Lindy J. Thompson

The potential effects of climate-change-associated temperature increases on the metabolic rate of a small Afrotropical bird

ABSTRACT Studies have only recently begun to underline the importance of including data on the physiological flexibility of a species when modelling its vulnerability to extinction from climate change. We investigated the effects of a 4°C increase in ambient temperature (Ta), similar to that predicted for southern Africa by the year 2080, on certain physiological variables of a 10–12 g passerine bird endemic to southern Africa, the Cape white-eye Zosterops virens. There was no significant difference in resting metabolism, body mass and intraperitoneal body temperature between birds housed indoors at 4°C above outside ambient temperature and those housed indoors at outside ambient temperature. We conclude that the physiological flexibility of Cape white-eyes will aid them in coping with the 4°C increase predicted for their range by 2080. Summary: The physiological flexibility of Cape white-eyes will aid them in coping with the 4°C increase predicted for their range by 2080.

Is the Cape White-eye Zosterops virens or Zosterops capensis?

The recent scientific literature employs three binomial names for the southern African endemic bird known as the Cape White-eye: Zosterops capensis, Z. pallidus and Z. virens. This unacceptable inconsistency reflects the contention regarding white-eye systematics. Recent molecular work by Oatley and colleagues led to the suggestion that Z. virens and Z. capensis should both fall under the name Z. virens. We urge ornithologists to adopt this convention, and we encourage further molecular stud ies in order to clarify the taxonomy of southern African white-eyes.

Circannual rhythm of resting metabolic rate of a small Afrotropical bird

Seasonal variation in avian metabolic rate is well established in Holarctic and temperate species, while trends in Afrotropical species are relatively poorly understood. Furthermore, given the paucity of data on circannual rhythm in avian metabolism, it is not known whether seasonal measurements made in summer and winter correspond with annual peaks and troughs in avian metabolic rate. Thus, we investigated how mean body mass, resting metabolic rate (RMR) and evaporative water loss (EWL) of a small Afrotropical bird, the Cape white-eye (Zosterops virens), changed monthly over the course of a year at 20°C and 25°C. Mean body mass was 12.2±1.0g throughout the study period. However, both EWL and RMR varied monthly, and peaks and troughs in RMR occurred in March and October respectively, which did not correspond to peaks and troughs in mean monthly outdoor ambient temperatures. These results suggest that measuring RMR at the height of summer and winter may underestimate the flexibility of which birds are capable in terms of their metabolic rate. We encourage further studies on this topic, to establish whether the lag between environmental temperature and RMR is consistent in other species.

Seasonal metabolic variation over two years in an Afrotropical passerine bird.

Seasonal trends in metabolic parameters are well established in avian populations from highly seasonal environments, however, seasonal trends in metabolism of birds from lower latitudes (and of Afrotropical birds in particular) are not well understood. We investigated seasonal trends in metabolism for a small (10-12g) Afrotropical bird, the Cape White-eye (Zosterops virens), using flow-through respirometry in two summers and two winters. There was no seasonal difference in body mass between consecutive seasons. The lower critical limit of thermoneutrality was lower in winter (23°C) than in summer (28°C), as expected for a small Afrotropical bird. In the first year of the study, mean whole animal basal metabolic rate (BMR) of Cape White-eyes was significantly lower in winter than in summer, while in the second year of the study this trend was reversed, and in the middle two seasons there was no significant difference in BMR. Differences in mean temperature and mean rainfall between seasons could not account for the seasonal trends in BMR. We conclude that seasonal trends in avian BMR may vary between years, within a population.

Removal (and attempted removal) of material from a Hooded Vulture Necrosyrtes monachus nest by a starling and a Hooded Vulture

Relatively little is documented about nest material theft in vultures. We used camera traps to monitor Hooded Vulture Necrosyrtes monachus nests for a year. We report camera trap photographs of a starling Lamprotornis sp. removing what appeared to be dung from an inactive Hooded Vulture nest on Cleveland Game Reserve, north-eastern South Africa, in October 2016. We also had evidence of a Hooded Vulture attempting to remove twigs from the same nest in August 2016. This behaviour is previously unrecorded in Hooded Vultures and, although seemingly rare, it represents an attempt to reduce the energetic costs of nest building in this species.

Visitors to nests of Hooded Vultures Necrosyrtes monachus in northeastern South Africa

Hooded Vultures Necrosyrtes monachus are critically endangered but little is known of their year-round use of nests or whether other species usurp Hooded Vulture nest sites. We investigated visitation rates by Hooded Vultures and other species (including potential nest predators and usurpers) to examine their effect on Hooded Vulture breeding success. We present observations of 33 species recorded by camera traps at 12 Hooded Vulture nests over a total of 93 nest-months (2 095 nest-days). Several pairs of Hooded Vultures visited their nests regularly during the non-breeding season, some adding nesting material, highlighting that pairs visited their nest(s) year round. Egyptian Geese Alopochen aegyptiaca, potential usurpers of raptor nests, were present at occupied and unoccupied Hooded Vulture nests, but we recorded no usurpation of nests by Egyptian Geese and they had no impact on vulture breeding success. Hooded Vulture breeding failure was linked to two species only: camera-trap imagery recorded one case of predation of a vulture egg by a Chacma Baboon Papio ursinus, and one case of a Martial Eagle Polemaetus bellicosus predating a vulture nestling. We recommend expanding the Hooded Vulture nest monitoring programme to include more pairs.

Thermal acclimation in a small Afrotropical Bird

Wild-caught animals are regularly used in physiological studies, yet the length of time it takes for completion of their acclimation to laboratory conditions remains largely unknown. In particular, Afrotropical species are relatively understudied compared with temperate and Holarctic species. Thus, we measured a number of metabolic variables in a 10g Afrotropical bird, the Cape White-eye (Zosterops virens), at weekly intervals, over an 8-week period, while birds were acclimating to two different constant thermal environments; 25°C and 29°C. Body mass increased significantly in the first three weeks, remaining approximately constant thereafter, with no significant difference between birds housed at 25°C and those housed at 29°C. However, whole animal resting metabolic rates remained constant throughout the eight-week study period, with values for birds housed at 29°C lower than for birds housed at 25°C. Rather than pointing to a minimum time period necessary for thermal acclimation, these results suggest that in some instances, freshly wild-caught small passerines may not need to be acclimated to laboratory conditions or respirometry equipment, prior to measurements of their resting metabolic rate.

A novel threat from invasive Lantana: stem exudate clogs the feet of small birds

ABSTRACT A hard, black deposit was found clogging birds’ feet at Ferncliffe Nature Reserve in South Africa. The reserve is infested with invasive Lantana (Lantana camara). We hypothesised that small frugivorous, nectarivorous and insectivorous birds which foraged in Lantana would be most affected by the hard deposit, which could enclose the toes, making the foot unusable. We investigated which bird species were affected by the hard deposit on their feet, and used liquid chromatography-mass spectrometry to compare samples of the deposit from the birds’ feet to samples from young Lantana stems. White-bellied Sunbirds (Cinnyris talatala), Tawny-flanked Prinias (Prinia subflava) and Spectacled Weavers (Ploceus ocularis) were the three species whose feet were most affected with this deposit, and results confirmed that these deposits originated from exudate on young Lantana stems. This is the first time that Lantana stem secretions have been reported to adversely affect birds, but we believe the phenomenon may occur more widely in Lantana’s native and invasive range.

Altitudinal variation in metabolic parameters of a small Afrotropical bird

Of the numerous factors affecting avian metabolic rate, altitude is one of the least studied. We used mass-flow respirometry to measure resting metabolic rate (RMR), evaporative water loss (EWL) and respiratory exchange ratio (RER) in two populations of a small (10-12g) Afrotropical bird, the Cape White-eye (Zosterops virens), in summer and in winter. In total, 51 freshly wild-caught adult Cape White-eyes were measured overnight. Altitude was included as a source of variation in the best approximating models for body mass, whole-animal RMR, RER, whole-animal standard EWL and whole-animal basal EWL. RER was significantly lower in winter, suggesting a greater proportion of lipid oxidation at lower ambient temperatures (Ta). Cape White-eyes were 0.8g heavier at the higher altitude site and 0.5g heavier in winter, suggesting they may have increased their metabolic machinery to cope with cooler temperatures. EWL was generally significantly lower in winter than in summer, suggesting that birds may increase EWL with increasing Ta, as the need for evaporative cooling increases. Our results support the argument that the subtle and complex effects of altitude (and ambient temperature) should be taken into account in studies on avian metabolic rate. WHAT IS ALREADY KNOWN Of the numerous studies known to affect avian metabolic rate, altitude is one of the least studied. Although trends are not always clear, generally, at higher altitudes, avian metabolic rate increases. WHAT THE STUDY ADDS There were statistically significant seasonal and altitudinal differences in various physiological parameters of Cape White-eyes. These results highlight the importance of accounting for altitude in studies of avian metabolic rate.

Causes of Admissions to a Raptor Rehabilitation Centre in KwaZulu-Natal, South Africa

With many species of southern African raptors becoming increasingly threatened, records from rehabilitation centres can give an indication of the threats faced by birds of prey in particular areas and to particular species. Thus, admissions records from a raptor rehabilitation centre in KwaZulu-Natal, South Africa, were analysed for trends. Over eight years (2004–2011), 547 birds from 39 raptor species were admitted to the centre. The majority of individuals were spotted eagle-owls (16.6%), western barn owls (15.2%) and yellow-billed kites (9.7%). The most frequent known causes of injury to raptors were motor vehicle accidents and injuries caused when birds flew into buildings. There was no significant difference in admissions of motor vehicle collision cases between seasons. People generally waited 3.8 days before bringing injured raptors in to the centre, and approximately half of the birds admitted were fed within that time, highlighting a need for public education regarding the general diets of raptors and the benefits of prompt medical attention.