Susan D. Healy

As synthetic materials have rapidly accumulated in the environment over the past decades, birds have increasingly incorporated them into their nests. However, it is not clear whether such materials affect the nest’s insulative properties, a builder’s behaviour and/or the hatching success of its clutch. Here, we used laboratory-bred zebra finches Taeniopygia guttata to test whether the use of synthetic fibres (acrylic yarn) as nesting material: (i) changes nest building and incubation behaviours and/or (ii), alters the insulation properties of a nest and whether any of these ultimately (iii) influence the hatching success of the builder’s eggs. We saw no impact of acrylic yarn on any of these variables relative to nests built with non-synthetic wool fibres. The main driver of hatching success was, instead, the degree to which parents managed to keep their clutch warm by attending their nest during incubation. Our results demonstrate that nests entirely built with either synthetically-produced or naturally-derived fibres do not necessarily differ in their insulation properties. It is therefore possible that the inclusion of some types of synthetic material into a nest is not always detrimental to the builder or their offspring.

Many birds practise biparental care, providing useful systems to study its evolution. Although nest building has largely been ignored as biparental behaviour, parental conflict and cooperation could begin during nest building, before incubation and offspring provisioning. While there are ample data on biparental incubation and provisioning in model species like zebra finches (Taeniopygia guttata), nest-building data largely concern material collection and preference in the males, not building by the females. Here, we collected data on building by both female and male zebra finches to test whether building behaviour depends on the behaviour of their mate or on the material they used to build their nest. Males held nest material more frequently when their female was in the nest, while females held nest material longer when their male was away from the nest. But neither females nor males altered their building behaviour in response to changes in their partner holding nest material. Males that built with stiff material held the material more frequently than those that built with flexible material, while females manipulated stiff and flexible materials similarly. The next step will be to determine whether these building interactions affect later stages of parental care in the wild or in other species.

While much is known about the functions of avian nests in reproduction, the role of experience in nest building has often been overlooked, especially in natural populations. Increasing evidence from captive birds suggests that the environment an individual experiences affects nest-building decisions, as does reproductive experience. Here we asked whether in a wild population of blue tits Cyanistes caeruleus, experience affected: (i) the materials and/or amounts of material with which the birds chose to build, and/or (ii) the location in which they built. We investigated the material composition and effectiveness of nests built by female blue tits between 2016 and 2022. We found that (i) a high insulation: structure ratio was associated with higher hatching success; (ii) the rate at which nests cooled was faster the more offspring had fledged from that nest; (iii) individuals that successfully fledged at least 1 chick were more likely to reduce the amount of insulating material they put into their nest the following year than were blue tits that previously had been unsuccessful; (iv) for unsuccessful birds, changing the nest design the following year improved their fledgling success; and finally, (v) unsuccessful birds were also more likely to move to a different nestbox the following year. In sum, we find that wild blue tits used their experience of reproduction in 1 yr to change their building decisions the following year. This effect mirrors responses made by birds building in the laboratory but over a much longer time interval.

Animals often balance asocial and social information strategically, adjusting when and from whom they copy based on context. Yet the cognition driving this dynamic—and its broader implications—remains poorly understood. We tested whether zebra finches use a copy-if-dissatisfied strategy by manipulating the quality of their initial nest-building or reproductive experience, showing them a conspecific nest-builder and tracking subsequent material choices. Builder-males were more likely to choose the demonstrated ‘social’ material—particularly at first choice—if they had previously used low-quality material. Using cognitive modelling, we estimated how latent learning mechanisms shaped decisions, identifying two asocial and two social parameters. These estimates provide the first formal evidence for the cognitive mechanisms of nest building. Forward simulations informed—but not predetermined—by these parameters approximated observed behaviour, supporting their causal role. We then used these parameters in exploratory simulations to test how choices might shift under novel payoff contexts. We found that payoff structure—not (dis)satisfaction—was the primary driver of social material use, though higher rewards did not proportionally increase copying. These exploratory simulation results offer preliminary insight into mechanisms underlying material-use variation. Our study illustrates how computational modelling can robustly link behaviour to underlying learning mechanisms and probe the generalizability of animal cognition—a rarity in this field.

Traditionally, evidence for spatial learning in animals involves experiments; however, tools developed for analysing tracking data are increasingly being used to infer the use of spatial memory and other cognitive processes in animal movements. In this study, we combined these statistical models with field experiments to analyse how patterns of hummingbird movements change as birds learn a rewarded location. Using hidden Markov models (HMMs), we used both changes in two movement states as well as experimental behavioural measures of spatial memory to determine how searching performance and behaviour changed as birds gained experience and how important local landmarks were for guiding search. Regardless of whether birds had a single training trial to learn a flower’s location or 12 repeated trials, hummingbirds learned the location of the flower although performance suffered when we removed the local landmarks. While the hovering locations suggested that removing landmarks led to a slight decrease in accuracy compared with when landmarks were present, the HMMs suggest that this was part of a larger shift from a memory-led search strategy to a more systematic searching process. Our results suggests that models used in movement ecology could provide a valuable tool for experiments in comparative cognition.

Reproductive success and its consequences for fitness are key to determining how natural selection shapes cognitive abilities, and thus how and why cognition might change over evolutionary time. However, demonstrating reproductive costs or benefits owing to variation in cognitive ability is hugely challenging, in part because traits such as body size and condition make the largest contribution to reproductive success. Our ability to discriminate a role for ‘being smart’ in fitness is then already limited. Additionally, most animals have many ways to solve problems, only some of which will depend on their cognitive abilities. However, specific instances in key parts of animal’s life may depend heavily on their cognitive abilities, and without them the animal will not survive or reproduce. Retrieving food stores is one example and nest building might be another. For food-storing, spatial ability is key, while for nest building the pertinent ability is learning what works. The importance of animals learning from previous experience may be very common but is rarely considered explicitly in cognitive terms. Work on fitness consequences of cognition should develop from the presentation of discrete tasks testing specific abilities to encompass how learning from experience influences behavioural evolution more broadly. This article is part of the Theo Murphy meeting issue ‘Selection shapes diverse animal minds’.

Behavioral outcomes, including foraging efficiency and reproductive success, often improve with age and with repeated breeding attempts. Here we examined the role of previous experience on the nest-building behavior of wild blue tits Cyanistes caeruleus. In particular, we focused on how previous success or failure in rearing nestlings shapes nest-building decisions in subsequent years. We found that previous breeding outcome is important for predicting nest building decisions in blue tits: birds that had previously raised fledglings added insulating material at a similar rate as they had when they built their first nest. Some birds that had been previously unsuccessful changed their rate of adding insulating material and then were more likely to produce fledglings. These responses indicate that at least some of the decisions made by wild nest-building birds are based on their own experience of past breeding seasons.