NOTE ON THE LONGEVITY OF THE VULTURINE SEA.EAGLE,CYPOHIERAX ANGOLENSIS (Gm.)

Herremans, M. &; Herremans-Tonnoeyr, D. 1994. Seasonal patterns in abundance of Lilacbreasted Rollers Coracias caudata and Purple Rollers Coracias naevia inferred from roadside counts in eastern and northern Botswana. Ostrich 65:66-73

The relative abundance of rollers (Coraciidae) in 45933 km of roadside counts made in eastern and northern Botswana between May 1991 and April 1994 was assessed by season and biome. Lilacbreasted Rollers appeared to move from breeding grounds in the northern Botswana woodlands into the northern Kalahari, and north-westward from breeding grounds in the Transvaal into the Limpopo drainage system and adjacent eastern Kalahari, during winter. Purple Rollers showed an influx during autumn and winter over most of eastern Botswana, but birds did not remain during the drought winter of 1992. The pattern indicated a large scale west-east or southwest-northeast migratory movement, from breeding grounds in the drier parts of the Kalahari to wintering grounds in the more humid periphery of the Kalahari.     

5. SOME NOTES RESULTING FROM A HOLIDAY TRIP THROUGH EAST GRIQUALAND

The study investigated the bird species diversity associated with vegetation communities found on a single mountain slope in the Usuthu Gorge Community Conservation Area, northern KwaZulu-Natal. Thirteen sample sites were surveyed on a monthly basis for 12 months. Over this period, 279 birds and 55 species were recorded, of which the Dark-capped Bulbul Pycnonotus tricolor was the most abundant. The Rattling Cisticola Cisticola chiniana was the indicator species in the highest community, Open Bushveld, which is characterised by grassland and bush patches. The White-bellied Sunbird Cinnyris talatala was an indicator in the second-lowest community, Dense Bushveld–Woodland, which is characterised by steep slopes and thickets. In Wooded Grassland, located between the above two communities, the highest beta diversity (species turnover) was recorded and this outcome was probably caused by large areas covered by rocks that compelled woodland birds to move through this community. Contrary to expectation, the gamma diversity per vegetation community increased with elevation from 18 to 33 species in Dense Bushveld–Woodland, Wooded Grassland and Open Bushveld. A future study should measure bird species diversity on larger elevational gradients, i.e. slopes from 500 to 3 000 m above sea level, which also include more distinct vegetation communities.     

Seasonal abundance and habitat use of bird species in and around Wondo Genet Forest,south‐central Ethiopia

The habitat use and seasonal migratory pattern of birds in Ethiopia is less explored as compared to diversity studies. To this end, this study aimed at investigating the patterns of distribution related to seasonality and the effect of habitat characteristics (elevation, slope, and average vegetation height) on habitat use of birds of Wondo Genet Forest Patch. A stratified random sampling design was used to assess the avian fauna across the four dominant habitat types found in the study area: natural forest, wooded grassland, grassland, and agroforestry land. A point transect count was employed to investigate avian species richness and abundance per habitat type per season. Ancillary data, such as elevation above sea level, latitude and longitude, average vegetation height, and percent slope inclination, were recorded with a GPS and clinometers per plot. A total of 33 migratory bird species were recorded from the area, of which 20 species were northern (Palearctic) migrants while 13 were inter‐African migrants. There was a significant difference in the mean abundance of migratory bird species between dry and wet seasons (t = 2.13, p = .038, df = 44). The variation in mean abundance per plot between the dry and wet seasons in the grassland habitat was significant (t = 2.35, p = .051, df = 7). In most habitat types during both dry and wet seasons, omnivore birds were the most abundant. While slope was a good predictor for bird species abundance in the dry season, altitude and average vegetation height accounted more in the wet season. The patch of forest and its surrounding is an important bird area for migratory, endemic, and global threatened species. Hence, it is conservation priority area, and the study suggests that conservation coupled with ecotourism development is needed for its sustainability.     

Effects of woodland modification by African elephant Loxodonta africana on bird diversity in northern Botswana

Bird diversity was assessed by point-transect-count sampling during the dry and the wet season in riverine gallery woodland and in Colophospermum mopane woodland with different levels of elephant impact Dramatic woodland degradation did not result in a dramatic overall reduction m bird diversity, but resulted in substantial changes in bird species composition and capacity for migrant birds Less affected, more dense woodlands functioned as dry season refuges for'resident'Afrotropical species, but this function was lost in degraded woodlands In contrast, secondanzed habitat had a much higher capacity for long distance migrants in the wet season Species endemic to the sub-region and subspecies with restricted ranges centred in the area were not negatively affected by woodland degradation The cumulative interference of past and current elephant numbers with the conservation of bird diversity appears to be insignificant in northern Botswana     

Water and energy fluxes during summer in an arid‐zone passerine bird

Endothermic animals resident in hot, arid terrestrial environments are likely to face a trade‐off between their ability to obtain water and elevated thermoregulatory water requirements. We assessed whether daily water flux (DWF) is higher on hot days, reflecting increases in evaporative cooling demands, in an arid‐zone bird that obtains its water through food intake. We obtained measurements of DWF (partitioned into water influx and efflux rates) in 71 White‐browed Sparrow‐Weavers Plocepasser mahali at a desert site and a semi‐desert site, during summer in the Kalahari Desert of southern Africa. We found no evidence that DWF varied with maximum daily air temperature (T_air, range = 27.6–39.2 °C). Instead, DWF was lower during dry periods than in the wet season at the semi‐desert site. Furthermore, birds showed deficits in water balance (water influx/water efflux) during the dry periods at both sites. Our data show that DWF is low in a non‐drinking bird that obtains its water through food, and that demands for evaporative water loss on very hot days (maximum T_air of 40–44 °C) may exceed water intake rates during hot and dry periods. Species that do not have opportunities to drink will experience strong trade‐offs between thermoregulation, hydration state and activity levels as temperatures increase.     

Variable strength of top‐down effects in Nothofagus forests: bird predation and insect herbivory during an ENSO event

Abstract Predators are thought to play a key role in controlling herbivory, thus having positive indirect effects on plants. However, evidence for terrestrial trophic cascades is still fragmentary, perhaps due to variation in top‐down forces created by environmental heterogeneity. We examined the magnitude of predation effects on foliar damage by chewing insects and mean leaf size, by excluding birds from saplings in ‘dry’ and ‘wet’Nothofagus pumilio forests in the northern Patagonian Andes, Argentina. The experiment lasted 2 years encompassing a severe drought during the La Niña phase of a strong El Niño/Southern Oscillation event, which was followed by unusually high background folivory levels. Insect damage was consistently higher in wet than in dry forest saplings. In the drought year (1999), bird exclusion increased folivory rates in both forests but did not affect tree leaf size. In the ensuing season (2000), leaf damage was generally twice as high as in the drought year. As a result, bird exclusion not only increased the extent of folivory but also significantly decreased sapling leaf size. The latter effect was stronger in the wet forest, suggesting compensation of leaf area loss by dry forest saplings. Overall, the magnitude of predator indirect effects depended on the response variable measured. Insectivorous birds were more effective at reducing folivory than at facilitating leaf area growth. Our results indicate that bird‐initiated trophic cascades protect N. pumilio saplings from insect damage even during years with above‐normal herbivory, and also support the view that large‐scale climatic events influence the strength of trophic cascades.     

Leaf flushing during the dry season: the paradox of Asian monsoon forests

Aim Most deciduous species of dry monsoon forests in Thailand and India form new leaves 1–2 months before the first monsoon rains, during the hottest and driest part of the year around the spring equinox. Here we identify the proximate causes of this characteristic and counterintuitive ‘spring‐flushing’ of monsoon forest trees. Location Trees of 20 species were observed in semi‐deciduous dry monsoon forests of northern Thailand with a 5–6‐month‐long severe dry season and annual rainfall of 800–1500 mm. They were growing on dry ridges (dipterocarp–oak forest) or in moist gullies (mixed deciduous–evergreen forest) at 680–750 m altitude near Chiang Mai and in a dry lowland stand of Shorea siamensis in Uthai Thani province. Methods Two novel methods were developed to analyse temporal and spatial variation in vegetative dry‐season phenology indicative of differences in root access to subsoil water reserves. Results Evergreen and leaf exchanging species at cool, moist sites leafed soon after partial leaf shedding in January–February. Drought‐resistant dipterocarp species were evergreen at moist sites, deciduous at dry sites, and trees leafed soon after leaf shedding whenever subsoil water was available. Synchronous spring flushing of deciduous species around the spring equinox, as induced by increasing daylength, was common in Thailand's dipterocarp–oak forest and appears to be prevalent in Indian dry monsoon forests of the Deccan peninsula with its deep, water‐storing soils. Main conclusions In all observed species leafing during the dry season relied on subsoil water reserves, which buffer trees against prolonged climatic drought. Implicitly, rainfall periodicity, i.e. climate, is not the principal determinant of vegetative tree phenology. The establishment of new foliage before the summer rains is likely to optimize photosynthetic gain in dry monsoon forests with a relatively short, wet growing season.     

Hydraulic and photosynthetic co-ordination in seasonally dry tropical forest trees

In the present study the linkage between hydraulic, photosynthetic and phenological properties of tropical dry forest trees were investigated. Seasonal patterns of stem‐specific conductivity (K_SP) described from 12 species, including deciduous, brevi‐deciduous and evergreen species, indicated that only evergreen species were consistent in their response to a dry‐to‐wet season transition. In contrast, K_SP in deciduous and brevi‐deciduous species encompassed a range of responses, from an insignificant increase in K_SP following rains in some species, to a nine‐fold increase in others. Amongst deciduous species, the minimum K_SP during the dry season ranged from 6 to 56% of wet season K_SP, indicating in the latter case that a significant portion of the xylem remained functional during the dry season. In all species and all seasons, leaf‐specific stem conductivity (K_L) was strongly related to the photosynthetic capacity of the supported foliage, although leaf photosynthesis became saturated in species with high K_L. The strength of this correlation was surprising given that much of the whole‐plant resistance appears to be in the leaves. Hydraulic capacity, defined as the product of K_L and the soil–leaf water potential difference, was strongly correlated with the photosynthetic rate of foliage in the dry season, but only weakly correlated in the wet season.     

Reproductive Phenology of Woody Species in a North Australian Tropical Savanna1

Interspecific and interannual variation in reproductive phenology was quantified for 50 common species of trees and shrubs from a mesic savanna near Darwin, northern Australia. The presence of buds, flowers, and fruit was noted over a 30-month period, from September 1992 to February 1995. Surveys were undertaken at monthly intervals for the less common species, and at bimonthly intervals for ten of the common trees and tall shrubs. The majority of species flowered each year at about the same time. There was no evidence of sub-annual or continuous regimes of reproductive phenology. There was no supra-annual carryover of seed-bearing fruit in the canopy of any species. The peak flowering periods were the mid to late dry season (July–August) and the transition between the dry season and the wet season (October–November). The two dominant trees–Eucalyptus miniata and E, tetrodonta– flowered during the dry season, thereby providing resources for some elements of the vertebrate fauna. Flowering and fruiting were uncommon at the end of the wet season (February/March), although two species that flower and fruit at this time (E. porrecta and Terminalia ferdinandianas may provide resources to consumers at a time when floral or fruit resources are otherwise scarce. Because the peak of reproductive activity takes place during the late dry season, fruit maturity and seed dispersal have occurred prior to the onset of the rainy season for most species, and germination and seedling establishment potentially may take effect in response to the first rains. Late dry season fires, which tend to be extensive and intense, are a potential threat to the floral and fruit reserves within these savannas.     

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.     

ABUNDANCE AND SEASONALITY OF THE SAVANNA AVIFAUNA AT PORT MORESBY, PAPUA NEW GUINEA

The results of 156 transect counts carried out over 30 months in savanna of the Coastal Hill Zone, Port Moresby, Papua New Guinea, are analysed. The avifauna is depauperate compared to similar habitats in New Guinea and temperate Australia. Twelve common species of the Port Moresby savannas were not so in the Coastal Hill Zone and reasons for their rarity are given. Most species present are solely savanna forms but some are dependent upon the presence of small patches of monsoon forest. Average density of birds was estimated at 55 per 10ha, a very low figure compared to New Guinean rainforests. Carnivores and mixed-feeders make up two thirds of numbers present but frugivores, because of their large individual size, are a significant proportion of biomass. There was little significant seasonal difference in overall numbers except for granivores which decline in numbers during the wet season. However, individual species show regular seasonal fluctuations reasons for which are postulated. A correlation exists between flowering of trees and numbers of certain species, and also between the annual grass-fires and numbers of certain grassland species. Merops ornatus, Lalage sueurii and Coracina novaehollandiae, considered in the literature to be wintering migrants, are also shown to be breeding residents. Breeding records for 462 species were analysed. Most breeding of insectivores and mixed-feeders occurs in the Austral spring during the dry season and ends before the onset of heavy rains. Granivores breed in the late wet season. The few records for frugivores indicate a wet season peak.     

Apparent carboxylation efficiency and relative stomatal and mesophyll limitations of photosynthesis in an evergreen cerrado species during water stress

Miconia albicans, a common evergreen cerrado species, was studied under field conditions. Leaf gas exchange and pre-dawn leaf water potential (Ψ_pd) were determined during wet and dry seasons. The potential photosynthetic capacity (P _Npmax) and the apparent carboxylation efficiency (ε) dropped in the dry season to 28.0 and 0.7 %, respectively, of the maximum values in the wet season. The relative mesophyll (L_m) and stomatal (L_s) limitations of photosynthesis increased, respectively, from 24 and 44 % in the wet season to 79 and 57 % at the peak of the dry season when mean Ψ_pd reached −5.2 MPa. After first rains, the P _Npmax, ε, and L_m recovered reaching the wet season values, but L_s was maintained high (63 %). The shallow root system growing on stonemason limited by lateral concrete wall to a depth of 0.33 m explained why extreme Ψ_pd was brought about. Thus M. albicans is able to overcome quickly the strains imposed by severe water stress.     

Strategies, punctuality of arrival and ranges of migrants in the Kalahari basin, Botswana

The timing and intensity of the first summer rains in the Kalahari basin are highly variable between years. Avian migrants to the area follow two principal strategies. Species arriving before November typically do so before significant rain can be expected and do not use ecological conditions as a proximal cue to time arrival; their arrival was unaffected by the failure of the early rains in 1994. Species arriving after mid-November respond to the timing and extent of the early rains and were progressively more delayed in parallel to a cumulative deficit in rainfall during the early part of the 1994 wet season. The second strategy results in erratic occupation of parts of the nonbreeding range, so that during drought years, rain-dependent, late-arriving species may remain absent from the Kalahari basin, complicating the assessment of the "effective" size of their nonbreeding range.     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

SEASONAL CHANGES IN NECTAR-FEEDING BY BIRDS AT ZARIA, NIGERIA

Nectar-feeding of birds was recorded during a phenological study of the woody vegetation at Zaria in the Northern Guinea Savanna of Nigeria. Throughout the dry season when it is in a non-breeding state, the Scarlet-breasted Sunbird Nectarinia senegalensis concentrates on the ornithophilous plants which flower in an overlapping sequence, and exploits the smaller-flowered species less frequently. As the flowering of the ornithophilous species decreases at the end of the dry season, the range of other plants exploited increases but, in the early rains as the flowering of the indigenous plants tails off, the sunbird switches to ornamental exotics and the indigenous, shrubby parasite, Tapinanthus globiferus. The bird is more conspicuously insectivorous during the wet season when it breeds. The Pygmy Sunbird Anthreptes platura is a breeding, dry-season visitor which exploits a somewhat different range of small-flowered, mainly entomophilous species and some exotics but also takes nectar from those ornithophilous species it can exploit, as well as the chiropterophilous Parkia clappertoniana. The bulk of the breeding population leaves the district before the flowering of the indigenous plant tails off. The five other species of sunbird recorded in the district are either very rare residents or more numerous wet-season visitors and passage migrants for which records of nectar-feeding are too few to draw conclusions about seasonal changes but the wet-season visitors appear to rely on the garden exotics in the comparative absence of flowering indigenous plants. Nectar-feeding on Bombax costatum and Parkia clappertoniana, where nectar is readily accessible and present in relatively large quantities, was noted for IS species of non-nectariniid birds, some of which were regular visitors. Some examples of flower consumption probably related to nectar-feeding are also mentioned.     

OBSERVATIONS ON THE BEHAVIOUR OF BIRDS IN SOUTHERN RHODESIA

Maclean, G. L. 1974. The breeding biology of the Rufouseared Warbler and its bearing on the genus Prinia. Ostrich 45: 9–14.

The Rufouseared Warbler Prinia pectoralis, a common species of the Kalahari scrub, nests after rain at any time of the year. Nest construction and nest sites are described. The clutch is normally three or four eggs. Incubation takes 12 to 13 days and the nestling period is 11 to 13 days. Data suggest that the Rufouseared Warbler is not a member of the genus Priniu, the generic position it currently occupies.     

Environmental control of flowering periodicity in Costa Rican and Mexican tropical dry forests

Aim We analyse the proximate causes of the large variation in flowering periodicity among four tropical dry forests (TDF) and ask whether climatic periodicity or biotic interactions are the ultimate causes of flowering periodicity. Location The four TDFs in Guanacaste (Costa Rica), Yucatan, Jalisco and Sonora (Mexico) are characterized by a 5–7 month long dry season and are located along a gradient of increasing latitude (10–30°N). Methods To dissect the differences in flowering periodicity observed at the community level, individual tree species were assigned to ‘flowering types’, i.e. groups of species with characteristic flowering periods determined by similar combinations of environmental flowering cues and vegetative phenology. Results Large variation in the fraction of species and flowering types blooming during the dry and wet season, respectively, indicates large differences in the severity of seasonal drought among the four forests. In the dry upland forests of Jalisco, flowering of leafless trees remains suppressed during severe seasonal drought and is triggered by the first rains of the wet season. In the other forests, leaf shedding, exceptional rainfall or increasing daylength cause flowering of many deciduous species at various times during the dry season, well before the summer rains. The fraction of deciduous species leafing out during the summer rains and flowering when leafless during the dry season is largest in the Sonoran TDF. Main conclusions In many wide‐ranging species the phenotypic plasticity of flowering periodicity is large. The distinct temporal separation of spring flowering on leafless shoots and subsequent summer flushing represents a unique adaptation of tree development to climates with a relatively short rainy season and a long dry season. Seasonal variation in rainfall and soil water availability apparently constitutes not only the proximate, but also the ultimate cause of flowering periodicity, which is unlikely to have evolved in response to biotic adaptive pressures.     

Evidence for altitudinal migration of forest birds between montane Eastern Arc and lowland forests in East Africa

Burgess, N.D. & Mlingwa, C.O.F. 2000. Evidence for altitudinal migration of forest birds between montane Eastern Arc and lowland forests in East Africa. Ostrich 71 (1 & 2): 184–190.

In this paper we assess the evidence for altitudinal movements of forest birds from the montane forests of the Eastern Arc mountains of East Africa to nearby lowland forest patches. For 34 montane species, including all the Eastern Arc endemics except Banded Green Sunbird Anthreptes rubritorques there is no evidence that they undertake seasonal movements to lower altitudes. An additional 26 montane species, of somewhat wider distribution, have been recorded at low (<500 m) altitudes during the cold/dry season (June to September). Most records of these montane birds at lower altitudes are from sites adjoining montane forest areas, although a few records are from lowland coastal forests at 100–240 km distance from montane areas. Only five of the 26 species (White-chested Alethe Alethe fulleborni, White-starred Forest Robin Pogonocichla stellata, Orange Ground Thrush Zoothera gurneyi, Evergreen Forest Warbler Bradypterus mariae and Barred Long-tailed Cuckoo Cercococcyx montanus) are regularly and commonly reported in the lowlands. They are also found in the lowlands in small numbers during the warm/wet season (October to February), when they may breed. The abundance of at least four, and probably more, of the forest birds with a more widespread distribution in the lowland and montane forests of East Africa declines greatly at high altitudes from the onset of the cold/wet season (February) and only increases again at the start of the warm/wet season (September). It is not known how far these species move as they cannot be easily separated from resident populations in lowland forests, and there are no ringing recoveries in different forests. Altitudinal migration of a proportion of the Eastern Arc avifauna is the most likely explanation for available data, although source-sink metapopulation theories may be helpful to explain the distributions of some species. As the movement of forest birds from the Eastern Arc to the lowland forests does not involve the rare endemics, they are of lower conservation concern, but the presence of montane and lowland forest may be important for the long-term survival of some more widely distributed forest species.     

Seasonal variation in grey crowned crane (Balearica regulorum) abundance in the Ngorongoro Crater,Tanzania

There are few quantitative estimates of numbers of Africa's endangered grey crowned cranes (Balearica regulorum), yet conservation of this species will depend on such estimates. We used line-transect distance sampling on multiple 2-km segments of an existing road network to estimate the abundance of grey crowned cranes in a portion of the Ngorongoro Crater, Tanzania, during the wet (April) and dry (August) seasons of 2016. We analysed data from 106 transects on which we observed 174 groups of 1–61 cranes (median and mode = 2). Abundance and density estimates on the areas surveyed were best modelled without group size as a covariate and indicated that mean crane densities were significantly lower in the wet season (2.4/km²) than in the dry season (20.2 cranes/km²). Even based on survey areas of different size, minimum estimated numbers of cranes in the Crater (wet season: 108–133; dry season: 362–401) likely reflect the concentration of cranes in the nonbreeding (dry) season in the perennial wetlands of the Crater and reinforce the notion of the Crater being a key seasonal habitat for crane populations in northern Tanzania, as previously suggested in the literature.     

Seasonal Variation in Polyspecific Associations Among Callimico goeldii, Saguinus labiatus, and S. fuscicollis in Acre, Brazil

Polyspecific associations (PSA) occur when 2 or more species maintain proximity or coordinate activities. PSA may provide ecological benefits similar to those of monospecific groups, i.e., protection against predation and improved foraging efficiency, but may also impart costs, such as feeding competition. I studied 3 New World Callitrichidae—Callimico goeldii, Saguinus fuscicollis, and S. labiatus—in northwestern Brazil over 18 mo between April 1999 and August 2003, during which single primary study groups of C. goeldii, S. labiatus, and S. fuscicollis consistently associated with one another. I compared patterns of PSA participation to variation in plant diets during wet and dry seasons. All 3 species associated an average 61% of observation time, but with significant seasonal variation in PSA. During the dry season, April–September, PSA occurred significantly less frequently than during the wet season, October–March (37% vs. 88%). The variation in PSA corresponded with seasonal shifts in plant food diets, resulting in less dietary overlap among all 3 species during the dry season, particularly between Callimico goeldii and Saguinus labiatus. Dietary richness, diversity, and evenness were also lower in the dry compared to the wet season for each species. The results suggest a link between PSA participation and diet among the taxa; foraging-related costs or feeding competition may constrain PSA during the dry season.