High temperatures inhibit quantity discrimination of conspecifics in a wild bird

Given the current pace of climate change, high temperature events will become increasingly frequent in many parts of the world. Predicting how high temperatures will impact the behavior of songbirds—highly sensitive to temperature change due to their tendency to be small in size, and to have high metabolic rates and diurnal habits—is therefore crucial and urgent. However, the behavioral impacts of high temperatures on acoustic communication in birds have rarely been studied. Responsiveness to antipredator signals is an important behavior to consider because failure to detect such signals could be lethal. We investigated whether, in great tits (Parus major), high temperatures would affect behavioral responses to playback of conspecific mobbing calls. We found a significant lag effect of temperature on how closely great tits would approach the playback speaker, with birds approaching less closely at higher temperatures. Further, we found that the emission of mobbing calls by great tits was affected by the current ambient temperature, with birds calling less at higher temperatures. The results suggest that at high temperatures, great tits change their tactic from active defense to less active response. High temperatures can thus induce behavioral shifts in great tits. In the current context of increasing average temperatures, such effect of temperature on response to vital indicators such as antipredator signals could impact survival when inducing greater risk of depredation.Significance statementClimate change is causing heatwaves to increase in number and intensity. High temperatures can reduce the ability of birds to respond to vocalizations. Here, we test if high temperatures affect the ability of great tits (Parus major) to respond to conspecific mobbing calls—these calls generally serve to mob a predator and to recruit conspecifics and heterospecifics to join the caller. At higher temperatures, great tits produce fewer mobbing vocalizations and approach the loudspeaker broadcasting mobbing calls less often.

The fat reserves of small birds are built up daily as insurance against starvation. They are believed to reflect a trade-off between the risks of starvation and predation such that in situations of high predation risk birds are expected either to reduce their fat reserves in response to mass-dependent predation risk or to increase them in response to foraging interruptions. We assessed the effect on fat reserves of experimentally altering the perceived (but not the actual) risk of predation of wild great tits at a winter feeding site. The perceived predation risk was alternated between 'safe' and 'risky'. Increasing the perceived risk of predation involved 'swooping' a model sparrowhawk over the feeder at four unpredictable times each day using a remote mechanism We produce evidence that the experiment was suceessfull in altering the perceived risk of predation. As predicted from the hypothesis of mass-dependent predation risk, great tits (Parus major) carried significantly reduced fat reserves during the 'risky' treatment. Furthermore, dominant individuals were able to reduce their reserves more than subordinates. As birds returned to feeders within seconds after a predator 'attack', the reduction in fat reserves cannot be attributed to an interruption in feeding.

Numerical competence—the ability to represent, discriminate, and process numerical quantity information—is a widespread cognitive ability in animals that influences survival and reproductive success. Little is known about the role of numerical competence during predator mobbing—when a prey moves toward and harasses a predator. Since being in a larger group dilutes the risk of injury or death during a mobbing event and large groups are more efficient than small groups at repelling predators, the capacity to evaluate the number of mobbers before joining the mobbing flock may be highly beneficial for individuals. We tested whether the strength of the mobbing response of great tits (Parus major), a songbird that frequently mobs predators, is related to the number of callers. The minimum distance to the loudspeaker tended to be lower, and the number of calls produced by great tits was higher during playbacks simulating several callers than during the playbacks of one caller. These results suggest that numerical competence plays a central role during mobbing and that great tits reduce uncertainty of information by collating information from several individuals. We suggest further studies testing whether birds use individual vocal discrimination to assess the number of heterospecifics during mobbing. Can animals count? Although historically the ability to count has distinguished humans apart from the rest of the animal kingdom, studies in the last decades have shown that numerical competence, the ability to represent, discriminate, and process numerical quantity information, is a widespread cognitive ability in animals. While this competence influences an individual’s survival success, little is known about the role of numerical competence during predator mobbing. Using a field-based playback experiment on a population of wild great tits (Parus major), we demonstrate that great tit responses to mobbing calls were affected by the number of individuals calling. The minimum distance to the loudspeaker tended to be lower and the number of calls produced by great tits tended to be higher during playbacks simulating multiple callers than during the playbacks of one caller. Thus, numerical assessments are used to decide whether or not to participate in mobbing responses.

Dispersal is a major determinant of the dynamics and genetic structure of populations, and its consequences depend not only on average dispersal rates and distances, but also on the characteristics of dispersing and philopatric individuals. We investigated whether natal dispersal correlated with a predisposed behavioural trait: exploratory behaviour in novel environments. Wild great tits were caught in their natural habitat, tested the following morning in the laboratory using an open field test and released at the capture site. Natal dispersal correlated positively with parental and individual exploratory behaviour, using three independent datasets. First, fast-exploring parents had offspring that dispersed furthest. Second, immigrants were faster explorers than locally born birds. Third, post-fledging movements, comprising a major proportion of the variation in natal dispersal distances, were greater for fast females than for slow females. These findings suggest that parental behaviour influenced offspring natal dispersal either via parental behaviour per se (e.g. via post-fledging care) or by affecting the phenotype of their offspring (e.g. via their genes). Because this personality trait has a genetic basis, our results imply that genotypes differ in their dispersal distances. Therefore, the described patterns have profound consequences for the genetic composition of populations.

Many species of birds use alarm calls to signal information about predators, including the level of threat. Previous playback experiments suggest that the urgency response towards heterospecific calls is phylogenetically conserved, notably in the Paridae family. Using playback experiments conducted on European great tits (Parus major), we tested whether this species perceives information about urgency in mobbing calls produced by an allopatric non‐Paridae species, the Southern house wren (Troglodytes aedon bonariae), by broadcasting calls with high‐calling rate (high threat) and calls with low‐calling rate (low threat). We found that great tits tend to approach the loudspeaker during playbacks of calls with high‐calling rate more often than during playbacks of calls with low‐calling rate. Female great tits gave more calls during playbacks of calls with high‐calling rate than during playbacks of calls with low‐calling rate, whereas there was no significant difference in the number of calls given by males between playbacks of calls with high‐ and low‐calling rates. Thus, our results suggested that great tits perceived the urgency message encoded in calls given by an allopatric non‐Paridae species.

Theoretical models of host–parasite coevolution assume a partially genetic basis to the variability in susceptibility to parasites among hosts, for instance as a result of genetic variation in immune function. However, few empirical data exist for free–living vertebrate hosts to support this presumption. In a cross–fostering experiment with nestling great tits, by comparing nestlings of the same origin we investigated (i) the variance in host resistance against an ectoparasite due to a common genetic origin, (ii) the effect of ectoparasite infestation on cell–mediated immunity and (iii) the variance in cell–mediated immunity due to a common genetic origin. Ectoparasitic hen fleas can impair the growth of nestling great tits and nestling growth was therefore taken as a measure of host susceptibility. A common origin did not account for a significant part of the variation in host susceptibility to fleas. There was no significant overall effect of fleas on nestling growth or cell–mediated immunity, as assessed by a cutaneous hypersensitivity response. A common rearing environment explained a significant part of the variation in cell–mediated immunity among nestlings, mainly through its effect on nestling body mass. The variation in cell–mediated immunity was also related to a common origin. However, the origin–related variation in body mass did not account for the origin–related differences in cell–mediated immunity. The results of the present study thus suggest heritable variation in cell–mediated immunity among nestling great tits.

To date, song research has focused primarily on the interactions of conspecifics. However, frequent interactions of songbirds with heterospecifics may necessitate adequate communication outside the species boundary. In this study, we focus on heterospecific communication behaviour of two small sympatric congeneric passerines, great and blue tits (Parus major and Parus caeruleus), which breed in overlapping territories and compete for food and nesting cavities. By means of a first playback experiment, we show that (1) heterospecific matching (imitating songs of the other species) is a strategy frequently used by great tits but not by blue tits, (2) both blue tit trilled and untrilled song can be accurately matched by great tits and that (3) almost half of the great tits in our study population match at least one blue tit song across all studied breeding stages, indicating that this heterospecific matching behaviour is a common feature in this population. A second playback experiment showed that these great tit imitations of blue tit songs do not function in intraspecific communication between male great tits. Hence, these heterospecific imitations appear to be designed for interspecific communication with blue tits. These findings suggest a strong heterospecific influence on the vocal learning process, repertoire composition and repertoire use in great tits and provide a possible mechanism that can drive song convergence in songbirds.

IntroductionAvian poxvirus infections are widespread in the domestic poultry population but are also reported in wild birds. In poultry, these infections cause significant economic losses, while wild birds may be a reservoir for poxvirus which affects breeding poultry. However, wild birds may also exhibit characteristic anatomopathological changes. This study concerns the infection of wild-living great tits (Parus major) with the avian poxvirus in Poland.Material and MethodsSamples of internal organs and skin collected from great tits were homogenised and total cellular DNA was isolated. In PCR, the primers complementary to gene encoding the core protein 4b of the HP44 strain of fowl poxvirus (FPV) were used.ResultsAfter electrophoresis in 2% agarose gel, the PCR product of 578 bp characteristic for FPV was obtained in DNA samples isolated from skin lesions and the heart. The analysis of the nucleotide sequence of the virus strain showed 99% similarity to many poxviruses previously isolated from great tits and other free birds at various sites in the world.ConclusionsThis paper is the first clinically documented evidence obtained in laboratory conditions of avian poxvirus cases in great tits in Poland.

Urbanization and climate change are two environmental factors that have most prominently affected breeding phenology of birds during recent decades. We examined such relationships in rural, suburban and urban nest box populations of Great Tits Parus major and Blue Tits P. caeruleus in the capital region of Finland in the 1980s and 1990s. We expected that mild winters and high spring temperatures may advance the breeding season of tits, but less so in urban habitats, where breeding should in any case start earlier than elsewhere. On average, Blue Tits began egg laying a few days earlier in spring than Great Tits. Contrary to expectations, tits bred later in the urban parks of the city than in other habitats, whereas breeding was earliest in suburban areas. It seems that these intermediate habitats, in some way, offer the advantages of both rural and urban habitats. During the study period, the timing of breeding in tits showed advancing temporal trends in rural habitats, and in the Blue Tit also in urban habitats. The effect of increasing winter temperatures on laying dates was mainly minor, but a significant delay emerged in urban Great Tits. The main effect of increasing April temperatures on laying dates was a significant advancement. In urban habitats, however, the advancing effect was in Great Tits significantly stronger and in Blue Tits significantly weaker than in other habitats. The results suggest that breeding of tits may advance also with warming climate but some urban populations might be more resistant to climate change than rural ones.

Great and blue tit feathers as biomonitors for heavy metal pollution

Elucidating associations between behavioural variation and genes may help to understand the co-existence of different behavioural phenotypes in natural populations. In birds, two main candidate genes are known to affect exploratory and risk-taking behaviour through the neurotransmitter system: the dopamine receptor D4 gene (DRD4) and the serotonin transporter gene (SERT/SLC6A4). In a small passerine bird, the great tit (Parus major), anti-predator responses (hissing or non-hissing behavioural type) towards a nest predator differ consistently between individuals. As defensive anti-predator behaviours are likely related to variations in neurotransmitter systems, we tested the associations between polymorphisms of the two candidate genes (SERT and DRD4) and the propensity to give hissing calls towards a nest predator in incubating female great tits. We found that acoustic anti-predator responses in wild birds were linked to a single-nucleotide polymorphism in the SERT gene (SNP187 in exon 1), but not in the DRD4 gene. The polymorphism in the SERT gene explains about 16% of the total variance in hissing behaviour. However, as the sample size in this study is quite small, these results are preliminary and should be replicated in future studies.

Great and Blue Tits as Indicators of Heavy Metal Contamination in Terrestrial Ecosystems

We tested the hypothesis that the weight lost by female Great and Blue Tits Parus major and P. caeruleus while raising their first brood influences their ability to start a second brood. The evening weight of female parents was recorded when the nestlings were 5 and 13 days old, in different years and habitats. Several predictions were tested: (1) both species lose weight while raising nestlings and Great Tit females which start a second brood lose less weight than females which do not; (2) differences in the average weight lost between years and areas correlate with differences in the proportion of second broods; (3) the relative weight loss in Blue Tits, which only rarely undertake second broods, is higher than in Great Tits in which second broods are more common. Other factors also are related to the probability of undertaking a second brood: more second broods are undertaken by more successful females, adult females and females that lay earlier.The comparison of Great and Blue Tits suggests that the two species use different reproductive strategies.

Increasingly frequent heatwaves require animals to spend more time thermoregulating at the expense of other fitness-related behaviours. Emerging evidence also indicates that high temperatures can impair cognitive function in wild animals. However, whether such heat-mediated cognitive impairment underpins altered behavioural responses during high temperatures remains unclear. We examined the link between naturally occurring high temperatures, cognitive performance and antipredator response in wild southern pied babblers (Turdoides bicolor). In a paired experimental design, we performed model predator presentations using a taxidermied common genet (Genetta genetta) and a box as the control, and we quantified associative learning performance—a cognitive trait involved in associating predator cues with a threat—for the same individuals under normal and high-temperature conditions. As predicted, individuals showed a stronger antipredator response (combining time spent vigilant, flying and alarming) when presented with the predator compared to the control under normal but not high temperatures. Associative learning performance also declined with increasing air temperatures. However, associative learning performance (whether measured under normal or high temperatures) did not predict the strength of the antipredator response. Our findings provide novel evidence for a reduced antipredator response under high temperatures and suggest that physiological constraints rather than learning impairment might explain this change.

Two semi-quantitative predictions about the intensity of defence against a predator based on the associated costs and benefits as a function of predator species, were examined in great tits (Parus major) feeding nestlings. One premise was that defence behaviour is adaptive. Defence comprised of vocalizing and homing in on a live raptor near the nest hole. The intensity of defence as judged by two measures of approaching (Minimum Distance, Average Distance) varies with the species of raptor, i.e. sparrowhawk ♀ (Accipiter nisus), pigmy owl (Glaucidium perlatum), and tawny owl (Strix aluco). With the exception of the response to the pigmy owl, defence intensities proved to conform to both predictions; the tits correctly assessed the relative overall risk from each predator ("predator pressure") i.e. its degree of specialization on great tits, and the immediate risk of defence. The failure to verify the predictions regarding the pigmy owl is thought to derive from our incomplete assessment of the cost function and/or from the response being mal-adaptive.The male takes a greater risk, exceeding the female's by an amount independent of the species of raptor. The sexual difference remains functionally unexplained.