P. Cassey’s research while affiliated with The University of Adelaide and other places

The invasion pathway is composed of a sequential series of stages that need to be quantified separately in order properly to understand the invasion process. Here, we examine the composition and characteristics of bird species being sold in the pet bird market in Taiwan. The bird trade in Taiwan is of high volume and financially lucrative. The identity of species in this trade is vital for informing later stages (introduction, establishment, spread) of the invasion pathway. We conducted interviews and surveys of 72 outlets selling pet birds from seven cities across Taiwan, from which we identified 247 bird species (within 34 families) for sale. Of these, 170 bird species (from 27 families) are exotic to Taiwan. Using randomization tests, we show that nine families are significantly over-represented in the pet trade (Psittacidae, Muscicapidae, Timaliidae, Sturnidae, Turdidae, Estrildidae, Chloropseidae, Zosteropidae and Fringillidae), and three after sequential Bonferroni correction (Psittacidae, Muscicapidae and Sturnidae). Species that have been identified in Taiwanese pet shops tend to have a larger native geographic range, originate further from the equator, are smaller-bodied, and have more aesthetically-pleasing songs than expected by chance. The native ranges of pet shop species are more likely to be situated in the Indo-Malay and Palearctic biogeographic realms, while fewer species than expected derive from the Neotropic, Afrotropic and Nearctic realms. Our results show that bird species for sale in Taiwan are determined by the interaction of species availability and societal demands.

Obligate avian brood parasites lay their eggs in hosts' nests and play no role in the provisioning of the progeny. Many parasites, including Cuculus cuckoos, hatch before their hosts and the altricial chick evicts hosts eggs and nestlings. A hypothesized, but so far untested parasite adaptation is that the embryos of cuckoos develop more quickly than the hosts' because the higher porosity of the parasite's eggshell allows greater gaseous exchange, potentially supporting more rapid development. We compared the water vapour conductance (GH2O) of common cuckoo (Cuculus canorus) eggshells and those of several passerines, including various cuckoo host species, and non-passerine species. Contrary to the prediction, the cuckoo eggs had lower GH2O than eggs of their hosts, and lower GH2O than predicted for their egg size and phylogeny. A potential advantage for the cuckoo egg of having a lower GH2O may be that the yolk is depleted at a slower rate, allowing more reserves to remain at the end of incubation, assisting the embryo with the energetically demanding tasks of hatching from a thicker eggshell, and evicting host eggs and nestmates.

Life-history theory posits that the evolutionary responses of hosts to avian brood parasitism will be shaped by the extent of the fitness costs of parasitism. Previous modelling work predicted that hosts of more virulent parasites should eject foreign eggs, irrespective of clutch size, whereas hosts of less virulent parasites, with smaller clutch sizes, should desert (abandon) parasitized clutches and, with larger clutch sizes, should eject foreign eggs. Egg rejection behaviour of European blackbirds (Turdus merula) and song thrush (T. philomelos) in their introduced range in New Zealand was induced by manipulating the colour of one of the birds’ own eggs. We also used parallel experimental manipulations in the common redstart (Phoenicurus phoenicurus), a regular host species with a large clutch size which pays a moderate cost when parasitized by the common cuckoo (Cuculus canorus). In all three species, eggs coloured entirely black were more often rejected than eggs coloured with black spots but with the rest of the background colour left visible. Rejections of black eggs occurred mainly through nest desertion in blackbirds, which have smaller clutch sizes, and mainly through egg ejection in song thrush, which have larger clutch sizes. As predicted, redstarts mostly ejected black eggs. Alternative egg rejection behaviours may have evolved in response to differently virulent brood parasitism across these species. For example, in the absence of interspecific parasitism in both their native and introduced ranges, selection by low-cost intraspecific brood parasitism may explain the experimentally-induced behavioural differences in egg rejection in blackbirds, with smaller clutch sizes, versus song thrushes, with larger clutch sizes. Such experimental approaches, informed by life-history theory, should be generally useful in larger-scale, comparative frameworks, to determine the relative roles of intra- versus interspecific brood parasitism in the evolution of egg rejection behaviours across diverse avian lineages.

Although the diversity in avian plumage coloration is striking, there is little known about the rate with which colour diverges. Eastern bluebirds on the island of Bermuda (Sialia sialis bermudensis) are considered endemic based upon differences in coloration from the mainland, but recent molecular evidence suggests they established on the island only 400 years ago. We explored sexual dichromatism and colour divergence in this isolated population, thus providing one of the few quantitative accounts of contemporary plumage change. Contrary to expectations that sexual dichromatism would decrease in this sedentary island population, we found that males and females have increased plumage ornamentation in a coordinated fashion that acts to preserve sexual dichromatism, while plumage colour is also altered to become brighter and bluer. These differences were in place at least 100 years ago based upon a separate analysis of museum specimens. Our results provide insight into the divergence of plumage colour in an incipient species, and we show the remarkable extent to which plumage colour can change over contemporary time frames.

The prevalence of passerines (mostly oscines, or songbirds) in international bird trade suggests that the possession or production of a song that is attractive or desirable to people may contribute to the likelihood of a species being traded. Testing this is difficult because we lack a general and readily available metric that quantifies attractiveness of bird song to humans. We propose and validate such a metric, based on the number of sound files lodged for a species on the Xeno-Canto website (www.xeno-canto.org). Our hypothesis is that species with more attractive songs are likely to be recorded more often, and so be represented more often in this online bird sound resource, all else being equal. Using a sample of North American and European passerines, we show that song repertoire size and geographic range size are consistently related to the number of recordings on Xeno-Canto. We use these results to derive a metric (the residuals of a model of the number of recordings in Xeno-Canto as a function of geographic range size) that may identify songs that are attractive to humans. Bird species whose songs are known to have inspired classical music, including several well known for their songs (e.g. common nightingale, European blackbird), have higher values of the metric than those that have not been referenced in classical music. The metric may help explain which bird species are present in trade, and so contribute to studies of invasion and conservation biology.

The three species of New Zealand’s endemic Mohoua genus are sole hosts of the obligate brood parasitic Long-tailed Cuckoo (Eudynamys taitensis), making their intrageneric phylogenetic relationships particularly important for coevolutionary studies. Also, recent molecular phylogenetic analyses have not identified the family-level placement of this genus. To resolve both intrageneric and family relationships, we generated new nuclear and mitochondrial sequence data and conducted phylogenetic analyses using Bayesian inference among representatives of endemic New Zealand passerines and Australasian ‘core Corvoidea’ lineages. The results establish strong intrageneric relationships of all three Mohoua species, confirm the monophyly of the genus, and suggest its placement in a re-erected monotypic family: Mohouidae.

Background/Question/Methods Species with cryptic origins (i.e. those that cannot be reliably classed as native or non-native) present a particular challenge to our understanding of the generation and maintenance of biodiversity. Such species may be especially common on islands given that islands have had a relatively recent history of human colonization. It is likely that select island species considered native may have achieved their current distributions via direct or indirect human actions. As an example, we explore the origins of eastern bluebirds on the island of Bermuda. Considered native to the island and a distinct subspecies, this population has diverged in morphology relative to mainland North America. We used microsatellite markers and plumage reflectance data to evaluate the history and status of this species group. Results/Conclusions We show that the Bermuda population of bluebirds is the likely result of a single human-assisted colonization event that occurred during the 1600s; making this species a cryptic invader. To our knowledge this is the youngest example of a terrestrial vertebrate cryptic invader and the only one designated as a subspecies. Furthermore, there are differences in plumage brightness and color that run counter to most island patterns; including increased brightness and increased plumage dimorphism. We suggest that the eastern bluebird is not an isolated case of cryptic invader either on Bermuda or elsewhere and that extreme caution be exercised when studying present-day distributions of organisms. Such cases require biologists to reconsider their definitions of native and non-native species.

We analysed inter-individual body mass variation of Japanese quail (Coturnix coturnix japonica) in an examination of the effectiveness of regulations governing daily food requirements. We measured the daily food intake of 26 adult female quail during a feeding trial over four consecutive days. Non-ingested food was weighed every morning and 70 g of food was provided to each bird for every day of the trial. This represented more than three times the theoretical recommended daily amount of food required by Japanese quail, as described in the literature. We then calculated a female-specific mean daily food requirement and found highly significant variation among individuals. Daily food intake was significantly repeatable within-female over the trial and mean food intake was highly correlated with female body mass. We suggest that using daily requirements for individuals based upon 'population' means, whilst ignoring differences in body mass among individuals might have severe consequences for the welfare of birds. Furthermore, these results have significant implications for studies where the aim is to perform identical experimental manipulations (as some studies intend and suggest), resulting in the drawing of unsubstantiated conclusions.