Luke Verburgt

Quantity versus quality: how does level of predation threat affect Cape ground squirrel vigilance?

How individuals balance time spent satisfying nutritional needs and time spent being vigilant to protect against potential predation has received abundant attention from researchers. Evidence indicates that both social conditions and predator risk affect how individuals perceive environmental threat, however, the relative influence of each type of risk remains unclear. The risk allocation hypothesis considers how individuals respond to predation risk over time by adapting their investment in high-quality or low-quality vigilance. Here we use the risk allocation hypothesis as a guide to examine how different risk factors influence vigilance quantity and quality in Cape ground squirrels, Xerus inauris. We tested how the social conditions of age, sex, distance to a safe refuge, distance from a nearest neighbour and predator risk affect the amount of time (quantity) individuals spend vigilant. Individuals were more vigilant in areas with more potential predators and when they were further from a safe refuge or nearest neighbour. We then tested whether these risk factors that affected vigilance quantity also affected vigilance quality by measuring exclusive vigilance (high-cost, high-quality) and shared-foraging–vigilance (low-cost, low-quality). Individuals in high-predation risk areas invested more time in high-cost vigilance behaviour than in low-cost vigilance/foraging behaviour compared with individuals in low-predation risk areas. Since squirrels invested in high-cost vigilance significantly more than in low-cost vigilance regardless of distance to a refuge or other squirrels, we suggest that combined foraging with vigilance compromises vigilance to lower its quality.

Dilute bird nectars: viscosity constrains food intake by licking in a sunbird

Floral nectars of bird-pollinated plants are relatively dilute. One hypothesis proposed to explain this concerns the difficulty for birds of drinking nectar of high viscosity. We examined the effects of viscosity, separately from those of sugar concentration, on feeding by captive whitebellied sunbirds (Cinnyris talatala). Viscosities of artificial nectar (sucrose solutions ranging in concentration from 0.25 to 1.5 mol/l) were altered with Tylose, an inert polysaccharide. Food consumption was measured over 3 h, and lick frequency and duration were recorded using photodetection devices on feeding apertures too small for the bill but large enough for the extended tongue. Volumetric intake rates (ml/s) were inversely proportional to nectar viscosity, and were similar over the range of sucrose concentrations when viscosity was held constant. Sucrose intake rates (mg/s) remained the same on pure sucrose solutions, but they decreased with increasing viscosity at a constant sucrose concentration. Lick frequencies and tongue loads were reduced at high viscosities, and lick duration increased, which confirms that sunbirds take longer to ingest viscous solutions. Licking behavior was remarkably similar in birds feeding on different sucrose concentrations if viscosity was held constant. Nectar ingestion rate is determined by viscosity; however, total food intake is mainly modulated by sugar concentration. Similar effects of food viscosity have been observed in insects that suck nectar.

Jettisoning ballast or fuel? Caudal autotomy and locomotory energetics of the Cape dwarf gecko Lygodactylus capensis (Gekkonidae)

Many lizard species will shed their tail as a defensive response (e.g., to escape a putative predator or aggressive conspecific). This caudal autotomy incurs a number of costs as a result of loss of the tail itself, loss of resources (i.e., stored in the tail or due to the cost of regeneration), and altered behavior. Few studies have examined the metabolic costs of caudal autotomy. A previous study demonstrated that geckos can move faster after tail loss as a result of reduced weight or friction with the substrate; however, there are no data for the effects of caudal autotomy on locomotory energetics. We examined the effect of tail loss on locomotory costs in the Cape dwarf gecko Lygodactylus capensis (∼0.9 g) using a novel method for collecting data on small lizards, a method previously used for arthropods. We measured CO2 production during 5–10 min of exhaustive exercise (in response to stimulus) and during a 45‐min recovery period. During exercise, we measured speed (for each meter moved) as well as total distance traveled. Contrary to our expectations, tailless geckos overall expended less effort in escape running, moving both slower and for a shorter distance, compared with when they were intact. Tailless geckos also exhibited lower excess CO2 production (CO2 production in excess of normal resting metabolic rate) during exercising. This may be due to reduced metabolically active tissue (tails represent 8.7% of their initial body mass). An alternative suggestion is that a change in energy substrate use may take place after tail loss. This is an intriguing finding that warrants future biochemical investigation before we can predict the relative costs of tail loss that lizards might experience under natural conditions.

Short-term energy regulation of whitebellied sunbirds (Nectarinia talatala): effects of food concentration on feeding frequency and duration.

SUMMARY Avian nectarivores show compensatory feeding by adjusting their volumetric intake in response to variation in nectar concentration. This study used an infrared photo-detection system to investigate the short-term feeding patterns of whitebellied sunbirds (Nectarinia talatala) consuming three different sucrose concentrations (10, 20 and 30% w/w). Sunbirds increased their feeding frequency on the most dilute diet, but there was no change in feeding duration. Thus, the increase in total time spent feeding on the dilute diet was due to the increased feeding frequency. No difference in short-term feeding patterns was found between the 20% and 30% diets. Total time spent feeding was extremely short on all diets (96-144 s in every hour). Birds maintained the same steady increase in body mass over the course of the day on all three diets. Daily rhythms in feeding patterns were evident, with longer feeding duration and lower feeding frequency in the early morning and evening than during the rest of the day. Because ingestion rates on a particular diet may vary through the day, caution must be exercised in using feeding duration as a surrogate for meal size. Individual birds varied greatly in their feeding patterns irrespective of diet concentration.

Nectar Intake of White‐Bellied Sunbirds (Cinnyris talatala): Can Meal Size Be Inferred from Feeding Duration?

A positive relationship between feeding duration and meal size of avian nectarivores has often been assumed in earlier studies. We investigated whether feeding duration can be used as a surrogate for the amount of sugar solution ingested by white‐bellied sunbirds, Cinnyris (Nectarinia) talatala. Feeding durations of sunbirds consuming three sucrose concentrations (10%, 20%, and 40% w/w) were measured using an infrared photodetection system, and the amounts consumed were recorded simultaneously by weighing the feeder throughout the experiment. For all three diet concentrations, a positive relationship was found between the time spent feeding per 30 min and the mass consumed. Therefore, feeding duration is demonstrated to be an index of the amount ingested on a particular sugar concentration. The rate of ingestion, however, depended on the sugar concentration, with the highest rate at the lowest concentration of 10% and the lowest rate at the 40% concentration. Less total time was spent feeding on the 20% solution than on the 10% solution, but time increased on the 40% diet because of viscosity effects. There appeared to be a weak relationship between feeding patterns and sex, but this was not significant, probably because of interindividual variation.

Interruptions in nectar availability: responses of White-bellied Sunbirds (Cinnyris talatala) and Brown Honeyeaters (Lichmera indistincta)

Abstract Limited food availability disrupts the energy balance of animals, and nectarivorous birds with high metabolic requirements that necessitate frequent feeding may be particularly affected. We kept White-bellied Sunbirds (Cinnyris talatala) and Brown Honeyeaters (Lichmera indistincta) at 10°C, fed them a 0.63-M sucrose solution, and exposed them to a 2-h fasting period at midday. Food intake increased following the fast, relative to uninterrupted feeding. A comparison with the maximal intake predicted by a digestive capacity model showed that both species fed at maximal levels in the hour following the fast. Although the short-term feeding pattern of the Honeyeaters was not investigated, the Sunbirds increased the duration of meals immediately after the fast, followed by a non-significant increase in meal frequency. In contrast to published data for hummingbirds, these two passerines accumulated energy at higher rates after the fast than on the control. However, food intake over the whole day was lower on the fasting day and birds weighed less in the evening compared with the control, indicating that the compensation of energy accumulation was incomplete. The two species from phylogenetically distinct nectarivorous avian taxa show similarities in their response to fasting periods, possibly owing to similar feeding behaviour and physiological constraints.

A new Reed Frog (Hyperoliidae: Hyperolius ) from coastal northeastern Mozambique

A new species of African reed frog (genus Hyperolius Rapp, 1842) is described from the Coastal Forests of the Eastern Africa Biodiversity Hotspot in northeastern Mozambique. It is currently only known from less than ten localities associated with the Mozambican coastal pans system, but may also occur in the southeastern corner of Tanzania. Phylogenetic reconstructions using the mitochondrial 16S marker revealed that it is the sister taxon of Hyperolius mitchelli (>5.6% 16S mtDNA sequence divergence) and forms part of a larger H. mitchelli complex with H. mitchelli and H. rubrovermiculatus. The new species is distinguished from other closely related Hyperolius species by genetic divergence, morphology, vocalisation, and dorsal colouration.

A new species of Scolecoseps (Reptilia: Scincidae) from coastal north-eastern Mozambique

ABSTRACT Seven specimens of Scolecoseps Loveridge, 1920 from the vicinity of Palma on the north coast of Mozambique are compared morphologically with other known material of this genus. The new material can be distinguished morphologically from all other Scolecoseps by the presence and position of certain head scales, particularly a supraciliary and four small suboculars, a small mental and high subcaudal counts. It is described as a new species, Scolecoseps broadleyi sp. nov. The new species is found in coastal savannah habitat under leaf litter of Berlinia orientalis trees, in sandy soils in close proximity to large wetlands. Its currently known distribution is south of the range of Scolecoseps litipoensis Broadley, 1995 and north of that of Scolecoseps boulengeri Loveridge, 1920. We provide a review of the available literature for the genus Scolecoseps and highlight the necessity for additional research on these poorly known fossorial skinks. ZooBank— Scolecoseps broadleyi: urn:lsid:zoobank.org:act:C4E3723C-F982-4CFA-900B-0B23A9AD5B84