D.H. de Swardt

Bio: D.H. de Swardt is an academic researcher. The author has contributed to research in topics: Promerops gurneyi & Sugarbird. The author has an hindex of 4, co-authored 7 publications receiving 58 citations.

The seasonal movements of gurney's sugarbird promerops gurneyi in the lydenburg area, transvaal

Abstract: Summary 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 ...

Factors affecting the densities of nectarivores in protea roupeuae woodland

Abstract: Summary De Swardt, D.H. 1993. Factors affecting the densities of nectarivores in Protea roupelliae woodland. Ostrich 64:172-177. Between December 1986 and December 1992, 812 birds were captured at eleven selected Protea roupelliae sites at Lydenburg in the eastern Transvaal, South Africa. In this sample were 638 nectarivores, of which high densities of Gurney's Sugarbird Promerops gurneyi (41,3%) and Malachite Sunbird Nectarinia famosa (27,7%) were captured. Mean densities of 4,6 Gurney's Sugarbirds ha−1 and 3,5 Malachite Sunbirds ha−1,746) were recorded. No significant correlation was found between the clump-sizes and the number of birds although higher densities were recorded at some of the smaller sites. Protea flowering period, dump-size and the effect of fire are factors influencing bird densities. Male sugarbirds show site tenacity while localized movements have been observed in individual sugarbirds.

Distribution, biometrics and moult of gurney's sugarbird promerops gurneyi

Abstract: Summary De Swardt, D. H. 1992. Distribution, biometrics and moult of Gurney's Sugarbird Promerops gurneyi. Ostrich: 63:13-20. Gurney's Sugarbird Promerops gurneyi was studied at Lydenburg, from December 1986 until December 1990. Its distributional range coincides with the high mountainous veld types in association with Protea spp (mainly P. roupelliae). A total of 97 males (31,7%), 115 females (37,6%0) and 94 unsexed sugarbirds (30, 7%) were mistnetted and biometric and moult data recorded. The mean culmen, total head, tarsus, wing and tail lengths of males were significantly loner than those of females. No seasonal variation in the body mass of the sexes was recorded although males were heavier than females. In both sexes, a significant correlation was found between wing/tail and total head/culmen lengths. Bulging in P6 in males was significantly correlated with wing length. Primary moult occurred between September and March, coinciding with the breeding season. Primaries were moulted descendantly and se...

Annual survival of Gurney's Sugarbird, Promerops gurneyi

Abstract: (2001). Annual survival of Gurney's Sugarbird, Promerops gurneyi. Ostrich: Vol. 72, No. 3-4, pp. 206-208.

A re-evaluation of morphological differences in the Karoo Thrush Turdus smithi – Olive Thrush Turdus olivaceus species complex

Abstract: There is confusion in the literature concerning the taxonomic status of the Turdus smithi – T. olivaceus species complex. Here we attempt to clarify morphological differences within this complex. In addition, we attempt to clarify identification of the respective taxa. Although mean measurements of morphometric features differed significantly between species and subspecies, these features are not useful in separating species or subspecies due to considerable overlap in measurements. Furthermore, there were often larger differences between subspecies of T. olivaceus (particularly the geographically isolated T. o. swynnertoni ) than between T. olivaceus and T. smithi . We therefore suggest that further work investigates the elevation of T. o. swynnertoni to full species status. Plumage characteristics proved more useful in separating T. olivaceus and T. smithi in the field, except in regions where the distributions overlap (potential hybridisation zones). We highlight the importance of clarifying the delineation of separate species particularly with respect to bird census data (e.g. Southern African Bird Atlas Project 2) and studies related to these species. OSTRICH 2009, 80(3): 171–175

Global biogeography and ecology of body size in birds

Abstract: In 1847, Karl Bergmann proposed that temperature gradients are the key to understanding geographic variation in the body sizes of warm-blooded animals. Yet both the geographic patterns of body-size variation and their underlying mechanisms remain controversial. Here, we conduct the first assemblage-level global examination of 'Bergmann's rule' within an entire animal class. We generate global maps of avian body size and demonstrate a general pattern of larger body sizes at high latitudes, conforming to Bergmann's rule. We also show, however, that median body size within assemblages is systematically large on islands and small in species-rich areas. Similarly, while spatial models show that temperature is the single strongest environmental correlate of body size, there are secondary correlations with resource availability and a strong pattern of decreasing body size with increasing species richness. Finally, our results suggest that geographic patterns of body size are caused both by adaptation within lineages, as invoked by Bergmann, and by taxonomic turnover among lineages. Taken together, these results indicate that while Bergmann's prediction based on physiological scaling is remarkably accurate, it is far from the full picture. Global patterns of body size in avian assemblages are driven by interactions between the physiological demands of the environment, resource availability, species richness and taxonomic turnover among lineages.

Do southern African songbirds live longer than their European counterparts

Abstract: Understanding life history evolution in tropical and southern hemisphere birds has been hindered by a paucity of knowledge of key life history traits and this is particularly true of African songbirds. Here we use a unique long-term mark-recapture data set collected over 16 years in Malawi (latitude 16°S) to estimate adult survival rates for 28 African passerine species. Survival of these and 11 other African songbirds (taken from the literature) showed a bi-modal distribution with annual survival of insectivores and nectarivores (bulbuls, thrushes, warblers and sunbirds) averaging 72% (quartiles 63-80%) compared to 54% (50-62%) in granivores (weavers, finches and canaries). The mean adult life expectancy of African insectivores and nectarivores (3.1 yr) was more than twice that of related European insectivores (1.4 yr) and nearly twice that of African granivores (1.6 yr). These marked differences in survival were highly significant after controlling for body mass and phylogeny. Among African songbirds there was a strong negative correlation between adult survival and clutch size with granivores laying relatively large clutches and living relatively short lives. We hypothesize that these differing life history trade-offs reflect variation in the seasonality of food resources whereby survival rates of northern temperate songbirds may be limited by food availability and cold weather during winter, while survival of southern African granivores may be limited by the influence of a variable and unpredictable rainfall regime on seed availability.

Do floral syndromes predict specialization in plant pollination systems? An experimental test in an "ornithophilous" African Protea.

Abstract: We investigated whether the “ornithophilous” floral syndrome exhibited in an African sugarbush, Protea roupelliae (Proteaceae), reflects ecological specialization for bird-pollination A breeding system experiment established that the species is self-compatible, but dependent on visits by pollinators for seed set The cup-shaped inflorescences were visited by a wide range of insect and bird species; however inflorescences from which birds, but not insects, were excluded by wire cages set few seeds relative to open-pollinated controls One species, the malachite sunbird (Nectarinia famosa), accounted for more than 80% of all birds captured in P roupelliae stands and carried the largest protea pollen loads A single visit by this sunbird species was enough to increase seed set considerably over unvisited, bagged inflorescences Our results show that P roupelliae is largely dependent on birds for pollination, and thus confirm the utility of floral syndromes for generating hypotheses about the ecology of pollination systems

Response of avian nectarivores to the flowering of Aloe marlothii : a nectar oasis during dry South African winters

Abstract: In southern Africa, Aloe marlothii flowers during the dry winter season and offers copious dilute nectar to a variety of birds. Avian abundance and community composition were monitored at an A. marlothii forest at Suikerbosrand Nature Reserve, South Africa. Sampling occurred during two summer months (February–March) when no flowers were present, and six months (May–October) that spanned the winter flowering. We hypothesized that an influx of occasional nectarivores to the A. marlothii forest during flowering would lead to significant changes in the avian community. Overall bird abundance increased 2–3 fold at the peak of nectar availability (August). We recorded 38 bird species, of 83 species detected during transects, feeding on A. marlothii nectar; this diverse assemblage of birds belonged to 19 families, including Lybiidae, Coliidae, Pycnonotidae, Sylviidae, Cisticolidae, Muscicapidae, Sturnidae, Ploceidae and Fringillidae. Surprisingly, only two species of sunbird (Nectariniidae) were observed feeding on A. marlothii nectar, and both occurred in low abundance. We predicted that competition for nectar resources would be high, but few aggressive inter- and intra-specific interactions occurred between birds while feeding on inflorescences. During peak flowering, insect feeders (insectivores, omnivores, nectarivores) fed on nectar during the cold morning when insect activity was low, whilst non-insect feeders (frugivores and granivores) fed on nectar in the middle of the day. Our study highlights the importance of A. marlothii nectar as a seasonal food and water source for a diverse assemblage of occasional nectarivores.