The annual migrations of three species of West African fruit bats (Chiroptera: Pteropodidae)

1983 ◽  
Vol 61 (10) ◽  
pp. 2266-2272 ◽  
Author(s):  
Donald W. Thomas
Keyword(s):  
High Amplitude ◽  
Dry Season ◽  
West African ◽  
Wet Season ◽  
Forest Zone ◽  
The North ◽  
Large Colony ◽  
Males And Females ◽  
Catch Rates ◽  
Eidolon Helvum

The seasonal movements of Eidolon helvum, Myonycteris torquata, and Nanonycteris veldkampi were studied over a 2-year period in West Africa. During the dry season, E. helvum roosts in at least one large colony (ca. 500 000 individuals) in the southern forest zone of Ivory Coast. Following the birth of young in February, males and females move into the savanna zones, and the progressive establishment and decline of colonies along a south–north axis indicates that E. helvum migrates at least to the Niger River basin by the middle of the wet season (July). During the dry season, both M. torquata and N. veldkampi are absent from savanna sites, but are common in the forest zone. With the onset of the rainy season in March, catch rates of both species increase first at a southern Guinea savanna site and subsequently at a savanna site 400 km to the north, indicating that both species migrate at least to the southern Sudanese savanna zone during the wet season. Both sexes of N. veldkampi migrate, but the migration of M. torquata is restricted to the immature male cohorts. I argue that the high amplitude of the seasonal fluctuations in fruit abundance at savanna sites creates a wet-season surplus of food which results in low intra- and inter-specific competition levels at these sites relative to the forest zone. This may provide the conditions leading to the observed annual migrations.

Migratory Labour from North-Wester Nigeria

Africa ◽  
1957 ◽  
Vol 27 (3) ◽  
pp. 251-261 ◽  
Author(s):  
R. Mansell Prothero
Keyword(s):  
Large Scale ◽  
Source Area ◽  
Dry Season ◽  
Labour Migration ◽  
Agricultural Activity ◽  
Wet Season ◽  
The North ◽  
The People ◽  
Limited Scale ◽  
Opening Paragraph

Opening ParagraphReaders of Africa will be well aware of population migration as a characteristic feature of a continent where movement between one part and another is largely unrestricted as compared with the more settled parts of the world. There is much evidence of large-scale tribal migrations in the past, of the age-old seasonal wanderings of herders, and of recent labour migration to centres of mineral and industrial production, the last particularly in Central and South Africa. Information is more limited concerning the features of labour migration in West Africa at the present day. In general it is thought that migrants leave their home areas, after the harvest at the commencement of the dry season, to seek work elsewhere for a period of from three to six months and then return to take up farming with the commencement of the next rains. The major source area for these migrants is to the north of the tenth parallel where the wet season is concentrated into a period of about four months, thus severely restricting agricultural activity. Cultivation during the dry season is possible only on a very limited scale. There is thus a considerable period of the year when the primary economic activity of the people is not possible. It is logical that they should seek work elsewhere.

Occurrence of the grasshopper pest Zonocerus variegatus (L.) (Orthoptera: Pyrgomorphidae) in south-western Nigeria in relation to the wet and dry seasons

1980 ◽  
Vol 70 (4) ◽  
pp. 621-633 ◽  
Author(s):  
W. W. Page
Keyword(s):  
Dry Season ◽  
Seasonal Abundance ◽  
Secondary Peak ◽  
Rapid Decline ◽  
Arid Zones ◽  
Zonocerus Variegatus ◽  
Wet Season ◽  
The North ◽  
Dry Seasons ◽  
Peak Abundance

AbstractAn investigation into the seasonal abundance of Zonocerus variegatus (L.) around Ibadan, Nigeria, showed that hatching occurs between October and March and peak abundance is in late November. Adults occur almost throughout the year. Oviposition takes place between March and October or possibly November, with a peak in April. Eggs laid in March and April hatch in October and November after a diapause, while those laid from June onwards do not appear to enter diapause. Thus eggs laid in June and July hatch at the same time as those laid in March and April. Parasitism by the sargophagid fly Blaesoxipha filipjevi (Rod.) during March and April results in a rapid decline in adult numbers which may be followed by a secondary peak in adult numbers when nymphs, which are present at the same time and are rarely parasitised, reach adult stage. Oviposition resulting from such a peak does not produce a secondary peak in hatching as this coincides with hatching from earlier layings. The fungus Entomophthora grylli plays an important role in controlling the abundance of nymphs and adults during the dry season despite the intermittent nature of the attacks. During the wet season, the fungus is able to germinate and disperse more readily, thus keeping the numbers of the insects low. It is concluded that there is one generation of Z. variegatus a year, with a peak in population coinciding with the dry season (November-March). It is suggested from the results that the grasshopper may have originated in the semi-arid zones of the north.

scholarly journals SEASONAL EFFECTS ON LAMB PRODUCTION UNDER TROPICAL CONDITIONS

2021 ◽  
Vol 11 (2) ◽  
pp. 168-174
Author(s):  
I. O. A. Adeleye
Keyword(s):  
Birth Weight ◽  
Inverse Relationship ◽  
Dry Season ◽  
West African ◽  
Seasonal Effects ◽  
Multiple Birth ◽  
Wet Season ◽  
Average Birth Weight ◽  
Tropical Conditions ◽  
Weaning Age

Observations were made over a period of three years on a total of 336 West African Dwarf (WAD) ewes that were mated to four rams in rotation. Out of a total of 753 lambs obtained, 459 (61%) were produced in the wet season as compared to 294 (39%) produced in the dry season. More lambs were produced as a result of multiple birth (twins and triplets) in the wet than in the dry season. Consequently, the average birth weight of the wet season lambs (1.58kg) was lower than the average birth weight (1.66 kg) of the dry season lambs. Despite this initial disadvantage, the wet season lambs had a higher average weaning weight (9.11 kg) than the dry season lambs (7.83 kg). The effects of season on pre weaning lamb mortality was minimal while the effects of type of birth were quite apparent. Lowest pre-weaning lamb mortality values were recorded for single lambs, followed by twins and triplets, in ascending order. The data also showed that a slightly higher proportion of the male lambs reached weaning age than female lambs. This observation could be associated with reported inverse relationship between lamb birth weight and mortality found in literature.

Growth Strategies of Eucalyptus camaldulensis Dehnh. At Three Sites in Northern Australia

1994 ◽  
Vol 21 (5) ◽  
pp. 653 ◽  
Author(s):  
A Gibson ◽  
EP Bachelard ◽  
KT Hubick
Keyword(s):  
Gas Exchange ◽  
Shoot Growth ◽  
Eucalyptus Camaldulensis ◽  
Dry Season ◽  
Growth Strategies ◽  
Wet Season ◽  
Wind Speeds ◽  
The North ◽  
Air Temperatures ◽  
Semi Arid

The morphology and physiology of trees of Eucalyptus camaldulensis growing in the field at two monsoonal and one semi-arid location were compared. In the wet season, shoot growth at the monsoonal locations was similar and larger than that at the semi-arid location. In the dry season, new shoot growth at the more humid monsoonal location (Petford) was similar to growth in the wet season while at the less humid (Katherine) and the semi-arid (Tennant Creek) locations, shoot growth was foreshortened and the leaves had larger dry weights per unit area. In the summer wet season, leaves on both the north and south sides of the trees were maintained at or below (by up to 5�C) air temperatures throughout the day except for north facing leaves at Petford which were consistently above (by up to 3�C) air temperatures. Midday gas exchange in the dry season at both monsoonal localities was restricted to trees at the water's edge, whereas most trees, including those at drier sites, at the semi-arid location exhibited significant rates of gas exchange. The results, which are discussed in relation to environmental variables (vapour pressure deficits, wind speeds) to which the trees are exposed, and to previous results obtained in the glasshouse, indicate that the differences in shoot growth and physiology are adaptations to the environment in which the trees have evolved.

Home-range and den use of the mahogany glider, Petaurus gracilis

2000 ◽  
Vol 27 (1) ◽  
pp. 49 ◽  
Author(s):  
Stephen M. Jackson
Keyword(s):  
Home Range ◽  
Dry Season ◽  
Home Ranges ◽  
Adjacent Area ◽  
Wet Season ◽  
Male And Female ◽  
Fragmented Habitat ◽  
Significant Difference ◽  
Socially Monogamous ◽  
Males And Females

The home-range of the mahogany glider was estimated, and its social behaviour examined, by following radio-collared animals over a two-year period within an area of continuous habitat and an adjacent area of fragmented habitat. The average home range within the continuous habitat was 19.25 ha for males and 20.34 ha for females, with male and female pairs occupying a combined area of 23.15 ha. In contrast, the average home range in the fragmented habitat was 11.05 ha for males and 6.80 ha for females, with a combined home-range of male and female pairs being 11.60 ha. The average overlap of the home ranges of paired males and females was 85.9%, compared with approximately 11% for non-paired individuals, which suggests that mahogany gliders are socially monogamous. For a total of 46 nights on which gliders were considered to behave normally for the entire night, the average foraging distance was 1506 m (range 590–3420 m) with no significant difference between males and females in either the continuous or fragmented habitat. There was, however, a significant difference in the distance individuals travelled during different times of the year, with longer distances being travelled during late dry season/wet season and shorter distances during the early to mid dry season. Mahogany gliders also travelled further when there was a high availability of nectar and pollen than when there was lower availability. A total of 83 dens (tree hollows) were recorded for the mahogany glider, with the poplar gum, Eucalyptus platyphylla, forest red gum, Eucalyptus tereticornis, and Clarkson's bloodwood, Corymbia clarksoniana, being most used.

scholarly journals PHOTOSYNTHETIC ACTIVITY AND EARLY GROWTH OF FOUR CACAO GENOTYPES AS INFLUENCED BY DIFFERENT SHADE REGIMES UNDER WEST AFRICAN DRY AND WET SEASON CONDITIONS

2012 ◽  
Vol 49 (1) ◽  
pp. 31-42 ◽  
Author(s):  
K. ACHEAMPONG ◽  
P. HADLEY ◽  
A. J. DAYMOND
Keyword(s):  
Leaf Area ◽  
Photosynthetic Activity ◽  
Vapour Pressure Deficit ◽  
Dry Season ◽  
West African ◽  
Limiting Factor ◽  
Genotypic Differences ◽  
Wet Season ◽  
Photosynthetic Rates ◽  
The Difference

SUMMARYThe physiological performance of four cacao clones was examined under three artificial shade regimes over the course of a year in Ghana. Plants under light shade had significantly higher photosynthetic rates in the rainy seasons whereas in the dry season there was a trend of higher photosynthetic rates under heavy shade. The results imply that during the wet seasons light was the main limiting factor to photosynthesis whereas in the dry season vapour pressure deficit was the major factor limiting photosynthesis through stomatal regulation. Leaf area was generally lower under heavier shade but the difference between shade treatments varied between clones. Such differences in leaf area allocation appeared to underlie genotypic differences in final biomass production in response to shade. The results suggest that shade for young cacao should be provided based on the current ambient environment and genotype.

scholarly journals FACTORS AFFECTING LIVEWEIGHT OF GOAT AND SHEEP IN TWO LOCATION WITHIN OGUN STATE.

2021 ◽  
Vol 23 (1) ◽  
pp. 12-15
Author(s):  
C. O. N. IKEOBI ◽  
O. A. FALETI
Keyword(s):  
Dry Season ◽  
West African ◽  
Wet Season ◽  
The West ◽  
Southwestern Nigeria ◽  
Factors Affecting ◽  
West African Dwarf ◽  
Ogun State ◽  
West African Dwarf Goat ◽  
The Mean

A study was conducted over two years  With the to determine the changes in the liveweight of Yankasa sheep and Maradi goat in goats and sheep in two locations in Ogun State, South-Western Nigeria Factors found to be important included breed of goat, season, location, and sex of the animal. The Maradi goat had a greater variation in its liveweight than the West African' dwarf goat. The mean weekly gain in the liveweight of goats was 0.18±02 dry season and 0.26±0.05 kg in the wet season. Liveweight changes were greater in yearling Yankasa sheep reared in this part of the Southwestern Nigeria than in older ones; these differences were significantly greater in the dry than in the wet season.

scholarly journals Water and Salt Transports in the Hengsha Channel of Changjiang Estuary

2022 ◽  
Vol 10 (1) ◽  
pp. 72
Author(s):  
Rui Ma ◽  
Jianrong Zhu
Keyword(s):  
Water Transport ◽  
Neap Tide ◽  
Spring Tide ◽  
Dry Season ◽  
Changjiang Estuary ◽  
Dynamic Mechanism ◽  
Gradient Force ◽  
Residual Water ◽  
Wet Season ◽  
The North

In a multilevel bifurcated estuary, the channels between the bifurcated branches play important roles in the exchanges of water and salt. In the Changjiang Estuary, the Hengsha Channel (HC) connects the North Channel (NC) and the North Passage (NP). In this paper, based on a two-way nesting unstructured quadrilateral grid, finite-differencing, three-dimensional estuarine and coastal ocean model, the tidal and seasonal variations in the water and salt transports in the HC were simulated, and their dynamic mechanism was analyzed. The residual water and salt transports in the HC both flow southward from the NC to the NP. In wet season, the residual water transport in the HC is 677 m3/s during neap tide and 245 m3/s during spring tide, and the residual salt transport is 0. In dry season, the residual water and salt transports in the HC are 1278 m3/s and 0.38 t/s during neap tide, respectively, and 1328 m3/s and 12.61 t/s during spring tide. Affected by the northerly wind and the southeastward baroclinic gradient force, the water and salt fluxes in dry season are much larger than those in wet season. The dynamic mechanism responsible for the water transport in the HC was numerically simulated and analyzed.

Activity Cycles ofGlossina pallidipesAust.,G. palpalis fuscipesNewst. andG. brevipalpisNewst

1965 ◽  
Vol 56 (1) ◽  
pp. 141-160 ◽  
Author(s):  
J. M. B. Harley
Keyword(s):  
Lake Victoria ◽  
Glossina Pallidipes ◽  
Physical Factor ◽  
Dry Season ◽  
Physical Factors ◽  
Wet Season ◽  
North East ◽  
The North ◽  
Morning Peak ◽  
Hot Dry Season

A series of 24-hr catches ofGlossina pallidipesAust.,G. palpalis fuscipesNewst. andG. brevipalpisNewst. was carried out on the north-east shore of Lake Victoria over a period of 11 months in 1962–63. The object was to define and compare the daily pattern of activity of the three species as indicated by the numbers caught hourly on three black cattle that were used as bait. Catching during the hours of darkness was done by the light of dimmed hurricane lamps. The period of observation covered successively a dry season, a wet season, a cool dry season and a hot dry season.At all seasons, males ofG. pallidipeswere caught in gradually increasing numbers from just before dawn until shortly before sunset, after which a rapid decrease took place. Females ofG. pallidipesexhibited a different pattern, with a gradual rise in activity in the morning until about midday, after which activity remained more or less constant until shortly before sunset, when a rapid fall occurred. There was never any indication of a morning peak in activity such as has been described for this species elsewhere. Activity during the night was at an extremely low level.Activity of both males and females ofG. p. fuscipesstarted about dawn, increased to a peak in the middle hours of the day, and then fell fairly rapidly in the evening; the exact time of the peak was variable. None was caught during the night.There was some activity ofG. brevipalpisthroughout the diel, but marked peaks of activity were exhibited by both sexes. In the open, these took place immediately after sunset and immediately before sunrise, the latter being the smaller. In the shade, the morning peak in both sexes was an hour later than in the open, and the evening peak in males alone was an hour earlier.These results are compared with those of other workers, and the influence of physical factors is discussed. Particular values of temperature and saturation deficit were not closely associated with particular levels of activity of any of the three species, and light intensity is probably the physical factor that is most consistently the same at times of particular levels of activity at all seasons.

Archaeology of West Africa

2019 ◽  
Author(s):  
Natalie Swanepoel
Keyword(s):  
West Africa ◽  
Early Period ◽  
State Level ◽  
Geographic Region ◽  
Middle Stone Age ◽  
West African ◽  
Stone Age ◽  
Forest Zone ◽  
The North ◽  
Pass Through

West Africa is a vast geographic region that in archaeological terms is usually circumscribed by the Tropic of Cancer in the north, Cameroon in the east, and the Atlantic Ocean in the west and south. It encompasses a great deal of variation and diversity on environmental, linguistic, cultural, and political fronts. One of its defining features is the parallel environmental zones that run east to west so that as the traveler moves south to north, they pass through coastal, forest, savanna (wooded and grassland), and Sahelian zones until they reach the Sahara in the north. The region’s modern-day political borders created by European colonialist competition cut through existing ethnolinguistic groups and erstwhile kingdoms and states. Politically, during the last 2,000 years West African societies ranged in scale from decentralized agricultural societies to mobile pastoralists to state-level societies and empires. As is to be expected, West African archaeology reflects this complexity. It is for this reason that, rather than reducing it to an “ages and stages” formulation, most West African(ist) archaeologists speak about the material record as a “mosaic” which varied over time and space. In comparison to the rest of the continent, very little is known about the very early period of human history, with scant evidence for settlement during the Early and Middle Stone Age periods. The region’s past is better known from about midway through the Holocene (Later Stone Age), 6,000 bce. This is also coincident with wide-ranging transformations in the lifestyles of hunter-gatherers in the region, as this is when the transition to food production occurs, first with pastoralism and later with crop cultivation. Iron technology was introduced in the 1st millennium bce, and the rise of complex societies with their accompanying institutions occurred in the 1st millennium ce. Any discussion of the literature will be partial, but this is exacerbated by the patchy archaeological coverage of the region. This is for a number of reasons: the size of the area to be covered, the variable history of archaeological research in different parts, the difficulty of working in some ecological settings such as the forest zone, conflict-ridden zones that make it unsafe to conduct research, and difficulties in African scholars accessing resources and funding. Despite this, considerable progress in our knowledge of the region has been made.

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