REMARKS ON THE DISTRIBUTION OF BIRDS COLLECTED IN MASHONALAND AND EASTERN SOUTHERN RHODESIA (Part I)

Oatley, T. B. 1983. Twenty-third ringing report for southern Africa. Ostrich. 54:141-149.

Bird ringing activities in southern Africa are summarized for a two-year period from July 1979 to June 1981. A total of 42 374 birds were ringed. Much ringing effort was devoted to marine buds. Palaearctic migrants comprised nearly 12% of the birds ringed, with waders, swallows and warblers being the most frequently ringed families. There were 747 recoveries or recaptures reported during the reviey period, of which 73 were foreign-ringed birds. The remainder involved 103 species of birds, only nine of which contributed 10 or more recoveries to the total. Five of the nine are marine birds and collectively account for 55% of all recoveries and recaptures. A selected list of recoveries and recaptures of southern African-ringed birds is given.     

Migration of red‐backed shrikes from the Iberian Peninsula: optimal or sub‐optimal detour?

The current Northern Hemisphere migration systems are believed to have arisen since the last glaciation. In many cases, birds do not migrate strait from breeding to non‐breeding areas but fly via a detour. All western European populations of red‐backed shrikes Lanius collurio are assumed to reach their southern African wintering grounds detouring via southeast Europe. Based on theoretical considerations under an optimality framework this detour is apparently optimal. Here, we use individual geolocator data on red‐backed shrikes breeding in Spain to show that these birds do indeed detour via southeast Europe en route to southern Africa where they join other European populations of red‐backed shrikes and return via a similar route in spring. Disregarding potential wind assistance, the routes taken for the tracked birds in autumn were not optimal compared to crossing the barrier directly. For spring migration the situation was quite different with the detour apparently being optimal. However, when considering potential wind assistance estimated total air distances during autumn migration were overall similar and the barrier crossing shorter along the observed routes. We conclude that considering the potential benefit of wind assistance makes the route via southeast Europe likely to be less risky in autumn. However, it cannot be ruled out that other factors, such as following a historical colonisation route could still be important.     

THE SEASONAL MOVEMENTS OF GURNEY'S SUGARBIRD PROMEROPS GURNEYI IN THE LYDENBURG AREA,TRANSVAAL

De Swardt, D. H. 1991. The seasonal movements of Gurney's Sugarbird Promerops gurneyi in the Ly-denburg area, Transvaal. Ostrich 62: 40–44.

The seasonal movements of Gurney's Sugarbird Promerops gurneyi were studied in the Lydenburg area, eastern Transvaal, South Africa. Influx into the suburban habitat occurred durin the winter when the birds left the mountains at the end of the flowering period of Protea roupelliae. Birifs were mistnetted and each adult colour-ringed with a unique combination for individual recognition. In all, 256 Sugarbirds were ed in the mountain habitat and 50 in the suburban habitat. Of the unringed individuals 22,2 % were ted on cliffs with aloes and 79,3 % around P. roupelliae clumps late in the season. Of the ringed birds 25 (9,7%) were retrapped at sites in the mountain and 10 (3.9%) showed seasonal movements; 6 (8,3%) were recaptured in the same town localities where originally ringed. Mean distance moved was 7 km. An overall recapture rate of 7,5% was recorded during this study. When nectar became scarce the birds started moving away and utilized other food sources. Protea roupelliae showed a flowering peak from October to February which coincided with the sugarbirds' breeding season.     

THE SOUTHWARD MIGRATION OF PALAEARCTIC BIRDS OVER NGULIA, KENYA

Since 1969 remarkable numbers of night migrants have been attracted during misty conditions in November and December to three 1 kW floodlights at a game viewing lodge on the northeastern side of the Ngulia ridge, a small range of hills in the Tsavo National Park (West), southeast Kenya. The main species involved have been Palaearctic passerines, principally the Marsh Warbler Acrocephalus palustris, the Whitethroat Sylvia communis and the Sprosser Luscinia luscinia. Data were collected at the Lodge in the late autumns of 1969–71, and in particular between November 1972 and early January 1973, when over 2500 Palaearctic passerines were caught and ringed. Large falls have depended on mist or rain during the latter part of the night, at any time during the month except around full moon. Highest numbers have occurred in late November and the first half of December. In 1973 falls continued into the second week of January. Grounded birds move on quickly, extremely few having been retrapped. During 1972–73, the species prominent in falls at the Lodge were abundant as transit migrants in Tsavo only from mid-December to early or mid January, at which time retrap rates were highest. The high weights and considerable fat deposits of many birds caught suggested they were grounded some distance north of their destination. Forty-two migrants analysed had a mean lipid content of 12·9% of their live weight; none was appreciably dehydrated. In 1972–73, highest weights were found at the beginning and end of the season. Individual species are discussed, and in several cases their African status reviewed. Several species were encountered at Ngulia in numbers far larger than those previously reported from elsewhere in Africa. In 1972–73, for instance, over 1000 Marsh Warblers were caught and many thousands of others seen, hundreds of River Warblers Locustella fluviatilis occurred, and White-throated Robins Irania gutturalis, Basra Reed Warblers Acrocephalus griseldis, Rufous Bush Chats Cercotrichas galactotes and Olive-tree Warblers Hippolais olivetorum were caught regularly. Most of the Basra Reed Warblers, Upcher's Warblers Hippolais languida and Olivaceous Warblers H. pallida, and many of the Whitethroats (apparently all of the eastern race icterops) handled during late December and early January were in fresh plumage, although these species are not known to moult north of the Sahara. They are presumed to have renewed their plumage in northeast Africa earlier in the autumn. In many Basra Reed Warblers and Whitethroats moult was only partly completed; in almost all such cases it was arrested. Itinerancy south of the Sahara is discussed. It seems clearly established that a regular southward migration, in the usually accepted sense of the word, occurs across Tsavo, of Palaearctic species which have already been in tropical Africa up to three months. Most species involved in this migration cross the equator on a remarkably narrow front, and are rarely recorded in Kenya west of Nairobi.     

ASPECTS OF THE POPULATION DYNAMICS OF CAPE VULTURES IN THE CAPE PROVINCE

Robertson, A. S. 1984. Aspects of the population dynamics of Cape Vultures in the Cape Province. Ostrich 55: 196–206.

Information gathered in 1981 and 1982 and collated from previous records on the numbers, spatial distribution, proportion of age classes, age and frequency of breeding, breeding success and causes of breeding failure, and the survival of immature and adult Cape Vultures Gyps coprotheres in the southern and southwestern areas of the Cape Province, South Africa, is presented. This sub-population of about 75 birds is apparently isolated from conspecifics in the rest of southern Africa; the implications of this are discussed. At the Potberg colony in both years an average of 85% of birds 5 years and older were involved in breeding attempts. The age of first breeding was 4–6 years. Nest sites were active for about two in every three years. Between 1975 and 1982, 0,51-0,67 nestlings were reared per active nest site (n=165). Four (possible maximum six) of 21 immatures were resighted one year after they had flown. Of 123 birds that had been ringed at Potberg to 1980, 14 (11%) were sighted in 1981; only four of 48(8%) colour-ringed birds 5 years old and older were breeding in 1981.     

TERMS,STUDIES AND EXPERIMENTS ON THE PROBLEMS OF BIRD DISPERSION*

A terminology of the dispersion of birds, and of the ways in which it comes about, is proposed and explained. An examination of recoveries of ringed female Pied Flycatchers Ficedula hypoleuca show that many first breed a considerable distance from their birthplace, in contrast to the situation in the Blue Tit Parus caeruleus and Nuthatch Sitta europaea. The degree of such dispersion in these species, and presumably therefore the gene flow, is inversely correlated with the number of geographical races they contain. Results of experiments designed to investigate the types of dispersion mechanism occurring in F. hypoleuca indicate that both “dispersal” and “spacing” occur in birds of all ages, and that they are usually not oriented, but that the spacing of older birds which have not been constantly faithful to place usually leads to a previously known place.     

Determining the boundaries of migratory bird flyways: a Bayesian model for Eurasian teal Anas crecca in western Europe

Accurate flyway delineation is a prerequisite for effective conservation and management of migratory bird populations, yet such limits have so far mostly been set subjectively. We present a statistical method to infer population boundaries from the analysis of ring recoveries, using a Bayesian framework. The approach was applied to Eurasian teal Anas crecca ringed in Camargue, southern France, and Abberton Reservoir, Essex, eastern England. The results presented show the boundaries of the two teal flyways in western Europe, with a zone of overlap, broadly matching those previously defined. The percentage of teal switching flyways (abmigration rate) was 2.4–2.6%, greater in birds ringed as juveniles than as adults. Abmigrants ended up at sites within the other flyway where the density of local birds was lower than expected by chance, suggesting abmigration resulted from exploratory or aberrant behaviour. The methodology presented here can be used to infer flyway boundaries of any bird with an adequate ring‐re‐encounter dataset, which has crucial consequences for the evaluation of their trends in abundance and hence conservation status, and the management of sustainable harvests.     

THE MIGRATION PATTERNS OF THE PURPLE SANDPIPER CALIDRIS MARITIMA

Summers, R. W. 1994. The migration patterns of the Purple Sandpiper Calidris maritima. Ostrich 65: 167–173.

The Purple Sandpiper breeds largely in the Arctic, and winters (boreal season) on the rocky shores of the north Atlantic, further north than any other sandpiper. As the populations from Canada, Greenland, Iceland, Svalbard, Norway and Russia differ in wing and bill lengths it is possible to match measurements taken from breeding birds with samples of birds caught in winter. Ringing recoveries, especially from colour marked birds, have also helped to determine migration routes and wintering areas. Four populations move to the nearest ice-free coast. Two populations move south of the nearest ice-free coast, being replaced by larger birds from a more northerly population (“chain migration”). Only the north Canadian population is believed to migrate a long distance, “leap-frogging” other winter populations. These patterns are discussed in relation to theories for the migration patterns of waders.     

THE BIOLOGY OF THE WAVED ALBATROSS DIOMEDEA IRRORATA OF HOOD ISLAND, GALAPAGOS

As a nesting species, the Waved Albatross Diomedea irrorata is restricted to Hood Island in the Galapagos archipelago where 12,000 pairs bred in 1971. Outside the islands the species occurs over the northern parts of the Humboldt Current. Two colonies were studied in detail (1970–1971). At the start of a season, males returned first to the colonies and defended a small territory. Copulation occurred without any elaborate ceremony and the female spent little time on land before laying. There was no fixed nest-site, even within a season, and birds moved their eggs considerable distances. This resulted in heavy egg losses. Younger birds bred later than older birds and laid longer but narrower eggs. The average incubation spell varied from four to five days at the extremes of the incubation period to 19 days in the middle. The average incubation and fledging periods were 60 and 167 days respectively. Pairs which lost an egg sometimes adopted the abandoned egg of another bird and successfully reared the chick. Most pairs nested in both seasons. Nesting success was extremely variable, both between years and between colonies. Between 1961 and 1971 at Punta Suarez, virtually no young were reared in four seasons. Even in 1970–71, where nesting success was good, some groups of birds deserted their eggs en masse whereas in neighbouring areas up to 80% of the pairs reared young. The main foods of the young were squid and fish. Birds did not moult wing and tail feathers at the breeding colonies, and about 50% retained some primaries for more than one season, suggesting that successful pairs had difficulty in fitting in a complete moult between breeding attempts. Old feathers were normally found among the inner primaries and at the next moult were preferentially replaced, though adjacent newer feathers were sometimes retained for another season. Some birds bred in their fourth years, but most not until a year or two older. Immatures were present at the colonies late in the breeding cycle, the youngest returning latest and remaining until the last young fledged. Survival of adults and young averaged at least 95% and 93% per annum over many years. Adults and young ringed in 1961 survived equally well. The significance of the timing of the return of immatures and of the large-scale desertion of eggs, apparently not due to food shortage or disturbance, is discussed.     

5. A NOTE ON THE PARADISE WHYDAHS

Vernon, C. J. 1975. Seventeenth ringing report for southern African. Ostrich 46:125-128.

A report on ringing activities in southern Africa from July 1973 to June 1974 is presented. A total of 51 561 birds of 451 species were ringed and are analysed according to distribution of ringers, groups of species and recovery rates. A list of those birds living longer than ten years is given. Analyses are needed of the most frequently ringed species in order to give greater purpose to future ringing.     

THE MIGRATION OF RAPTORS AND STORKS THROUGH THE NEAR EAST IN AUTUMN

Between 1963 and 1965 three expeditions have investigated the autumn migration of raptors and storks, on two occasions in southeast Turkey, and once in Lebanon.
Nearly all the soaring birds leaving Europe by the Bosphorus cross Asia Minor and turn south at the Gulf of Iskenderun. The commonest of these migrants are White Stork Ciconia ciconia , Honey Buzzard Pernis apivorus , and Eagles Aquila spp.
Other species such as Common Buzzard Buteo buteo are not usually seen crossing the Bosphorus, but occur in large numbers in the flocks seen south of the Gulf of Iskenderun. It is suggested that these are birds from Russia and north Turkey. Common Buzzards also occur on Cyprus in autumn, but their point of origin is not clear. Short-toed Eagles Circuetus gullicus and vultures join the migration from their breeding grounds in Turkey and the Levant.
Different species tend to migrate at different times of year. White Storks, Egyptian Vultures Neophron percnopterus and Black Kites Milvus migruns move chiefly between late August and mid-September, while eagles Aquilu spp. start in late September and continue until November. Other species are intermediate, or spread their migration out over a longer period.
The volume of migration at different times of day is discussed. No general conclusions are possible but in 1964 a correlation was obtained between cloud cover and the start of the migration.     

Genetic differentiation in Eurasian Woodcock (Scolopax rusticola) from the Azores

The Eurasian Woodcock Scolopax rusticola is a widespread Palaearctic migratory wader, with purportedly sedentary populations occurring in the Macaronesian archipelago of the Azores. Here we used microsatellite markers to investigate patterns of genetic diversity and differentiation in these insular birds, and compared Azorean populations with those from mainland Europe. Azorean populations show a (non-significant) trend for reduced diversity, and low but consistent differentiation from mainland populations; evidence for widespread over-water migration (in either direction) is weak but must occasionally occur given the recovery of an Azorean ringed bird in France. It is thus likely that the Azorean populations diverged recently from their mainland counterparts, but gene flow is currently restricted.     

Assortative mating in two populations of Short‐tailed Albatross Phoebastria albatrus on Torishima

Assortative mating is an important pre‐mating isolation mechanism that has been observed in some wild populations of seabirds. The Short‐tailed Albatross Phoebastria albatrus is a globally Vulnerable seabird that breeds mainly on Torishima and the Senkaku Islands in the north‐western Pacific Ocean. Our previous studies suggested that two genetically distinct populations exist, one on Torishima and the other on the Senkaku Islands. Recently, however, several un‐ringed birds in subadult plumage have been observed breeding on Torishima in the Hatsunezaki colony. As almost all birds hatched on Torishima since 1979 have been ringed, the natal site of the un‐ringed birds was suspected to be the Senkaku Islands. Genetic differences between the two populations would reveal the natal sites of un‐ringed birds. By observing the ring status (ringed or un‐ringed) of mating pairs and analysing the mitochondrial DNA (mtDNA) control region 2 of un‐ringed birds, we assessed whether birds that originated from Torishima and the Senkaku Islands achieved pre‐mating isolation. There was a small number of pairs on Torishima that consisted of one ringed and one un‐ringed bird, but the observed number was significantly lower than that expected if ringed and un‐ringed birds mated randomly. Furthermore, mtDNA analyses of nine un‐ringed birds demonstrated that all belonged to a particular haplotype clade from the Senkaku Islands. These results show that birds from Torishima and the Senkaku Islands mate assortatively but that there is incomplete pre‐mating isolation between birds from the two island groups. The pre‐mating isolation of these two populations of Short‐tailed Albatross could arise from differences in the timing of breeding and incompatibility in mating displays. As the divergence between the two populations is unlikely to be sufficient to achieve complete post‐mating isolation, the two groups are likely to be hybridizing. Further studies using molecular and/or behavioural analyses would be required to reveal the evolutionary significance of hybridization between these two populations.     

Ringing or colour-banding does not increase predation mortality in redshanksTringa totanus

The use of metal and colour‐rings or bands as a means of measuring survival, movements and behaviour in birds is universal and fundamental to testing ecological and evolutionary theories. The practice rests on the largely untested assumption that the rings do not affect survival. However this assumption may not hold for several reasons, for example because the ‘oddity effect’ predicts predators select prey that appear different to their neighbours in order to avoid the ‘confusion effect’. We compared the foraging behaviour and the death rates of redshanks Tringa totanus conspicuously marked with six colour rings and one metal ring each to unmarked birds in a study system, where routinely up to 50% of the total population are killed by avian predators during a winter. If avian predators selectively target and/or have a higher capture success of ringed birds then we would predict the proportion of colour‐ringed birds in the population to decline through a winter. The proportion of colour‐ringed birds in the population did not change over the course of three separate winters, and in one winter the ratio of marked:unmarked birds found killed by sparrowhawks Accipiter nisus was the same as the ratio of marked birds alive in the population. In the year with largest sample size, power was sufficient to detect a greater than 2.2% difference in predation rate between ringed and unringed groups. The average kill rate difference between ringed and unringed birds across the three winters was less than 1% (0.73±2.2%) suggesting that even if there were differences in predation rate that were not detected because of low statistical power they were extremely small. There were no differences in any foraging measures comparing ringed and unringed birds, suggesting that the rings did not affect the ability of birds to meet their daily energy budgets. The results showed that colour‐ringed birds were not preferentially targeted or killed by avian predators, and suggest that the presence of a metal and even several large colour‐rings is unlikely to affect behaviour and predation mortality even under extreme selection.     

Philopatry analysis of the great reed warbler (Acrocephalus arundinaceus) based on ringing data in Europe

Ringing databases of the EURING Data Bank and the Hungarian Bird Ringing Centre were analysed in order to investigate the philopatry of the great reed warbler (Acrocephalus arundinaceus) in three European regions. The aim of the study was to find out if there are continent-scale geographic trends in philopatry with respect to the age of the birds. Three clusters were assigned according to their geographic positions: (i) southern part of Europe (Region 1: between 36°–43° latitudes), (ii) middle part of Europe (Region 2: between 43°–49° latitudes) and (iii) northern part of Europe, (Region 3: between 49°–56° latitudes). No significant differences were found between the natal and breeding philopatry in any Regions, except Region 3. The birds ringed as adults in Region 3 were less faithful to their breeding site than those of the other two regions. Natal philopatry of juveniles did not differ between Region 1 and Region 2, but both of them differed in this respect from Region 3. A method for choosing appropriate breeding periods in philopatry studies is also proposed.     

DISPERSION, POPULATION ECOLOGY AND MIGRATION OF EASTERN GREAT REED WARBLERS ACROCEPHALUS ORIENTALIS WINTERING IN MALAYSIA

A population of 400–600 Acrocephalus orientalis wintering in a Phragmites habitat at 3°N in West Malaysia was studied during four northern hemisphere winters, by means of systematic mist-netting. Data from other study-areas, other habitats and other winters are also used. Intensive mist-netting appears to have made birds move over longer distances than they did in the absence of disturbance, and to have led to the emigration of marked birds from the study-area. Trapping also affected feeding behaviour, resulting in weight-loss; repeated trapping may have increased mortality. Males and females could be separated by means of wing-length in fresh plumage. Females were largely confined to Phragmites; males were more numerous on the edge of reed-beds and in scrub vegetation. Males suffered greater feather-wear than females. As measured by the trapping rate, birds were uniformly distributed throughout the Phragmites habitat, at the same density in different winters. Undisturbed birds used a “home-range” of 1–4 ha, overlapping with 15–50 other individuals. Disturbed birds overlapped with 100–200 others. Individual birds returned to exactly the same “home-range” in successive winters. After correcting for the effects of disturbance and incomplete sampling, the proportion of adults ringed in one winter which returned in the next is estimated as 65% in each of two study-areas. This is a minimum estimate of the annual survival rate for adults. Mean total body-weights were at a minimum in midwinter (November-February). Fat-free weights were also lower in midwinter than in autumn and spring. Body-moult was observed in March and April. Moult of the flight-feathers takes place between July and September, on the breeding grounds or slightly to the south. Females departed on spring migration between 10 and 25 May; males some 11–14 days earlier. Adults arrived in autumn between 8 September and 7 October; males and females often came in in separate “waves”. Females were absent for only about 127 days, about the minimum required for migration, breeding and moult. Dates of migration match those of the more northern breeding populations. Spring departure is later than dates of passage recorded in south China; hence birds of this population appear to make long nights. On average, birds departing in spring carried about 9 g of fat, roughly 40% of total fat-free body-weight. This is about half the energy reserve required for the entire journey. Dates of passage in central China are consistent with a hypothesis that they make the journey (4,500-5,000 km) in two “hops”. A few birds which remained light until very late in the spring showed a significantly lower return rate in the next year. Most birds arriving in autumn appear to have carried 1–2 g of fat, but some were at or below the normal fat-free weight. Many birds appear to have lost weight soon after arrival. Returning ringed adults were amongst the very first birds trapped in September. Individual birds appear to have migrated on very similar dates in different years: many of the dates of trapping differed by 2 days or less in successive years. Trapping rates reached a peak in early October and then declined rapidly, reaching the midwinter level by 21 October. The decline coincided with the differential disappearance of juvenile birds. However, birds collected at this time had adequate fat reserves, and the disappearance appears to have preceded the period of food-shortage. It is suggested that the loss of juvenile birds resulted from behavioural interactions favouring the more dominant individuals, as has been described for several temperate zone residents. The first few weeks in the wintering area may thus be the critical period of mortality during the year. Because birds from different breeding areas are expected to be mixed in the winter-quarters, and vice versa, local mortality factors in winter may affect a number of breeding populations. High adult survival rates have been recorded in several other birds which breed in the temperate zones and winter in the tropics. In general their breeding success appears to be high, so the first-year mortality must be high. The closely related A. arundinaceus, which winters in Africa, differs from A. orientalis in size, wing-shape, timing of spring migration and timing of moult. These differences can be interpreted as adaptations to different environmental (primarily climatic) factors experienced during migration and on the breeding grounds. The segregation of males and females into different habitats probably reduces inter-sexual competition in winter, but this is not necessarily its primary function. Males collected in the evening in Phragmites had smaller fat reserves than females, suggesting that the females are better adapted to this habitat. The large size of the males is probably maintained in part by sexual selection in the breeding season. On the other hand, the size of females and their habitat is probably limited by the specialisation of their nest. These factors would suffice to explain the sexual dimorphism in size and habitat.     

ON THE BIRDS OF THE SANDVELD KALAHARI OF SOUTH WEST AFRICA

Keffen, R. H. &; Jarvis, M. J. F. 1984. Some measurements relating to Ostrich eggs. Ostrich 55:182-187.

Eggs from wild Zimbabwean Ostriches Struthio camelus australis and domesticated South African hybrid birds, were compared. Formulae were tested to determine their accuracy when used to calculate egg weights, surface area and density. Calculated values were compared with some actual measurements. The main motivation for the study was the need to calculate fresh egg weights of wild Ostriches, as an aid to determining weight loss during incubation under natural conditions. Eggs from wild birds were, on average, smaller than those from domesticated birds, even though the wild adults were larger than domesticated birds. However, newly batched chicks from hybrid eggs weighed less than those from wild eggs.     

ABUNDANCE OF RINGED SEALS (PUSA HISPIDA) IN THE FJORDS OF SPITSBERGEN, SVALBARD, DURING THE PEAK MOLTING PERIOD

Ringed seal (Pusa hispida) abundance in Spitsbergen, Svalbard, was estimated during the peak molting period via aerial, digital photographic surveys. A total of 9,145 images, covering 41.7%–100% of the total fast‐ice cover (1,496 km²) of 18 different fjords and bays, were inspected for the presence of ringed seals. A total of 1,708 seals were counted, and when accounting for ice areas that were not covered by images, a total of 3,254 (95% CI: 3,071–3,449) ringed seals were estimated to be hauled out during the surveys. Extensive behavioral data from radio‐tagged ringed seals (collected in a companion study) from one of the highest density fjords during the molting period were used to create a model that predicts the proportion of seals hauled out on any given date, time of day, and under various meteorological conditions. Applying this model to the count data from each fjord, we estimated that a total of 7,585 (95% CI: 6,332–9,085) ringed seals were present in the surveyed area during the peak molting period. Data on interannual variability in ringed seal abundance suggested higher numbers of seals in Van Keulenfjorden in 2002 compared to 2003, while other fjords with very stable ice cover showed no statistical differences. Poor ice conditions in general in 2002 probably resulted in seals from a wide area coming to Van Keulenfjorden (a large fjord with stable ice in 2002). The total estimated number of ringed seals present in the study area at the time of the survey must be regarded as a population index, or at least a minimum estimate for the area, because it does not account for individuals leaving and arriving, which might account for a considerable number of animals. The same situation is likely the case for many other studies reporting aerial census data for ringed seals. To achieve accurate estimates of population sizes from aerial surveys, more extensive knowledge of ringed seal behavior will be required.     

Movement patterns of Common Crossbills Loxia curvirostra in Europe

Over much of Europe, Common Crossbills Loxia curvirostra depend primarily on the seeds of Norway Spruce Picea abies , and their breeding and movement patterns are governed largely by the cropping patterns of this tree species. Good cone crops occur only every few years in particular areas, but in different years in different areas. The main period of movement is in summer, when the previous year's crop is coming to an end, and a new crop is forming in different areas. In years when the Norway Spruce crop is poor over a wide area, and when Common Crossbills are abundant, they leave the boreal forest in large numbers, and appear as irruptive migrants in southwest Europe, with at least 40 invasions reaching Britain in the 120-year period 1881–2000. On irruptions the main migration axis is from northeast to southwest or west. Recoveries of birds ringed mainly in Germany confirm that these birds do not return to the boreal forest in northern Russia in the same calendar year as their irruption, but do so only in a later calendar year, when a new Norway Spruce crop is becoming available. The findings agree with an earlier interpretation of Common Crossbill movements, but not with an alternative hypothesis that irrupting Common Crossbills return to their region of origin in the same calendar year as the outward movement. Recoveries also suggest that some individual Common Crossbills may have bred in widely separated localities in different years (records up to 3170 km apart), and sometimes in localities far removed from their natal sites (records up to 2950 km apart).     

SEASONAL INCIDENCE OF BREEDING, MOULT AND LOCAL DISPERSAL OF RED-BILLED FIREFINCHES LAGONOSTICTA SENEGALA IN ZAMBIA

Red-billed Firefinches were netted and ringed in Lochinvar National Park, Zambia, in 1972 and 1973 and were netted sporadically through 1975. Most nested from March to May, i.e., in the late rainy season and in the early dry season, though some nested as late as August. Nearly all evidently bred in their first year. Moult generally began after breeding was completed, and the indicated average duration of moult was 3–5-4 months. The main foods taken at all times of year were seeds of the seasonal grasses Echinochloa colonum and Setaria spp.
Local population densities, estimated by two methods, were in the range 33–86 birds per km². Ringing results demonstrated overlapping activity ranges in the breeding season. Dispersal movements were non-directional, and varied up to 14 km. Some ringed birds moved regularly each year between a particular waterhole and a breeding site; other did not move from the site of original ringing. Most dispersal was evident in the dry season (June and July) and in the early rains (October and November). Genetically effective dispersal of young from the site of birth to the site of the first breeding season was up to 6'8 km, and some adults were netted in sites a few kilometres apart in successive breeding seasons. Some dispersing firefinches crossed the song dialect boundaries of the Village Indigobirds.