GABB: A global dataset of alpine breeding birds and their ecological traits.

Alpine ecosystems represent varied climates and vegetation structures globally, with the potential to support rich and functionally diverse avian communities. High mountain habitats and species are under significant threat from climate change and other anthropogenic factors. Yet, no global database of alpine birds exists, with most mountain systems lacking basic information on species breeding in alpine habitats, their status and trends, or potential cryptic diversity (i.e., sub-species distributions). To address these critical knowledge gaps, we combined published literature, regional monitoring schemes, and expert knowledge from often inaccessible, data-deficient mountain ranges to develop a global list of alpine breeding bird species with their associated distributions and select ecological traits. This dataset compiles alpine breeding records for 1,310 birds, representing 12.0% of extant species and covering all major mountain regions across each continent, excluding Antarctica. The Global Alpine Breeding Bird dataset (GABB) is an essential resource for research on the ecological and evolutionary factors shaping alpine communities, as well as documenting the value of these high elevation, climate-sensitive habitats for conserving biodiversity.

Evaluation of counting methods for monitoring populations of a cryptic alpine passerine, the rock wren (Passeriformes, Acanthisittidae, Xenicus gilviventris).

Developing and validating methods to determine trends in populations of threatened species is essential for evaluating the effectiveness of conservation interventions. For cryptic species inhabiting remote environments, this can be particularly challenging. Rock wrens, Xenicus gilviventris, are small passerines endemic to the alpine zone of southern New Zealand. They are highly vulnerable to predation by introduced mammalian predators. Establishing a robust, cost-effective monitoring tool to evaluate population trends in rock wrens is a priority for conservation of both the species and, more broadly, as part of a suite of indicators for evaluating effectiveness of management in New Zealand's alpine ecosystems. We assessed the relative accuracy and precision of three population estimation techniques (mark-resight, distance sampling and simple counts on line transects) for two populations of rock wrens in the Southern Alps over six breeding seasons (2012-2018). The performance of these population estimators was compared to known rock wren population size derived from simultaneous territory mapping. Indices of abundance derived from counts on transects were correlated with territory mapping at both study areas, and performed better than either mark-resight methods or distance sampling. Simple counts on standardised line transects are a highly cost-effective method of monitoring birds because they do not require banding a population. As such, we recommend that line transect counts using the design outlined in this paper be adopted as a standard method for long-term monitoring of rock wren populations. Although species-specific testing is required to validate use of low-cost population indices, our results may have utility for the monitoring of other cryptic passerines in relatively open habitats.

Does the New Zealand rockwren (Xenicus gilviventris) hibernate?

In this study, we examined the thermal physiology of the endangered New Zealand rockwren (Xenicus gilviventris), a member of the Acanthisittidae, a family unique to New Zealand. This family, derived from Gondwana, is thought to be the sister taxon to all other passerines. Rockwrens permanently reside above the climatic timberline at altitudes from 1000 to 2900 m in the mountains of South Island. They feed on invertebrates and in winter face ambient temperatures far below freezing and deep deposits of snow. Their body temperature and rate of metabolism are highly variable. The rockwrens in our study regulated their body temperature at ca. 36.4°C, which in one individual decreased to 33.1°C at an ambient temperature of 9.4°C; its rate of metabolism decreased by 30% and its body temperature then spontaneously returned to 36°C. The rate of metabolism in a second individual twice decreased by 35%, nearly to the basal rate expected from its mass without a decrease in body temperature. The New Zealand rockwren's food habits, entrance into torpor and continuous residence in a thermally demanding environment suggest that it may hibernate. However, for that conclusion to be accepted, evidence of its use of torpor for extended periods is required. Acanthisittids are distinguished from other passerines by the combination of their permanent temperate distribution, thermal flexibility and a propensity to evolve a flightless condition. These characteristics may principally reflect their geographical isolation in a temperate environment isolated from Gondwana for 82 million years in the absence of mammalian predators.

The energetics of torpor in a temperate passerine endemic to New Zealand, the Rifleman (Acanthisitta chloris).

Compared to other birds, passerines, reflecting their small mass, have a narrow set of behavioral characteristics. One difference is that few enter torpor, especially in temperate environments. The few that do include swallows, none of which live throughout the year in cold-temperate environments, because their food, flying insects, is not available in winter and no passerine is known to hibernate. They seasonally migrate to warm-temperate and tropical environments. We present data on the energetics of the Rifleman (Acanthisitta chloris), a small, insectivorous member of the Acanthisittidae, a passerine family endemic to temperate New Zealand. This family is considered to be the sister taxon to all living passerines, which raises the question whether its physiological and behavioral characteristics reflect its evolutionary status in a manner that distinguishes it from other passerines. Only two of the eight known species in this family survive; four of the extinct species were flightless, a condition that evolved independently three times and is almost absent from other passerines. The Rifleman readily enters torpor, which is facilitated by its small mass. It enters torpor at ambient temperatures that are commonly encountered in its wet, cool-to-cold environment. As a result, its body temperature and rate of metabolism are highly variable. An estimate of the basal rate of metabolism is similar to that expected from body mass. Unlike some  torpor-prone birds, the Rifleman is a permanent resident in a temperate environment. This residency is possible, because the Rifleman gleans insect prey from surfaces, which does not require insects to have high body temperatures for activity. Its only living relative, the endangered, insectivorous Rock Wren (Xenicus gilviventris), is a permanent resident at altitudes from ca. 1000 to 2500 m in the mountains of South Island, New Zealand. There it faces severe winter conditions that are not avoided by descent to lower altitudes. Its response to these conditions may be an extended period of torpor. The repeated evolution of a flightless condition possibly reflects some distinctive property of the acanthisittids. The evolution of torpor and a flightless condition in acanthisittids may have facilitated their survival on a geographically isolated, temperate landmass, and these character states permitted by the absence of endemic mammalian predators.