a black swan: How a single bird shows navigational abilities during repeat crossings of the Greenland Icecap

Despite the wealth of studies on seasonal movements of birds between southern nonbreeding locations and High Arctic breeding locations, the key mechanisms of navigation during these migrations remain elusive. A flight along the shortest possible route between pairs of points on a sphere (‘orthodrome’) requires a bird to be able to assess its current location in relation to its migration goal and to make continuous adjustment of heading to reach that goal. Alternatively, birds may navigate along a vector with a fixed orientation (‘loxodrome’) based on magnetic and/or celestial compass mechanisms. Compass navigation is considered especially challenging for summer migrations in Polar regions, as continuous daylight and complexity in the geomagnetic field may complicate the use of both celestial and magnetic compasses here. We examine the possible use of orientation mechanisms during migratory flights across the Greenland Icecap. Using a novel 2 g solar-powered satellite transmitter, we documented the flight paths travelled by a female red knot ( Calidris canutus islandica ) during two northward and two southward migrations. The geometry of the paths suggests that red knots can migrate across the Greenland Icecap along the shortest-, orthodrome-like, path instead of the previously suggested loxodrome path. This particular bird’s ability to return to locations visited in a previous year, together with its sudden course changes (which would be appropriate responses to ambient wind fields), suggest a map sense that enables red knots to determine location, so that they can tailor their route depending on local conditions.

Journal of Avian Biology↗

USGS2018

Fuelling conditions at staging sites can mitigate Arctic warming effects in a migratory bird

Under climate warming, migratory birds should align reproduction dates with advancing plant and arthropod phenology. To arrive on the breeding grounds earlier, migrants may speed up spring migration by curtailing the time spent en route , possibly at the cost of decreased survival rates. Based on a decades-long series of observations along an entire flyway, we show that when refuelling time is limited, variation in food abundance in the spring staging area affects fitness. Bar-tailed godwits migrating from West Africa to the Siberian Arctic reduce refuelling time at their European staging site and thus maintain a close match between breeding and tundra phenology. Annual survival probability decreases with shorter refuelling times, but correlates positively with refuelling rate, which in turn is correlated with food abundance in the staging area. This chain of effects implies that conditions in the temperate zone determine the ability of godwits to cope with climate-related changes in the Arctic.

Nature Communications↗

USGS2017

Energetic solutions of Rock Sandpipers to harsh winter conditions rely on prey quality

Rock Sandpipers Calidris ptilocnemis have the most northerly non-breeding distribution of any shorebird in the Pacific Basin (upper Cook Inlet, Alaska; 61°N, 151°W). In terms of freezing temperatures, persistent winds and pervasive ice, this site is the harshest used by shorebirds during winter. We integrated physiological, metabolic, behavioural and environmental aspects of the non-breeding ecology of Rock Sandpipers at the northern extent of their range to determine the relative importance of these factors in facilitating their unique non-breeding ecology. Not surprisingly, estimated daily energetic demands were greatest during January, the coldest period of winter. These estimates were greatest for foraging birds, and exceeded basal metabolic rates by a factor of 6.5, a scope of increase that approaches the maximum sustained rate of energetic output by shorebirds during periods of migration, but far exceeds these periods in duration. We assessed the quality of their primary prey, the bivalve Macoma balthica , to determine the daily foraging duration required by Rock Sandpipers to satisfy such energetic demands. Based on size-specific estimates of M. balthica quality, Rock Sandpipers require over 13 h/day of foraging time in upper Cook Inlet in January, even when feeding on the highest quality prey. This range approaches the average daily duration of mudflat availability in this region ( c . 18 h), a maximum value that annually decreases due to the accumulation of shore-fast ice. Rock Sandpipers are likely to maximize access to foraging sites by following the exposure of ice-free mudflats across the upper Cook Inlet region and by selecting smaller, higher quality M. balthica to minimize foraging times. Ultimately, this unusual non-breeding ecology relies on the high quality of their prey resources. Compared with other sites across their range, M. balthica from upper Cook Inlet have relatively light shells, potentially the result of the region's depauperate invertebrate predator community. Given the delicate balance between environmental and prey conditions that currently make Cook Inlet a viable wintering area for Rock Sandpipers, small variations in these variables may affect the suitability of the site in the future.

Alaska↗

USGS2015

Testing an attachment method for solar-powered tracking devices on a long-distance migrating shorebird

Small solar-powered satellite transmitters and GPS data loggers enable continuous, multi-year, and global tracking of birds. What is lacking, however, are reliable methods to attach these tracking devices to small migratory birds so that (1) flight performance is not impacted and (2) tags are retained during periods of substantial mass change associated with long-distance migration. We developed a full-body harness to attach tags to Red Knots (Calidris canutus), a medium-sized shorebird (average mass 124 g) that undertakes long-distance migrations. First, we deployed dummy tags on captive birds and monitored them over a complete migratory fattening cycle (February–July 2013) during which time they gained and lost 31–110 g and underwent a pre-alternate moult of body feathers. Using each individual’s previous year fattening and moult data in captivity as controls, we compared individual mass and moult differences between years between the tagged and reference groups, and concluded that the attachment did not impact mass and moult cycles. However, some birds shed feathers under the tags and under the polyester harness line commonly used in avian harnesses. Feather shedding was alleviated by switching to smoothed-bottom tags and monofilament harness lines. To field-trial this design, we deployed 5-g satellite transmitters on ten Red Knots released on 3 October 2013 in the Dutch Wadden Sea. Bird movements and tag performance appeared normal. However, nine tags stopped transmitting 11–170 days post-release which was earlier than expected. We attribute this to bird mortality rather than failure of the attachments or transmitters and suggest that the extra weight and drag caused by the tag and its feather-blocking shield increased the chance of depredation by the locally common Peregrine Falcons (Falco peregrinus). Our results demonstrate that species- and place-specific contexts can strongly determine tagging success. While captive trials are an important first step in developing an attachment method, field trials are essential to fully assess attachment designs.

Wadden Sea↗

USGS2013

Ecological correlates of variable organ sizes and fat loads in the most northerly-wintering shorebirds

Shorebirds at northern latitudes during the nonbreeding season typically carry relatively large lipid stores and exhibit an up-regulation of lean tissues associated with digestion and thermogenesis. Intraspecific variation in these tissues across sites primarily reflects differences in environmental conditions. Rock (Calidris ptilocnemis (Coues, 1873)) and Purple (Calidris maritima (Brünnich, 1764)) sandpipers are closely related species having the most northerly nonbreeding distributions among shorebirds, living at latitudes up to 61°N in Cook Inlet, Alaska, and up to 71°N in northern Norway, respectively. Cook Inlet is the coldest known site used by nonbreeding shorebirds, and the region’s mudflats annually experience extensive coverage of foraging sites by sea and shore-fast ice. Accordingly, Rock Sandpipers increase their fat stores to nearly 20% of body mass during winter. In contrast, Purple Sandpipers exploit predictably ice-free rocky intertidal foraging sites and maintain low (<6.5%) fat stores. Rock Sandpipers increase the mass of lean tissues from fall to winter, including contour feathers, stomach, and liver components. They also have greater lean pectoralis and supracoracoideus muscle and liver and kidney tissues compared with Purple Sandpipers in winter. This demonstrates a combined emphasis on digestive processes and thermogenesis, whereas Purple Sandpipers primarily augment organs associated with digestive processes. The high winter fat loads and increased lean tissues of Rock Sandpipers in Cook Inlet reflect the region’s persistent cold and abundant but sporadically unavailable food resources.

Alaska↗

USGS2013

Identical metabolic rate and thermal conductance in Rock Sandpiper ( Calidris ptilocnemis ) subspecies with contrasting nonbreeding life histories

Closely related species or subspecies can exhibit metabolic differences that reflect site-specific environmental conditions. Whether such differences represent fixed traits or flexible adjustments to local conditions, however, is difficult to predict across taxa. The nominate race of Rock Sandpiper (Calidris ptilocnemis) exhibits the most northerly nonbreeding distribution of any shorebird in the North Pacific, being common during winter in cold, dark locations as far north as upper Cook Inlet, Alaska (61°N). By contrast, the tschuktschorum subspecies migrates to sites ranging from about 59°N to more benign locations as far south as ~37°N. These distributional extremes exert contrasting energetic demands, and we measured common metabolic parameters in the two subspecies held under identical laboratory conditions to determine whether differences in these parameters are reflected by their nonbreeding life histories. Basal metabolic rate and thermal conductance did not differ between subspecies, and the subspecies had a similar metabolic response to temperatures below their thermoneutral zone. Relatively low thermal conductance values may, however, reflect intrinsic metabolic adaptations to northerly latitudes. In the absence of differences in basic metabolic parameters, the two subspecies’ nonbreeding distributions will likely be more strongly influenced by adaptations to regional variation in ecological factors such as prey density, prey quality, and foraging habitat.

The Auk↗

USGS2011

Functional ecology of saltglands in shorebirds: Flexible responses to variable environmental conditions

1. Birds of marine environments have specialized glands to excrete salt, the saltglands. Located on the skull between the eyes, the size of these organs is expected to reflect their demand, which will vary with water turnover rates as a function of environmental (heat load, salinity of prey and drinking water) and organismal (energy demand, physiological state) factors. On the basis of inter- and intraspecific comparisons of saltgland mass (msg) in 29 species of shorebird (suborder Charadrii) from saline, fresh and mixed water habitats, we assessed the relative roles of organism and environment in determining measured msg species. 2. The allometric exponent, scaling dry msg to shorebird total body mass (mb), was significantly higher for coastal marine species (0Æ88, N = 19) than for nonmarine species (0Æ43, N = 14). Within the marine species, those ingesting bivalves intact had significantly higher msg than species eating soft-bodied invertebrates, indicating that seawater contained within the shells added to the salt load. 3. In red knots (Calidris canutus), dry msg varied with monthly averaged ambient temperature in a U-shaped way, with the lowest mass at 12Æ5 C. This probably reflects increased energy demand for thermoregulation at low temperatures and elevated respiratory water loss at high temperatures. In fuelling bar-tailed godwits (Limosa lapponica), dry msg was positively correlated with intestine mass, an indicator of relative food intake rates. These findings suggest once more that saltgland masses vary within species (and presumably individuals) in relation to salt load, that is a function of energy turnover (thermoregulation and fuelling) and evaporative water needs. 4. Our results support the notion that msg is strongly influenced by habitat salinity, and also by factors influencing salt load and demand for osmotically free water including ambient temperature, prey type and energy intake rates. Saltglands are evidently highly flexible organs. The small size of saltglands when demands are low suggests that any time costs of adjustment are lower than the costs of maintaining a larger size in this small but essential piece of metabolic machinery.

Functional Ecology↗

USGS2006

Shorebird avoidance of nearshore feeding and roosting areas at night correlates with presence of a nocturnal avian predator

We here report two anecdotes about avian interactions relevant to the interpretation of differences in shorebird habitat use between day and night . Several studies have reported that shorebirds avoid feeding and roosting along nearshore areas at night yet commonly use these sites during daytime. This suggests that nighttime avoidance of nearshore places is a response to increased danger of predation. When mist-netting during autumn 2005 on nearshore intertidal habitats along South Spit, Egegik Bay (Alaska Peninsula), Alaska, we discovered that shorebirds that occurred there in large numbers during daytime low tides and roosted there during daytime high tides (especially Dunlin Calidris alpina, Rock Sandpipers Calidris ptilocnemis, Black-bellied Plover Pluvialis squatarola, and Surfbirds Aphriza virgata), were absent at night . Their avoidance of the area correlated with Short-eared Owls Asio flammeus concurrently hunting over the beach and adjacent intertidal habitats. Spotlighting over nearby expansive intertidal mudflats confirmed that the same suite of species continued to forage or roost nearby at night. To bring the story full circle, the morning following one mist-netting effort we found a Short-eared Owl on the beach that had been killed earlier by a Gyrfalcon Falco rusticolus. In the owl’s stomach were remains of a freshly devoured Dunlin.

Wader Study Group Bulletin↗