PALAEARCTIC MIGRANTS IN NIGERIA

An account is given of the topography, climate and vegetation belts of Nigeria to illuminate the ecology of the Palaearctic migrants to the country. The faunistic relationship of the resident and migrant avifauna is considered and it is shown that approximately one species in six is migrant. It is shown that the more arid vegetation belts support the largest numbers of migrant species, the forest belt supporting only very few species. Some species appear to overfly the most northern areas. Rather few observations of visual migration are available but those known are recorded. A summary of ringing recoveries affecting Nigeria is given and it is shown that there is clear evidence of species returning to the same wintering grounds each year. The status of 135 migrant species is briefly treated and other species are mentioned where negative information is valuable. Calandrella rufescens, Cyanosylvia svecica, and Emberiza hortulana, notmentioned by Bannerman (1930-53) are included and Cettia cetti is recorded from West Africa for the first time. Several species have had their range extended to include Nigeria. A comparison of breeding areas with the Mediterranean/Sahara crossing zones and Nigerian occurrences shows that most terrestrial species in Nigeria move fairly closely to the lines of longitude. Many aquatics, mostly herons and ducks, breed much to the east of the longitude of Nigeria. It is suggested that the unexpected number of Palaearctic migrants which winter in the arid north of Nigeria indicates that food is less scarce than the appearance of the country in the late dry season indicates. There is a great need for an ornithological and ecological research station in Nigeria in an area such as southwest Lake Chad.     

AUTUMN AND SPRING WEIGHTS OF SOME PALAEARCTIC MIGRANTS IN CENTRAL NIGERIA

During the winters 1963/64 and 1964/65 some 700 weights of 19 species of Palaearctic migrants caught in Central Nigeria were obtained. Where there were adequate weights for analysis, mean weights in the spring were significantly heavier than mean autumn weights; mean weight gains in the spring varied from 47% (Pied Flycatcher) to 21% (Garden Warbler and Spotted Flycatcher). Individual gains were higher.     

FACTORS AFFECTING THE FOOD SUPPLY AND BREEDING SEASON OF RESIDENT BIRDS AND MOVEMENTS OF PALAEARCTIC MIGRANTS IN A TROPICAL AFRICAN SAVANNAH

The fact that Palaearctic migrants arrive in the northern tropical savannah of Africa during the dry season suggests potential competition for food with African species. Moreover, in the southern tropical savannah African species breed during the rainy seasons, when Palaearctic migrants are present. In the equatorial area of Serengeti, East Africa, an index of the food supply for insectivorous birds was obtained from 3 years of light-trap measurements and sweep net samples. Adults of Lepidoptera, Coleoptera, Orthoptera and Isoptera are sparse in the dry season but become locally abundant after the first rainstorms that mark its close. They are apparently blown by converging winds ahead of the inter-tropical front and settle to lay eggs where rain has fallen. These early storms therefore produce localized superabundances of food. In the ensuing rainy seasons insect abundance remains high. African insectivorous birds breed during the wet period, reaching a peak two months after the insect increase. It is suggested that this lag is due to the need to recover body condition, build up reserves for eggs, develop gonads and wait for vegetation and insect larvae to develop. In the samples available, breeding records of above-ground nesters peaked in the first rains, while ground-nesters peaked in the second (main) rains. Predators bred towards the end of the rains, when there is an abundance of fledglings and small mammals. Thus the food supply could act as the ultimate factor determining the timing of the breeding season in this area. Palaearctic migrants arrive in the Serengeti 4–10 weeks ahead of the main rain front. However, most species are only found where rain has fallen recently. When conditions dry up they move on to other wet areas. Thus they overlap with African species only where there is a superabundance of insects. When the rains become widespread Palaearctic migrants disperse into their usual habitats, and therefore appear not to compete for available resources with closely related species of African birds. The situation in West Africa, where residents and migrants overlap throughout the dry season, cannot be explained in the same terms.     

OBSERVATIONS ON WINTERING BIRDS AND SPRING MIGRANTS IN TRIPOLITANIA

Between 30 November 1960 and 19 April 1961 observations were made on wintering birds and the spring migration in Tripolitania. The main additions and differences from Guichard's (1956-57) observations are recorded here and a full systematic list is deposited at the Edward Grey Institute, Oxford.     

NOTES ON NORTHERN MIGRANTS OBSERVED INLAND IN BRITISH GUIANA

1. The scarcity of northern migrants in British Guiana and the South American tropics generally is commented on.
2. 40 species of migrants, exclusing rare vagrants, from North America are known to occur in British Guiana; 24 of these have been recorded from the Bartica district. In each case nearly half are waders.
3. The number of species found in the Bartica district of British Guiana is compared with the number recorded in a recent intensive study of an inland area near the Caribbean coast of northeastern Venezuela, where 12 of the 16 northern migrants noted were waders.
4. A list of migrants from North America observed at the tropical research station of the New York Zoological Society at Kartabo (Bartica district) is criticized.
5. Notes from the writer's own observations on inland occurrences in British Guiana of 19 migrants and one rare vagrant are given.
6. Notes on two other species, the Swallow-tailed Kite Elanoides forficatus (a resident race occurs), and the Black Swift Nephoecetes niger , whose winter range is unknown, are included.