MIGRATION OF THE NORTHWESTERN EUROPEAN POPULATION OF THE CUCKOO CUCULUS CANORUS, AS SHOWN BY RINGING

The migration of the Cuckoo Cuculus canorus is described from recoveries of ringed birds. Young birds begin to migrate in August and most go southwards by September—those in continental Europe move southeast, south or southwest, while those from the British Isles move southeast. In spring, migrants arrive in Europe in April/May, second-(calendar) year birds doing so later than post-second-year birds. In autumn old birds depart in advance of first-year birds; and the individual bird may move stepwise through Europe. Old birds showed a marked tendency to return to the same places inhabited in previous breeding seasons, and birds ringed as nestlings subsequently tended to return to the general vicinity of the natal site.     

SEASONAL VARIATION IN METABOLIC FUNCTIONS OF BRAMBLINGS

Seasonal variation in the rate of oxygen consumption during rest at different test temperatures and in the respiratory quotient (RQ) was observed in male Bramblings Fringilla montifringilla which had been caught as immature birds during autumn migration and kept under outdoor conditions for one year. Resting oxygen consumption measured from +31^o to – 4^oC during one night was significantly lower in late April and October (migratory seasons) as compared to the preceding and the following December. Because of marked seasonal changes in body weight, the significance of differences in metabolic rate between different seasons was largely dependent on the manner of expressing the rate of oxygen consumption, either per bird or as the 0–67 power of body weight (“surface coefficient”). The lower resting rate of oxygen consumption during the migratory seasons was interpreted as one possible factor responsible for allowing fat deposition by reducing total energy expenditure. This modification occurred only in birds kept under quasi-natural conditions outdoors and not in birds which were kept in cages under constant conditions of light and temperature in the laboratory.     

辽西中生代鸟类跗跖骨测量数据的统计分析及意义

跗跖骨是鸟类后肢骨骼的重要组成之一,其形态特征对恢复鸟类的行为和习性具有重要的指示意义。本文以鸟类的跗跖骨为研究对象,共观察了200余例有代表性的现生鸟类标本,并对其中15个目中的154例标本进行了多组数据的测量。还将跗跖骨各形态特征进行量化分析研究,引入相关分析和因子分析等统计分析方法。对现生鸟类跗跖骨5组(12个)变量进行分析,研究各变量间的相关程度,对变量进行主成分分析,提取出2个主成分,其中第1主成分包括第Ⅱ,Ⅲ,Ⅳ三个跖骨的宽度变量;第2主成分包括第Ⅱ跖骨滑车相对于第Ⅲ跖骨滑车的上下及前后位置两变量,以及第Ⅳ跖骨滑车相对于第Ⅲ跖骨滑车的前后位置变量。对这6个变量的分析表明,它们对于区别鸟类的栖息习性具有显著的指示作用。通过对在中国(辽西为主)已发现的25例中生代鸟类跗跖骨远端4个变量的统计分析,表明它们同样具有区别树栖和地栖鸟类的显著意义,而且分析的结果与参考鸟类其他特征(如爪的形态、脚趾的比例等)所得出的结论基本一致。     

SPATIAL AND TEMPORAL ABUNDANCE PATTERNS OF WATERBIRDS IN THE SOUTHERN CAPE PROVINCE. PART 3: WADING BIRDS

Boshoff, A.F., Palmer, N.G. & Piper, S.E. 1991. Spatial and temporal abundance patterns of water-birds in the southern Cape Province. Part 3: Wading birds. Ostrich 62:197-214.

Wading birds (herons, egrets, spoonbills, flamingoes and waders) were counted, and water-level and water transparency measured, on a monthly basis from 1980 to 1983 or 1984, at the six waterbodies comprising the Wilderness-Sedgefield Lakes Complex, southern Cape Province. The fluctuating status of the submerged aquatic macrophytes, and the trophic status of the waterbodies, was documented. The counts reflect the monthly status of the birds, and allow the calculation of densities (birds/ha). Linear and logarithmic models aided the interpretation of the count data. Spatial and temporal patterns and trends are described, and discussed in relation to changes in water-level, water transparency and aquatic macrophyte biomass regimes in the study area. Water-level was an important environmental parameter and was generally negatively correlated with abundance.     

Differences in measures of boldness even when underlying behavioral syndromes are present in two populations of the song sparrow (<Emphasis Type="Italic">Melospiza melodia</Emphasis>)

One commonly studied behavioral syndrome is the correlation between aggression and boldness. Studies in song sparrows (M. melodia) have found greater aggression and boldness in urban populations and a correlation between aggression and boldness in rural populations, but not within urban populations. In previous studies, boldness was measured as flight initiation distance (FID), which may reflect habituation by urban birds to human presence. In this study, we measured boldness using playbacks of heterospecific alarm calls and investigated whether higher boldness is a general trait of urban birds and whether the same pattern of correlations between aggression and boldness would be seen. We conducted trials involving FID, alarm call playbacks and conspecific song playbacks on 25 birds from both an urban and a rural site. The results showed that urban birds were bolder, as measured by FID and response to alarm calls. Boldness and aggression were correlated in rural birds with each method of measuring boldness but were correlated in urban birds only when using alarm call playbacks. Our results suggest that a behavioral syndrome exists in both urban and rural populations but that urban birds are able to decrease their response to human disturbance.     

MINUTES OF THE ANNUAL GENERAL MEETING OF THE SOUTH AFRICAN ORNITHOLOGICAL SOCIETY,HELD AT CAPE TOWN, 26 JUNE 1959

Brown, C. J. 1989. Plumages and measurements of the Bearded Vulture in southern Africa. Ostrich 60: 165–171.

Four different age classes of the southern African Bearded Vulture Gypaetus barbatus are recognized and their plumages described: juvenile (3–24 months old), immature (24–45 months), subadult (45–60 months) and adult (60+ months). There was no significant difference in size between adult male and female birds. Adults were larger than juvenile birds in bill width, beard length, wingspan and mass, and had a higher aspect ratio and wing loading, while juvenile birds were larger than adults in the length of their outer rectrices, tail area, wing breadth and wing area. These features are considered to be adaptive to young birds inexperienced in flying. Immature and subadult birds were intermediate in size between juveniles and adults. Bearded Vultures differ from other large raptors in two sets of physical characteristics, (a) those adapted to cold, mountainous habitat, e.g. feathered head and face, unusually long wings, a high aspect ratio and a particularly long tail, and (b) those adapted to their diet of mainly bones, e.g. wide gape, beard and relatively long talons for carrying food.     

Differential effects of exotic predator-control on nest success of native and introduced birds in New Zealand

The introduction of mammalian predators has been detrimental to many native birds in New Zealand. One solution to this problem has been the creation of “mainland islands” in which exotic predators are systematically removed. Although mainland islands have been effective in increasing some native bird populations, few studies have measured the effect of predator-control on nest success nor what effect control measures have on sympatric populations of introduced birds. We measured the effect of predator-control on nest survival rates in both native and introduced passerines in a mainland island near Kaikoura, New Zealand. Nest survival was significantly higher in Waimangarara Bush (the site with experimental predator-control) than in Kowhai Bush (the site with no predator-control) and this pattern was found in both groups of birds. However, mammalian predator-control increased nest success of native species significantly more than nest success of introduced species. This suggests that native birds benefit disproportionately from control of introduced predators, most likely because they lack behavioural defences against mammalian predators that are present among the introduced birds.     

PARASITISM OF THE MASKED WEAVER PLOCEUS VELATUS ARUNDINACEUS

Williams, G. D., Coppinger, M. P. &; Maclean, G. L. 1989. Distribution and breeding of the Rock Pratincole on the Upper and Middle Zambezi river. Ostrich 60: 55–64.

The Rock Pratincole Glareola nuchalis was studied on the Upper and Middle Zambezi fromMayto November 1986 and from April to December 1987. Altogether 1938 Rock Pratincoles were counted; their distribution was closely associated with the availability of breeding habitat. The first birds were seen in mid-August and the species was still present in December. They nested in loose colonies on midstream rocks separated from the shore by flowing water. Sixty-four clutches (mean clutch size 1,8 eggs) were found and 44 eggs measured (mean size 29,2 x 21,5 mm). The eggs were usually laid on bare rock less than 1 m above the surface of the water and were sometimes in shade. Both sexes incubated and the frequency of nest relief was greatest during the hottest times of the day. The responses of incubating birds to overheating were bill-opening, panting, dorsal-feather erection, holding the wrists away from the body, and belly-soaking. Non-incubating birds drank often and did not seek shade. After hatching the young sought refuge in rock overhangs and crevices. The important breeding sites in the study area were identified and possible effects of future hydro-electric schemes are discussed.     

A STUDY OF THE CINNAMON-BREASTED ROCK BUNTING Fringillaria tahapisi tehepisi

Brown, C. J. &; Piper, S. E. 1988. Status of Cape Vultures in the Natal Drakensberg and their cliff site selection. Ostrich 59:126-136.

Ground, aerial and questionnaire surveys on the status of the Cape Vulture Gyps coprotheres in the Little and High Drakensberg mountain ranges of Natal were carried out from 1981–1983. The area supported at least 1325 Cape Vultures, 60% on the High Drakensberg in 17 nesting colonies (mean of 31 birds per colony) and 38 roosts (mean of 7 birds). In the Little Drakensberg 17 sites were found, six of which were confirmed nesting colonies (mean of 53 birds) and seven were roosts (mean of 16 birds). A minimum of 215 nests was recorded while the actual number of breeding pairs was probably about 325. In the Natal Drakensberg 84% of nests and 77% of roosting birds occupied ledges that faced between east and south, on the lee side of the generally westerly and northwesterly “Bergwind”. Nesting ledges in the High Drakensberg were on average about 100 m lower than roosting ledges. The northern Drakensberg supported the largest numbers of Cape Vultures (19 birds per 10 km of cliffs), while the smallest numbers were recorded in the south (8 birds per 10 km of cliffs). In the south smallstock farming predominates and the availability of carrion is higher than in the north where mainly largestock are farmed. The use of poisons (mainly strychnine) for killing mammalian predators on farms is considered to be the main reason for fewer birds occurring in the south, and is the main threat to Cape Vultures in the Natal Drakensberg.     

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.     

从c-mos和12S rRNA基因序列探讨现生鸟类早期历史和三趾鹑类的系统地位

通常认为古腭型鸟类处在现生鸟类系统进化树的基部,最近的分子水平研究则认为今腭型鸟类中雀形目种类构成了现生鸟类中一个最古老的支系.本研究通过对现生鸟类中21目39种核c-mos基因和线粒体12S rRNA基因部分序列的分析,从分子角度对现生鸟类的早期进化及三趾鹑鸟类的系统发生进行了探讨.研究结果表明,鸡雁类是现生鸟类最古老的一个支系,现生鸟类的祖先并不是经白垩纪到第三纪大灭绝后残留下来的一些过渡性水鸟(transitional shorebirds).在现生鸟类中,今腭型鸟类为并系发生,古腭型鸟类为单系发生.三趾鹑类在系统发生中晚于鸡雁类和古腭型鸟类,早于今腭型鸟类中非鸡雁类鸟类与鹤形目鸟类的亲缘关系较远.建议将现生鸟类分为初鸟下纲和新鸟下纲2个下纲,三趾鹑类属新鸟下纲的三趾鹑目(Turniciformes).     

4. MIGRATION OF AFRICAN BIRDS

Dean, W. R. J. 1978. Plumage, reproductive condition and moult in non-breeding Wattled Starlings. Ostrich 49:97-101. A random sample of Wattled Starlings Creatophora cinerea taken from a large flock (about 5000 birds) that was exhibiting pre-breeding displays was found to have a male:female ratio of 63:50. Less than 15% of the total sample were in breeding plumage, in spite of testis and ovarian follicle development that suggested that the whole flock was capable of breeding. The weight of dehydrated flight muscles gave a reliable indication of general body condition, but could not be correlated with reproductive condition, The presence of helminths (Diplotriaena tricuspis) does not appear to affect the birds adversely. Of the 113 birds in the sample, 13.2% were in active primary moult, 53,9% were in new plumage, and 32.9% were either old or indeterminable. Of 108 stomachs examined. 38.8% (42) contained fruit, 41,6% (45) contained insects and fruit, 17,5% (19) contained insects and 49% (1) contained a lizard.     

SPRING WEIGHTS AND PASSAGE OF SEDGE WARBLERS ACROCEPHALUS SCHOENOBAENUS IN CENTRAL KENYA

Weight and other data were collected on over 1300 Sedge Warblers Acrocephalus schoenobaenus in central Kenya, mainly during spring (April-May). The weight, fattening rate and length of stay of spring passage birds varied from one site to another. In scrub and thicket at Kariobangi, Nairobi, passage and new arrival continued each year into May; few birds stayed to fatten, and weights over 16 g (40% above mean winter weight) were practically never recorded. At Lake Nakuru, thousands of birds were present during late April-early May 1972; many stayed to fatten for 1–3 weeks, and weights over 16 g (maximum 215 g) were not uncommon; new arrivals of lean birds continued into May. At Athi River, in 1971, many of the birds present during mid-late April stayed 1–2 weeks and fattened rapidly; 20% of all late April weights were in the range 16–21 g. Mean fattening rates at Nakuru and Athi River were 0.31 and 0.64 g/d respectively. The migration strategy and potential flight range of Kenyan spring birds is discussed. Active wing moult was rarely recorded. Most locally wintering birds and spring passage birds were judged to have renewed their plumage during the preceding October-January.     

COMPARISONS AND FUNCTIONS OF SKY-DANCING DISPLAYS OF CIRCUS HARRIERS: UNTANGLING THE MARSH HARRIER COMPLEX

Simmons, R. 1991. Comarisons and functions of sky-dancing displays of Circus harriers: untangling the marsh harrier complex. Ostrich 62:45-51.

African Marsh Hamers Circus ranivorus perform aerial displays known as “sk-dancing” most frequently just before breeding and at other times during territorial takeovers. Both mares and females display and food supplements to seven pairs over two years verified sexual selection arguments that birds in better condition display more freuently than unfed controls. Typical sky-dancing birds soared to 400 m or more, and performed up to 20 U-shaped undulations in a horizontal plane, while sky-spiruffing birds performed vertical displas, dropping in a series of descending U-shaped undulations, whilst twisting about their axis. Displaying girds stimulated others to perform and up to eight birds displayed in the same aerial arena. I interpret both displas as mainly territorial in function but rovide evidence that they also have a mate attraction component. in form, the display resembles that or the Australasian Hamer C. uproxi mans, but not that of the European Marsh (C. aeruginosus) nor the Reunion Malagasy (C. a. maifardii Hamer, providing evidence contrary to the traditional belief that African birds are subspecies of aeruginosus     

BIRDS OF THE UNDERSTORY OF LAKE-SHORE FORESTS ON THE ENTEBBE PENINSULA, UGANDA

Monthly mist-netting of low-flying forest birds was conducted in three lake-shore forests in southern Uganda from September 1970 to July 1972. It was found that the edge of the forest formed a distinct ecological barrier that was rarely crossed by species on either side of it. Catches were concentrated in the hours of daylight, in two peaks, a morning peak at 09.00 hrs and an afternoon peak at 16.00 hrs (sun-time) for all birds combined, although there were slight species differences. Most bird species were found to be sedentary in a fixed home-range, and covered lateral distances of up to c. 300 m. No movement between the different forests was recorded.
The most common birds such as bulbuls were often caught at heights between 0·6 and 1·8 m above the ground, but the upper limit of their vertical range was not determined. It is suggested that the bi-modality of flight activity may be intrinsic, even though it may be correlated with such extrinsic factors as light and radiation. On a month to month basis, the numbers of birds caught reflected breeding and moult activity. This was best shown by the Pygmy Kingfisher, taken in higher numbers towards the end of the first rainy season when a majority of the birds caught were young and many birds were moulting the remiges. On the other hand higher numbers of Olive Sunbird were found during the second rainy season, again at a time corresponding to a general moulting of remiges. The bulbuls showed fluctuations in numbers caught that were matched by an equally fluctuating pattern of moult. The role of food as a possible limiting factor in bird breeding is discussed.     

Earlier hatching time predisposes Cobb broiler chickens to tibial dyschondroplasia

Fertile eggs from Cobb 500 broiler breeder hens were incubated to provide low starting egg shell temperatures (EST; 36.9°C to 37.3°C) which were gradually increased to 37.8°C during the first 7 to 15 days of incubation compared with eggs incubated with a constant EST of 37.8°C (standard conditions) over the first 18 days of incubation. Time of individual chick hatching (measured at 6 h intervals from 468 h of incubation), chick weight, chick length and yolk weight were measured at take-off and BW was measured at 7, 14, 28, 34 and 42 days of age. Male birds at 34 and 42 days of age were assessed for their ability to remain standing in a latency-to-lie test. At 34 and 42 days, male birds were examined for leg symmetry, foot pad dermatitis, hock bruising and scored (scale 0 to 4, where 0=no lesion and 4=lesions extending completely across the tibial growth plate) for tibial dyschondroplasia (TD) lesions. The lower EST profiles caused chicks to hatch later than those incubated under the standard EST profile. Chicks which hatched at ⩽498 h incubation grew faster over the first 7 days than those that hatched later. There were significantly more birds (only males were studied) that hatched from the lower EST profiles with TD scores of 0 and 1 and fewer with score 4 at 34 days than those hatched under the standard profile. Male birds at 34 days with TD lesions ⩾3 stood for significantly shorter times than males with TD scores ⩽2. Moreover, male birds at 34 and 42 days with TD lesion scores of ⩾3 hatched significantly earlier and grew significantly faster over the first 2 weeks of age than did male birds with TD scores ⩽2. It appears possible to decrease the severity and prevalence of TD in the Cobb 500 broiler by ensuring that the birds do not hatch before 498 h of incubation.     

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.     

THE EFFECT OF AGE ON THE BREEDING BIOLOGY OF THE KITTTWAKE RISSA TRIDACTYLA

1. From 1954 to 1956 inclusive, the biology of individual marked Kittiwakes was studied at North Shields, Northumberland.
2. It was concluded that older Kittiwakes reacted to the breeding stimulus earlier, more intensively and with greater success than younger breeding birds.
3. Birds with previous breeding experience returned to the colony before birds breeding for the first time and these before non-breeders.
4. Before breeding started, birds which had bred previously spent more of their time at the colony than those about to breed for the first time.
5. Birds breeding for at least the second time laid the first egg 7·5 days earlier than those breeding for the first time.
6. Breeding started one day later for every four days the return to the colony was postponed.
7. Older breeding birds showed greater nest-site tenacity, laid larger clutches and had greater breeding success than younger birds.
8. The chicks in broods of two (but not of one) increased in weight more rapidly where the parents had previous experience.
9. Breeding Kittiwakes showed strong colony tenacity, but 24% of the marked non-breeding birds were subsequently seen in other colonies.
10. Over half the birds retained the same mate as in the previous year.     

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.     

NOTES ON THE BEHAVIOUR OF THE MOCKING CHAT THAMNOLAEA CINNAMOMEIVENTRIS (LAFR.) IN WESTERN TRANSVAAL

Martin, A. P. &; Baird, D. 1987. Seasonal abundance and distribution of birds on the Swartkops estuary, Port Elizabeth. Ostrich 58:122-134. Counts of estuarine birds were made on the Swartkops estuary, Port Elizabeth, between September 1983 and August 1985. Seasonal variations in the numbers of both migrant and resident species were investigated; in the austral summer, over 4000 birds were recorded, whereas in winter, fewer than 1200 birds were counted. Five species made up 74% of the total number of birds: Kelp Gulls Larus dominicanus (21%), Grey Plovers Pluvialis squatarola (21%), Whimbrels Numenius phaeopus (12%), Common Terns Sterna hirundo (10%) and Curlew Sandpipers Calidris ferruginea (10%). The majority of birds (92%) were recorded on the intertidal mud and sand, and a positive correlation was found between bird density and the biomass of a major prey species, Upogebia africana. The avifauna of the estuary has changed considerably since the beginning or this century, probably reflecting long-term trends in the bird populations.