Colleen T. Downs

Digestive efficiency of a generalist avian feeder, the Cape White-eye (Zosterops pallidus)

Digestive processes determine whether the particular diet of a bird is utilized efficiently and whether energetic demands are met. Assimilation efficiency is often used as an index of whether a diet is digested optimally. Studies on the digestive processing of generalist feeders are scarce. Cape White-eyes (Zosterops pallidus) have a diverse diet of fruit, nectar and insects. The nutrient contents of these three diets vary considerably and require quite different digestive processing. This study compared the digestive efficiencies of Cape White-eyes on these three diets by measuring transit times and assimilation efficiency. Cape White-eyes lost body mass significantly when fed fruit, while they maintained and gained body mass on nectar and mealworm diets, respectively. Assimilation efficiency varied significantly between the three diet types (nectar>mealworms>apples). When given a choice of diets, Cape White-eyes selected the diet, which was most efficiently digested and yielded the greatest energetic reward. Diet preference trials further showed that Cape White-eyes regulated daily energy intake. Assimilation efficiency depends on the accessibility of nutritional contents of a diet. Cape White-eyes did not maximize assimilation efficiency. Instead, they adjusted transit time to maximize the rate of energy gain per gram of food in order to maintain energy balance.

The role of shading behaviour in the thermoregulation of breeding crowned plovers (Vanellus coronatus)

This study assessed the role of shading behaviour in the thermoregulation of incubating crowned plovers (Vanellus coronatus). Core bird body temperature was measured with an implanted telemeter. Shading behaviour occurred predominantly in summer. Ambient conditions were most extreme at ground level, with the effect of direct solar exposure being significantly lower at a height of 5 cm. Bird behaviour was correlated with real egg and core bird temperature under different ambient conditions. Shading behaviour was shown to play an important role in maintaining incubating bird temperatures at a constant level rather than been used primarily to cool eggs. r 2002 Elsevier Science Ltd. All rights reserved.

Effects of Acacia condensed tannins on urinary parameters, body mass, and diet choice of an Acacia specialist rodent, Thallomys nigricauda.

The aim of this study was to investigate the dietary and physiological effects of condensed tannin ingestion on foregut fermenters, using Thallomys nigricauda, a folivorous rodent, as a model. We initially investigated the variability in physiological parameters, such as daily body mass (DMb), daily feed intake, daily fecal energy loss (FE), daily energy intake (DEI), daily urine pH, and daily urinary ammonia and urea concentrations, in response to different diets with low condensed tannin levels. This experiment was conducted to identify which physiological variables showed the least variation in the absence of tannin. In a second experiment, we investigated the response of the same dietary and physiological parameters to the effects of high dietary condensed tannin ingestion in T. nigricauda. We hypothesized that DMb, daily feed intake, FE, and DEI of T. nigricauda would be adversely affected by high dietary tannin content. We predicted that detoxification activity by T. nigricauda would increase at higher tannin levels. Ingestion of tannins affected the nutritional status of T. nigricauda, as shown by a decrease in body mass at high tannin levels. We also found that fewer ammonium ions were excreted in the urine by T. nigricauda, as would be expected if this were a means of regulating metabolic acidosis. The urine produced was more alkaline. This result indicates that T. nigricauda is not metabolizing these allelochemicals. Urea production was initially reduced, indicating conservation of bicarbonate ions that will neutralize blood acidity if there is detoxification. A diet choice experiment showed that tree rats avoid high tannin diets, even to the extent that they lose body mass on an alternative diet. This last-mentioned result is noteworthy because previous studies of the effects of tannins on herbivorous mammals have shown that there is physiological control rather than behavioral avoidance of the negative effects of tannin ingestion.

Breeding biology of the Cape Parrot, Poicephalus robustus

Breeding biology and nesting requirements of Cape Parrots in their natural habitat and in captivity were investigated. Few nests were found, suggesting that nest-sites are limiting, and that the parrots have specific nesting requirements. Nests were secondary cavities in dead Podocarpus spp. (branches), high up in forest canopy trees. Breeding usually occurred from August to February, but was observed in other months, particularly in captive birds. Clutch size varied from 2–5, incubation was by the female and lasted 28–30 days, with fledging a further 55–79 days. In captive birds the ovaries are mature at 2.5 years, but age at first breeding is usually at 4–6 years.

Thermal parameters of four species of Gerbillurus

Abstract 1. 1.Thermal parameter of the four Gerbillurus species measured in the laboratory were examined in relation to their micro-environments in a xeric habitat. 2. 2.Basal metabolic rates (BMR) were lower than predicted, while thermoneutral zonds (TNZ) were narrow and exceeded burrow temperatures. 3. 3.Body temperatures ( T b ) were regulated over a range of ambient temperatures ( T a ). Evaporative water loss was used as a short-term cooling mechanism to reduce hyperthermia above the TNZ. 4. 4.Conductance was low below the TNZ to reduce heat loss. 5. 5.Adaptation to low temperatures is important for gerbils when active at night. 6. 6.The adaptive significance of the thermal biology of Gerbillurus is discussed in relation to phylogeny, distribution, food availability and nocturnal activity.

Fruiting in two afromontane forests in KwaZulu-Natal, South Africa: the habitat type of the endangered Cape Parrot Poicephalus robustus

Monthly fruiting data including general fruit-fall of species fruiting, and stage of fruit development and quantity of Podocarpus spp. were collected for two southern African afromontane forests, Hlabeni and Ingeli, over a period of three years. Fruits of the dominant Podocarpus species were the most abundant fruit resource at Hlabeni. The percentage of species fruiting (fruit-fall) differed significantly between months for each study site. Peak fruiting period, expressed as a percentage of species in fruit, occurred during winter months (June – August) and was lowest during spring (September – November). Peak fruiting production occurred during winter at Ingeli, but was not significantly different between months at Hlabeni. Most of the dominant canopy fruiting species, particularly the Podocarpus spp., showed unpredictable fruiting patterns. Fruiting periods were extended (greater than 2 months) in some species including the Podocarpus spp. However, total fruit production of some canopy fruiting species differed monthly rather than seasonally. During periods of low fruit production, spring, Kiggelaria africana and Ptaeroxylon obliquum were available. However, these are not keystone species as they are not a food source for avian frugivores, including Cape Parrots Poicephalus robustus.

Species richness and seasonality of forest avifauna in three South African Afromontane forests

Presence data were recorded and analysed for avian bird species in a study of three separate Afromontane Forests in the KwaZulu-Natal Midlands, South Africa. Levels of endemism for South Africa and forest-specificity were investigated. In total, 136 species were identified utilizing forest, yet not all species occurred in all three forests. Slight differences in species composition are attributable to latitudinal and altitudinal differences as well as differences in disturbance regime. However, the respective subsets of forest-specific, frugivorous or migrant birds were similar between forests. Almost all forest-specific species were found at all three study sites and the absence of particular species may be attributable to extinction or rarity. Subsets of endemic frugivores and endemic forest-specific species were also similar between forests. Relatively high levels, for South Africa, of forest-specificity (about 24%) and endemicity (about 17%) were recorded, showing little seasonal variation in species numbers whereas frugivorous and migrant species showed seasonality in their presence. The importance of these forests in conserving avifaunal biodiversity in the region is highlighted. Bird ringing was conducted at two forests to supplement observational data, and assisted in detecting rare and cryptic species. Recommendations are made for the conservation of the larger forest patches, within a naturally fragmented biome.

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

Abstract 1. 1. The response of oxygen consumption (VO 2 ), thermal conductance ( C d and C min , body temperature ( T b ), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures ( T a ) from 5–35°C. 2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O 2 g −1 h −1 and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O 2 g −1 h −1 ). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents. 3. 3. D. auricularis and T. leucogaster regulated T b over the range T a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T a = 30°C. 4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Territoriality of Cape Sugarbirds (Promerops cafer) between and within breeding seasons

Cape Sugarbirds are southern African endemics, found in fynbos vegetation of the Western and Eastern Cape Provinces of South Africa, and they feed almost exclusively on the nectar of Protea inflorescences. Breeding male Sugarbirds are highly territorial and defend resources for themselves, their mates and their offspring. Sugarbirds, however, often leave their breeding territories in search of food during the dry season and return to the same breeding sites each year, thus experiencing an annual cycle of movement from one food source to another. Male territory size as well as breeding success, were determined over two breeding seasons for a population in the Helderberg Nature Reserve in the Western Cape Province. Sugarbird fledgling success was significantly greater for males defending large territories. Males moved or increased the size of their territories between seasons, possibly to improve breeding success, but no changes in territory size were observed during the breeding season.

Wax digestion by the lesser honeyguide Indicator minor

Records of the lesser honeyguide feeding on beeswax in the wild are common. However, little is known about the ability of these birds to digest wax. We studied the wax preference, digestive efficiency, retention time and gut structure of the lesser honeyguide in the laboratory. Wax was found to be eaten daily by the lesser honeyguide. Birds ate significantly more new beeswax and foundation wax than old, black beeswax, but required an additional source of protein to maintain body mass. In the absence of other feed, the digestive efficiency for foundation wax was above 90%, with a long transit time of 256 min. Examination of the digestive tract showed no specialisation and no crop. The presence of digestive enzymes, including lipase, in the pancreas and small intestine and very few microbes in the digestive tract of the lesser honeyguide suggests that wax digestion occurs through a biochemical pathway with endogenous avian enzymes.