R. W. Summers

Three-year cycles in breeding productivity of Knots Calidris canutus wintering in southern Africa suggest Taimyr Peninsula provenance

Annual breeding productivity of Knots Calidris canutus was estimated by the proportion of first-year birds in winter ringing samples. Significant associations were found between the productivity of Knots, other species that are known to breed on the Taimyr Peninsula, and lemming abundance in that region. It is inferred from this that Knots wintering in southern Africa are of the Russian subspecies canutus unlike British wintering birds which do not show these correlations and are subspecies islandica.

Methods for estimating the proportions of Icelandic and British Redshanks Tringa totanus in mixed populations wintering on British coasts

Both British and Icelandic Redshanks may be found in Britain in the nonbreeding season. They are indistinguishable, though their average measurements differ. Samples of breeding Redshanks were caught in Iceland and Britain to collect biometric information to he used to estimate the proportions of Icelandic and British Redshanks in mixed winter populations. Wing, bill and foot were the only structures whose lengths were significantly different between the 2 populations and which could be measured with reasonable precision. Two methods were used to estimate the proportions in mixed samples: discriminant analysis and a maximum likelihood analysis of Mixtures of Normal distributions. A simple graphical method based on the discriminant analysis was devised. The methods resulted in similar estimates of the proportions of Icelandic Redshanks when used on mixed samples. Estimates from captured samples in eastern Scotland indicated that there is an equal mix of Icelandic and British Redshanks in autumn, but that a...

Habitat preferences of waders (Charadrii) on the coast of the Orkney Islands

Capsule Twelve species of wader were surveyed on 494 coastal sections, revealing features in addition to substratum type that are important in habitat selection. Aims To determine which habitat characteristics affect the probability of waders occurring on coastal sections of Orkney in winter, and to measure the strength of these habitat preferences. Methods A total of 494 sections of shoreline in the Orkney Islands were surveyed for 12 species of wader in winters 1982/3 and 1983/4. A series of environmental variables (exposure, substratum type within the inter-tidal zone, shore width and steepness) were noted in the field and taken from maps. Logistic regression models were used to examine the probability of a given species occurring on a section, with given physical characteristics. Results Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Bar-tailed Godwit Limosa lap-ponica preferred sand shores; Lapwing Vanellus vanellus, Snipe Gallinago gallinago, Redshank Tringa totanus, Curlew Numenius arquata and Dunlin Calidris alpina preferred mud; Oystercatcher Haematopus ostralegus, Golden Plover Pluvialis apricaria and Purple Sandpiper Calidris maritima preferred rock; and Turnstone Arenaria interpres preferred gravel and rock shores. The strength of a preference for substratum type was greatest in Sanderling, Bar-tailed Godwit, Lapwing and Purple Sandpiper, and least in Oystercatcher, Curlew, Golden Plover and Turnstone. Some species displayed additional preferences for exposed shores (Purple Sandpiper, Ringed Plover and Bar-tailed Godwit), sheltered shores (Curlew and Redshank) and wide shores (Sanderling, Purple Sandpiper, Dunlin, Bar-tailed Godwit and Turnstone). No species preferred steep shores or cliffs. Conclusions Simple habitat descriptions coupled with map-derived variables, can provide an initial insight into the habitat preferences of waders. Further work relating wader distribution to invertebrate food supplies is required.

The dispersion of red knots Calidris canutus in Africa—is southern Africa a buffer for West Africa?

The Siberian subspecies of the red knot Calidris canutus canutus spends the non-breeding season largely in West Africa (Mauritania and Guinea Bissau), where approximately half a million occurred in the 1980s. It was a rarely seen in southern Africa in the early part of the 20th century, but there were about 12 500 in the 1970s and 1980s. The main sites were Langebaan Lagoon, Berg River Estuary, Olifants River Estuary (South Africa) and Walvis Bay Lagoon (Namibia). There was a decline in the number of red knots at Langebaan Lagoon in the 1990s, to around 20% of the number that occurred there in the 1980s. Numbers remained low in the 2000s. In addition, the percentage that remained during the austral winter (the breeding season in the Arctic) declined, and there was none during the period 2001–2009. This suggested that first-year birds, which largely comprise the austral winter population, were no longer travelling to southern Africa. The decline in numbers coincided with the decline in West Africa, but it was disproportionately larger in southern Africa. The observed pattern of change is consistent with a buffer effect, whereby southern Africa represents an extension to the range to less suitable habitat (requiring a 6 000 km extension to the migration) when the population size and competition is high in the main localities in West Africa. We are probably now witnessing the gradual decline in the number of adult birds who are fixed in their use of southern Africa as their non-breeding quarters.