THE MIGRATION SYSTEM OF THE CURLEW SANDPIPER CALIDRIS FERRUGINEA IN AFRICA

Elliot, C: C. H., Waltner, M., Underhill. L. G., Pringle, J. S. & Dick, W. J. A. 1976. The migration system of the Curlew Sandpiper Calidris ferruginea in Africa. Ostrich 47:191-213. Data on ringing and recoveries of Curlew Sandpiper, mainly from the Cape, South Africa are presented. Possible migration routes to the breeding grounds are considered in the light of these and other recoveries from the rest of Africa. Retraps show that the species exhibits ortstreue and some evidence is presented which suggests that some birds may travel together and stay in the south in the same flock during one and subsequent migrations. Sex ratio statistics show an excess of females. Adults complete a full primary moult in the Cape between September and February, taking about 140 days but there is a lot of individual variation. Data from Mauritania show primary moult starting faster, a month earlier than in the Cape, and arrested moult in a few adults. The difference may be because Mauritanian birds move on further south while the Cape is the end point of the migration. Kenyan moult records from the Rift Valley follow the Cape pattern except that some birds arrest moult and finish later. Juvenile moult is shown to be different from that of adults, involving only a moult of the outer primaries and taking place during the overwintering period, April to August. All juveniles in the Cape are thought to overwinter and the modified moult to be an adaptation to this behaviour. The weight of adults but not juveniles increases markedly in the six weeks before migration. Fat and protein analyses suggest that the increase is entirely due to deposition of migratory fat. Kenyan birds have lower mean weights and deposit fat about two weeks later than those at the Cape. The nearer the non-breeding quarters are to the breeding grounds, the earlier moult starts and the later fat deposition takes place.     

Primary moult,biometrics, mass and age composition of Grey Plovers Pluvialis squatarola in southeastern India

Little is known about the biology of waders wintering in southern Asia; this paper deals with the Grey Plover Pluvialis squatarola, a species extensively studied only in western Europe. Adult Grey Plovers wintering in southeastern India underwent primary moult in autumn; the duration was estimated to be 127 days, with mean starting date 1 September and mean completion date 5 January. Some first-year Grey Plovers initiated primary moult in late winter and spring, and completed this moult the following spring. The average mass of adults on arrival in September was 200 g, fluctuated close to 220 g from October to February, and increased to 280 g near the end of May. The mass variation did not show the January peak observed in western Europe. Breeding productivity, measured as the percentage of first-year birds in winter catches, varied between 5% and 70% over six years, and showed a positive correlation with that of Dark-bellied Brent Geese Branta b. bernicla in western Europe and Curlew Sandpipers Calidris ferruginea in South Africa.     

Age‐specific variation in relationship between moult and pre‐migratory fuelling in Wood Sandpipers Tringa glareola in southern Africa

Trans‐equatorial avian migrants tend to breed, moult and migrate – the main energy‐requiring events in their lifecycle – at different times. Little is known about the relationship between wing moult and pre‐migratory fuelling in waders on their non‐breeding grounds, where time is less constrained than during their brief high‐latitude breeding season. We determined age‐related strategies of Wood Sandpipers Tringa glareola to balance the energetic demands of primary moult against pre‐migratory fuelling in southern Africa by analysing body mass and primary moult at first capture of 1721 birds mist‐netted in 1972–96 at waterbodies in Zimbabwe. Adults moulted all their primaries in August–December, but immatures underwent a supplemental moult of varying numbers of outer primaries in December–April, close to departure. We used locally weighted linear regression to estimate trends in Wood Sandpiper body mass from 1 July to 1 May. They maintained low mass from arrival in July–September to February–early March. Adults fuelled from 10 February to 1 May at a mean rate of 0.25 g/day (sd = 0.16). Most adults (98%) began fuelling 10–75 days after completing primary moult. Immatures fuelled from 4 March to 13 April at 0.24 g/day (sd = 0.14). They used varying strategies depending on their condition: a brief gap between moult and fuelling; an overlap of these processes near departure, leading to slower fuelling; or skipping fuelling altogether and staying in southern Africa for a ‘gap year’. Immatures moulting three or five outer primaries fuelled more slowly than post‐moult birds. Immatures moulting four outer primaries started fuelling 3 weeks later but at a higher rate than did post‐moult birds of this group. In post‐moult immatures, the later they ended moult, the later and faster they fuelled. The heaviest adults and immatures using all moult patterns accumulated fuel loads of c. 50% of lean body mass, and could potentially cross 2397–4490 km to reach the Great Rift Valley in one non‐stop flight. Immatures were more flexible in the timing and extent of moult and in the timing and rate of fuelling than adults. This flexibility enables inexperienced Wood Sandpipers to cope with inter‐annual differences in feeding conditions at Africa's ephemeral inland waterbodies.     

Primary moult of continental Black-tailed Godwits Limosa limosa limosa in the Doñana wetlands,Spain

Capsule: Most Continental Black-tailed Godwits Limosa limosa limosa using the Doñana wetlands during post-breeding migration appear to begin moult before they arrive and suspend moult before they migrate onwards to West Africa.

Aims: We aim to describe the primary moult strategies and patterns in the Continental Black-tailed Godwits using the Doñana wetlands, a major passage and wintering area for waterbirds in southern Spain.

Methods: Individual godwits were captured, marked and their primary moult was scored in Doñana during the non-breeding season (June–March) in 2011 and 2012. Data from resightings of colour-marked godwits and birds equipped with satellite transmitters were used to estimate stopover duration during post-breeding migration (June–September) to determine if godwits move to West Africa before completing their primary moult.

Results: Average primary moult duration was estimated to be 84 days?±?9 se, during 29 June–21 September and did not differ between sexes. Only 2% of individuals were observed with suspended moult. We estimated stopover duration in Doñana to be 13 days?±?2 se before migrating to West Africa.

Conclusions: Most godwits stage for about two weeks in the Doñana wetlands during southward migration, moult their primaries and appear to suspend moult before crossing the Sahara. Others may complete their primary moult in Doñana, or elsewhere in Europe and overwinter in Doñana where increasing numbers of godwits have been detected in recent years. A few individuals may finish the moult in Doñana and migrate to West Africa late in the post-breeding season.     

Age and environment affect constitutive immune function in Red Knots (Calidris canutus)

We studied subspecies, age and environmental effects on constitutive immune function (natural antibody and complement titres, haptoglobin activity and leukocyte concentrations) in Red Knots (Calidris canutus). We compared C. c. islandica and C. c. canutus in the Wadden Sea and found no difference in immune function between subspecies. However, C. c. canutus on their wintering grounds in Banc d’Arguin had higher natural antibody and lower complement levels than C. c. canutus or C. c. islandica in the Wadden Sea. This suggests that immune function is determined more by the surrounding environment than by subspecies. We also compared age classes in the Wadden Sea and found that first year birds had significantly lower natural antibody levels than adults, but that second year birds no longer differed from adults. Finally, we examined the interaction of age and environment in Banc d’Arguin. We found that first year birds (but not adults) in a low quality habitat had higher leukocyte concentrations than first year birds or adults in a high quality habitat. Differences in available resources and defence needs between environments, and differences among individuals differentially distributed between sites, are likely important contributors to the variation in immune function we report. Future studies, which examine these factors on wild birds, will be important for our understanding of how animals function in their natural environment. (220).     

Sex‐specific patterns of fuelling and pre‐breeding body moult of Little Stints Calidris minuta in South Africa

The timing and duration of each stage of the life of a long‐distance migrant bird are constrained by time and resources. If the parental roles of males and females differ, the timing of other life stages, such as moult or pre‐migratory fuelling, may also differ between the sexes. Little is known about sexual differences for species with weak sexual dimorphism, but DNA‐sexing enables fresh insights. The Little Stint Calidris minuta is a monomorphic long‐distance migrant wader breeding in the Arctic tundra. Males compete for territories and perform elaborate aerial displays. Females produce two clutches a season. Each sex may be a bigamist and incubate one nest a season, each with a different partner. We expect that these differences in breeding behaviour entail different preparations for breeding by males and females, so we aimed to determine whether Little Stints showed any sex differences in their strategies for pre‐breeding moult and pre‐migratory fuelling at their non‐breeding grounds in South Africa. We used body moult records, wing length and body mass of 241 DNA‐sexed Little Stints that we caught and ringed between 27 January and 29 April in 2008–2018 at two neighbouring wetlands in North West Province, South Africa. For each individual we assessed the percentage of breeding plumage on its upperparts and took blood samples for DNA‐sexing. We calculated an adjusted Body Moult Index and an adjusted Wing Coverts Moult Index, then used the Underhill–Zucchini moult model to estimate the start dates and the rate of body moult in males and females. We estimated the changes in the sex ratio of the local population during their stay in South Africa, and also estimated the timing and rate of pre‐migratory fuelling and the potential flight ranges for males and females. The males started body moult on average on 7 February and the females on 12 February, but the sexes did not differ in their timing of wing covert moult, which started on average on 10 February. In January to mid‐February, males constituted c. 57% of the population, but their proportion declined afterwards, indicating an earlier departure than females. We estimated that both sexes began pre‐migratory fuelling on average on 15 March. The sexes did not differ in fuelling rate, but most females stayed at the non‐breeding site longer than the males, and thus accumulated more fuel and had longer potential flight ranges. These patterns of moult and fuelling suggest sex differences in preparations for breeding. We suggest that the males depart from South Africa earlier but with smaller fuel loads than the females to establish breeding territories before the females arrive. We conclude that for each sex the observed trade‐offs between fuelling and moult at the non‐breeding grounds are precursors to different migration strategies, which in turn are adaptations for their different roles in reproductive behaviour.     

Contrasting strategies for wing‐moult and pre‐migratory fuelling in western and eastern populations of Common Whitethroat Sylvia communis

Trade‐offs between moult and fuelling in migrant birds vary with migration distance and the environmental conditions they encounter. We compared wing moult and fuelling at the northern and southern ends of migration in two populations of adult Common Whitethroats Sylvia communis. The western population moults most remiges at the breeding grounds in Europe (e.g. Poland) and migrates 4000–5000 km to western Africa (e.g. Nigeria). The eastern population moults all remiges at the non‐breeding grounds and migrates 7000–10 000 km from western Asia (e.g. southwestern Siberia) to eastern and southern Africa. We tested the hypotheses that: (1) Whitethroats moult their wing feathers slowly in South Africa, where they face fewer time constraints than in Poland, and (2) fuelling is slower when it coincides with moulting (Poland, South Africa) than when it occurs alone (Siberia, Nigeria). We estimated moult timing of primaries, secondaries and tertials from moult records of Polish and South African Whitethroats ringed in 1987–2017 and determined fuelling patterns from the body mass of Whitethroats ringed in all four regions. The western population moulted wing feathers in Poland over 55 days (2 July–26 August) at a varying rate, up to 13 feathers simultaneously, but fuelled slowly until departure in August–mid‐September. In Nigeria, during the drier period of mid‐February–March they fuelled slowly, but the fuelling rate increased three‐fold in April–May after the rains before mid‐April–May departure. The eastern population did not moult in Siberia but fuelled three times faster before mid‐July–early August departure than did the western birds moulting in Poland. In South Africa, the Whitethroats moulted over 57 days (2 January–28 February) at a constant rate of up to nine feathers simultaneously and fuelled slowly from mid‐December until mid‐April–May departure. These results suggest the two populations use contrasting strategies to capitalize on food supplies before departure from breeding and non‐breeding grounds.     

DISTRIBUTION AND NUMBERS OF COASTAL WADERS (CHARADRII) IN THE SOUTHWESTERN CAPE,SOUTH AFRICA,SUMMER 1975–76

Summers, R. W., Cooper, J. & Pringle, J. S. 1970. Distribution and numbers of coastal waders (Charadrii) in the southwestern Cape, South Africa, summer 1975–76. Ostrich 48: 85–97. A survey of the distribution and numbers of waders (suborder Charadrii) in the coastal regions of the southwestern Cape was conducted from November 1975 to February 1976. Forty-four coastal wetlands and 49 sections of coastline were visited between the Olifants and Groot-Brak rivers. The estimated total wader population was 119 008 of which 102 841 (86,4%) were Palaearctic migrants. Langebaan Lagoon and the Berg estuary supported the largest numbers. The Curlew Sandpiper Calidris ferruginea and Sanderling Calidris alba were the most numerous species. The abundance of waders was greater on west coast shores than along the south coast.     

Seasonality in basal metabolic rate and thermal conductance in a long-distance migrant shorebird,the knot (Calidris canutus)

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three islandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.     

Rapid or slow moult? The choice of a primary moult strategy by immature Wood Sandpipers Tringa glareola in southern Africa

Immature migrant waders have more complex patterns of primary moult than adults, but these have been described only fragmentarily. The Wood Sandpiper Tringa glareola breeds in the taiga region of the Palearctic and part of the population migrates to southern Africa. We selected this population for a study of the primary moult strategies of an immature wader. After analysing the moult formulae of 674 immatures, we discuss potential factors that influence the choice of moult strategy. All moulters replaced two to six outer primaries; 91% moulted four or five. We used the Underhill–Zucchini model to estimate the timing and duration of moult in immatures replacing different numbers of primaries. A slow moult of five or six primaries, adopted by 29%, lasted on average 98–111 days, beginning on average 8–16 December. Moult of four primaries (63%) began on 6 January and averaged 73 days. A rapid moult of three primaries (7%) began on 24 January and averaged 55 days. All groups ended their moult between 19 and 28 March. GLM models showed that heavier immatures were more likely to start moulting than leaner birds. This tendency was more pronounced in November–January than in later months. The later the moult started, the fewer feathers were replaced and the faster the process. Departure time set the limit for the end of moult. We suggest the ability to choose different strategies allows immature Wood Sandpipers to adjust their moult to the variable conditions they encounter at wetlands in southern Africa.     

Sociable Weaver biometrics and primary moult

The biometric and primary moult data housed at the South African Bird Ringing Unit (SAFRING) were analysed for the Sociable Weaver Philetairus socius. The average body mass and wing length was 27.9g (SD = 2.2) and 74.1mm (SD = 2.5), respectively. Variation in these parameters is not clearly correlated with region, season or climate, other than a negative correlation of body mass with average annual water deficiency. Body mass of Sociable Weavers near Kimberley showed a longterm decrease of 2.9g, probably due to stabilising selection on mass. Primary moult duration varied from 152 days to 169 days and started between 26 January and 31 December in two populations (socius and South African eremnus respectively). Individual primaries moulted mainly one at a time, each taking 20–28 days to grow fully. Prolonged moult duration in this species is probably an adaptation to reduce energy expenditure, and to grow more durable feathers due to abrasion in entering the nest. The lack of clear patterns of geographical variation in biometrics indicates that the contiguous populations of Sociable Weaver should belong to the nominate species. The biometric and primary moult data housed at the South African Bird Ringing Unit (SAFRING) were analysed for the Sociable Weaver Philetairus socius. The average body mass and wing length was 27.9g (SD = 2.2) and 74.1mm (SD = 2.5), respectively. Variation in these parameters is not clearly correlated with region, season or climate, other than a negative correlation of body mass with average annual water deficiency. Body mass of Sociable Weavers near Kimberley showed a longterm decrease of 2.9g, probably due to stabilising selection on mass. Primary moult duration varied from 152 days to 169 days and started between 26 January and 31 December in two populations (socius and South African eremnus respectively). Individual primaries moulted mainly one at a time, each taking 20–28 days to grow fully. Prolonged moult duration in this species is probably an adaptation to reduce energy expenditure, and to grow more durable feathers due to abrasion in entering the nest. The lack of clear patterns of geographical variation in biometrics indicates that the contiguous populations of Sociable Weaver should belong to the nominate species.     

Duration of primary moult affects primary quality in Grey Plovers Pluvialis squatarola

Feather wear is the natural degradation and breakage of feather structure during the interval between moults. Different rates of feather wear have been observed for primaries of free-living populations of several species of passerines and waders, and this variability has been linked to different concentrations of melanins. In this study primary moult duration explained 59% of the variation in annual rates of primary abrasion (percentage wing length loss) of seven Grey Plover wintering populations, while migration distance explained 14%. The analysis suggests that primary moult duration plays a key role in determining primary durability and hence primary quality. Long distance migrants might evolve more durable primaries, despite the higher predation risks and energetic costs of a prolonged moult. Partial or complete pre-breeding primary moults of first-year waders and complete biannual moults of some passerines might have evolved under selective forces favouring migration with unabraded primaries.     

Variability in the area,energy and time costs of wintering waders responding to disturbance

Birds’ responses to human disturbance are interesting due to their similarities to anti‐predator behaviour, and understanding this behaviour has practical applications for conservation management by informing measures such as buffer zones to protect priority species. To understand better the costs of disturbance and whether it will impact on population size, studies should quantify time‐related responses as well as the more commonly reported flight initiation distance (FID). Using waders wintering on an estuarine area, we experimentally disturbed foraging birds on the Wash Embayment, UK, by walking towards them and recording their responses (FID, alert time, time spent in flight, time taken to resume feeding, and total feeding time lost). We present data for 10 species of conservation concern: Curlew Numenius arquata, Oystercatcher Haematopus ostralegus, Bar‐tailed Godwit Limosa lapponica, Grey Plover Pluvialis squatarola, Redshank Tringa totanus, Knot Calidris canutus, Turnstone Arenaria interpres, Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Dunlin Calidris alpina. Larger species responded more strongly, response magnitude was greater under milder environmental conditions, and responses varied over both small and large spatial scales. The energetic costs of individual responses, however, were low relative to daily requirements and disturbance events were unlikely to be frequent enough to seriously limit foraging time. We suggest, therefore, that wintering wader populations on the Wash are not currently significantly negatively impacted by human disturbance during the intertidal foraging period. This is also likely to be the case at other estuarine sites with comparable access levels, visitor patterns, invertebrate food availability and environmental conditions.     

NOTICES

Schmitt, M. B., Baur, S. &; Von Malitz, F. 1980. Observations on the Steppe Buzzard in the Transvaal: Ostrich 51:151-159.

During a three year study 247 Steppe Buzzards Buteo buteo vulpinus were captured in the Transvaal, South Africa. Density, mensural data and moult are discussed and compared with findings from the Cape Province. Linear density is 7,3 times lower in the Transvaal as compared with the Cape. Identification criteria for second-year birds are given. Second-year birds moult primaries descendently and symmetrically, secondary moult is mainly ascendent and symmetrical, tail moult irregular but symmetrical. Adult birds moult irregularly. Recorded food items are listed.     

Travelling on a budget: predictions and ecological evidence for bottlenecks in the annual cycle of long-distance migrants

Long-distance migration, and the study of the migrants who undertake these journeys, has fascinated generations of biologists. However, many aspects of the annual cycles of these migrants remain a mystery as do many of the driving forces behind the evolution and maintenance of the migrations themselves. In this article we discuss nutritional, energetic, temporal and disease-risk bottlenecks in the annual cycle of long-distance migrants, taking a sandpiper, the red knot Calidris canutus, as a focal species. Red knots have six recognized subspecies each with different migratory routes, well-known patterns of connectivity and contrasting annual cycles. The diversity of red knot annual cycles allows us to discuss the existence and the effects of bottlenecks in a comparative framework. We examine the evidence for bottlenecks focusing on the quality of breeding plumage and the timing of moult as indicators in the six subspecies. In terms of breeding plumage coloration, quality and timing of prealternate body moult (from non-breeding into breeding plumage), the longest migrating knot subspecies, Calidris canutus rogersi and Calidris canutus rufa, show the greatest impact of bottlenecking. The same is true in terms of prebasic body moult (from breeding into non-breeding plumage) which in case of both C. c. rogersi and C. c. rufa overlaps with southward migration and may even commence in the breeding grounds. To close our discussion of bottlenecks in long-distance migrants, we make predictions about how migrants might be impacted via physiological 'trade-offs' throughout the annual cycle, using investment in immune function as an example. We also predict how bottlenecks may affect the distribution of mortality throughout the annual cycle. We hope that this framework will be applicable to other species and types of migrants, thus expanding the comparative database for the future evaluation of seasonal selection pressures and the evolution of annual cycles in long-distance migrants. Furthermore, we hope that this synthesis of recent advancements in the knowledge of red knot annual cycles will prove useful in the ongoing attempts to model annual cycles in migratory birds.     

Unravelling the migration and moult strategies of a long-distance migrant using stable isotopes: Red Knot Calidris canutus movements in the Americas

For long‐distance migrants, such as many of the shorebirds, understanding the demographic implications of behavioural strategies adopted by individuals is key to understanding how environmental change will affect populations. Stable isotopes have been used in the terrestrial environment to infer migratory strategies of birds but rarely in marine or estuarine systems. Here, we show that the stable isotope ratios of carbon and nitrogen in flight feathers can be used to identify at least three discrete wintering areas of the Red Knot Calidris canutus on the eastern seaboard of the Americas, ranging from southeastern USA to Patagonia and Tierra del Fuego. In spring, birds migrate northwards via Delaware Bay, in the northeastern USA, the last stopping point before arrival in Arctic breeding areas, where they fatten up on eggs of spawning Horseshoe Crabs Limulus polyphemus. The isotope ratios of feather samples taken from birds caught in the Bay during May 2003 were compared with feathers obtained from known wintering areas in Florida (USA), Bahia Lomas (Chile) and Rio Grande (Argentina). In May 2003, 30% of birds passing through the Bay had Florida‐type ‘signatures’, 58% were Bahia Lomas‐type, 6% were Rio Grande‐type and 7% were unclassified. Some of the southern wintering birds had started moulting flight feathers in northern areas, suspended this, and then finished their moult in the wintering areas, whereas others flew straight to the wintering areas before commencing moult. This study shows that stable isotopes can be used to infer migratory strategies of coastal‐feeding shorebirds and provides the basis for identifying the moult strategy and wintering areas of birds passing through Delaware Bay. Coupled with banding and marking birds as individuals, stable isotopes provide a powerful tool for estimating population‐specific demographic parameters and, in this case, further our understanding of the migration systems of the declining Nearctic populations of Red Knot.     

The ‘chaotic’ flight feather moult of the Steppe Buzzard Buteo buteo vulpinus

Steppe Buzzards breed in Eurasia and spend the non-breeding season in Africa. Adults moult some flight feathers during the breeding season and some during the non-breeding season. Moult is arrested during migration. The extent of moult of flight feathers in adults is highly variable between individuals in southern Africa, with the renewal of two primaries, three secondaries and five rectrices as the most frequently encountered pattern. Time spent on the non-breeding grounds in South Africa is too short to allow for a sequential moult. Moult of flight feathers is restricted to the almost synchronous dropping of a number of feathers upon arrival, with few being replaced subsequently. Any of the flight feathers can be replaced in southern Africa, and the pattern of renewal in primaries and secondaries cannot be distinguished from random. Tail feathers are replaced in an alternating (transilient) pattern. Moult in the non-breeding areas may primarily be complementary to moult on the breeding grounds, but these two partial moults per year are insufficient to renew all flight feathers annually. Middle secondaries and central tail feathers are regularly carried over to a third moult, but this is rare for primaries.     

WADER POPULATIONS (CHARADRII) OF THE MARINE LITTORAL OF THE CAPE PENINSULA,SOUTH AFRICA

Pringle, J. S. & Cooper, J. 1977. Wader populations (Charadrii) of the marine littoral of the Cape Peninsula, South Africa. Ostrich 48: 98–105.

Waders (Charadrii) were counted regularly on two stretches of coastline, totalling 5,6 km, on the Cape Peninsula from January 1975 to July 1976. Eight Palaearctic species and seven indigenous species were observed. Arrival of migrants extended from mid-August to January. Autumn departure of Curlew Sandpipers Calidris ferruginea occurred approximately six weeks before departure of Sanderlings C. albu. No overwintering populations of migrant waders were observed. Information is presented which suggests that overwintering Turnstones Arenaria interpres, but not Sanderlings, Maycongregate at a sheltered coastal wetland. Observations of marked birds suggest that individual Sanderlings regularly use particular feeding localities. Populations of indigenous waders showed little seasonal variation in numbers, Flocking was observed in winter.     

1. BIRD-LIFE AT THE ORANGE RIVER MOUTH

Kalejta, B. 1993. Diets of shorebirds at the Berg River estuary, South Africa: spatial and temporal variation. Ostrich 64: 123–133.

The diets of three common migrant waders; Curlew Sandpiper Calidris ferruginea. Grey Plover Pluvialis-squatarola and Greenshank Tringa nebularia and three resident species, Blacksmith Vanellus armatus, Kittlitz's Charadrius pecuarius and Whitefronted Plovers C. marginatus, were studied at the Berg River estuary, South Africa from December 1987 to April 1989. Direct observations of feeding were combined with analyses of stomach contents, pellets and droppings. Nereid worms, Ceratonereis erythraeensis and C. keiskama, were the principal food of all species studied except Greenshanks, which fed mostly on crabs, Hymenosoma orbiculare. Despite considerable overlap in the diets of all bird species, there were differences in the size classes of nereids taken by different bird species. Visually-foraging plovers (Charadriidae) were highly selective, feeding on the largest nereids regardless of their abundance. Tactile foragers, represented by Curlew Sandpipers, were non-selective, and consumed different size-classes of worms in proportion to their abundance in the substratum. Seasonal variations in the diet of waders are linked to seasonal changes in the availability of prey species.     

Inferring the ecology of willow warblers during their winter moult by sequential stable isotope analyses of remiges

We present a comparison of feather stable isotope (δ¹³C, δ¹⁵N) patterns representing the habitat and diet conditions for two subspecies of willow warblers Phylloscopus trochilus that breed in parapatry, but winter in different regions of sub‐Saharan Africa. Previous analyses have shown that on average winter moulted innermost primaries (P1) show subspecific differences in δ¹⁵N values, although individuals show substantial variation for both δ¹³C and δ¹⁵N within the subspecies. We examined whether corresponding variation in the timing of the winter moult, as reflected by consistent intra‐wing correlations for individual's δ¹³C and δ¹⁵N values, could explain some of the previously observed isotopic variation. Further, differential subspecific adaptations to winter precipitation patterns across Africa might result in a variable degree of site fidelity or itinerancy during moult. We found no consistent trend in isotopic values from innermost to outermost primaries, thus inter‐individual variation in the timing of moult does not explain the subspecific isotopic variation for P1. Patterns in wing feather δ¹³C and δ¹⁵N values indicated that 41% of the individuals from both subspecies shifted their diet or habitats during winter moult. Importantly, despite well‐documented itinerancy in willow warblers during the winter, 59% of the individuals had feather isotope values consistent with stable use of habitats or diets during winter moult. Repeatability analyses suggest that individuals of both subspecies initiate moult in similar habitats from year‐to‐year while feeding on isotopically similar diets.