Arid-zone Birds Research Articles

A trait-based assessment of southern African arid-zone birds' vulnerability to climate change

Trait-based assessments allow rapid evaluation of species' vulnerability to climate change, but often overlook subtle yet consequential interspecific variation in behavioural and physiological traits. We assessed 241 southern African arid-zone bird species' vulnerability to increasing air temperature associated with climate change. Species' sensitivity was scored using organismal traits (three morphological, 25 ecological, four behavioural, three physiological). We assessed sensitivity under different trait weightings and data availability scenarios to account for data gaps and uncertainty in traits' relative importance. Relative vulnerability was assigned by combining sensitivity and exposure scores. Between 7 % and 17 % of species assessed are highly vulnerable. Passeriformes emerged as the most vulnerable order, relative to other orders assessed, on account of modest heat tolerance limits and reliance on panting, a relatively inefficient avenue of evaporative heat dissipation. Bucerotiformes, Charadriiformes, Accipitriformes and Falconiformes are also highly vulnerable. Caprimulgiformes, Columbiformes, and Strigiformes are least vulnerable, on account of pronounced evaporative cooling capacities and high heat tolerance limits. Vulnerability of Galliformes, Apodiformes and Otidiformes was inconsistent, varying substantially with trait weightings and scenarios, making them priority taxa for research and conservation. Whereas the method tends to inflate sensitivity scores for species with little available data and despite weighting uncertainty, we were able to identify taxa that consistently scored as highly vulnerable and require close attention, based on current knowledge of determinants of climate change sensitivity. Similar trait-based assessments may prove critical for ensuring population declines in unexpectedly vulnerable, or typically overlooked, species do not go unnoticed and appropriate conservation efforts are initiated.

An evaluation of a biophysical model for predicting avian thermoregulation in the heat.

Survival and reproduction of endotherms depend on their ability to balance energy and water exchange with their environment, avoiding lethal deficits and maximising gains for growth and reproduction. At high environmental temperatures, diurnal endotherms maintain body temperature (Tb) below lethal limits via physiological and behavioural adjustments. Accurate models of these processes are crucial for predicting effects of climate variability on avifauna. We evaluated the performance of a biophysical model (NicheMapR) for predicting evaporative water loss (EWL), resting metabolic rate (RMR) and Tb at environmental temperatures approaching or exceeding normothermic Tb for three arid-zone birds: southern yellow-billed hornbill (Tockus leucomelas), southern pied babbler (Turdoides bicolor) and southern fiscal (Lanius collaris). We simulated metabolic chamber conditions and compared model outputs with thermal physiology data collected at air temperatures (Tair) between 10 and 50°C. Additionally, we determined the minimum data needed to accurately model diurnal birds' thermoregulatory responses to Tair using sensitivity analyses. Predicted EWL, metabolic rate and Tb corresponded tightly with observed values across Tair, with only minor discrepancies for EWL in two species at Tair≈35°C. Importantly, the model captured responses at Tair=30-40°C, a range spanning threshold values for sublethal fitness costs associated with sustained hot weather in arid-zone birds. Our findings confirm how taxon-specific parameters together with biologically relevant morphological data can accurately model avian thermoregulatory responses to heat. Biophysical models can be used as a non-invasive way to predict species' sensitivity to climate, accounting for organismal (e.g. physiology) and environmental factors (e.g. microclimates).

The impact of a massive wildfire event on avian species richness and abundance in an arid African savanna ecosystem

Fire shapes ecological diversity, but its influence on bird communities is poorly understood. Fire is often considered crucial to management of savanna systems. Here, we assess effects of fire on bird species richness and density after a wildfire in September 2021, in an arid South African savanna where fire is infrequent. Point counts initially surveyed in 2004 now occurred in burnt and unburnt habitats, and were revisited five times across seasons from December 2021 to January 2023. This enabled identification of interaction effects of change over time and with fire from linear models using site and survey as predictor variables in a Before-After Control-Impact (BACI) framework. Patterns of bird species richness were explored using subsets of repeated points and those of summer to autumn surveys. To explore fire impacts on bird density, we used ‘Distance Sampling’ using additional surveys. Although total species richness during counts did not differ between survey periods and burnt and unburnt areas, densities of all birds were ca. 50% higher in unburnt veld relative to burnt, with this difference driven mostly by granivores. Three of 24 common species were significantly negatively influenced by fire. Fires may profoundly affect this arid zone bird community, a finding that would be overlooked if only species richness had been considered, and densities not accounted for. Fire, although potentially positive for biodiversity in mesic savannas, may negatively impact multiple taxa in arid savannas, which have a very different evolutionary and ecological history to that of more mesic savannas. These differences must be considered in management strategies.

Breeding patterns in an Australian arid-zone landbird community

In 1990–1994, over nine survey periods, we recorded a total of 684 breeding attempts deriving from 51 species in a landbird community in arid north-western New South Wales. We investigated whether breeding effort was related to regular seasonal patterns (spring vs winter) or to irregular fluctuations in rainfall (pre-drought vs drought vs isolated thunderstorm vs above-average rainfall post-drought). The total breeding effort and number of species breeding in the study area were not correlated with the numbers of individuals or species present at a given time. The overall breeding effort was influenced primarily by season but was modified by rainfall. Spring breeding predominated but the timing and magnitude of the breeding efforts of different movement groups (residents, nomads and migrants) and dietary groups varied. Within these groups, there were inconsistencies between individual species. Residents bred mainly in spring but only in low numbers during the drought. Some resident species with relatively stable food supplies also bred, though to a lesser extent, in winter. Residents did not respond to the breaking of the drought with prolonged or aseasonal breeding. The breeding of nomads appeared to follow rainfall more closely. The greatest nesting effort by nomads occurred in the spring after the drought broke, possibly because of a peak in the availability of foods suitable for the nomads at this time. The uncertainty and extremes of the arid-zone environment are now being exacerbated by ongoing anthropogenic climate change, which is likely to severely impact the breeding efforts of arid-zone birds.

Use of nesting resources in an Australian arid-zone landbird community

We investigated the use of nesting resources in a landbird community in the arid zone near Peery Lake, northwestern New South Wales. Over a 3.5-year period (1990–1994), which encompassed pre-drought, drought and post-drought conditions, we recorded 504 active nests and 51 breeding species, including open- (45% of all breeding species), hollow- (27%), mud- (8%), ground- (8%) and tunnel-nesters (4%), and species that nested both in the open and in hollows (8%). Almost 90% of observed nests were located in run-on habitats – major creeklines and minor creeklines. Forty-two species nested in, and 24 species nested only in, run-on habitats. Only 23 species nested in the much more extensive surrounding run-off habitats, but the nests of six species were located only in run-off areas. Most nests (90%) were located in plants, all of which were perennials, with 408 nests in live plants and 47 nests in dead plants. The live plants included 20 tree and shrub species ≥0.5 m tall and 4 subshrub and grass species <0.5 m tall. Most (88%) nests in perennial plants were in trees >4 m tall but often low down in the tree (only 47% of all nests in perennial plants were at heights >4 m). Different bird species favoured different plant species. Favoured trees included River Red Gum Eucalyptus camaldulensis for hollow-nesters, and Whitewood Atalaya hemiglauca and Black Box Eucalyptus largiflorens for open- and mud-nesters. Though fewer nests were located in plants <4 m tall, they were in a wider variety of plant species (16 species) than the larger number of nests in plants >4 m tall (14 plant species). Some nomadic species nested in low vegetation which, though perennial, died back and was unavailable in dry times. To support the nesting requirements of all birds, and to retain the diversity of arid-zone birds, the floristic and structural diversity of perennial plants needs to be maintained. This will be difficult to achieve if the current pattern of ongoing, incremental loss of trees and shrubs continues in the arid zone, particularly as the rate of loss is likely to be exacerbated by the impacts of climate change.

Life history characteristics and alarm calling in Australian arid-zone birds

ABSTRACT In prey species, it is often the case that individuals give alarms when they are threatened. In birds, such signals are frequently vocal signals that alert conspecifics to the presence of a threat. The responses to these calls by receivers may include fleeing to cover or approaching to mob the predator. Although most birds do give alarm calls when threatened, not all species do. We used Australian arid-zone bird species (n = 171) to test the hypothesis that alarm calling behaviour is determined by ecological, behavioural, and morphological characteristics. Eighty-nine percent of birds analysed possessed an alarm call, highlighting the prevalence of this behaviour. Our study found three variables – number of food types eaten, mobility, and breeding system – that were associated with predicting alarm calling behaviour in these species. The correspondence of alarm calling with these key life history attributes provides insight into benefits of having alarm calls and the evolutionary processes that have given rise to this behaviour.

Collapse of Breeding Success in Desert-Dwelling Hornbills Evident Within a Single Decade

Rapid anthropogenic climate change potentially severely reduces avian breeding success. While the consequences of high temperatures and drought are reasonably well-studied within single breeding seasons, their impacts over decadal time scales are less clear. We assessed the effects of air temperature (Tair) and drought on the breeding output of southern yellow-billed hornbills (Tockus leucomelas; hornbills) in the Kalahari Desert over a decade (2008–2019). We aimed to document trends in breeding performance in an arid-zone bird during a time of rapid global warming and identify potential drivers of variation in breeding performance. The breeding output of our study population collapsed during the monitoring period. Comparing the first three seasons (2008–2011) of monitoring to the last three seasons (2016–2019), the mean percentage of nest boxes that were occupied declined from 52% to 12%, nest success from 58% to 17%, and mean fledglings produced per breeding attempt from 1.1 to 0.4. Breeding output was negatively correlated with increasing days on which Tmax (mean maximum daily Tair) exceeded the threshold Tair at which male hornbills show a 50% likelihood of engaging in heat dissipation behavior [i.e., panting (Tthresh; Tair = 34.5°C)] and the occurrence of drought within the breeding season, as well as later dates for entry into the nest cavity (i.e., nest initiation) and fewer days post-hatch, spent incarcerated in the nest by the female parent. The apparent effects of high Tair were present even in non-drought years; of the 115 breeding attempts that were recorded, all 18 attempts that had ≥ 72% days during the attempt on which Tmax > Tthresh failed (equivalent to Tmax during the attempt ≥ 35.7°C). This suggests that global warming was likely the primary driver of the recent, rapid breeding success collapse. Based on current warming trends, the Tmax threshold of 35.7°C, above which no successful breeding attempts were recorded, will be exceeded during the entire hornbill breeding season by approximately 2027 at our study site. Therefore, our findings support the prediction that climate change may drive rapid declines and cause local extinctions despite the absence of direct lethal effects of extreme heat events.

Not-so-forbidden fruit: the potential conservation role of toxic Pimelea microcephala subsp. microcephala fruits for native arid zone birds

ABSTRACT Food resources in arid habitats are important for the survival of native fauna, especially where resources provide water or key nutrients during dry periods. However, food resource plants can be susceptible to grazing species or may not be suitable for revegetating arid areas. Pimelea microcephala subsp. microcephala (P.m.microcephala) is an Australian dioecious shrub bearing bright fruit that are likely to attract birds. The plant is also noted for its production of simplexin, a compound toxic to mammals. The aims of our study were 1) to assess the nutrient and simplexin content of P.m.microcephala fruits, and 2) to confirm the identity of native avian species that consume the fruits. With both pieces of information, we could then determine the conservation utility of P.m.microcephala. Combining chemical analysis of fruit nutrients with field observations, we found that ripe fruits contain 60.5% water, 2.8% sugar, and potent antioxidants, which would likely be of nutritional benefit to consuming frugivores. The fruits also contain high levels of the toxin simplexin, which comprised 3.6% of ripe fruits by weight. We identified eight bird species interacting with P.m.microcephala, with at least five of these consuming ripe fruits. Our study demonstrates the potential for P.m.microcephala to contribute to revegetation and provide a food resource for arid zone birds, whilst being protected from grazing by the presence of simplexin. Further studies are needed to establish the species’ absolute significance in terms of fruits as a source of water and nutrients to arid zone bird diets.

Potential effects of arid shrubland degradation on habitat suitability for a declining arid zone bird, the Chestnut‐rumped Thornbill (Acanthiza uropygialis)

AbstractAustralia's arid shrublands have been impacted by a variety of threatening processes since European settlement, and changes to ecosystem structure and function have been observed at multiple levels. The lack of recruitment and regeneration of the perennial shrub and tree layer in these communities has implications for many shrubland birds, including species of conservation concern such as the Chestnut‐rumped Thornbill (Acanthiza uropygialis: Acanthizidae). We documented foraging behaviour and habitat selection of the Chestnut‐rumped Thornbill at the Arid Recovery Reserve in South Australia and surveyed vegetation characteristics within the Reserve and in an adjacent pastoral property. We found that Chestnut‐rumped Thornbills preferentially use certain plant species: Callitris glaucophylla, Acacia aneura, Acacia ligulata and Acacia tetragonophylla, and that these species were significantly less abundant at our study sites outside the Reserve than inside. Major differences in the structure and composition of the vegetation inside and outside the Reserve suggest that changes in habitat structure and composition occurring in the broader landscape (outside the fenced area) decrease the suitability of arid shrubland habitat for the Chestnut‐rumped Thornbill and may contribute to their absence in unprotected areas. Our study indicates that deterioration of the perennial shrub layer could have significant consequences for the persistence of the Chestnut‐rumped Thornbill in arid rangelands. Our findings highlight the importance of rangeland management and restoration of Australia's arid shrublands in preventing declines of the Chestnut‐rumped Thornbill and other insectivorous birds.

The role of fringing vegetation in supporting avian access to arid zone waterholes

ABSTRACT Access to drinking water is essential for many avian species in arid landscapes, especially in hot and dry periods when metabolic requirements for water increase. The role of fringing vegetation in facilitating surface water access by arid zone bird communities was investigated over a 14-month period during which water demand increased. Bird visitation to six long-lasting waterholes in the MacDonnell Ranges Bioregion in central Australia was recorded over two summers and one winter using camera traps. Species were assigned to functional classes based on their size and preferred foraging substrate. Generalised linear mixed models were used to test relationships between fringing vegetation variables and the independent trapping events for each functional class. Fringing vegetation was critical for small and intermediate-sized canopy foragers to access waterhole sites. Their activity declined to almost zero in areas where the nearest tree or shrub cover was greater than 10 m. The strength of this relationship was consistent as weather conditions became drier and hotter. However, activity of small and intermediate-sized canopy foragers was negatively related to the percent canopy cover of the nearest tree or shrub, potentially because sparse vegetative cover offers greater visibility when approaching the water’s edge. In contrast, ground forager and raptor activity at waterhole sites was unrelated to surrounding vegetation, and these groups frequently accessed water from open areas. Under future warming scenarios, small and intermediate canopy foragers may be vulnerable to predation if they are forced to access water at sites away from nearby fringing vegetation.

Where nothing stands still: quantifying nomadism in Australian arid-zone birds

ContextNomadism is a movement strategy in response to non-seasonal environmental variability. Knowledge of nomadic species movements is poor but is necessary to understand life histories and develop appropriate conservation strategies.ObjectivesWe provide a first quantification of nomadism among Australia’s arid bird community, which is presumed to be highly nomadic, by measuring variation in species’ occurrence and abundance among years to determine whether there are clear nomadic and non-nomadic strategists.MethodsWe surveyed birds annually from 2012 to 2016. We measured how many years each species was present at a site and estimated inter-annual variability in species abundance, using both measures to infer species movement patterns. We used results to inform existing movement classifications.ResultsMost arid species showed low site persistence, with species detected at the same site, on average, 1.8 out of the five survey years. Movement varied along a continuum rather than grouping into distinct nomadic and non-nomadic groups. Species classified as nomadic showed higher variation in abundance and lower site persistence than species classified as resident. Our method of quantifying nomadism closely replicated existing expert-derived movement classifications of arid zone bird species.ConclusionsRather than a fixed attribute, movements of many species in our study can be heavily environment-dependent, and individuals of a single species can display a continuum of movements in different times and places. This complicates the conservation of species, but the growing recognition of the complexity of species movements offers opportunities for a more nuanced understanding of the relationship between species and environment.

Direct and indirect effects of high temperatures on fledging in a cooperatively breeding bird

Abstract High temperatures and low rainfall consistently constrain reproduction in arid-zone bird species. Understanding the mechanisms underlying this pattern is critical for predicting how climate change will influence population persistence and to inform conservation and management. In this study, we analyzed Southern Pied Babbler Turdoides bicolor nestling survival, daily growth rate and adult investment behavior during the nestling period over three austral summer breeding seasons. High temperatures were associated with lower body mass, shorter tarsi, and reduced daily growth rates of nestlings. Our piecewise structural equation models suggested that direct impacts of temperature had the strongest influence on nestling size and daily growth rates for both 5-day-old and 11-day-old nestlings, followed by temperature-related adjustments to provisioning rates by adults. Rainfall and group size influenced the behavior of provisioning adults but did not influence nestling growth or survival. Adjustments to adult provisioning strategies did not compensate for direct negative effects of high air temperatures on nestling size or daily growth rates. Detailed mechanistic data like these allow us to model the pathways by which high temperature causes nest failure. In turn, this could allow us to design targeted conservation action to effectively mitigate climate effects.

High temperatures drive offspring mortality in a cooperatively breeding bird.

An improved understanding of life-history responses to current environmental variability is required to predict species-specific responses to anthopogenic climate change. Previous research has suggested that cooperation in social groups may buffer individuals against some of the negative effects of unpredictable climates. We use a 15-year dataset on a cooperative breeding arid zone bird, the southern pied babbler Turdoides bicolor, to test (i) whether environmental conditions and group size correlate with survival of young during three development stages (egg, nestling, fledgling) and (ii) whether group size mitigates the impacts of adverse environmental conditions on survival of young. Exposure to high mean daily maximum temperatures (mean Tmax) during early development was associated with reduced survival probabilities of young in all three development stages. No young survived when mean Tmax > 38°C, across all group sizes. Low survival of young at high temperatures has broad implications for recruitment and population persistence in avian communities given the rapid pace of advancing climate change. Impacts of high temperatures on survival of young were not moderated by group size, suggesting that the availability of more helpers in a group is unlikely to buffer against compromised offspring survival as average and maximum temperatures increase with rapid anthropogenic climate change.

Sublethal fitness costs of chronic exposure to hot weather vary between sexes in a threatened desert lark

ABSTRACT Behavioural trade-offs between foraging and thermoregulation result in negative relationships between diurnal body mass (M b) gain and daily maximum air temperature (T max) in arid-zone birds. However, it remains unclear how these trade-offs are affected by habitat type or sexually dimorphic behaviour. Using the South African arid-zone endemic Red Lark (Calendulauda burra) as a model taxon and focusing solely on non-breeding adults, we evaluated predictions that a) time-activity budgets are more strongly affected by air temperature (T a) than is the case for species occurring in arid savanna habitats with greater access to shaded microsites, and b) the effects of T max on diurnal M b gain differ between males and females. Behavioural observations revealed an effect of T a on activity, and sex differences in the temperature-dependence of resting and wing-spreading. Moreover, M b data obtained from habituated larks trained to perch on an electronic balance revealed that in males, but not females, diurnal M b gain was negatively related to T max, with diurnal M b gain equivalent to average overnight M b loss when T max = 33.5°C and zero diurnal M b gain (i.e. net 24-hr M b loss of ~ 5 %) when T max = 40.0°C. Under recent climate conditions, male Red Larks rarely, if ever, experienced consecutive days with T max > 40.0°C but, under an unmitigated climate change scenario, will experience 10–15 consecutive days per summer by the end of the 21st century. Our findings suggest that this threatened lark species is unlikely to persist across much of its current range by 2100.

High temperatures are associated with substantial reductions in breeding success and offspring quality in an arid-zone bird.

During hot weather, terrestrial animals often seek shaded thermal refugia. However, this can result in missed foraging opportunities, loss of body condition and impaired parental care. We investigated whether such costs could compromise breeding success in a widespread southern African bird: the Southern Yellow-Billed Hornbill Tockus leucomelas. We predicted that hornbills might be especially vulnerable to temperature-dependant reductions in parents' foraging capacity due to extreme asymmetry in sex-specific roles during breeding: females are confined within the nest cavity for most of the nesting period and the burden of provisioning falls solely on the male during this time. We followed 50 hornbill nesting attempts in the Kalahari Desert between 2012 and 2015, collecting data on provisioning rates, adult and nestling body mass, fledging success and size of fledglings. Mean daily maximum air temperatures (Tmax) during nesting attempts ranged from 33.2 to 39.1°C. The likelihood of successful fledging fell below 50% at mean Tmax > 35.1°C; a threshold now regularly exceeded at our study site due to recent climate warming. Additionally, offspring fledging following the hottest nesting attempts were > 50% lighter than those fledging following the coolest. Sublethal costs of keeping cool including loss of body condition, production of poor-quality offspring and breeding failure are likely to become issues of serious conservation concern as climate change progresses; even for currently widespread species. Missed-opportunity costs associated with behavioral thermoregulation and direct sublethal costs of temperature exposure should not be overlooked as a potential threat to populations, especially in environments that are already hot.

Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

Insensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

Weighing the cost: the impact of serial heatwaves on body mass in a small Australian passerine

Rising temperatures pose a grave risk to arid zone birds because they are already living close to their physiological limits and must balance water conservation against the need for evaporative cooling. We assess how extreme temperatures affect a wild population of small passerines by monitoring daily mass change in individual jacky winters Microeca fascinans (a small Australasian robin) across a series of severe heatwaves that afflicted southern Australia in the summer of 2018–2019. Daily maximum temperature and duration of heat exposure were negatively related to the birds’ ability to maintain body mass. At maximum temperatures ≥ 42°C, birds lost 2.0% of their body mass daily and at ≥ 45°C, 2.6%. Apparent mortality increased almost three‐fold, and all breeding birds abandoned their nests. Nevertheless, net daily mass loss was less than might be expected from laboratory‐based findings, presumably because wild jacky winters undertook behavioural thermoregulation. The birds also regained some mass between heatwave events and suffered no long‐term reduction in body condition.

HISTOLOGICAL AND STEREOLOGICAL STUDY ON THE KIDNEYS IN SPARROWS LIVING IN WET AND ARID ZONES

The structure of the kidneys of sparrows living in wet and arid zones was compared to each other. A stereological study was conducted to quantify the components of the bird’s kidneys. A total of 10 female sparrows living in wet and arid zones were collected. The length of the kidneys was measured before blocking. The transverse serial sections were taken with a thickness of 5 μm. The sections were stained with haematoxylin and eosin (H & E) as well as periodic acid Schiff- alcian blue (PAS- AL). The kidneys of the sparrows consisted mostly of a cortex with only a small portion as medulla. The medulla was arranged in the form of cones with different lengths, which were randomly distributed within the kidney. The medullary nephron tubules were arranged sequentially. Thick and thin limbs of loop of Henle were separated by the collecting ducts. The histological structure and absolute volumes of the kidneys and components of the nephron were quantified. The absolute volumes of the structures within the right and left kidneys were not significantly different. The volume of the whole kidney (p<0.001) in the wet zone was larger than that in the arid zone. Furthermore, the volume proportion of the proximal tubule as well as cortex to whole kidney size was higher than that in wet zone birds. Whereas, the volume proportion of the medulla, distal tubule, cortical collecting tubule, medullary collecting duct and thin limb of loop of Henle to whole kidney size was higher than that in arid zone birds (p≤0.001). This feature indicates that the arid zone bird species had a more high ability to conserve water by producing concentrated urine. Key words: sparrow; stereology; histology; kidney; environment ><0.001) in the wet zone was larger than that in the arid zone. Furthermore, the volume proportion of the proximal tubule as well as cortex to whole kidney size was higher than that in wet zone birds. Whereas, the volume proportion of the medulla, distal tubule, cortical collecting tubule, medullary collecting duct and thin limb of loop of Henle to whole kidney size was higher than that in arid zone birds (p≤0.001). This feature indicates that the arid zone bird species had a more high ability to conserve water by producing concentrated urine.Key words: sparrow; stereology; histology; kidney; environmentHISTOLOŠKA IN STEREOLOŠKA ŠTUDIJA LEDVIC VRABCEV, ŽIVEČIH V VLAŽNIH IN SUHIH OBMOČJIHPovzetek: V opisani raziskavi smo primerjali strukturo ledvic vrabcev, ki živijo v vlažnih in sušnih območjih. Izvedena je bila stereološka raziskava, s katero smo količinsko opredelili različne tkivne strukture v ptičjih ledvicah. Zbrali smo vzorce 10 samic vrabcev, ki živijo v vlažnih in sušnih območjih. Pred nadaljnjo histološko obdelavo vzorcev smo izmerili dolžino ledvic. Pripravljene so bile prečne serijske rezine ledvic debeline 5 μm. Rezine so bile obarvane s hematoksilinom in eozinom (barvanje H&E) ter s PAS histokemijsko reakcijo z dodatkom alcianskega modrila (PAS-AL). Ledvice vrabcev so večinoma sestavljala področja skorje in manjši deli sredice. Sredico so sestavljali stožci različnih dolžin, ki so bili naključno razporejeni znotraj ledvice. Središčne cevke nefrona so potekale ena ob drugi. Debelejši in tanjši deli zanke nefrona so bili ločeni z zbirnimi cevkami. Histološka zgradba ledvic, absolutna prostornina ledvic in sestavni deli nefrona so bili kvantitativno ovrednoteni. Absolutna prostornina struktur se med levo in desno ledvico ni značilno razlikovala. Prostornina celotne ledvice vrabcev v vlažnem območju je bila večja od prostornine ledvic vrabcev iz sušnega področja (p < 0,001). Poleg tega je bil prostorninski delež proksimalne cevke in področje skorje v primerjavi s celotno velikostjo ledvic večji pri pticah iz sušnega področja kot pri pticah iz vlažnega področja. Prostorninski delež sredice, distalne cevke, zbirne cevke v skorji, zbirnega kanala v sredici in tankega dela zanke nefrona v celotni velikosti ledvic pa je bil višji pri vrabcih iz vlažnih področij kot pri vrabcih iz sušnih področij (p ≤ 0,001). Opisane značilnosti ledvic kažejo na to, da bi lahko imele ptice iz sušnih območij večjo sposobnost ohranjanja vode s proizvodnjo koncentriranega urina.Ključne besede: vrabec; stereologija; histologija; ledvica; okolje

The costs of keeping cool: behavioural trade-offs between foraging and thermoregulation are associated with significant mass losses in an arid-zone bird.

Avian responses to high environmental temperatures include retreating to cooler microsites and/or increasing rates of evaporative heat dissipation via panting, both of which may affect foraging success. We hypothesized that behavioural trade-offs constrain the maintenance of avian body condition in hot environments, and tested predictions arising from this hypothesis for male Southern Yellow-billed Hornbills (Tockus leucomelas) breeding in the Kalahari Desert. Operative temperatures experienced by the hornbills varied by up to 13°C among four microsite categories used by foraging males. Lower prey capture rates while panting and reductions associated with the occupancy of off-ground microsites, resulted in sharp declines in foraging efficiency during hot weather. Consequently, male body mass (Mb) gain between sunrise and sunset decreased with increasing daily maximum air temperature (Tmax), from ~ 5% when Tmax < 25°C to zero when Tmax = 38.4°C. Overnight Mb loss averaged ~ 4.5% irrespective of Tmax, creating a situation where nett 24-h Mb loss approached 5% on extremely hot days. These findings support the notion that temperature is a major determinant of body condition for arid-zone birds. Moreover, the strong temperature dependence of foraging success and body condition among male hornbills provisioning nests raises the possibility that male behavioural trade-offs translate into equally strong effects of hot weather on female condition and nest success. Our results also reveal how rapid anthropogenic climate change is likely to substantially decrease the probability of arid-zone birds like hornbills being able to successfully provision nests while maintaining their own condition.

Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century

Birds inhabiting hot, arid regions are among the terrestrial organisms most vulnerable to climate change. The potential for increasingly frequent and intense heat waves to cause lethal dehydration and hyperthermia is well documented, but the consequences of sublethal fitness costs associated with chronic exposure to sustained hot weather remain unclear. Using data for species occurring in southern Africa's Kalahari Desert, we mapped exposure to acute lethal risks and chronic sublethal fitness costs under past, present, and future climates. For inactive birds in shaded microsites, the risks of lethal dehydration and hyperthermia will remain low during the 21st century. In contrast, exposure to conditions associated with chronic, sublethal costs related to progressive body mass loss, reduced nestling growth rates, or increased breeding failure will expand dramatically. For example, by the 2080s the region will experience 10-20 consecutive days per year on which Southern Pied Babblers (Turdoides bicolor) will lose ∼4% of body mass per day, conditions under which this species' persistence will be extremely unlikely. Similarly, exposure to air temperature maxima associated with delayed fledging, reduced fledgling size, and breeding failure will increase several-fold in Southern Yellow-billed Hornbills (Tockus leucomelas) and Southern Fiscals (Lanius collaris). Our analysis reveals that sublethal costs of chronic heat exposure are likely to drive large declines in avian diversity in the southern African arid zone by the end of the century.