Zebra finches select nest material appropriate for a building task

Choice of props for courtship dancing in estrildid finches

Among the diverse sexual signals used by birds, the possible signaling functions of non-bodily objects during mating/courting displays remain unexplained. It is unclear whether such object-holding gestures are purely ritualistic or serve as an advertisement of an extended phenotype to potential mates. Estrildid finches (family Estrildidae) are characterized by mutual courtship, during which either a male or female will hold nesting material (usually grass stems or straw) in the beak while singing and dancing toward the opposite sex. We predicted that this display of potential nesting material advertises the ability of an individual to collect and transport such materials. Captive adult red-cheeked cordon-bleus (Uraeginthus bengalus) and star finches (Neochmia ruficauda) were presented with different string lengths in choice tests, and results were compared with those obtained from field observations of courtship displays among U. bengalus and blue-capped cordon-bleus (Uraeginthus cyanocephalus). Both captive and wild estrildid finches preferred longer strings for displays, which is compatible with the idea that non-bodily ornaments (strings) convey information on the maximum performance potential. The evolution of nesting material holding displays is likely associated with the nesting ecology of estrildid finches, which is characterized by a high predation risk and joint nest building by mating pairs.

Architectural traditions in the structures built by cooperative weaver birds

Humans cooperate to build complex structures with culture-specific architectural styles. However, they are not the only animals to build complex structures nor to have culture. We show that social groups of white-browed sparrow weavers (Plocepasser mahali) build structures (nests for breeding and multiple single-occupant roosts for sleeping) that differ architecturally among groups. Morphological differences are consistent across years and are clear even among groups with territories a few meters apart. These repeatable differences are not explained by among-group variation in local weather conditions, bird size, tree height, or patterns of genetic relatedness. Architectural styles are also robust to the immigration of birds from other groups.

Zebra finches have style: Nest morphology is repeatable and associated with experience

We investigated whether birds build nests in repeatable styles and, if so, whether styles were associated with past nest-building experience. Laboratory, captive bred zebra finches in an Experimental group were given nest-building experience, whereas, birds in a Control group were not. Each pair (n = 20) then built four nests that underwent image analyses for nest size, geometric shape and entrance orientation. Birds built nests in repeatable styles, with lower morphometric variation among nests built by the same pair and higher morphometric variation among nests built by different pairs. Morphology was not associated with construction time, body weight, nor age of birds. We found lower morphometric variation among nests built by the Experimental group, which also used less material to build nests compared to the Control group. Prior experience may therefore have been advantageous, as learning to reduce material usage while achieving a similar product (nest) may have lowered building costs.

Plastic is a widely used and selectively chosen nesting material for pied flycatchers (Ficedula hypoleuca) in rural woodland habitats

There is increasing concern about the burgeoning effects of discarded plastic on the earth's biodiversity. Quantifying the presence of plastic and other anthropogenic waste in the environment can be logistically and financially challenging, although it is possible that bird' nests can be used as bioindicators. Many birds in heavily modified terrestrial ecoystems, such as urban environments, incorporate plastic and other anthropogenic materials into their nests but our understanding of the presence of discarded plastic in nests in rural woodlands remains poor. Here, we show that plastic and other anthropogenic materials were present in 35 % of 325 pied flycatcher (Ficedula hypoleuca) nests from 17 rural woodlands throughout Great Britain, although the woodlands did vary in the amount of material incorporated into nests. Then, in an experimental test at one study site, where flycatchers were provided with a choice of two types of natural and two types of anthropogenic nest materials, they preferentially selected one natural and one anthropogenic material. In another test, the flycatchers were provided with plastic of four colours and overwhelmingly selected white and avoided orange, blue and yellow plastic. Although the flycatcher's selectivity for certain material types and colours preclude their nests being a reliable indicator of plastic in the environment, our study nonetheless demonstrates that bird species incorporate anthropogenic materials, such as plastic, into their nests in rural woodlands.

Adding the neuro to cognition: from food storing to nest building

Typically, investigations of animal cognition couple careful experimental manipulations with examination of the animal's behavioural responses. Sometimes those questions have included attempts to describe the neural underpinnings of the behavioural outputs. Over the past 25 years, behaviours that involve spatial learning and memory (such as navigation and food storing) has been one context in which such dual or correlated investigations have been both accessible and productive. Here I review some of that work and where it has led. Because of the wealth of data and insights gained from that work and song learning before it, it seems that it might also be useful to try to add some neurobiology to other systems in animal cognition. I finish then, with a description of recent work on the cognition and neurobiology of avian nest building. It is still relatively early days but asking questions about the cognition of nest building has already shown both neural correlates of nest building and that learning and memory play a much greater role in this behaviour than previously considered. While it is not yet clear how putting these components together will be synergistic, the examples of song learning and food storing provide encouragement. Perhaps this might be true for other behaviours too?

Among-individual differences in auditory and physical cognitive abilities in zebra finches

Among-individual variation in performance on cognitive tasks is ubiquitous across species that have been examined, and understanding the evolution of cognitive abilities requires investigating among-individual variation because natural selection acts on individual differences. However, relatively little is known about the extent to which individual differences in cognition are determined by domain-specific compared with domain-general cognitive abilities. We examined individual differences in learning speed of zebra finches across seven different tasks to determine the extent of domain-specific versus domain-general learning abilities, as well as the relationship between learning speed and learning generalization. Thirty-two zebra finches completed a foraging board experiment that included visual and structural discriminations, and then these same birds went through an acoustic operant discrimination experiment that required discriminating between different natural categories of acoustic stimuli. We found evidence of domain-general learning abilities as birds' relative performance on the seven learning tasks was weakly repeatable and a principal components analysis found a first principal component that explained 36% of the variance in performance across tasks with all tasks loading unidirectionally on this component. However, the few significant correlations between tasks and high repeatability within each experiment suggest the potential for domain-specific abilities. Learning speed did not influence an individual's ability to generalize learning. These results suggest that zebra finch performance across visual, structural, and auditory learning relies upon some common mechanism; some might call this evidence of "general intelligence"(g), but it is also possible that this finding is due to other noncognitive mechanisms such as motivation.

The significance of building behavior in the evolution of animal architecture

Animals make a diverse array of architectures including nests, bowers, roosts, traps, and tools. Much of the research into animal architecture has focused on the analysis of physical properties such as the dimensions and material of the architectures, rather than the behavior responsible for creating these architectures. However, the relationship between the architecture itself and the construction behavior that built it is not straightforward, and overlooking behavior risks obtaining an incomplete or even misleading picture of how animal architecture evolves. Here we review data about animal architectures broadly, with a particular focus on building by birds and social insects. We then highlight three ways in which a better understanding of building behavior could benefit the study of animal architecture: by clarifying how behavior leads to physical properties; by examining the costs and benefits of building behavior; and by determining the role of learning and how this interacts with selection on behavior. To integrate questions about building behavior alongside those about architectures, we propose a framework inspired by Niko Tinbergen's four questions, examining the mechanistic, ontogenetic, phylogenetic, and functional basis of animal building. By integrating the study of behavior and architecture across levels of analysis, we can gain a more holistic view of the behavior-architecture interactions, and a better understanding of how behavior, cognition, and evolution interact to produce the diversity seen in animal architecture.

Do sex differences in construction behavior relate to differences in physical cognitive abilities?

Nest-building behaviour in birds may be particularly relevant to investigating the evolution of physical cognition, as nest building engages cognitive mechanisms for the use and manipulation of materials. We hypothesized that nest-building ecology may be related to physical cognitive abilities. To test our hypothesis, we used zebra finches, which have sex-differentiated roles in nest building. We tested 16 male and 16 female zebra finches on three discrimination tasks in the following order: length discrimination, flexibility discrimination, and color discrimination, using different types of string. We predicted that male zebra finches, which select and deposit the majority of nesting material and are the primary nest builders in this species, would learn to discriminate string length and flexibility-structural traits relevant to nest building-in fewer trials compared to females, but that the sexes would learn color discrimination (not structurally relevant to nest building) in a similar number of trials. Contrary to these predictions, male and female zebra finches did not differ in their speed to learn any of the three tasks. There was, however, consistent among-individual variation in performance: learning speed was positively correlated across the tasks. Our findings suggest that male and female zebra finches either (1) do not differ in their physical cognitive abilities, or (2) any cognitive sex differences in zebra finches are more specific to tasks more closely associated with nest building. Our experiment is the first to examine the potential evolutionary relationship between nest building and physical cognitive abilities.

Reproductive consequences of material use in avian nest construction

Birds' nests represent a rich behavioural 'fingerprint', comprising several important decisions-not the least of which is the selection of appropriate material. Material selection in nest-building birds is thought to reflect, in part, builder-birds' use of the 'best' material-in terms of physical properties (e.g., rigidity)-refined across generations. There is, however, little experimental evidence to link the physical properties of nest material to both birds' nest-building and breeding performance. We examined individual-level material-use consequences for breeding zebra finches by manipulating the kind of material available to laboratory-housed pairs: stiff or flexible same-length string. We show that higher fledgling numbers were related to: (i) fewer pieces used in nest construction by stiff-string builders; and conversely, (ii) more pieces used in nest construction by flexible-string builders. Together, these data suggest that physical differences in nest material can affect avian reproduction (here, the trade-off between nest-construction investment and fledgling success), highlighting the adaptive significance of nest-building birds' material selectivity.

Complex nests but no use of tools: An investigation of problem solving in weaverbirds (Ploceidae)

Few avian species use tools in the wild. Yet, several birds build nests of great complexity and many aspects of tool use may also apply to nest building. It has long been hypothesised that tool use may select for specialised cognitive adaptations or even general cognitive skills. This might similarly pertain to species that build complex nests. In this study, we investigated the problem-solving capacity of a complex nest builder, a weaverbird species, in a foraging context that either required or did not require the use of tools. First, we tested the capacity of yellow-crowned bishops (Euplectes afer ssp. afer) to use a tool for retrieving an out-of-reach reward during three problem-solving tasks offering different nest/non-nest materials (Experiment 1). Next, subjects were confronted with two problem-solving tasks that required no tools (Experiment 2). No subject was able to use a tool in Experiment 1. However, 11 out of 12 subjects succeeded in using their beak in the first problem-solving task, and 9 in the second problem-solving task of Experiment 2. These results suggest that weaverbirds showed flexible problem-solving if the use of tools was not required.

Climate as an Evolutionary Driver of Nest Morphology in Birds: A Review

Avian nests are critical for successful reproduction in birds. Nest microclimate can affect egg development, chick growth and fledgling success, suggesting that nest building behavior should be under strong selective pressure to nesting conditions. Given that the internal microclimate of the nest is critical for avian fitness, it is expected that nest morphology is shaped by the local environment. Here we review the relationship between nest morphology and climate across species’ distributions. We collate growing evidence that supports a link between environmental conditions and particular nest traits, within species and across species. We discuss the degree to which phenotypic plasticity in nesting behavior can contribute to observed variation in nest traits, the role of phylogenetic history in determining nest morphology, and which nest traits are likely to be influenced by climatic conditions. Finally, we identify gaps in our understanding of the evolution of nest morphology and suggest topics for future research. Overall, we argue that nests are part of the extended phenotype of a bird, they play a crucial role in their reproductive success, and may be an important factor in determining which species will be able to persist in the face of ongoing climate change.

Lining the nest with more feathers increases offspring recruitment probability: Selection on an extended phenotype in the blue tit

Birds, among various other taxa, construct nests. Nests form an extended phenotype of the individual building it. Nests are used to extend control over the conditions in which offspring develop, and are therefore commonly considered to be shaped by selection. Nevertheless, scarcely any scientific evidence exist that nest composition is under selection. Here, we demonstrate with data from over 400 blue tit (Cyanistes caeruleus) nests collected over 8 years that a higher proportion of feathers in the nest lining is positively associated with the probability of offspring to recruit as a breeding adult later in life. Strikingly, the extended phenotype (nest) was associated stronger with recruitment probability than phenotypic traits that have typically been considered important in selection (laying date, and female size and condition). Our findings suggest that the choice of nest material could be a maternal behavior with potential lifelong effects on her offspring.

Nest ornaments and feather composition form an extended phenotype syndrome in a wild bird

Abstract

Many species throughout the animal kingdom construct nests for reproduction. A nest is an extended phenotype—a non-bodily attribute—of the individual building it. In some bird species, including our study population of blue tits (Cyanistes caeruleus), conspicuous feathers or other material are placed on top of the nest. These so-called nest ornaments do not contribute to nest insulation, but are hypothesised to have a signalling function. Here, we apply the concept of behavioural syndromes, with focus on between-individual variation (repeatability) and between-individual correlations, to the study of avian nest construction. We find that nest ornamentation is a moderately repeatable trait in female blue tits, which suggests it is an extended phenotype of the female. Furthermore, the tendency to ornament the nest covaries across females with another aspect of her extended phenotype, the composition of the nest lining material, and these two traits thus form an extended phenotype syndrome. Assuming the correlation is reflected on a genetic level, it implies that nest ornamentation and composition of the nest lining do not evolve in isolation; one aspect may be an evolutionary by-product of selection on the other aspect and their overall flexibility to respond to change is reduced.

Significance statement

The avian nest is an extended phenotype (a non-bodily attribute) of its builder with potentially multiple functions in terms of insulation and signalling. In particular, many bird species’ nests contain nest ornaments, feathers or other materials that are placed on top of the nest and that stand out from the nest material due to their colour and/or size. We quantified between-individual variation (repeatability) of nest ornamentation behaviour in a wild population of blue tits and between-individual covariation (syndrome) of nest ornamentation to other features of nest construction. We find that nest ornamentation is a repeatable trait limited to females in our study population. The tendency to ornament the nest covaries across females with another aspect of her extended nest phenotype, the composition of the nest lining material. These correlated traits thus form an extended phenotype syndrome. It hence becomes crucial to recognise that a study of a single aspect of nest construction in isolation captures only a part of the complexity, as one aspect may have evolved as a correlated response of selection on the other aspect. Moreover, such a syndrome implies limited flexibility in the range of adaptive response.

Juvenile socio-ecological environment shapes material technology in nest-building birds

Variation in animal material technology, such as tool use and nest construction, is thought to be caused, in part, by differences in the early-life socio-ecological environment—that is, who and what is around—but this developmental hypothesis remains unconfirmed. We used a tightly controlled developmental paradigm to determine whether adult and/or raw-material access in early life shape first-time nest construction in laboratory-bred zebra finches Taeniopygia guttata at sexual maturity. We found that juvenile access to both an unrelated adult and raw material of one color led to a majority preference (75%) by novice builders for this color of material over that for either natal-nest or novel-colored material, whereas a lack of juvenile access to both an unrelated adult and raw material led to a 4- and nearly 3-fold reduction in the speed at which novice builders initiated and completed nest construction, respectively. Contrary to expectation, neither the amount of time juveniles nor their adult groupmate spent handling the raw material appear to drive these early-life effects on zebra finches’ first-time nest construction, suggesting that adult presence might be sufficient to drive the development of animal material technology. Together these data show that the juvenile socio-ecological environment can trigger variation in at least two critical aspects of animal material technology (material preference and construction speed), revealing a potentially powerful developmental window for technological advancement. Thus, to understand selection on animal material technology, the early-life environment must be considered.

Experimental evidence of non-random nest material selection in pied flycatchers

Nest building is a taxonomically widespread behaviour that consists of the construction of a suitable receptacle with collected materials for the incubation of eggs and sometimes for the raising of offspring. The use of specific nest materials has important fitness consequences for avian parents and offspring because they help to determine the thermal, parasitic and bacterial environment within nests and may also influence parental investment via intraspecific signalling. However, we presently know very little about the process by which nest materials are selected from the wider environment and specifically, it is unclear whether wild birds randomly or non-randomly select nest materials in relation to their local availability. Here, we report an experiment in which we provided experimental pairs of pied flycatchers (Ficedula hypoleuca) with wool, feathers and deer hair - commonly used nest materials found in their woodland habitats - close to their nests during the nest building period whilst control pairs were not provided with any materials. We found that females at experimental nests showed very clear preferences for deer hair, whilst almost completely avoiding the wool and feathers, thereby demonstrating that females exhibited very strong preferences for certain nest materials but not others. We therefore conclude that birds select nest materials in a non-random manner and do not simply use the materials most commonly available to them.

Social learning in nest-building birds watching live-streaming video demonstrators

Determining the role that social learning plays in construction behaviors, such as nest building or tool manufacture, could be improved if more experimental control could be gained over the exact public information that is provided by the demonstrator, to the observing individual. Using video playback allows the experimenter to choose what information is provided but will only be useful in determining the role of social learning if observers attend to, and learn from, videos in a manner that is similar to live demonstration. The goal of the current experiment was to test whether live-streamed video presentations of nest building by zebra finches Taeniopygia guttata would lead observers to copy the material choice demonstrated to them. Here, males that had not previously built a nest were given an initial preference test between materials of 2 colors. Those observers then watched live-stream footage of a familiar demonstrator building a nest with material of the color that the observer did not prefer. After this experience, observers were given the chance to build a nest with materials of the 2 colors. Although two-thirds of the observer males preferred material of the demonstrated color after viewing the demonstrator build a nest with material of that color more than they had previously, their preference for the demonstrated material was not as strong as that of observers that had viewed live demonstrator builders in a previous experiment. Our results suggest researchers should proceed with caution before using video demonstration in tests of social learning.

Mercury alters initiation and construction of nests by zebra finches, but not incubation or provisioning behaviors

Mercury is an environmental contaminant that impairs avian reproduction, but the behavioral and physiological mechanisms underlying this effect are poorly understood. The objective of this study was to determine whether lifetime dietary exposure to mercury (1.2 µg/g wet weight in food) impacted avian parental behaviors, and how this might influence reproductive success. To distinguish between the direct effects of mercury on parents and offspring, we created four treatment groups of captive-bred zebra finches (Taeniopygia guttata), with control and mercury-exposed adults raising cross-fostered control or mercury-exposed eggs (from maternal transfer). Control parents were 23% more likely to fledge young than parents exposed to mercury, regardless of egg exposure. Mercury-exposed parents were less likely to initiate nests than controls and spent less time constructing them. Nests of mercury-exposed pairs were lighter, possibly due to an impaired ability to bring nest material into the nestbox. However, nest temperature, incubation behavior, and provisioning rate did not differ between parental treatments. Unexposed control eggs tended to have shorter incubation periods and higher hatching success than mercury-exposed eggs, but there was no effect of parental exposure on these parameters. We accidentally discovered that parent finches transfer some of their body burden of mercury to nestlings during feeding through secretion in the crop. These results suggest that, in mercury-exposed songbirds, pre-laying parental behaviors, combined with direct exposure of embryos to mercury, likely contribute to reduced reproductive success and should be considered in future studies. Further research is warranted in field settings, where parents are exposed to greater environmental challenges and subtle behavioral differences might have more serious consequences than were observed in captivity.

Construction patterns of birds' nests provide insight into nest-building behaviours

Previous studies have suggested that birds and mammals select materials needed for nest building based on their thermal or structural properties, although the amounts or properties of the materials used have been recorded for only a very small number of species. Some of the behaviours underlying the construction of nests can be indirectly determined by careful deconstruction of the structure and measurement of the biomechanical properties of the materials used. Here we examined this idea in an investigation of Bullfinch (Pyrrhula pyrrhula) nests as a model for open-nesting songbird species that construct a “twig” nest, and tested the hypothesis that materials in different parts of nests serve different functions. The quantities of materials present in the nest base, sides and cup were recorded before structural analysis. Structural analysis showed that the base of the outer nests were composed of significantly thicker, stronger and more rigid materials compared to the side walls, which in turn were significantly thicker, stronger and more rigid than materials used in the cup. These results suggest that the placement of particular materials in nests may not be random, but further work is required to determine if the final structure of a nest accurately reflects the construction process.

How do great bowerbirds construct perspective illusions?

Many animals build structures to provide shelter, avoid predation, attract mates or house offspring, but the behaviour and potential cognitive processes involved during building are poorly understood. Great bowerbird (Ptilinorhynchus nuchalis) males build and maintain display courts by placing tens to hundreds of objects in a positive size-distance gradient. The visual angles created by the gradient create a forced perspective illusion that females can use to choose a mate. Although the quality of illusion is consistent within males, it varies among males, which may reflect differences in how individuals reconstruct their courts. We moved all objects off display courts to determine how males reconstructed the visual illusion. We found that all individuals rapidly created the positive size-distance gradient required for forced perspective within the first 10 objects placed. Males began court reconstruction by placing objects in the centre of the court and then placing objects further out, a technique commonly used when humans lay mosaics. The number of objects present after 72 h was not related to mating success or the quality of the illusion, indicating that male skill at arranging objects rather than absolute number of objects appears to be important. We conclude that differences arise in the quality of forced perspective illusions despite males using the same technique to reconstruct their courts.

Social learning in nest-building birds: a role for familiarity

It is becoming apparent that birds learn from their own experiences of nest building. What is not clear is whether birds can learn from watching conspecifics build. As social learning allows an animal to gain information without engaging in costly trial-and-error learning, first-time builders should exploit the successful habits of experienced builders. We presented first-time nest-building male zebra finches with either a familiar or an unfamiliar conspecific male building with material of a colour the observer did not like. When given the opportunity to build, males that had watched a familiar male build switched their material preference to that used by the familiar male. Males that observed unfamiliar birds did not. Thus, first-time nest builders use social information and copy the nest material choices when demonstrators are familiar but not when they are strangers. The relationships between individuals therefore influence how nest-building expertise is socially transmitted in zebra finches.