Factors affecting nestling condition and timing of egg-laying in the endangered Carnaby’s cockatoo, Calyptorhynchus latirostris

Carnaby’s cockatoo, Calyptorhynchus latirostris, is endemic to south-western Australia. It has undergone a major decline in range and abundance as a result of extensive removal of breeding and foraging habitat. It is now classified as endangered by the State of Western Australia, the Australian government, and internationally. In order to plan effective conservation management for the species it is important to assess the success of breeding populations throughout its range. In this paper we examine the efficacy of using the relationship between growth in the length of a nestling’s folded left wing and body mass to assess nestling condition, and examine known breeding failure in relation to nestling condition in two breeding populations: one at Coomallo Creek (studied from 1970–2017), and the other at Manmanning (1969–76). Results demonstrated that the lighter the nestlings, the higher the rate of breeding failure. Data from the Coomallo Creek population were used to prepare a table of nestling folded left wing length and body mass as a benchmark for assessing nestling condition in 10 other breeding populations, based on data collected from 1970 to the present. Following extensive clearing that removed foraging and breeding habitat, two of the 10 populations produced nestlings that were significantly lighter than the benchmark, and both populations subsequently declined to extinction. The commencement of egg-laying each season at Coomallo Creek was strongly influenced by total rainfall in the first half of autumn. The length of the egg-laying period between 1970–76 and 2009–17 increased by 5.2 weeks (40%). This increase was related to changes in rainfall and temperature over more than four decades. Despite the lengthening of the egg-laying period, nestling condition was unaffected, suggesting that, at least in the short term, the Carnaby’s cockatoo population at Coomallo Creek is coping with the effects of climate change.

Autumn freeze-thaw events carry over to depress late-winter reproductive performance in Canada jays

Evidence suggests that range-edge populations are highly vulnerable to the impacts of climate change, but few studies have examined the specific mechanisms that are driving observed declines. Species that store perishable food for extended periods of time may be particularly susceptible to environmental change because shifts in climatic conditions could accelerate the natural degradation of their cached food. Here, we use 40 years of breeding data from a marked population of Canada jays ( Perisoreus canadensis ) located at the southern edge of their range in Algonquin Provincial Park, Ontario, to examine whether climatic conditions prior to breeding carry over to influence reproductive performance. We found that multiple measures of Canada jay reproductive performance (brood size, nest success and nestling condition) in the late winter were negatively correlated with the number of freeze–thaw events the previous autumn. Our results suggest that freeze–thaw events have a significant detrimental impact on the quality and/or quantity of cached food available to Canada jays. Future increases in such events, caused by climate change, could pose a serious threat to Canada jays and other food caching species that store perishable foods for long periods of time.

Effect of Nest Characteristics on Thermal Properties, Clutch Size, and Reproductive Performance for an Open-Cup Nesting Songbird

Maintaining avian eggs and young at optimum temperatures for development can increase hatching success and nestling condition, but this maintenance requires parental energetic demands. Bird nests, which often provide a structure to safely hold the eggs and nestlings and protect them from predators, can additionally be designed to help maintain eggs’ optimum temperatures by minimising heat loss, especially in climates where eggs cool rapidly when unattended. We collected and measured Prairie Warbler ( Setophaga discolor) nests in western Massachusetts, U.S. in 2009 and conducted a climate-controlled, nest-cooling experiment to determine how nest characteristics affect thermal properties for small, open-cup nesting birds. We then assessed if nests with better insulation properties resulted in any fitness benefits, and also tested if nest structural characteristics affected birds’ fitness. We found that nest characteristics influenced their thermal properties, with thicker, heavier, and larger nests having slower cooling rates and higher predicted equilibrium egg temperatures. Both nest cup depth and clutch size significantly declined over the breeding season, and we observed a trend, although non-significant, that nests with shallower cups had smaller clutches. Contrary to studies on cavity-nesting birds, we found no significant effects of nest thermal properties or nest structure on hatching and fledging success, nestling condition, brood parasitism, or nest survival. Prairie Warblers in our study site may already be adapted to build nests within a range that maximises their fitness. Furthermore, studies have shown that open-cup nests of other species are relatively thicker and more insulated in colder environments at higher latitudes than our study. Instead of building nests to solely minimise heat loss, open-cup nesting birds in temperate climates may also be driven by opposing selection pressures when building their nests, such as to prevent nestlings from overheating during hot days.

The breeding ecology of the barn swallow Hirundo rustica gutturalis in South China

Some animal species are found in many environments and over wide distributions and may have adaptations to live in such different areas. The barn swallow Hirundo rustica is an example of a species that is able to thrive over a large geographic range and in many different environments. However, little is known of the breeding biology of this species in southern China. Here, we studied 18 breeding pairs of barn swallow H. r. gutturalis in Nanning, Guangxi, between April and July 2015. We studied its breeding fitness and parental investment. We found that tropical barn swallows bred from early April to early July and had from two to five fledglings per brood. We also recorded a strong seasonal decrease of breeding success and nestling condition that has also been found in temperate regions. Nevertheless, nestlings showed relatively long wings and low body masses, which may have enabled three sets of parents to raise three broods per breeding season, more than in other Chinese populations. Generally, barn swallows breeding in the tropics showed a similar ecology to their conspecifics from temperate regions, probably due to the species’ niche specificity in urban settings. Morphological differences detected in this study require further research based on larger sample sizes and on more detailed data from different climatic regions of Asia.

Vector abundance determines Trypanosoma prevalence in nestling blue tits

SUMMARYThe effect of insect vectors on avian exposure to infection by pathogens remains poorly studied. Here, we used an insect repellent treatment to reduce the number of blood-sucking flying insects in blue tit Cyanistes caeruleus nests and examined its effect on nestling health status measured as body mass, nestling phytohaemagglutinin (PHA) response and blood parasite prevalence. We found that (i) the insect repellent treatment significantly reduced the number of blood-sucking flying insects in nests and (ii) the number of blood-sucking flying insects had a significant effect on the prevalence of the blood parasite Trypanosoma independently of the treatment. In addition, we found support for an adverse effect of parasite infections on nestling PHA response. Nestlings infected by Trypanosoma mounted a weaker response against PHA than non-parasitized ones. In addition, the number of blowflies in the nest was negatively associated with nestling PHA response. Overall, we found support for the hypothesis that blood-sucking flying insects attacking nestlings increase their exposure to parasite infections. Our results further substantiate the adverse effect of parasites on nestling condition.