Joop Jukema

The interplay between habitat availability and population differentiation

We present STRUCTURE HARVESTER (available at http://taylor0.biology.ucla.edu/structureHarvester/), a web-based program for collating results generated by the program STRUCTURE. The program provides a fast way to assess and visualize likelihood values across multiple values of K and hundreds of iterations for easier detection of the number of genetic groups that best fit the data. In addition, STRUCTURE HARVESTER will reformat data for use in downstream programs, such as CLUMPP.

Baseline and Stress‐Induced Plasma Corticosterone during Long‐Distance Migration in the Bar‐Tailed Godwit, Limosa lapponica

The specific roles of corticosterone in promotion of avian migration remain unclear even though this glucocorticosteroid is elevated in many migrating bird species. In general, glucocorticosteroids promote metabolic homeostasis and may elicit effects on feeding and locomotion. Because the migratory stages of refueling and flight are characterized by distinct behaviors and physiology, the determination of corticosterone levels during each stage should help identify potential processes in which corticosterone is involved. We measured baseline levels of corticosterone in bar‐tailed godwits (Limosa lapponica) during two distinct stages of migration: (1) immediately after arrival at a false stopover site just short of the Wadden Sea and (2) throughout the subsequent 4‐wk refueling period on the Wadden Sea. Plasma corticosterone was higher in arriving than in refueling birds. In addition, corticosterone increased with size‐corrected body mass during the refueling phase, suggesting that corticosterone rises as birds prepare to reinitiate flight. Therefore, elevated corticosterone appears associated with migratory flight and may participate in processes characterizing this stage. We also performed a capture stress protocol in all birds and found that corticosterone increased in both arriving and refueling godwits. Therefore, the normal course of migration may be typified by corticosterone concentrations that are lower than those associated with stressful and life‐threatening episodes.

RED BREASTS AS HONEST SIGNALS OF MIGRATORY QUALITY IN A LONG-DISTANCE MIGRANT, THE BAR-TAILED GODWIT

Bar-tailed Godwits (Limosa lapponica) partially molt contour feathers before flying to their subarctic breeding grounds. This molt starts in February on the West African wintering grounds, is suspended in late April before the flight to the staging sites in western Europe, and is continued by more than half of the birds during their stage in May in the Dutch Wadden Sea. During molt the appearance of the plumage changes from the dull grey of a winter plumage to an intense rusty-red in males and a beige-rufous in females with a complete breeding plumage. The total mass of the plumage remains the same. Molt is scheduled earlier and is more intense in males than in females. The duration of contour feather growth on the Dutch staging area is estimated to be 12 days, leading to an estimated daily dry feather production of 0.09-0.13 g/day. On the Dutch staging area molting individuals of either sex had a more complete breeding plumage than non-molting birds and were always heavier. Very few birds started molt in the last 12 days before northward departure indicating that time provides a critical constraint on the occurrence of molt. Although the extra costs of molt are estimated at only 7% of the costs of the simultaneous energy storage, the site-related difference in the mass of molting individuals suggests that the decision to molt depends also on nutritional factors. We argue that in view of the tight time/energy schedules faced by these long-distance migrant godwits, only individuals which have sufficient energy/nutrient reserves for the time of the year due to better feeding or flying performances, can afford to upgrade their plumage on the staging areas. The extent and quality of the breeding plumage could thus provide males as well as females with an indicator of the migratory, and possible concomitant, qualities of potential mates.

Build-up of Red Blood Cells in Refuelling Bar-Tailed Godwits in Relation to Individual Migratory Quality

We examined hemoglobin concentration, hematocrit and mean cell hemoglobin concentration (MCHbC) in Bar-tailed Godwits Limosa lapponica during the latter half of their staging period in May in the Wadden Sea of The Netherlands. Here they recover from a 4,000-5,000 km long flight from West African wintering areas and refuel in preparation for a flight of similar length toward the arctic Siberian breeding grounds. Hemoglobin concentration and hematocrit levels showed no differences between the sexes, but were higher than expected for a bird species of their size. Bar-tailed Godwits that were on schedule with regard to molt and body mass gains, had elevated concentrations of red blood cells all the time during 19-30 May. In contrast, late-arriving, nutritionally stressed individuals, recognizable by the absence of contour feather molt, showed an increase in both hemoglobin concentration and hematocrit over time before scheduled departure on 1 June, converging to similar values as the group of high migratory quality. There were no time-related and categorical variations in MCHbC. We interpret the relatively low concentrations of red blood cells in late arriving light-weight individuals to indicate that long-distance migration flights may result in light anemia. The quick recovery and maintenance of high hemoglobin and hematocrit levels throughout the latter half of the staging period indicates that high concentrations of red blood cells are as necessary for rapid refuelling as for long-distance flights. The increased viscosity of blood with high hematocrit values was reflected in co-occurring increases in the size of the heart.

Permanent female mimics in a lekking shorebird

Female mimics are known from many species, but permanent, non-conditional, alternative mating strategies are only known from an isopod, a fish, a lizard and a bird. The single bird example refers to lek-breeding ruffs Philomachus pugnax, a shorebird for which two strategies (independent and satellite) have been known for over 50 years. Ruffs also provided the single case of an animal with two, rather than three, permanent alternative mating strategies. Here, we describe a rare female-like morph of ruffs: the ‘missing’ third alternative mating strategy, which we have called ‘faeder’. Faeders are slightly larger than females and in late April have testes 2.5 time the size of testes of normal males. On leks in aviaries and in the wild they appear to combine feminine and masculine behaviours. Faeders may represent the ancestral, care-giving, male strategy, but their relatively large testes suggest that currently they behave as sneakers.

Metabolic profile of long-distance migratory flight and stopover in a shorebird

Migrating birds often complete long non–stop flights during which body energy stores exclusively support energetic demands. The metabolic correlates of such long–distance travel in free–living migrants are as yet poorly studied. Bar–tailed godwits, Limosa lapponica taymyrensis, undertake a 4500 km flight to their single spring stopover site and thus provide an excellent model in which to determine the energy fuels associated with endurance travel. To this end, we evaluated plasma concentrations of six key metabolites in arriving godwits caught immediately upon landing near their stopover site. Initial metabolite levels were compared with levels after 5 h of inactive rest to determine how flight per se affects energy metabolism. Birds refuelling on the stopover site were also examined. Arriving godwits displayed elevated plasma free fatty acids, glycerol and butyrate, confirming the importance of lipid fuel in the support of extended migratory activity. Furthermore, elevated plasma triglycerides in these birds suggest that fatty acid provisioning is facilitated through hepatic synthesis and release of neutral lipids, as previously hypothesized for small migrants with high mass–specific metabolic rates. Finally, elevations in plasma uric acid suggest that protein breakdown contributes to the support of long–distance movement, to possibly maintain citric acid cycle intermediates, gluconeogenesis and/or water balance.

WATER BALANCE DURING REAL AND SIMULATED LONG-DISTANCE MIGRATORY FLIGHT IN THE BAR-TAILED GODWIT

Abstract We examined Bar-tailed Godwits (Limosa lapponica), a long-distance migratory shorebird, for evidence of dehydration toward the end of their 4,300-km migratory flight from West Africa to the Dutch Wadden Sea. Bar-tailed Godwits are ideal subjects for research on flight range constraints because they can readily be caught in migratory flight. Because godwits are capable of long nonstop travel, we hypothesized that they are physiologically adapted to minimize en route water loss, and therefore, do not experience water imbalance under standard migratory conditions. To test this hypothesis, we compared the hydration state of flying Bar-tailed Godwits at the end of a long bout of migratory flight to that of recently-landed godwits. Flying godwits were hydrated to the same degree as birds with free access to water, suggesting that godwits maintain water balance during migratory flight. To corroborate these empirical results, we ran a theoretical simulation of flight-incurred loss of water and energy in a male Bar-tailed Godwit based on the published model by Klaassen et al. (1999). When a low body drag is assumed, model output suggests that Bar-tailed Godwits flying at altitudes ranging from sea level to 3,000 m will avoid dehydration, and that flight at about 3,000 m will result in the longest possible flight range.

Contrast in adaptive mass gains: Eurasian golden plovers store fat before midwinter and protein before prebreeding flight

Before predictable periods of high nutritional demand and little or no intake, vertebrates store fuel mainly composed of energy–dense lipids or energy–poor but protein–rich muscle tissue. Documenting contrasts in fuel composition and storage patterns within species, or even within individuals, would greatly help to elucidate the functional significance of the variety of storage strategies demonstrated in birds. We show here that the 40–50 g mass gain of 200 g in Eurasian golden plovers (Pluvialis apricaria) in autumn in The Netherlands consists of fat only, but that the similar gain in body mass in spring consists of proteinaceous tissue (pectoral and other skeletal muscle and possibly skin tissue). That the same golden plovers store energy in autumn and store protein in spring suggests that they face energy deficits in early winter and risk protein deficits in spring, especially perhaps after arrival on the breeding grounds in late April and early May. In autumn and winter their diet consists largely of protein–rich earthworms, but upon arrival on Low Arctic and montane tundras, golden plovers tend to eat berries which are rich in sugars but notably poor in proteins. We therefore propose that the build-up of proteinaceous tissue in spring reflects a strategic storage of a nutritional resource that is likely to be in short supply somewhat later in the year.

Foraging Site Selection of Two Subspecies of Bar-tailed Godwit Limosa lapponica: Time Minimizers Accept Greater Predation Danger Than Energy Minimizers

Different spatial distributions of food abundance and predators may urge birds to make a trade-off between food intake and danger. Such a trade-off might be solved in different ways in migrant birds that either follow a time-minimizing or energy-minimizing strategy; these strategies have been assigned to two sub-species of Bar-tailed Godwits Limosa lapponica that use the European Wadden Sea during northward migration. At the study area on Terschelling we recorded feeding site selection, time budgets and intake rates (prey/min) in the period that both lapponica (energy minimizer) and taymyrensis (time minimizer) sub-species were present (late April till the end of May 2007). Prey availability (number of prey/m2) was negatively correlated to the distance from cover. Based on resightings of colour-ringed Bar-tailed Godwits, taymyrensis was foraging closer to cover, and for a higher proportion of time than lapponica (67% vs. 33%). During the high tide period taymyrensis was also foraging on inland coastal meadows, Moreover, taymyrensis was more vigilant than lapponica, whereas lapponica showed more resting and preening behaviour. Lapponica had a higher instantaneous intake rate, but taymyrensis had a higher overall intake rate and the birds were more successful in taking larger prey items than lapponica. Supposedly, due to the increased foraging time and additional foraging on the inland meadows, the time-minimizing taymyrensis achieved a higher fuel deposition rate than lapponica. Taymyrensis shifted towards food-rich areas, apparently accepting higher predation risks, whereas energy-minimizing lapponica avoided predation danger by foraging further from cover.

Energetic Demands During Incubation and Chick Rearing in a Uniparental and a Biparental Shorebird Breeding in the High Arctic

ABSTRACT.— Rearing of young has long been considered the energetically most demanding phase of the avian breeding cycle. Arctic-breeding shorebirds expend large amounts of energy during breeding. Because they are too small to carry sufficient stores to sit out the incubation period, they regularly interrupt incubation to feed and still can run short of energy, particularly in species in which one adult takes care of the eggs and chicks alone (uniparental). We measured daily energy expenditure (DEE) and time budgets during incubation and chick rearing in the smallest uniparental Arctic shorebird, the Little Stint (Calidris minuta). Daily energy expenditure decreased with increasing temperature but did not differ between the incubation and chick-rearing periods. Because of the increase in potential foraging time from incubation to the chick-rearing phase, the foraging intake rate required to balance the budget dropped by two-thirds. To evaluate the effect of uniparental care on energy budgets, we also measured DEE in the Dunlin (C. alpina), a sympatric congener in which both parents incubate but the female deserts the brood after hatching. Daily energy expenditure decreased with temperature, was the same during incubation and chick rearing, and was higher in males. Our results are discussed in relation to the timing of breeding of Arctic shorebirds with different systems of parental care.