Exploring the patterns of genetic structure in the context of geographical and phenotypic variation is important to understand the evolutionary processes involved in speciation. We investigated population and subspecies differentiation in the Common Ringed Plover Charadrius hiaticula, a high latitude wader that breeds in arctic and temperate zones from northeast Canada across Eurasia to the Russian Far East. Three subspecies, hiaticula, tundrae and psammodromus, are currently widely recognised, whereas a fourth subspecies, kolymensis, has been proposed based on geographic isolation and phenotypic differences. We genotyped 173 samples from eleven Common Ringed Plover breeding sites, representing all four putative subspecies, at eight polymorphic microsatellite loci to examine the patterns of population and subspecies differentiation. Bayesian clustering identified three genetic clusters among samples, corresponding to the breeding sites of the three currently recognised subspecies. The existence of the subspecies kolymensis was not supported. We also detected the presence of a previously unknown hybridisation zone extending from Northern Scandinavia to Belarus. Differentiation of the subspecies tundrae and hiaticula most likely occurred in allopatry on the Eurasian continent during past glaciation events, followed by population expansion leading to colonisation of Iceland and Greenland. The lack of genetic differentiation within the tundrae subspecies is consistent with ongoing range expansion and high gene flow maintained through migratory behaviour. We discuss the importance of historic climate changes, migratory behaviour and mating system on shaping the observed pattern of genetic differentiation.

1. Predators hunting by sight often search for prey from elevated perches or hovering positions above the prey habitat. Theory suggests that prey visibility depends strongly on predator perch height and distance, but their quantitative effects have not been experimentally tested in natural habitats.2. We estimate for the first time how prey visibility depends on predator perch height, distance and vegetation height in an open natural habitat, based on visibility measurements of two targets: a mounted bird and a graduated plate, from five perch heights (0.2-8 m) and six distances (5-120 m).3. For both targets, their proportion visible increases strongly with observer perch height and proximity. From the lowest perch, visibility of the target bird declines to <5% beyond 20 m distance, but 40% of it remains visible from the highest perch even at 120 m.4. Models of predator search suggest that hunting success and predation rate depend strongly on the prey detection rate, which is expected to decline with distance r approximately as r(-d). However, d, the distance decay parameter, has not previously been empirically estimated in natural predator habitats. For distance - prey visibility relationships similar to those observed here, we find a realistic estimate of d to be 2.1-2.4.5. The results demonstrate the crucial role of relative perch and vegetation height for prey visibility, which is of relevance for habitat management. The strong increase of prey visibility with predator search height suggests that removal of predator perches can improve the survival of endangered prey populations in open habitats. Conversely, perch preservation or addition can improve habitat suitability for some predator species where perches are rare or lacking.

Ground-nesting birds have declined world-wide, probably partly due to high nest predation. A non-lethal method for decreasing predation uses protective cages at nests. Tests have mainly looked at the effect of such nest exclosures on hatching success and adult predation, but several additional aspects need to be explored for a comprehensive evaluation of this conservation technique. Here, we test the effect of nest exclosures in two common European shorebirds: northern lapwing (Vanellus vanellus) and redshank (Tringa totanus), measuring hatching success, incubation length, hatching synchrony, hatchability, partial clutch loss, chick condition, and adult predation. In both species, protected nests had higher hatching success than unprotected nests. Taking into account incubation time, nest abandonment, hatchability and partial clutch loss, protected nests still hatched more young than unprotected controls. In lapwings, but not in redshanks, protected nests were incubated longer, but this did not impair the condition of lapwing chicks. Protected redshanks suffered increased predation on incubating adults, which often sit on the nest until a predator is close by. Our results emphasize the need for caution in the use of nest exclosures, particularly in redshanks and other species with similar incubation behaviour. Exclosures can, however, be a useful management tool in shorebirds that leave their nest early, when an approaching predator is still far away.

Coastal pastures and other wet grasslands are important but decreasing breeding habitats for many waders (Charadrii). Since loss of suitable habitat is a major reason for population declines, protection and restoration of these habitats is crucial. Reduction of the often high rate of nest predation is a potentially important tool in future conservation work. Here, we focus on predators’ use of raised structures in the landscape when searching for prey. Hooded crows (Corvus corone cornix) use man-made structures such as stone walls and barbed wire fences when foraging on coastal pastures in SW Sweden. However, few studies have examined wader breeding success in relation to man-made structures, and the extent to which such structures are used by searching nest predators. We measured the spatial distribution and rate of predation on wader nests in relation to such structures. Crows spent more time at or near man-made structures than expected by chance, but we found no significant difference in nest predation relative to distance from man-made structures. However, wader nests were placed farther away from man-made structures than expected by chance in two out of three years. Waders thus tend to avoid breeding close to man-made structures, which therefore reduce the suitable breeding area and probably also the local wader population size.

A common trend in size differences between males and females is a long-standing puzzle. A study of shorebirds shows that the type and strength of competition for mates may explain much of the pattern.

The reasons for conspicuous "V" and other flight formations in birds are debated. Theory and recent empirical advances show that energy saving is one important function of flight formations, but some aspects remain poorly understood. Combining theories of animal flight and sociality, we suggest that some of the variation in flight formations has its base in kin selection and reciprocation. The bird leading an acute V formation saves less energy than does the trailing participants. The disadvantage of leading is reduced in more obtuse formations, and when the longitudinal distance between neighbors is small, the leading bird can save about as much energy as others. Therefore, acute V formations are predicted to occur mainly in circumstances conducive to kin selection or reciprocity. These mechanisms seem possible, for example, in small flocks of adults with offspring, such as in swans, geese, and cranes. Inclusive fitness advantages may then favor an energetically expensive leader role for adults. In small groups, reciprocity is also possible among unrelated adults that recognize each other and take turns leading the V formation. In contrast, obtuse formations are expected in large flocks of unrelated individuals, such as spring flocks of waders migrating long distances. Possibilities for testing these ideas are discussed.

single probe, have been shown to reflect genetic relatedness accurately in the redwinged blackbird (Agelaius phoeniceus). We maintain that our application of this method in testing for differences in the average level of relatedness between groups is justified. We agree with Griffith and Montgomerie that alternative explanations may need to be considered before concluding that mate choice is based on genetic diversity and kin discrimination. But, as we saw a similar pattern in three species with different ecology and social behaviour, we contend that our proposal of adaptive extra-pair copulation with genetically dissimilar mates warrants further testing in these and other species. Donald Blomqvist, Malte Andersson, Clemens Küpper, Innes C. Cuthill, János Kis, Richard B. Lanctot, Brett K. Sandercock, Tamás Székely, Johan Wallander, Bart Kempenaers* *Max Planck Research Centre for Ornithology, PO Box 1564, 82305 Starnberg (Seewiesen), Germany e-mail: b.kempenaers@erl.ornithol.mpg.de

Evolutionary theory predicts adaptive adjustment in offspring sex ratio by females. Seasonal change in sex ratio is one possibility, tested here in two sister species, the Common sandpiper and the Spotted sandpiper Actitis hypoleucos and A. macularia. In the monogamous Common sandpiper, males are the most competitive sex. In each of 3 years, there was a change from mainly sons in early clutches to mainly daughters in late clutches. This seasonal adjustment of clutch sex ratio took place within the female before the eggs were laid, not by differential egg or chick survival. The sex of all eggs laid in the clutches used here was determined molecularly from chick blood taken at the time of hatching. The Spotted sandpiper in contrast is polyandrous, with partly reversed sex roles. There was no seasonal trend from sons to daughters in this species. When tested together, the two species differed significantly as predicted by the hypothesis of adaptive sex ratio adjustment by females.

Parental behavior during incubation is an important aspect of the breeding system, which varies greatly among shorebirds. There are, however, few studies of incubation sex roles in shorebirds during darkness. In Charadrius species, mates are believed to perform most of the incubation during the night. In this study of night- and daytime incubation sex roles in the Common Ringed Plover (Charadrius hiaticula), males tended to do more of the nighttime incubation (58%) than did females; during the day the roles tended to be reversed (males 45%), but the differences were not statistically significant. The reasons why mates of the Common Ringed Plover seem to share nocturnal incubation more equally than do other Charadrius species are not clear but may involve differences in food levels and day length between areas.

Reproductive tactics of ringed plovers Charadrius hiaticula were studied at three localities in SW Sweden during five seasons. The usual clutch size is four, but removal experiments showed that females can produce five eggs in succession, with similar intervals between all eggs. High predation made mean breeding success per clutch low, 6.3% of eggs resulting in fledged young. Replacement clutches were common, and many pairs laid again after rearing their first brood to fledging. Egg laying spanned three months, much longer than for other waders in this region. Between years, reproductive success varied unpredictably with time of the season, but averaged over several years, the expected success was low and similar for the different parts of the breeding season. Chicks from late clutches had similar survival and recruitment as others. Because of the long breeding season and high rate of nest failure a female may produce up to five clutches of four eggs per season, containing in total about 3.7 times her own mass. Yearly local survival of adult females and males was estimated to 84.6 and 88.6%, respectively. Ability to produce many clutches with similar expected success throughout the season favours a long reproductive period, sometimes leading to double‐brooding. Possible life‐history trade‐offs are discussed.

Matings between close relatives often reduce the fitness of offspring, probably because homozygosity leads to the expression of recessive deleterious alleles1,2,3,4,5. Studies of several animals have shown that reproductive success is lower when genetic similarity between parents is high4,5,6,7, and that survival and other measures of fitness increase with individual levels of genetic diversity8,9,10,11. These studies indicate that natural selection may favour the avoidance of matings with genetically similar individuals. But constraints on social mate choice, such as a lack of alternatives, can lead to pairing with genetically similar mates. In such cases, it has been suggested that females may seek extra-pair copulations with less related males4, but the evidence is weak or lacking4,5. Here we report a strong positive relationship between the genetic similarity of social pair members and the occurrence of extra-pair paternity and maternity (‘quasi-parasitism’) in three species of shorebirds. We propose that extra-pair parentage may represent adaptive behavioural strategies to avoid the negative effects of pairing with a genetically similar mate.

Several hypotheses have been raised to explain the upper limit of clutch size at four eggs in waders (suborder Charadrii), which may play an important role in the evolution of the variety of mating and parental care systems in this group. Experimental tests of the hypotheses have produced conflicting results. It was recently suggested that the combined effects of several incubation costs of a larger clutch suffice to limit its size to four eggs in this group. Here we test the incubation-limitation hypothesis in a field experiment, in redshank Tringa totanus. We created five-egg clutches by adding one egg from another nest to a just completed four-egg clutch. Four-egg control clutches were created by replacing one of the eggs by an egg from another nest. All egg removals, additions and replacements were done before incubation started. Incubation time in five-egg clutches increased by 1 day to 24.3±0.23 days, compared to 23.3±0.32 days in four-egg clutches. Egg hatchability and nest predation rates did not differ significantly between treatments. On average five-egg clutches produced one extra chick at hatching (4.5±0.26 chicks) compared to four-egg clutches (3.5±0.27 chicks). Also when several additional costs from incubating enlarged clutches are added, redshanks by laying a fifth egg would on average increase their reproductive success at hatching by an estimated 22%. The incubation-limitation hypothesis therefore is clearly rejected in this species. Possible mechanisms behind the four-egg clutch limit in waders and ways of testing the alternatives are discussed.

Production of successive clutches within the same breeding season has received less attention than many other aspects of avian reproduction. Waders are of particular interest because in these birds, multiple clutches are associated with at least three different breeding systems: double-clutching (uniparental care), monogamous double-brooding (biparental care) and polyandry (uni- or biparental care). Data from eight species and twelve breeding populations suggest that early second clutches, and thus brood overlap, are associated with parental role division and uniparental care, whereas species or populations with biparental care tend to have long intervals between successive clutches. We suggest that ecological factors influencing the relative timing of the second clutch will have consequences for the parental care system. In particular, conditions that favour early laying of the second clutch (large brood overlap) are likely to lead to parental role division, as found in double-clutching species. Factors determining the timing of second clutches are discussed, as are possibilities for testing these ideas.

Among birds, waders (suborder Charadrii) show a remarkable variation in social mating systems. Their genetic mating systems are, however, less well known, especially in socially monogamous species. Here, we use DNA fingerprinting and behavioral studies to examine genetic parentage and male mate guarding in the ringed ploverCharadrius hiaticula, a monogamous wader with biparental care. None of the putative parents was excluded as a genetic parent of the chicks attended (57 young from 21 families). Statistical resampling supported that extra‐pair parentage occurs only rarely, if ever, in the ringed plover. We found no evidence for male mate guarding by close following as a paternity assurance strategy. Lack of extra‐pair paternity in the ringed plover is therefore probably not a consequence of male mate guarding, but of high costs and/or low benefits from extra‐pair copulations for females.

Small-bowel transplantation (SBT) using an nonsuture cuff technique was carried out on 137 rats. Preparation of the donor graft was carried out according to conventional procedures. Graft perfusion was done at a fixed pressure of 35 cm water. The left renal vessels of the recipient were dissected, the native kidney removed, and the graft was connected to the vessels by a nonsuture cuff technique. Of the animals, 92% survived for at least 5 days posttransplant. Three different combinations were investigated: (1) isografts; (2) semisyngeneic grafts from nontreated Lewis----(Lewis x DA) F1 hybrids; and (3) semisyngeneic grafts from rabbit antilymphocyte globulin (ALG)-pretreated Lewis----(Lewis x DA) F1. In group 1, 80% of the grafts were unaffected after 1 month; flow studies showed slight or no impairment of circulation in the graft. In group 2, the recipients developed clinical signs of graft-versus-host disease (GVHD) after 1 week, and at the end of the 2nd week the animals showed signs of severe illness, leading to death due to GVHD. There was also a higher percentage of complications in this group. In group 3, 65% of the animals died. However, 27% showed intact grafts and no signs of GVDH after 1 month, indicating that antibody pretreatment of the donor may successfully prevent GVHD SBT.