Slow continuous wing-moult of Zebra Finches Poephila guttata from southeast Australia

Moult of the remiges was studied over eight years in a population of Zebra Finches from southeast Australia. In first-year birds the first primary was lost at mean age of 80 days in both sexes; moult took 204 days to complete in males and 223 in females. Birds hatched in autumn postponed the start of their primary moult until spring. Primaries were replaced slowly in a rigid, non-overlapping, ascending order from #1 to #9 but the secondaries did not display a rigid sequence.
Adult Zebra Finches moulted remiges throughout the year. Primary moult was initiated in any month. Primary moult had a mean duration of 229 days for males and 240 days for females. Primaries moulted in continuous waves: the interval between successive moults in males was –16 days and +6 days in females. Limited food, low temperatures and breeding slowed, but did not stop, wing-moult. Birds caring for eggs and young actively replaced remiges.
The pattern of wing-moult displayed here by Zebra Finches is exceptional for passerines and may be related to the opportunistic breeding strategy necessary in an arid, unpredictable environment. Its presence in the Victorian birds may be non-adaptive.     

Tritiated water measurements of water flux in nestling and adult zebra finches (Poephila guttata)

• 1.1. Total body water volume (TBWV) and daily water turnover rates (WTR) were measured in nestling and adult zebra finches using tritiated water (TOH).
• 2.2. TBWV and daily WTR increased with age up to 13 days post hatching.
• 3.3. TBWV and WTR approached adult levels after 13 days of age. WTR varied among ages and nest mates. All nestlings turned over at least 50% of their body water pool per day.
• 4.4. The WTR data for adult birds are consistent with natural history data suggesting zebra finches are dependent on water for breeding and survival.

     

Changes in the muscle condition of female Zebra Finches Poephila guttata during egg laying and the role of protein storage in bird skeletal muscle

Samples of pectoral muscle tissue from Zebra Finches Poephila guttata were taken from birds at various stages of egg laying. As egg laying progressed, there was a significant loss of both water-soluble and alkali-soluble proteins. Gel filtration of the water-soluble proteins showed three peaks, only one of which changed significantly during the laving cycle. This was a high-molecular-weight protein that declined in concentration during the period of egg laying. This protein may function as a reserve, enabling female birds to provide amino acids for egg protein production from their muscle tissue without impairing normal muscle function.     

斑胸草雀的鸣声学习

鸣声是鸟类重要的生物学特征和分类特征。由于生理结构和神经控制方面的差异,不同种群和同一种群的不同个体都有自己特有的鸣声特征,正是利用这些特征,鸟类才能在集群、取食、迁徙、喂雏、御敌和求偶等行为中进行通讯。作为一种能够利用语音信息进行交流的高等脊椎动物,斑胸草雀的鸣声特别是鸣啭能力获得,需要有一个适宜的学习对象,并在一段特定的时间内,经历复杂的学习过程才能实现。     

Audience Effect Alters Male Mating Preferences in Zebra Finches (Taeniopygia guttata)

The social environment of animals strongly influences the mating preferences of both the choosing and the observing individuals. Notably, there is recent evidence that polygamous males decrease their selectivity when being observed by competitors in order to direct their rivals' attention away from their true interest and, consequently, reduce sperm competition risk. Yet, other mechanisms, whose importance remains unexplored, could induce similar effects. In monogamous species with mutual choice, particularly, if males adjust their selectivity according to the risk of being rejected by their preferred mate, they should as well become less selective when potential rivals are present. Here, we investigated whether the presence of bystanders modifies male mating preferences when the risk of sperm competition is low, by carrying out mate-choice experiments with male zebra finches (Taeniopygia guttata) whose preferences for two females were measured twice: with and without an audience. We found that the presence of potential rivals had no effect on the males' choosiness. However, with an audience, they spent more time with the female that was considered as the less attractive one in the control condition. These findings support the hypothesis that monogamous males alter their mate choice decisions in the presence of a male audience to reduce the risk of remaining unpaired. Thus, our results indicate that several explanations can account for the changes in male preferences due to the presence of competitors and highlight the importance of assessing the relative role of each mechanism potentially involved, to be able to make conclusions about the effect of an audience on signal evolution.     

Survivorship, dispersal and sex ratios of Zebra Finches Taeniopygia guttata in southeast Australia

Membership of three permanent breeding colonies of Zebra Finches Taeniopygia guttata studied in farmland changed continually due to arrival and departure of birds from distant colonies. Sixty-six percent of adults stayed for less than 1 month, and many that stayed longer disappeared for extended periods. Over 78% of adults captured were hatched in other colonies and only 23% made a breeding attempt in their natal colony. There was no sex-biased natal dispersal or philopatry, but there were sex differences in the timing of dispersal. Sex ratios at the end of parental care were variable and may depend on food resources. Adult ratios were slightly male-biased. Annual losses of adults ranged from 72 to 82% across colonies, but mortalities and dispersal were heavily confounded by high adult mobility. The oldest bird was more than 5 years old. A total of 67% of young were lost between fledging and nutritional independence at 35 days of age, and only 20% of fledglings survived to day 80, the age of first breeding. Artificial supplies of seed at baited walk-in traps prolonged the stay of dispersing adults from other colonies, enhanced the survivorship of young hatched in the colony and possibly affected the secondary sex ratio. In this southeast part of their Australia-wide distribution, Zebra Finch populations appear to be highly mobile over a very large home range with extensive free interchange of members among a number of permanent breeding colonies. High mobility may be adaptive for exploiting patches of seed and water in a highly erratic environment.     

Personality and body condition have additive effects on motivation to feed in Zebra Finches Taeniopygia guttata

Several hypotheses have been proposed to account for the adaptive evolution of personality, defined as inter‐individual differences in behaviour that are consistent over time and across situations. For instance, the ‘pace‐of‐life syndrome’ hypothesis suggests that personality evolved as a behavioural correlate of life‐history trajectories that vary within populations. Thus, proactivity, corresponding to higher exploratory tendencies or higher boldness levels, has been linked to higher productivity or mortality rates. However, the extent to which proactivity is associated with a higher motivation to forage remains poorly understood. Moreover, although personality and its effects on foraging behaviour are usually considered to be independent of any motivational or nutritional state, few studies so far have challenged this. Here we show that personality traits, both individually or combined using a principal component analysis, and body condition have additive effects on latency to feed following food deprivation in the Zebra Finch Taeniopygia guttata, with personality accounting for 41% and body condition for about 20% of the total variation in latency to feed. In accordance with the pace‐of‐life syndrome hypothesis, latency to feed was negatively related to the degree of proactivity and positively related to body condition. Thus, proactive individuals and individuals in poorer condition were quicker to start feeding after a period of food deprivation. The absence of a significant interaction between personality and body condition further suggests that the effect of personality was independent of body condition. We discuss the relevance of our results in relation to the different factors influencing foraging in birds. Moreover, we place our results within a life‐history framework by emphasizing the correlated evolution of life‐history traits and personality.     

Tissue mass dynamics during egg-production in female Zebra Finches Taeniopygia guttata: dietary and hormonal manipulations

Changes in tissue masses associated with egg production were investigated in female Zebra Finches Taeniopygia gutatta using dietary and hormonal manipulations. We tested three hypotheses: that changes in organ masses, (a) reflect utilisation of endogenous nutrient stores due to inadequate daily dietary intake, (b) involve changes in organ structure or 'functional capacity', and (c) are initiated by onset of reproductive development (e.g. elevated plasma estrogen or yolk precursor levels, oviduct growth). Pectoral muscle lean dry mass was 18–22% lower in breeding females at the 1-egg stage compared to non-breeders, and this was independent of nutritional plane, i.e. similar changes occurred in birds provided with supplemental protein or egg food. Heart lean dry mass was also lower (16%) in breeding females, but only in birds on a low-quality seed diet, not in birds on supplemented diets. Decreases in total liver mass (14%) were due to changes in lipid content not lean dry mass, and were diet-dependent. These results demonstrate that changes in organ masses associated with egg production are complex, and do not simply reflect a general mobilisation of stored protein. We discuss why there is no hypertrophy of biosynthetic or metabolic 'machinery' associated with egg production in birds (cf. reproducing mammals). Exogenous 17β-estradiol induced plasma levels of yolk precursors typical of breeding birds, and initiated oviduct growth (to 31% of mature size). However, estradiol treatment caused no change in mass of pectoral muscle, heart or liver, demonstrating that there is no simple relationship between onset of reproductive development and associated tissue mass changes.     

Intra‐specific variance in sperm morphometry: a comparison between wild and domesticated Zebra Finches Taeniopygia guttata

The Zebra Finch Taeniopygia guttata is a model bird species for the experimental study of behavioural and evolutionary concepts in captivity and especially sexual selection. The validity of sexual selection studies of domesticated birds is of long‐standing concern as little is known about the influence of domestication on sexually selected traits. Most domesticated Zebra Finch populations are maintained under a strict breeding regime to avoid potential inbreeding. However, these breeding regimes may interfere with the processes of sexual selection and influence the evolution of sexually selected traits because they may limit or prohibit active mate choice. Here, we investigated the potential impact of a monogamous breeding scheme in a domesticated population in which active mate choice is largely inhibited, on the evolution of sperm morphometry as a sexually selected trait. We compared sperm morphometric traits (total sperm length and length of sperm head, midpiece and flagellum), and the variance thereof, between a domesticated and two wild Zebra Finch populations. Although we found significant differences between the three populations for certain sperm traits (head length, midpiece length), which may be of importance in postcopulatory sexual selection, overall, variance in sperm morphometry did not differ between the domesticated and the wild Zebra Finch populations. Our results validate the use of domesticated Zebra Finches for further studies of postcopulatory sexual selection and sperm competition.     

The Strength of Species Recognition in Captive Female Zebra Finches (Taeniopygia guttata): A Comparison Across Estrildid Heterospecifics

Conspecific recognition is essential for sexually reproducing species. Captive zebra finches ( Taeniopygia guttata ) are a model system in which the behavioural, ontogenetic and neurobiological bases of own-species (conspecific) recognition have been studied in detail. To assess the potential role of phylogeographic effects on species recognition, we examined the spatial preferences of unmated captive-bred female zebra finches between unfamiliar captive males of conspecific and estrildid heterospecific male stimuli. In accordance with prior studies using domesticated Bengalese finches ( Lonchura striata vars. domestica ), we found significant spatial and behavioural preference for conspecific males by female zebra finches, irrespective of heterospecific male phylogeographic origin mating status, or individual behaviour. This result has ramifications for the interpretation of social and mate preferences in this model species as it implies a consistency of species discrimination by captive female zebra finches.     

No evidence of assortative mating on the basis of putative ornamental traits in Long‐tailed Finches Poephila acuticauda

When multiple ornaments are expressed in both sexes, they are generally assumed to be maintained by mutual sexual selection and have a function in mate choice. In the Long‐tailed Finch Poephila acuticauda both sexes exhibit multiple ornaments that vary in their expression in either size (pintail and throat patch) or colour (bill) between individuals and sexes. We assessed whether these ornaments are maintained by mutual sexual selection by exploring whether individuals in a wild population paired assortatively with respect to these ornamental traits, and the degree to which the expression of these ornamental traits was indicative of reproductive success. We found no evidence of assortative pairing with respect to variation in homologous ornaments or body condition in the two sexes. In addition, we found no effect of ornament expression on the reproductive success of either males or females. Our findings suggest that the expression of these apparently ornamental traits in both sexes of this species may play no current role in mutual mate selection or as indicator traits of reproductive performance. We are currently unable to identify any function for these very elaborate ornaments in either sex of this species and suggest that the typical assumption that all such traits have an ornamental function may need further examination.     

The source of the nutrients required for egg production in zebra finches Poephila guttata

The source of nutrients used for egg formation are poorly known for most bird species. This study of the zebra finch Poephila guttata showed that food intake did not increase during egg production, but the decline in female body reserves of protein and fat were sufficient to account for most of the nutrients in a clutch of four eggs. Female birds significantly reduced their activity levels during ova enlargement, which may play a role in diverting resources to egg production. Birds increased their intake of calcium-rich food items when eggs were being laid, and this intake accounted for all the calcium needed for eggshell formation. The zebra finch depends heavily on stored body reserves for egg formation, which is probably unusual in small passerines.     

Sex-Specific Audience Effect in the Context of Mate Choice in Zebra Finches

Animals observing conspecifics during mate choice can gain additional information about potential mates. However, the presence of an observer, if detected by the observed individuals, can influence the nature of the behavior of the observed individuals, called audience effect. In zebra finches (Taeniopygia guttata castanotis), domesticated males show an audience effect during mate choice. However, whether male and female descendants of the wild form show an audience effect during mate choice is unknown. Therefore, we conducted an experiment where male and female focal birds could choose between two distinctive phenotypes of the opposite sex, an artificially adorned stimulus bird with a red feather on the forehead and an unadorned stimulus bird, two times consecutively, once without an audience and once with an audience bird (same sex as test bird). Males showed an audience effect when an audience male was present and spent more time with adorned and less time with unadorned females compared to when there was no audience present. The change in time spent with the respective stimulus females was positively correlated with the time that the audience male spent in front of its cage close to the focal male. Females showed no change in mate choice when an audience female was present, but their motivation to associate with both stimulus males decreased. In a control for mate-choice consistency there was no audience in either test. Here, both focal females and focal males chose consistently without a change in choosing motivation. Our results showed that there is an audience effect on mate choice in zebra finches and that the response to a same-sex audience was sex-specific.