Nest visit synchrony is high and correlates with reproductive success in the wild Zebra finch Taeniopygia guttata

Nest visit synchrony, whereby adults coordinate their visits to the nest, has been documented in several species of cooperative breeders. Visit synchrony may reduce nest predation rate or sibling competition, or instead follow from synchronisation of other behaviours, such as foraging. However, nest visit synchrony has rarely been considered in species with bi-parental care, even though it could conceivably bring similar fitness benefits to that seen in cooperative breeders. In addition, in species with bi-parental care, we might expect nest visit synchrony to reflect the quality of the pair or the overall coordination of breeding activity between partners. Here, we tested whether nest visit synchrony occurs in a classic avian model for the study of bi-parental care, the zebra finch Taeniopygia guttata. We found that in the wild, both zebra finch parents visited the nest very infrequently during nestling provisioning, with only one visit per hour, and that nest visits were highly synchronised with parents visiting the nest together on 78% of the visits. In addition, we found that nest visit synchrony was correlated with hatching rate, brood size at hatching and the number of offspring in the nest a few days prior to fledging. Our results suggest that, while more work is required to understand the benefits of nest visit synchrony in this species, considering behavioural synchrony and cooperation between mated partners may offer new insight into the study of parental investment, including in species with bi-parental care.

Conspecific attraction and nest site selection in a nomadic species, the zebra finch

Conspecific nesting density affects many aspects of breeding biology, as well as habitat selection decisions. However, the large variations in breeding density observed in many species are yet to be fully explained. Here, we investigated the settlement patterns in a colonial species with variable breeding density and where resource distribution could be manipulated. The zebra finch, Taeniopygia guttata, is a classic avian model in evolutionary biology but we know surprisingly very little about nest site selection strategies and nesting densities in this species, and in fact, in nomadic species in general. Yet, important determinants of habitat selection strategies, including temporal predictability and breeding synchrony, are likely to be different in nomadic species than in the non-nomadic species studied to date. Here, we manipulated the distribution of nesting sites (by providing nest boxes) and food patches (feeders) to test four non-exclusive habitat selection hypotheses that could lead to nest aggregation: 1) attraction to resources, 2) attraction to breeding conspecifics, and 3) attraction to successful conspecifics and 4) use of private information (i.e. own reproductive success on a site). We found that wild zebra finches used conspecific presence and possibly reproductive success, to make decisions over where to locate their nests, but did not aggregate around water or food within the study areas. Moreover, there was a high degree of inter-individual variation in nesting density preference. We discuss the significance of our results for habitat selection strategy in nomadic species and with respect to the differential selection pressures that individuals breeding at different densities may experience.

Does coloniality improve foraging efficiency and nestling provisioning? A field experiment in the wild Zebra Finch

The foraging benefits of coloniality, whereby colony members exchange information about food location, have been suggested as a primary factor influencing the evolution of coloniality. However, despite its longstanding popularity, this hypothesis has rarely been tested experimentally. Here, we conducted a field experiment in the wild Zebra Finch Taeniopygia guttata to test whether colonial birds are better at finding food than solitary individuals. We manipulated food patch location and directly measured foraging activity of many colonial and solitary parents at those patches using an electronic monitoring system. We provided nesting sites in excess to alleviate nest site competition and manipulated brood size to eliminate the possible correlation between brood size, nesting density, and individual quality (including foraging activity). We found that solitary birds found experimental food patches first, closely followed by colonial birds. Moreover, solitary parents adjusted the amount of food per nestling to experimental brood size, whereas colonial parents did not, although overall, nestlings were fed more per capita in colonial than in solitary nests. In addition, brood size and, to a lesser extent, nesting density negatively affected nestling growth. Therefore, with the effect of provisioning rate, sibling competition, and cost of coloniality combined, nestling mass was not affected by the brood manipulation in solitary nests, whereas nestlings were lighter in enlarged than in reduced broods in colonies. Our results therefore suggest that individuals settling in solitary nests were intrinsically better foragers and more optimal parents. While they do not invalidate the possibility of information transfer at colonies, our findings highlight the importance of considering settlement bias in future studies and add to the existing evidence that the effects of nesting density on fitness are both complex and multiple.

Resource allocation across the egg laying sequence in the wild zebra finch Taeniopygia guttata

Zebra finches have played a central role in the discovery of a variety of maternal effects over the past decade, with females shown to adjust resource allocation to their eggs in response to variables such as the appearance of their partner, their own condition, and the diet on which they are maintained. In addition to being the focus of some of the most high profile individual studies that have influenced maternal effects research in birds, the multitude of zebra finch studies together provide the most comprehensive set of data to illuminate general patterns and compare different maternally derived variables. Surprisingly, to date, virtually all of this work has focused on captive populations of the zebra finch that have been domesticated for many generations, and which are typically held under relatively constant environmental and dietary conditions. Here we report the first data on resource allocation across the egg laying sequence in a free-living wild population. Reassuringly we find that the patterns that have been found in the majority of studies of domesticated populations with respect to investment across the laying sequence were all present in the wild population. The size and mass of eggs increased through the laying sequence whilst the concentration of carotenoids significantly decreased across the laying sequence. Although there was no significant pattern with respect to testosterone across the laying sequence the first two eggs had a higher level of testosterone than the last few eggs in the clutch, which is also consistent with the findings of earlier studies in captive populations. © 2011 The Authors.

The size and composition of social groups in the wild zebra finch

Despite the zebra finch (Taeniopygia guttata) being used as a model species in behavioural science, the size and composition of social groups in which individuals typically live in the wild when they are not breeding is not well described. We observed the group size and composition of free-ranging zebra finches during two brief non-breeding periods near semipermanent water sources in the arid zone of Australia. We conducted 15 observation sessions at two artificial dams during late 2011, and five transects in April 2012. We found that individuals most commonly foraged, watered and travelled around the colonies in groups of two, the overwhelming majority of which (94.2%) were mixed-sex, which most likely reflected sexual partnerships, or in larger groups of 3-10 individuals, with few observations of groups larger than this observed. These observations indicate the central importance of the pair bond, even during periods outside of active breeding. We also saw very few single-sex groups, in contrast to the way in which they are often housed in captivity. Our results suggest that researchers working on captive zebra finches should attempt to keep individuals in pairs or small social groups to best emulate the social environment they generally experience in the wild.

Physiological, morphological and behavioural effects of selecting zebra finches for divergent levels of corticosterone

The effects of environmental stress on the physiology and behaviour of higher vertebrates has become an important avenue of research in recent years. Evidence from recent studies has suggested that the avian stress-related hormone corticosterone (CORT) may play a role in immunocompetence and sexual selection. We tested whether CORT is immunosuppressive by studying humoral and cell-mediated immune responses in populations of captive zebra finches selected for divergent peak levels of CORT. We also investigated whether selection for peak CORT has an effect on the quality of several sexually selected regions of the male zebra finch; in addition we compared morphometric parameters and the dominance ranking in males from the different selection lines. We also tested whether different components of the immune system compete for limited resources. We found that selection for divergent levels of peak CORT had little effect on humoral immunity, male sexual signal quality or dominance ranking. However, contrary to expectations, we did find a positive relationship between CORT titre and cell-mediated immunity, as well as a greater cell-mediated response in the birds selected for high CORT titre than those selected for low CORT titre. Consistent with predictions, significant negative relationships were found between both testosterone and CORT titre on humoral immunity. Birds from the low CORT lines were significantly larger in terms of skeletal size than those from the high CORT lines. Overall, our results suggest that the cell-mediated immune response is associated with a reduction in the humoral response, but only in males, and that there is no simple relationship between peak CORT levels and immune function.

Mate choice in zebra finches: does corticosterone play a role?

The importance of stress as a factor in influencing life history strategies has received considerable attention in recent years, because it appears to have a substantial impact on an individual's behaviour and physiology. Birds respond to environmental and social stressors by the production of corticosterone, a glucocorticoid hormone released by the adrenal gland. In this experiment, we tested whether female zebra finches preferred males selected to produce low or high peak levels of circulating plasma corticosterone. Plasma corticosterone and testosterone levels of the males were recorded, as were morphometric measurements and perch activity. Spectrophotometric measurements were also taken from several putatively sexually selected regions of the males. The females preferred the males from the low corticosterone lines to the high corticosterone males. In addition to, and consistent with this effect, females preferred males with the lowest corticosterone titres. Male activity, testosterone level, body size and mass had no effect on female preference. Leg and beak brightness were important, however, as were the brightness and chromaticity of the male cheek patch. These results are discussed in relation to contemporary hypotheses in sexual selection, particularly in the context of stress-mediated signalling.

Spatial ability is impaired and mineralcorticoid receptor mRNA expression in zebra finches (Taeniopygia guttata) selected for acute high corticosterone response to stress

In mammals, stress hormones have profound influences on spatial learning and memory. Here, we investigated whether glucocorticoids influence cognitive abilities in birds by testing a line of zebra finches selectively bred to respond to an acute stressor with high plasma corticosterone (CORT) levels. Cognitive performance was assessed by spatial and visual one-trial associative memory tasks. Task performance in the high CORT birds was compared with that of the random-bred birds from a control breeding line. The birds selected for high CORT in response to an acute stressor performed less well than the controls in the spatial task, but there were no significant differences between the lines in performance during the visual task. The birds from the two lines did not differ in their plasma CORT levels immediately after the performance of the memory tasks; nevertheless, there were significant differences in peak plasma CORT between the lines. The high CORT birds also had significantly lower mineralocorticoid receptor mRNA expression in the hippocampus than the control birds. There was no measurable difference between the lines in glucocorticoid receptor mRNA density in either the hippocampus or the paraventricular nucleus. Together, these findings provide evidence to suggest that stress hormones have important regulatory roles in avian spatial cognition.

Short- and long-term consequences of early developmental conditions : a case study on wild and domesticated zebra finches

Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life-history manipulation, compared to birds taken directly from the wild. In a ‘common aviary’ experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short- and long-term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short- and long-term morphological and life-history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life-history strategies and investment trade-offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life-history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.

Vocal communication at the nest between mates in wild zebra finches : a private vocal duet?

Bird vocal duets are joint displays where two individuals, generally a mated pair, produce temporally coordinated vocalizations. Duets may contribute to pair bond maintenance, mate guarding or collaborative defence of resources. The degree of coordination between mates and the variety of vocalizations, however, vary considerably. Although only 3–4.3% of bird species have been reported to duet, this may be because studies have generally focused on conspicuous duets, and more private forms of duet might have been overlooked. We investigated private vocal communication between mates in wild zebra finches, Taeniopygia guttata, a gregarious Australian songbird that forms life-long pair bonds. The partners are inseparable unless nest building, incubating or brooding. Using microphones inside nestboxes, we monitored interactive communication between partners at the nest and its variation during different stages of breeding. After periods of separation, partners performed coordinated mutual vocal displays involving specific soft vocal elements that fulfilled all the criteria used to define duets. In addition, using playback experiments, we obtained preliminary results suggesting that these soft calls could allow mate recognition. Thus, we propose that mutual displays at the nest in zebra finches represent private vocal duets and may function to mediate pair bond maintenance.

Artificial ornaments manipulate intrinsic male quality in wild-caught zebra finches (Taeniopygia guttata)

The addition of red and green color bands is a commonly used method for manipulating male attractiveness in the zebra finch (Taeniopygia guttata), providing insight into the study of maternal investment and sexual selection. The addition of artificial ornaments has been assumed to manipulate a females’ perception of the male, rather than affecting intrinsic qualities of the male himself. Here, however, we reveal that the artificial band color worn by a male changes his body mass, condition, and courtship display rate. Males wearing red color bands in aviaries prior to mate-choice trials had a significantly higher song rate during trials than those wearing green color bands, alongside a significant increase in mass change and condition. Male song rate was found to significantly correlate with female preference alongside a female preference for red-banded males. However, male song rate in turn increased when female response was positive, suggesting a social feedback between the interacting birds. Our data suggest the presence of socially mediated feedback mechanisms whereby the artificial increase in attractiveness or dominance of a male directly affects other aspects of his attractiveness. Therefore, housing birds in social groups while manipulating attractiveness can directly influence other male qualities and should be accounted for by future studies.

Low level of extrapair parentage in wild zebra finches

The captive zebra finch, Taeniopygia guttata, has become one of the key vertebrate model systems for studying a range of behavioural, physiological and neurological phenomena. In particular, this species has played a key role in developing our understanding of sexual selection and sperm competition. In contrast with the large number of studies using domesticated zebra finches, relatively few studies have focused on free-living populations of wild zebra finches. Investigating the incidence of extrapair paternity in zebra finches in the Australian desert, we found a very low level; 1.7% of 316 offspring from four of 80 broods fathered outside the pair bond. These numbers contrast with the high levels of extrapair paternity observed in domesticated aviary populations, and suggest a low level of sperm competition and sexual selection in natural populations. Our finding of such a low rate of extrapair paternity in the wild zebra finch suggests that it is one of the most genetically monogamous of all passerine species and that has important implications for future studies of this model organism in studies of sexual selection and reproductive biology. In addition, we found that 5.4% of 316 offspring were not related to either putative parent and hatched from eggs that had been dumped by intraspecific brood parasites.

Sex steroid profiles and pair-maintenance behavior of captive wild-caught zebra finches (taeniopygia guttata)

Here, we studied the life-long monogamous zebra finch, to examine the relationship between circulating sex steroid profiles and pair-maintenance behavior in pairs of wild-caught zebra finches (paired in the laboratory for >1 month). We used liquid chromatography-tandem mass spectrometry to examine a total of eight androgens and progestins [pregnenolone, progesterone, dehydroepiandrosterone (DHEA), androstenediol, pregnan-3,17-diol-20-one, androsterone, androstanediol, and testosterone]. In the plasma, only pregnenolone, progesterone, DHEA, and testosterone were above the limit of quantification. Sex steroid profiles were similar between males and females, with only circulating progesterone levels significantly different between the sexes (female > male). Circulating pregnenolone levels were high in both sexes, suggesting that pregnenolone might serve as a circulating prohormone for local steroid synthesis in zebra finches. Furthermore, circulating testosterone levels were extremely low in both sexes. Additionally, we found no correlations between circulating steroid levels and pair-maintenance behavior. Taken together, our data raise several interesting questions about the neuroendocrinology of zebra finches.