Browsing by Author "McKechnie, Andrew E"

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    Does the availability of shade limit use of water troughs by desert birds?
    (2015) Abdu, Salamatu; Cunningham, Susan J; Ryan, Peter G; McKechnie, Andrew E
    Climate change poses a major threat to living organisms, with maximum temperatures expected to continue to rise over the next few decades. Hot desert environments are particularly at risk because they experience high environmental temperatures, scarce vegetation, low productivity and unpredictable water sources. Endotherms such as birds face the challenge of maintaining a stable body temperature while avoiding dehydration. This study was carried out in the southern Kalahari, in South Africa's Northern Cape, where about 50% of bird species (36 species) depend on free-standing drinking water. Livestock farms within this area provide artificial water points, which benefit birds as well as livestock. This study determined the role of shade and cover in the use of these artificial water points by birds. An experiment was conducted at six waterholes using the Before-After, Control-Impact (BACI) design. After an initial baseline was established, three waterholes were shaded while the other three were left unshaded. Camera traps were used to record the pattern and intensity of water use by bird species at different times of the day and at varying air temperatures. A total of 36 bird species drank at the water holes, but data analysis was confined to the ten most abundant species. Of the ten, six species responded to the presence of shade/cover, with four species reacting positively (Cape Glossy Starling Lamprotornis nitens , Red - headed Finch Amadina erythrocephala , Black - throated Canary Serinus atrogularis , and Laughing Dove Spilopelia senegalensis ), four showing no significant change in drinking patterns, and two showing a decrease in visitor numbers when the site was shaded (Cape Turtle - Dove Streptopelia capicola, Namaqua Dove Oena capensis). This suggests that providing shade at waterholes is not a universal solution to the problem of increasing heat stress experienced by birds coming to drink. Certain species such as the Laughing Doves and Cape Turtle-Doves avoided waterholes during the warmest time of the day while the Namaqua Doves were frequent visitors at this time. However, the Laughing Dove took advantage of the shade provided at midday (warmest temperatures) as their numbers increased. The Red-headed Finch and Black-throated Canary also increased at water holes with temperature irrespective of the time of day. These patterns imply that the provision of shade modifies the behavior of some bird species in response to predation risk or heat stress. These species utilized shade at different times of day and with varying intensities as temperatures rose.
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    Effects of temperature and food availability on the reproductive ecology of an arid-zone bird
    (2024) Pattinson, Nicholas B; Cunningham, Susan; McKechnie, Andrew E
    For arid-zone birds that breed in spring and summer, the heightened energy, water, and time demands of reproduction and development coincide with the hottest period of the year. For these species, rapid anthropogenic climate warming is exacerbating trade-offs between thermoregulation and self-maintenance or reproduction, posing a severe threat to breeding and population dynamics. There has been a surge in research into the effects of high and increasing environmental temperature on avian ecology. However, the potential for resource availability to moderate environmental temperature effects on birds' behaviour, physiology, morphology, and success during breeding remains understudied. I investigated these lesser-known concepts through monitoring breeding, conducting a supplementary feeding experiment (providing breeding pairs with access to either a high supplementation (high supp.) treatment of ~25g of Zophobas morio or a low supplementation (low supp.) treatment of ~5g of Z. morio every day of the breeding attempt), and analysing long-term data from a population of Southern Yellow-billed Hornbills (Tockus leucomelas; hornbills) in the Kalahari Desert. These hornbills are long-lived and have an unusual breeding strategy whereby the female seals herself inside the nest cavity for the majority of the breeding attempt, leaving the free-ranging male as the sole provisioner to the nest. Hornbills do not drink, with their water inputs comprised entirely of dietary and metabolic water. Therefore, ‘food' equates to ‘resources' (i.e., food and water combined) in this species. I found that supplementary feeding affected the thermoregulation of free-ranging male parents, incarcerated female parents in the nest, and chicks: hornbills in the high supp. treatment showed more gradual increases in body temperature (Tb) and increased hyperthermia avoidance in response to rising nest temperature (Tnest), although high air temperature (Tair) and Tnest still resulted in facultative hyperthermic responses. Some negative effects of high environmental temperatures persisted regardless of resource availability: breeding male hornbills showed Tair-dependent nest provisioning patterns and chicks showed impaired development (i.e., reduced structural growth) and increased stress responses (indicated by increased feather corticosterone [CORT]) at high Tnest irrespective of resource availability. Collectively, these patterns suggested there were some mediating effects of resource availability on hornbill breeding ecology, but that high environmental temperatures nonetheless had negative effects. This study took place during a period of unprecedented climate extremes, from 2018 – 2021. Therefore, it includes detailed data from two very different summer breeding seasons: a hot and dry breeding season (2019/20) and a cool and very wet breeding season which included a 1-in-100-year flooding event (2020/21). During an earlier year of the study (2018/19), drought conditions were so extreme that no hornbills attempted to breed at the study site, therefore no data for this breeding season are included in the thesis. In the cool and wet breeding season, I recorded a) higher provisioning effort by male parents, b) improved hyperthermia avoidance and more gradual increases in Tb in male and female parents and chicks, c) higher post-hatch body mass (Mb), faster tail feather growth, and lower tail feather barb density in breeding females, d) less time in the nest (i.e., fledging sooner), faster Mb gain, and longer tarsi at fledge and faster tail feather growth in chicks, and e) higher breeding success, compared to the hot and dry breeding season. These differences were mostly unexplained by environmental temperature effects, suggesting they were driven by higher resource availability or quality in the cool and wet breeding season. The lack of any effects of the supplementary feeding experiment on variables other than thermoregulation indicated that it could be resource quality, rather than availability, that was the most important resource-related factor affecting the hornbill ecology during this study. However, I did not have resource quality data to test that possibility. An alternative explanation is that the supplementary feeding experiment did not provide enough extra food and water to influence factors other than thermoregulation, or the signal was simply swamped by the unprecedented influx of natural resources associated with incredibly high primary productivity in the flood year. In systems or periods where resources are not limiting one might not expect a significant effect of resource supplementation. Either of these could have undermined my ability to detect potential resource availability effects. Crucially, I found no significant Tnest effects on female parent morphology or on breeding success, in strong contrast to previous findings in this study population, and in the long-term breeding data analysed in this thesis. This was likely a result of significantly reduced Tnest caused by new nest boxes with an insulation layer, compared to previous studies on this population using uninsulated nest boxes. These findings highlight the need for multi-season studies, and the possibility that improved design of nest boxes can positively affect nest microclimate, thereby mitigating severe high Tnest effects. Overall, this thesis attempted to investigate iv whether high environmental temperatures are currently limiting because of a concurrent lack of energy and water aggravating costly trade-offs. If so, then provisioning of supplementary food and water may present viable conservation options for severely affected and conservation dependant species. Moreover, successful breeding in high rainfall years (corresponding to high resource availability) despite high environmental temperatures may facilitate population persistence. Broadly, based on the predominant lack of supplementary feeding effects, results suggested resource availability was not a strong driver of variation in hornbill reproductive ecology. Rather, the results indicated that high environmental temperatures were limiting regardless of resource availability (i.e., for provisioning rate and developing chicks), despite improved hyperthermia avoidance and more gradual increases in Tb at high Tnest. The results also indicated potential effects of resource quality, or that the supplementary feeding experiment was not completely effective, in that the amount of supplementary food may still not have been enough, or may not have met the nutrient or water requirements (i.e., food quality requirements) of the female parents or chicks. The amount of food in the high supp. treatment was designed to be ~100% of the daily requirements of the nest based on previous studies of this population, but the males in the cool and wet season showed that they could considerably increase the amount of food provisioned to the nest compared to what had been recorded before, suggesting that the amount of supplementary food was well-below what could possibly be provisioned. I lacked the data to investigate these possibilities. Results, therefore, leave avenues for future research to investigate, for example, quality versus quantity effects or the effects of ad libitum food and water supplementation. This PhD contributes to disentangling the independent effects of high environmental temperatures and resource availability on arid-zone avian ecology. Several key potential effects of resource availability or quality on behaviour, physiology, morphology, and breeding success were identified, which ultimately will hopefully aid in understanding avian ecology and designing future research and conservation interventions in the face of rapid climate warming.
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    Implications of climate change on the reproductive success of the Southern Yellow-billed Hornbill, Tockus leucomelas
    (2017) Van de Ven, Tanja M F N; Hockey, Phil A R; Ryan, Peter G; McKechnie, Andrew E
    The effects of environmental warming on the reproductive performance of birds are most easily studied in desert habitats where birds already experience air temperatures (Tₐs) close to their upper thermal tolerance. Many desert birds coincide breeding with periods of food availability triggered by rainfall during the summer season. Daily maximum air temperatures (ₘₐₓ) during the Kalahari summer season frequently reach the lower forties (°C) and recent years have been characterised by reduced rainfall and increased Tₐ. Breeding Southern Yellow-billed Hornbills (Tockus leucomelas) could be particularly vulnerable to high Tₐ due to their breeding strategy whereby the females are confined to the nest cavity for most of the nesting period. During this time their male partners are solely responsible for food provisioning, which imposes a considerable energetic demand. In this thesis, I investigated the extent to which Tₐ affects the ability and willingness of breeding males to provision their female partners and offspring. And consequently, the extent to which male investment and the thermal environment affect female body mass (Mb) and chick development rates in Southern Yellowbilled Hornbills in the Kalahari. During three consecutive hornbill breeding seasons (October - March, between 2012 and 2015), I collected life history data during 50 breeding attempts by 32 hornbill pairs. At the study site, Southern Yellow-billed Hornbills readily breed in artificial nest boxes and this allowed me to assess the internal nest climate using temperature and relative humidity loggers which were placed in most of the nests. The male hornbills in the study population were semi-habituated which facilitated behavioural observations. Weather data were recorded at an on-site weather station. Morphometric data from females and chicks were collected on a daily basis at selected nests and perch scales installed at nest entrances recorded Mb data of the provisioning males. From chick hatching to chick fledging, I observed the behaviour of the males during 30-min focal follows and focussed on foraging behaviour, prey allocation decisions (nest versus self), microsite use and thermoregulatory behaviour. Male hornbills spent more than half of their time panting at Tₐs above 34.5 °C. Days on which this threshold temperature was exceeded were therefore described as 'hot days'. The male hornbills experienced trade-offs on hot days between foraging efficiency and panting behaviour, indicating that the additional cost of thermoregulation and high Tₐ affected foraging success (Chapter 2). Males would always provision larger prey items to the nest and consumed the smaller prey items themselves. As Tₐ increased, the males increased their foraging effort, but caught fewer and smaller prey items overall, reducing the total biomass they provisioned to the nest as well as the biomass they consumed. As a result, males were unable to maintain their Mb on days when Tₐ exceeded 37.9 °C (Chapter 3). A similar effect of hot days on Mb maintenance was observed in females and chicks within the nest. Independent of chick age, females departed the nest when their Mb reached a lower limit of 189.3 ± SD 18.1 g. The females would then aid the males in nest provisioning, however the negative effect of increasing ₘₐₓ on provisioning rate was still evident; i.e. females were not able to compensate for reduced male provisioning rates on hot days. High Tₐs during the nesting period resulted in smaller and lighter fledglings and overall reduced the probability of a successful nesting attempt (Chapter 4). A thermal imaging experiment revealed that the large beak of hornbills (both males and females) plays an important role in non-evaporative heat loss. Hornbills were observed to dissipate up to 19.9 % of the total non-evaporative body heat loss via the beak. This water-saving mechanism can be highly advantageous to hornbills living in arid regions where water availability is limited (Chapter 5). Lastly, a comparison of the results of the current study with those of a study on the same hornbill population carried out between 2008 and 2011 revealed that mean ₘₐₓ as well as rainfall during the nesting period had an important impact on overall hornbill reproductive effort and success (Chapter 6). Long-lived species are expected to prioritise future reproductive opportunities over current broods. However, the predicted scenario for the Kalahari is that high Tₐs become more extreme and periods of drought become more frequent. Therefore, I predict an increased risk of breeding failure among Southern Yellow-billed Hornbills in the future which could affect the persistence of this population.
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    Mapping evaporative water loss in desert passerines reveals an expanding threat of lethal dehydration
    (National Academy of Sciences, 2017) Albright, Thomas P; Mutiibwa, Denis; Gerson, Alexander R; Smith, Eric Krabbe; Talbot, William A; O’Neill, Jacqueline J; McKechnie, Andrew E; Wolf, Blair O
    Extreme high environmental temperatures produce a variety of consequences for wildlife, including mass die-offs. Heat waves are increasing in frequency, intensity, and extent, and are projected to increase further under climate change. However, the spatial and temporal dynamics of die-off risk are poorly understood. Here, we examine the effects of heat waves on evaporative water loss (EWL) and survival in five desert passerine birds across the southwestern United States using a combination of physiological data, mechanistically informed models, and hourly geospatial temperature data. We ask how rates of EWL vary with temperature across species; how frequently, over what areas, and how rapidly lethal dehydration occurs; how EWL and die-off risk vary with body mass; and how die-off risk is affected by climate warming. We find that smaller-bodied passerines are subject to higher rates of mass-specific EWL than larger-bodied counterparts and thus encounter potentially lethal conditions much more frequently, over shorter daily intervals, and over larger geographic areas. Warming by 4 °C greatly expands the extent, frequency, and intensity of dehydration risk, and introduces new threats for larger passerine birds, particularly those with limited geographic ranges. Our models reveal that increasing air temperatures and heat wave occurrence will potentially have important impacts on the water balance, daily activity, and geographic distribution of arid-zone birds. Impacts may be exacerbated by chronic effects and interactions with other environmental changes. This work underscores the importance of acute risks of high temperatures, particularly for small-bodied species, and suggests conservation of thermal refugia and water sources.