During the Anthropocene, Earth has experienced unprecedented habitat loss, native species decline... more During the Anthropocene, Earth has experienced unprecedented habitat loss, native species decline, and global climate change. Concurrently, greater globalisation is facilitating species movement, increasing the likelihood of alien species establishment and propagation. There is a great need to understand what influences a species' ability to persist or perish within a new or changing environment. Examining genes that may be associated with a species' invasion success or persistence informs invasive species management, assists with native species preservation, and sheds light on important evolutionary mechanisms that occur in novel environments. This approach can be aided by coupling spatial and temporal investigations of evolutionary processes. Here we use the common starling, Sturnus vulgaris, to identify parallel and divergent evolutionary change between contemporary native and invasive range samples and their common ancestral population. To do this, we use reduced-representation sequencing of native samples collected recently in north-western Europe and invasive samples from Australia, together with museum specimens sampled in the UK during the mid-19th Century. We found evidence of parallel selection on both continents, possibly resulting from common global selective forces such as exposure to pollutants. We also identified divergent selection in these populations, which might be related to adaptive changes in response to the novel environment encountered in the introduced Australian range. Interestingly, signatures of selection are equally as common within both invasive and native range contemporary samples. Our results demonstrate the value of including historical samples in genetic studies of invasion and highlight the ongoing and occasionally parallel role of adaptation in both native and invasive ranges.
Light pollution or artificial light at night (ALAN) is an increasing, worldwide challenge that af... more Light pollution or artificial light at night (ALAN) is an increasing, worldwide challenge that affects many aspects of animal behaviour. Interestingly, the response to ALAN varies widely among individuals within a population and variation in personality (consistent individual differences in behaviour) may be an important factor explaining this variation. Consistent individual differences in exploration behaviour in particular may relate to the response to ALAN, as increasing evidence indicates its relation with how individuals respond to novelty and how they cope with anthropogenic modifications of the environment. Here, we assayed exploration behaviour in a novel environment as a proxy for personality variation in great tits (Parus major). We observed individual sleep behaviour over two consecutive nights, with birds sleeping under natural dark conditions the first night and confronted with ALAN inside the nest box on the second night, representing a modified and novel roosting env...
The Science of the total environment, Jan 15, 2018
Anthropogenic contaminants could alter traits central to animal behavioral types, or personalitie... more Anthropogenic contaminants could alter traits central to animal behavioral types, or personalities, including aggressiveness, boldness and activity level. Lead and other toxic metals are persistent inorganic pollutants that affect organisms worldwide. Metal exposure can alter behavior by affecting neurology, endocrinology, and health. However, the direction and magnitude of the behavioral effects of metal exposure remain equivocal. Moreover, the degree to which metal exposure simultaneously affects suites of correlated behavioral traits (behavioral syndromes) that are controlled by common mechanisms remains unclear, with most studies focusing on single behaviors. Using a model species for personality variation, the great tit (Parus major), we explored differences in multiple behavioral traits across a pollution gradient where levels of metals, especially lead and cadmium, are elevated close to a smelter. We employed the novel environment exploration test, a proxy for variation in pe...
Artificial light at night (ALAN) or light pollution is an increasing and worldwide problem. There... more Artificial light at night (ALAN) or light pollution is an increasing and worldwide problem. There is growing concern that because of the disruption of natural light cycles, ALAN may pose serious risks for wildlife. While ALAN has been shown to affect many aspects of animal behaviour and physiology, few studies have experimentally studied whether individuals of different species in the wild respond differently to ALAN. Here, we investigated the effect of ALAN on sleep behaviour in two closely related songbird species inhabiting the same study area and roosting/breeding in similar nest boxes. We experimentally exposed free-living great tits (Parus major) and blue tits (Cyanistes caeruleus) to artificial light inside their nest boxes and observed changes in their sleep behaviour compared to the previous night when the nest boxes were dark. In line with previous studies, sleep behaviour of both species did not differ under dark conditions. ALAN disrupted sleep in both great and blue tits. However, compared to blue tits, great tits showed more pronounced effects and more aspects of sleep were affected. Light exposed great tits entered the nest boxes and fell asleep later, woke up and exited the nest boxes earlier, and the total sleep amount and sleep percentage were reduced. By contrast, these changes in sleep behaviour were not found in light exposed blue tits. Our field experiment, using exactly the same light manipulation in both species, provides direct evidence that two closely related species respond differently to ALAN, while their sleep behaviour under dark conditions was similar. Our research suggests that findings for one species cannot necessarily be generalised to other species, even closely-related species. Furthermore, species-specific effects could have implications for community dynamics.
Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestli... more Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestling period, and is followed by a sleep rebound Reference: Raap Thomas, Pinxten Rianne, Eens Marcel.-Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestling period, and is followed by a sleep rebound Environmental pollution
The immune system is one of the most important adaptations that has evolved to protect animals fr... more The immune system is one of the most important adaptations that has evolved to protect animals from a wide range of pathogens they encounter from early life onwards. During the early developmental period this is particularly true for the innate immunity, as other components of the immune system are, as yet, poorly developed. But innate immunity may not only be crucial for early life survival, but may also have long-lasting effects, for example if early life immunity reflects the functioning of the immune system as a whole. For this reason, we investigated the importance of four constitutive innate immune parameters (natural antibodies, complement activity, concentrations of haptoglobin, and concentrations of nitric oxide) for recruitment in free-living great tits. We compared nestling immunity of recruits with nestling immunity of their nonrecruited siblings. We also investigated within individual consistency of these innate immune parameters for those individuals that recruited, which may be taken as a measure of immune capacity. In accordance with previous studies, we found a clear effect of tarsus length and a trend for body mass on the likelihood to recruit. Nevertheless, we found no evidence that higher levels of constitutive innate immunity as a nestling facilitated local recruitment. Furthermore, individual innate immunity was not consistent across life stages, that is to say, nestling immune parameters did not determine, or respectively, reflect adult innate immune parameters. This plasticity in innate immune components may explain why we did not find long-lasting survival benefits.
In an urban environment, birds are exposed to metals, which may accumulate in their tissues and c... more In an urban environment, birds are exposed to metals, which may accumulate in their tissues and cause oxidative stress. Female birds may eliminate these pollutants through depositing them into eggs, thus eggs become suitable bioindicators of pollution. In this study, we aimed to analyse whether eggshell spotting pattern, egg volume, eggshell thickness and egg yolk antioxidant (lutein, tocopherol, retinol and selenium) levels were related to the breeding area (woodland versus urban) and the metal levels in the eggshell of a small passerine species, the great tit (Parus major). In the urban habitat, soil and eggshells contained higher concentrations of metals, and soil calcium level was also higher than that in the woodland. Eggshell spotting intensity and egg volume did not differ between eggs laid in the woodland and the urban park, and these traits were not related to the metal levels of the eggshell, suggesting that these egg characteristics are not sensitive indicators of metal pollution. A more aggregated eggshell spotting distribution indicated a higher Cu concentration of the eggshell. We found that eggshells were thinner in the less polluted woodland habitat, which is likely due to the limited Ca availability of the woodland area. Great tit eggs laid in the urban environment had lower yolk lutein, retinol and selenium concentrations, however, as a possible compensation for these lower antioxidant levels, urban females deposited more tocopherol into the egg yolk. It appears that females from different breeding habitats may provide similar antioxidant protection for their offspring against oxidative damage by depositing different specific dietary antioxidants. Egg yolk lutein and retinol levels showed a negative relationship with lead concentration of the eggshell, which may suggest that lead had a negative impact on the amount of antioxidants available for embryos during development in great tits.
The importance of genes in regulating phenotypic variation of personality traits in humans and an... more The importance of genes in regulating phenotypic variation of personality traits in humans and animals is becoming increasingly apparent in recent studies. Here we focus on variation in the vasopressin receptor gene 1a (Avpr1a) and oxytocin receptor gene (OXTR) and their effects on social personality traits in chimpanzees. We combine newly available genetic data on Avpr1a and OXTR allelic variation of 62 captive chimpanzees with individual variation in personality, based on behavioral assessments. Our study provides support for the positive association of the Avpr1a promoter region, in particular the presence of DupB, and sociability in chimpanzees. This complements findings of previous studies on adolescent chimpanzees and studies that assessed personality using questionnaire data. In contrast, no significant associations were found for the single nucleotide polymorphism (SNP) ss1388116472 of the OXTR and any of the personality components. Most importantly, our study provides additional evidence for the regulatory function of the 5′ promoter region of Avpr1a on social behavior and its evolutionary stable effect across species, including rodents, chimpanzees and humans. Although it is generally accepted that complex social behavior is regulated by a combination of genes, the environment and their interaction, our findings highlight the importance of candidate genes with large effects on behavioral variation.
Relationships between female quality, egg mass and eggshell blue-green colouration in southern ro... more Relationships between female quality, egg mass and eggshell blue-green colouration in southern rockhopper penguins : a test of the sexual signalling hypothesis Polar biology
The extended pace-of-life syndrome (POLS) hypothesis suggests that variation in boldness-like beh... more The extended pace-of-life syndrome (POLS) hypothesis suggests that variation in boldness-like behaviors has co-evolved with variation in life-history strategies within populations, yet both theoretically driven experiments and evidence for phenotypic correlations between boldness-like behaviors and reproduction-related activities are scarce. Here we test the prediction that more exploratory individuals should be willing to provide more effort into current reproduction than less exploratory ones by investigating the association between exploration behavior and parental effort in wild great tits (Parus major). To this end, we assessed exploration behavior following a standardized assay. Then, we estimated individual willingness to provide parental effort into brood provisioning as (1) individual increase in nest visit rate after the brood had been artificially enlarged and (2) individual latency to return to the nest after this manipulation. Fast male explorers were quicker than slow explorers to return to the nest after the manipulation. Males paired with a partner of similar exploration score-either a fast or slow female explorer-increased their nest visit rate more than males paired with a partner of dissimilar exploration score. The relationship between exploration and parental effort then depended on one's partner's behavior. Our test thus provides only partial support for the extended POLS hypothesis and highlights the potential importance of the social environment in shaping the relationship between boldness-like behaviors and fitness-maximizing traits.
Kacelnikl proposes a puzzle for optimal foraging theorists, arising from experiments of Races and... more Kacelnikl proposes a puzzle for optimal foraging theorists, arising from experiments of Races and Nutiez2, who found that leaf-cutting ant (Acromyrmex lundi) workers changed their behavior in response to foragmg-quality information that was only known to scouts. The workers cut and transferred smaller pieces of parafilm when the scouts had been exposed to a 10% sugar solution than when they were exposed to a 1% solution. Optimal foraging theory, according to Kacelnik, predicts no such dependence of load upon resource quality. After considering several possible explanations, Kacelnik concludes that 'there is no winning functional model, although the rnformabon transfer hypothesis [smaller loads mean more activity, which increases the rate of transfer of information] is in my view the strongest candidate'.
There is a wide literature concerning the duration of incubation, as well as the ability of paren... more There is a wide literature concerning the duration of incubation, as well as the ability of parent birds to manipulate both the duration of incubation and asynchronous hatching within their clutches (see reviews in . Some studies have focused on intrinsic differences between eggs, while others have stressed the important role of the behavior of the incubating adults. Penguins have often been used as a model to test this
Abstract: Isolation of a population can result in decreased genetic variability as a consequence ... more Abstract: Isolation of a population can result in decreased genetic variability as a consequence of inbreeding, random genetic drift and reduced gene flow. This effect is reinforced when it concerns as small population. We used two molecular techniques, ...
We recorded songs of male blue tits Parus caeruleusduring the fertile and egg-laying period in a ... more We recorded songs of male blue tits Parus caeruleusduring the fertile and egg-laying period in a Belgian and Spanish population and compared several song characteristics in order to investigate the extent of macrogeographic variation in song features such as syntax, repertoire size and the proportion of trills in the repertoire. Repertoire size differed considerably between populations: it was twice as large in southern Spain (11.6 song types) as in Belgium (5.4 song types). Song syntax also differed significantly between the two populations. The most remarkable difference, however, was found in the proportion of trills. Trilled song types were rare in southern Spain (18 %) whereas more than half of the song types in the repertoire of Belgian blue tits included a trill (53 %). A recent hypothesis explains variation in blue tit song as a result of interspecific competition, suggesting that blue tit repertoire size decreases with increasing density of great tits Parus majorand that the proportion of trills increases with increasing great tit density. This hypothesis does not appear to explain our findings. Although both populations differed strongly in both song parameters, the relative great tit density appeared to be very similar. Furthermore, we provide the first evidence of a striking negative relationship between repertoire size and the proportion of trills in the repertoire. Thus, birds with a large repertoire tend to have only a small proportion of trills, whereas birds with a small repertoire usually have a large proportion of trills.
TSCHARNTKE, 1999). A possible explanation for this decrease could be that some species are no lon... more TSCHARNTKE, 1999). A possible explanation for this decrease could be that some species are no longer able to find all of their resources (food, spawning area, shelter,..) in the reduced habitat (SPELLERBERG, 1996). Another con-sequence of isolation is that the exchange of ...
During the Anthropocene, Earth has experienced unprecedented habitat loss, native species decline... more During the Anthropocene, Earth has experienced unprecedented habitat loss, native species decline, and global climate change. Concurrently, greater globalisation is facilitating species movement, increasing the likelihood of alien species establishment and propagation. There is a great need to understand what influences a species' ability to persist or perish within a new or changing environment. Examining genes that may be associated with a species' invasion success or persistence informs invasive species management, assists with native species preservation, and sheds light on important evolutionary mechanisms that occur in novel environments. This approach can be aided by coupling spatial and temporal investigations of evolutionary processes. Here we use the common starling, Sturnus vulgaris, to identify parallel and divergent evolutionary change between contemporary native and invasive range samples and their common ancestral population. To do this, we use reduced-representation sequencing of native samples collected recently in north-western Europe and invasive samples from Australia, together with museum specimens sampled in the UK during the mid-19th Century. We found evidence of parallel selection on both continents, possibly resulting from common global selective forces such as exposure to pollutants. We also identified divergent selection in these populations, which might be related to adaptive changes in response to the novel environment encountered in the introduced Australian range. Interestingly, signatures of selection are equally as common within both invasive and native range contemporary samples. Our results demonstrate the value of including historical samples in genetic studies of invasion and highlight the ongoing and occasionally parallel role of adaptation in both native and invasive ranges.
Light pollution or artificial light at night (ALAN) is an increasing, worldwide challenge that af... more Light pollution or artificial light at night (ALAN) is an increasing, worldwide challenge that affects many aspects of animal behaviour. Interestingly, the response to ALAN varies widely among individuals within a population and variation in personality (consistent individual differences in behaviour) may be an important factor explaining this variation. Consistent individual differences in exploration behaviour in particular may relate to the response to ALAN, as increasing evidence indicates its relation with how individuals respond to novelty and how they cope with anthropogenic modifications of the environment. Here, we assayed exploration behaviour in a novel environment as a proxy for personality variation in great tits (Parus major). We observed individual sleep behaviour over two consecutive nights, with birds sleeping under natural dark conditions the first night and confronted with ALAN inside the nest box on the second night, representing a modified and novel roosting env...
The Science of the total environment, Jan 15, 2018
Anthropogenic contaminants could alter traits central to animal behavioral types, or personalitie... more Anthropogenic contaminants could alter traits central to animal behavioral types, or personalities, including aggressiveness, boldness and activity level. Lead and other toxic metals are persistent inorganic pollutants that affect organisms worldwide. Metal exposure can alter behavior by affecting neurology, endocrinology, and health. However, the direction and magnitude of the behavioral effects of metal exposure remain equivocal. Moreover, the degree to which metal exposure simultaneously affects suites of correlated behavioral traits (behavioral syndromes) that are controlled by common mechanisms remains unclear, with most studies focusing on single behaviors. Using a model species for personality variation, the great tit (Parus major), we explored differences in multiple behavioral traits across a pollution gradient where levels of metals, especially lead and cadmium, are elevated close to a smelter. We employed the novel environment exploration test, a proxy for variation in pe...
Artificial light at night (ALAN) or light pollution is an increasing and worldwide problem. There... more Artificial light at night (ALAN) or light pollution is an increasing and worldwide problem. There is growing concern that because of the disruption of natural light cycles, ALAN may pose serious risks for wildlife. While ALAN has been shown to affect many aspects of animal behaviour and physiology, few studies have experimentally studied whether individuals of different species in the wild respond differently to ALAN. Here, we investigated the effect of ALAN on sleep behaviour in two closely related songbird species inhabiting the same study area and roosting/breeding in similar nest boxes. We experimentally exposed free-living great tits (Parus major) and blue tits (Cyanistes caeruleus) to artificial light inside their nest boxes and observed changes in their sleep behaviour compared to the previous night when the nest boxes were dark. In line with previous studies, sleep behaviour of both species did not differ under dark conditions. ALAN disrupted sleep in both great and blue tits. However, compared to blue tits, great tits showed more pronounced effects and more aspects of sleep were affected. Light exposed great tits entered the nest boxes and fell asleep later, woke up and exited the nest boxes earlier, and the total sleep amount and sleep percentage were reduced. By contrast, these changes in sleep behaviour were not found in light exposed blue tits. Our field experiment, using exactly the same light manipulation in both species, provides direct evidence that two closely related species respond differently to ALAN, while their sleep behaviour under dark conditions was similar. Our research suggests that findings for one species cannot necessarily be generalised to other species, even closely-related species. Furthermore, species-specific effects could have implications for community dynamics.
Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestli... more Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestling period, and is followed by a sleep rebound Reference: Raap Thomas, Pinxten Rianne, Eens Marcel.-Artificial light at night disrupts sleep in female great tits (**Parus major**) during the nestling period, and is followed by a sleep rebound Environmental pollution
The immune system is one of the most important adaptations that has evolved to protect animals fr... more The immune system is one of the most important adaptations that has evolved to protect animals from a wide range of pathogens they encounter from early life onwards. During the early developmental period this is particularly true for the innate immunity, as other components of the immune system are, as yet, poorly developed. But innate immunity may not only be crucial for early life survival, but may also have long-lasting effects, for example if early life immunity reflects the functioning of the immune system as a whole. For this reason, we investigated the importance of four constitutive innate immune parameters (natural antibodies, complement activity, concentrations of haptoglobin, and concentrations of nitric oxide) for recruitment in free-living great tits. We compared nestling immunity of recruits with nestling immunity of their nonrecruited siblings. We also investigated within individual consistency of these innate immune parameters for those individuals that recruited, which may be taken as a measure of immune capacity. In accordance with previous studies, we found a clear effect of tarsus length and a trend for body mass on the likelihood to recruit. Nevertheless, we found no evidence that higher levels of constitutive innate immunity as a nestling facilitated local recruitment. Furthermore, individual innate immunity was not consistent across life stages, that is to say, nestling immune parameters did not determine, or respectively, reflect adult innate immune parameters. This plasticity in innate immune components may explain why we did not find long-lasting survival benefits.
In an urban environment, birds are exposed to metals, which may accumulate in their tissues and c... more In an urban environment, birds are exposed to metals, which may accumulate in their tissues and cause oxidative stress. Female birds may eliminate these pollutants through depositing them into eggs, thus eggs become suitable bioindicators of pollution. In this study, we aimed to analyse whether eggshell spotting pattern, egg volume, eggshell thickness and egg yolk antioxidant (lutein, tocopherol, retinol and selenium) levels were related to the breeding area (woodland versus urban) and the metal levels in the eggshell of a small passerine species, the great tit (Parus major). In the urban habitat, soil and eggshells contained higher concentrations of metals, and soil calcium level was also higher than that in the woodland. Eggshell spotting intensity and egg volume did not differ between eggs laid in the woodland and the urban park, and these traits were not related to the metal levels of the eggshell, suggesting that these egg characteristics are not sensitive indicators of metal pollution. A more aggregated eggshell spotting distribution indicated a higher Cu concentration of the eggshell. We found that eggshells were thinner in the less polluted woodland habitat, which is likely due to the limited Ca availability of the woodland area. Great tit eggs laid in the urban environment had lower yolk lutein, retinol and selenium concentrations, however, as a possible compensation for these lower antioxidant levels, urban females deposited more tocopherol into the egg yolk. It appears that females from different breeding habitats may provide similar antioxidant protection for their offspring against oxidative damage by depositing different specific dietary antioxidants. Egg yolk lutein and retinol levels showed a negative relationship with lead concentration of the eggshell, which may suggest that lead had a negative impact on the amount of antioxidants available for embryos during development in great tits.
The importance of genes in regulating phenotypic variation of personality traits in humans and an... more The importance of genes in regulating phenotypic variation of personality traits in humans and animals is becoming increasingly apparent in recent studies. Here we focus on variation in the vasopressin receptor gene 1a (Avpr1a) and oxytocin receptor gene (OXTR) and their effects on social personality traits in chimpanzees. We combine newly available genetic data on Avpr1a and OXTR allelic variation of 62 captive chimpanzees with individual variation in personality, based on behavioral assessments. Our study provides support for the positive association of the Avpr1a promoter region, in particular the presence of DupB, and sociability in chimpanzees. This complements findings of previous studies on adolescent chimpanzees and studies that assessed personality using questionnaire data. In contrast, no significant associations were found for the single nucleotide polymorphism (SNP) ss1388116472 of the OXTR and any of the personality components. Most importantly, our study provides additional evidence for the regulatory function of the 5′ promoter region of Avpr1a on social behavior and its evolutionary stable effect across species, including rodents, chimpanzees and humans. Although it is generally accepted that complex social behavior is regulated by a combination of genes, the environment and their interaction, our findings highlight the importance of candidate genes with large effects on behavioral variation.
Relationships between female quality, egg mass and eggshell blue-green colouration in southern ro... more Relationships between female quality, egg mass and eggshell blue-green colouration in southern rockhopper penguins : a test of the sexual signalling hypothesis Polar biology
The extended pace-of-life syndrome (POLS) hypothesis suggests that variation in boldness-like beh... more The extended pace-of-life syndrome (POLS) hypothesis suggests that variation in boldness-like behaviors has co-evolved with variation in life-history strategies within populations, yet both theoretically driven experiments and evidence for phenotypic correlations between boldness-like behaviors and reproduction-related activities are scarce. Here we test the prediction that more exploratory individuals should be willing to provide more effort into current reproduction than less exploratory ones by investigating the association between exploration behavior and parental effort in wild great tits (Parus major). To this end, we assessed exploration behavior following a standardized assay. Then, we estimated individual willingness to provide parental effort into brood provisioning as (1) individual increase in nest visit rate after the brood had been artificially enlarged and (2) individual latency to return to the nest after this manipulation. Fast male explorers were quicker than slow explorers to return to the nest after the manipulation. Males paired with a partner of similar exploration score-either a fast or slow female explorer-increased their nest visit rate more than males paired with a partner of dissimilar exploration score. The relationship between exploration and parental effort then depended on one's partner's behavior. Our test thus provides only partial support for the extended POLS hypothesis and highlights the potential importance of the social environment in shaping the relationship between boldness-like behaviors and fitness-maximizing traits.
Kacelnikl proposes a puzzle for optimal foraging theorists, arising from experiments of Races and... more Kacelnikl proposes a puzzle for optimal foraging theorists, arising from experiments of Races and Nutiez2, who found that leaf-cutting ant (Acromyrmex lundi) workers changed their behavior in response to foragmg-quality information that was only known to scouts. The workers cut and transferred smaller pieces of parafilm when the scouts had been exposed to a 10% sugar solution than when they were exposed to a 1% solution. Optimal foraging theory, according to Kacelnik, predicts no such dependence of load upon resource quality. After considering several possible explanations, Kacelnik concludes that 'there is no winning functional model, although the rnformabon transfer hypothesis [smaller loads mean more activity, which increases the rate of transfer of information] is in my view the strongest candidate'.
There is a wide literature concerning the duration of incubation, as well as the ability of paren... more There is a wide literature concerning the duration of incubation, as well as the ability of parent birds to manipulate both the duration of incubation and asynchronous hatching within their clutches (see reviews in . Some studies have focused on intrinsic differences between eggs, while others have stressed the important role of the behavior of the incubating adults. Penguins have often been used as a model to test this
Abstract: Isolation of a population can result in decreased genetic variability as a consequence ... more Abstract: Isolation of a population can result in decreased genetic variability as a consequence of inbreeding, random genetic drift and reduced gene flow. This effect is reinforced when it concerns as small population. We used two molecular techniques, ...
We recorded songs of male blue tits Parus caeruleusduring the fertile and egg-laying period in a ... more We recorded songs of male blue tits Parus caeruleusduring the fertile and egg-laying period in a Belgian and Spanish population and compared several song characteristics in order to investigate the extent of macrogeographic variation in song features such as syntax, repertoire size and the proportion of trills in the repertoire. Repertoire size differed considerably between populations: it was twice as large in southern Spain (11.6 song types) as in Belgium (5.4 song types). Song syntax also differed significantly between the two populations. The most remarkable difference, however, was found in the proportion of trills. Trilled song types were rare in southern Spain (18 %) whereas more than half of the song types in the repertoire of Belgian blue tits included a trill (53 %). A recent hypothesis explains variation in blue tit song as a result of interspecific competition, suggesting that blue tit repertoire size decreases with increasing density of great tits Parus majorand that the proportion of trills increases with increasing great tit density. This hypothesis does not appear to explain our findings. Although both populations differed strongly in both song parameters, the relative great tit density appeared to be very similar. Furthermore, we provide the first evidence of a striking negative relationship between repertoire size and the proportion of trills in the repertoire. Thus, birds with a large repertoire tend to have only a small proportion of trills, whereas birds with a small repertoire usually have a large proportion of trills.
TSCHARNTKE, 1999). A possible explanation for this decrease could be that some species are no lon... more TSCHARNTKE, 1999). A possible explanation for this decrease could be that some species are no longer able to find all of their resources (food, spawning area, shelter,..) in the reduced habitat (SPELLERBERG, 1996). Another con-sequence of isolation is that the exchange of ...
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