Density dependent effects between three competitive bird species

Summary Density and breeding success of the great tit Parus major, blue tit Parus caeruleus and collared flycatcher Ficedula albicollis were studied in nest box colony in oak forest over a period of 19 years.Intraspecific density dependent clutch size reduction was found with blue tit and great tit. In interspecific relation the high density of blue tits reduced the clutch size of great tits.In the hatching period neither intraspecific nor interspecific density dependence were showed between the tits when the third competitive species, collared flycatcher was present. The collared flycatcher significantly reduced the hatching success of both tit species and the number of fledglings of great tit.The effects of the great tits and combined density of the great and blue tits on the hatching failure and number of fledglings of collared flycatcher were found when the density of the tits was high. There were not significant relationships to the single density of blue tits.The temporal variability of the competition of the three bird species is discussed.     

Interspecific aggression declines seasonally in breeding great tits Parus major

During the breeding season, great tits show aggression to protect their nest from intra‐ and interspecific intruders. Aggression is a labile trait that can be plastically expressed as a result of individual differences (e.g., personality), seasonal gradients in the costs and benefits of aggression, or other environmental components (e.g., number of competitors). Competitors may try to take over great tit nests, because the number of suitable nesting sites is limited, and great tits may guard high quality territories. Taking over a great tit nest may be especially fruitful in early phenological stages (egg laying) when great tits frequent their nests less often. However, great tits may compensate for this vulnerability by being more aggressive toward intruders during early nesting stages, a pattern that has already been established in an intraspecific context. Previous studies have shown that interspecific intruders were most likely to die from great tit aggression during great tit egg laying, suggesting great tits may also be more aggressive during this phase in an interspecific context. Here, I tested this hypothesis with simulated territorial intrusions in great tit territories using taxidermized blue tits Cyanistes caeruleus (hereafter called blue tit models). Great tit aggression (number of calls and approach distance toward blue tit model) was assayed during egg laying, incubation, and chick rearing in the breeding season of 2014. Although sample size was low due to a high fraction of non‐responders (n = 44 out of 89 assays across 26 out of 35 individuals), I found that great tits showed a seasonal decline in aggressiveness, which is congruent with intraspecific results on this study species. I discuss my findings in the context of differential adjustment to climate change between interspecific competitors.     

Rival imprinting: interspecifically cross-fostered tits defend their territories against heterospecific intruders

Failure to recognize conspecifics in social interactions such as mate choice and aggressive encounters will often result in reduced fitness. Studies on mate choice show that the ability to recognize conspecifics as mates is not universally present at birth, but often needs to be learned. In contrast, little is known about the ontogeny of intrasexual species recognition. To test whether learning influences the recognition of sexual rivals, we compared the aggressive response towards intruders of interspecifically cross-fostered individuals and controls reared by conspecific parents. We simulated territorial intrusion by presenting either a caged individual or playback song near the nest of breeding pairs of great tits, Parus major, and blue tits, P. caeruleus. Great tits reared by blue tit parents responded much more to blue tit stimuli than did great tit controls, and furthermore showed stronger responses to blue tit stimuli than to those of their own species. Blue tits reared by great tits responded much more to great tit stimuli than did blue tit controls. In contrast, blue tits cross-fostered to coal tits, P. ater, did not respond more to coal tits than did blue tit controls. There was a species difference in the response to conspecifics: blue tits cross-fostered to great tits responded more to conspecifics than did cross-fostered great tits. The results were similar for males and females. We conclude that learning influences intrasexual species recognition in these tits. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Do Fleas,and/or Old Nest Material,Influence Nest-site preference in Hole-nesting Passerines?

This study examined nest-site choice in a migratory population of pied flycatchers (Ficedula hypoleuca) and sympatric populations of three resident tit species (Parus major, P. caeruleus and P. palustris) in central Sweden. All four species are secondary-cavity nesters which naturally breed in pre-formed tree cavities but readily use artificial nest boxes. We asked whether flycatchers and tits discriminate between nest boxes that: 1. Are ‘empty’; 2. Contain old nests without ectoparasites (fleas Ceratophyllus sp.); or 3. Contain old nests with ectoparasites. We found that pied flycatchers preferred nest boxes containing old nests, regardless of whether these nests held parasites. In contrast, tits did not discriminate between the three types of boxes. Tits may pay a cost for their lack of choosiness: after the breeding season, tit nests contained more fleas than flycatcher nests. Nevertheless, parasites did not affect the choice of a nest site in any of the species studied. We suggest that the migratory flycatchers are in a hurry to start breeding upon arrival and use the presence of an old nest as a shortcut cue to assess nest-site quality. Also, they may save valuable time by copying the choice of previous breeders. Non-migratory tits may have more time to inspect nest sites, but do not seem to use the same cues in nest-site selection as the pied flycatcher.     

Climate change can alter competitive relationships between resident and migratory birds

Climate change could affect resource competition between resident and migratory bird species by changing the interval between their onsets of breeding or by altering their population densities. We studied interspecific nest-hole competition between resident great tits and migrant pied flycatchers in South-Western Finland over the past five decades (1953-2005). We found that appearance of fatal take-over trials, the cases where a pied flycatcher tried to take over a great tit nest but was killed by the tit, increased with a reduced interspecific laying date interval and with increasing densities of both tits and flycatchers. The probability of pied flycatchers taking over great tit nests increased with the density of pied flycatchers. Laying dates of the great tit and pied flycatcher are affected by the temperatures of different time periods, and divergent changes in these temperatures could consequently modify their competitive interactions. Densities are a result of reproductive success and survival, which can be affected by separate climatic factors in the resident great tit and trans-Saharan migrant pied flycatcher. On these bases we conclude that climate change has a great potential to alter the competitive balance between these two species.     

Parent birds assess nest predation risk: influence of cavity condition and avian nest predator activity

Skutch hypothesized that nest predators visually assess parental activities to locate a prey nest, whereas parents modify fitness‐related traits to reduce the probability of nest predation. We examined how cavity condition and parental activity interact with avian nest predators to shape the nest success of two coexisting parid species, marsh tits Poecile palustris and oriental tits Parus minor, breeding in nest‐boxes during the incubation period. Nest‐boxes were manipulated to create a prolonged risk of nest predation (entrance diameter 2.6 cm control vs 5.5 cm treatment) soon after clutch completion. To measure changes in parental behavior, we also simultaneously simulated a pulsed risk of nest predation, using sound playbacks of a coexisting control bird and an avian nest predator. We found that the parent tits merely responded the pulsed risk, presumably due to an environment with high avian nest predator encounters, compared to the prolonged risk. Instead, both species spent more time on vigilance at the nest, only under prolonged risk conditions. The activity of corvids near the nest‐box was higher in the marsh tit than that in oriental tits. This activity was also higher in the treatment nest box than that in the control nest‐box. Nest predation during the incubation period was higher in marsh tits than in oriental tits, presumably due to higher and more plastic vigilance in oriental tits, compared to marsh tits. Our results highlight that the differences in cavity condition and parental activities at the nests of two coexisting non‐excavators may contribute to differential nest predation by attracting avian nest predators.     

Predation by sparrowhawks decreases with increased breeding density in a songbird,the great tit

Predators may regulate prey populations if predation rate increases with prey density. Alternatively, if space-limited (e.g. territorial) predators become satiated when prey exceed a certain density, increased prey abundance may lead to reduced predation rate. These alternatives have been difficult to test experimentally for mobile prey in the wild. We present such a test, manipulating the density of great tits (Parus major) by adding nest boxes in territories of sparrowhawks (Accipiter nisus). Predation rate was measured for young tits after they left the nests. Although the great tit is an important prey, there was no evidence for regulation during the breeding season: the rate of hawk predation declined with increasing density of tits. This result was not confounded by changes in breeding density of alternative prey species (other songbirds). Hawk predation can therefore favour dense breeding in a territorial (solitary) bird, and conspecific attraction and aggregation reported in several territorial species may partly result from predation pressure. This result also has potential implications for conservation work.     

Effect of an ectoparasite on lay date, nest-site choice, desertion, and hatching success in the great tit (Pants major)

Ectoparasites are common in most bird species, but experimentalevidence of their effects on life-history traits is scarce.We investigated experimentally the effects of the hematophagoushen flea (Ceratophyllus gallinae) on timing of reproduction,nest-site choice, nest desertion, clutch size, and hatchingsuccess in the great tit (Parus major). When great tits wereoffered a choice on their territory between an infested anda parasite-free nest-box, they chose the one without parasites.When there was no choice, the great tits in a territory containingan infested nest-box delayed laying the clutch by 11 days ascompared with the birds that were offered a parasite-free nestingopportunity. The finding that there was no difference in phenotypictraits related to dominance between the birds nesting in infestedboxes and birds nesting in parasite-free boxes suggests thatthe delay is not imposed by social dominance. Nest desertionbetween laying and shortly after hatching was significandy higherin infested nests. There was no difference between infestedand parasite-free nests in clutch size, but hatching successand hence brood size at hatching were significantly smallerin infested nests. Nest-box studies of great tits have beenseminal in the development of evolutionary, ecological, andbehavioral theory, but recently a polemic has arisen in theliterature about the validity of the conclusions drawn fromnest-box studies where the naturally occurring, detrimentalectoparasites are eliminated by the routine removal of old nestsbetween breeding seasons. Our study suggests that this criticismis valid and that the evaluation of the effects of ectoparasitesmay improve our understanding of behavioral traits, life-historytraits, or population dynamics     

Are nest sites actively chosen? Testing a common assumption for three non-resource limited birds

Many widely-accepted ecological concepts are simplified assumptions about complex situations that remain largely untested. One example is the assumption that nest-building species choose nest sites actively when they are not resource limited. This assumption has seen little direct empirical testing: most studies on nest-site selection simply assume that sites are chosen actively (and seek explanations for such behaviour) without considering that sites may be selected randomly. We used 15 years of data from a nestbox scheme in the UK to test the assumption of active nest-site choice in three cavity-nesting bird species that differ in breeding and migratory strategy: blue tit (Cyanistes caeruleus), great tit (Parus major) and pied flycatcher (Ficedula hypoleuca). Nest-site selection was non-random (implying active nest-site choice) for blue and great tits, but not for pied flycatchers. We also considered the relative importance of year-specific and site-specific factors in determining occupation of nest sites. Site-specific factors were more important than year-specific factors for the tit species, while the reverse was true for pied flycatchers. Our results show that nest-site selection, in birds at least, is not always the result of active choice, such that choice should not be assumed automatically in studies of nesting behaviour. We use this example to highlight the need to test key ecological assumptions empirically, and the importance of doing so across taxa rather than for single “model” species.     

千岛湖栖息地片段化对大山雀营巢资源利用的影响

为了解栖息地片段化对次级洞巢鸟营巢资源利用的影响, 我们于2008年2-8月, 在千岛湖地区选取21个岛屿, 采用悬挂人工巢箱方法进行大山雀(Parus major)招引实验。通过测定岛屿面积、岛屿隔离度、捕食者活动率、人工巢箱周围植被盖度和人工巢箱巢向等5种参数, 分析大山雀人工巢箱利用与上述参数间的关系。实验期间, 共悬挂443个人工巢箱, 其中有72个(16.3%)被大山雀利用。大山雀倾向于选择捕食者活动率低、植被盖度低、巢口向东或向南的人工巢箱; 岛屿面积和隔离度对大山雀利用人工巢箱不存在显著的直接影响, 但岛屿面积可通过影响捕食者的活动率, 对大山雀利用人工巢箱产生间接影响。因此, 我们认为在栖息地片段化后, 应更多关注对洞巢鸟营巢资源利用有直接影响的栖息地特征因素, 以及片段化效应的间接影响。     

Birds as predators of the pine processionary moth (Lepidoptera: Notodontidae)

The beneficial role of insectivorous birds potentially contributing to the biological control of forest insect pests appears crucial in the context of climate warming, especially for species currently expanding their range such as the pine processionary moth Thaumetopoea pityocampa. Larvae of T. pityocampa are aposematic and carry true urticating setae which, together with overwintering in silk winter nests, prevent them from predation by most insectivorous forest birds. The present review aims at pointing out which bird species can regularly feed on this key forest defoliator throughout its distribution range, and which predation strategies allow birds to cope with the urticating setae carried by late-instar larvae. At least seven bird species can be considered as regular predators of the pine processionary moth: four large migrant specialists (great spotted cuckoo Clamator glandarius, common cuckoo Cuculus canorus, European nightjar Caprimulgus europaeus and Eurasian hoopoe Upupa epops) and three small sedentary generalists (great tit Parus major, crested tit Lophophanes cristatus and coal tit Periparus ater). Each species has developed morphological traits and foraging techniques to feed on different life stages of T. pityocampa throughout the year: (i) gizzard wall structure allowing the consumption of caterpillars with urticating setae (cuckoos); (ii) nocturnal foraging on moth imagos by aerial hawking (nightjars); (iii) ground probing on below-ground pupae with long curved bill (hoopoe); and (iv) shifted predation period in autumn and winter on eggs, early- and late-instar larvae, with particular feeding technique allowing to eat only the inner parts of urticating larvae stages (tits). Although several avian predators regularly feed on T. pityocampa, only a few specialist and generalist insectivorous birds may contribute to regulate its populations, especially when population density of the moth is low. Moreover, their efficiency may possibly be threatened by mismatches associated with climate change.     

Plant–plant interactions change during succession on nurse logs in a northern temperate rainforest

Plant–plant interactions change through succession from facilitative to competitive. At early stages of succession, early‐colonizing plants can increase the survival and reproductive output of other plants by ameliorating disturbance and stressful conditions. At later stages of succession, plant interactions are more competitive as plants put more energy toward growth and reproduction. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) and bryophyte succession. How bryophyte‐tree seedling interactions vary through log succession remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 1.0 m² plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA, to test the hypothesis that bryophyte‐tree seedling interactions change from facilitative to competitive as the log decays. Tree seedling density was highest on young logs with early‐colonizing bryophyte species (e.g., Rhizomnium glabrescens) and lowest on decayed logs with Hylocomium splendens, a long‐lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6× higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by forest floor plants, such as H. splendens. Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs enable both tree seedlings and smaller bryophyte species to avoid competition with forest floor plants, including the dominant bryophyte, H. splendens. H. splendens is likely a widespread driver of plant community structure given its dominance in northern temperate forests. Our findings indicate that plant–plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.     

Geographic variation in bird songs: examination of the effects of sympatric related species on the acoustic structure of songs

Birdsong evolution has influenced by various ecological and social factors. When related species that sing similar songs coexist, the acoustic properties of the songs of one or both species may shift, and the songs may diverge. We investigated geographic variation in the songs of the Japanese tit (Parus minor) and the varied tit (Poecile varius) in the Ryukyu Archipelago, Japan, whose islands harbor either one or both species. The songs of the two species exhibited similar structure, but acoustic measurements differed between them. For example, varied tits sang songs at higher frequency than Japanese tits did. The songs of both species varied geographically. At sites with higher relative densities of varied tits, Japanese tits sang lower frequency songs, indicating that in areas of coexistence, Japanese tits sang songs that had acoustically diverged from those of varied tits. Song variation in varied tits was not related to sympatry with Japanese tits. These asymmetric results suggest that the subordinate Japanese tit modified the acoustic characteristics of its song to avoid harassment by the dominant varied tit. We observed no effects of genetic divergence or local intraspecific density on Japanese tit or varied tit songs. This study used geographic variation to examine hypotheses of song evolution, and the results highlight the importance of character displacement.     

Intraspecific Variation and Interspecific Differences in the Bacterial and Fungal Assemblages of Blue Tit (Cyanistes caeruleus) and Great Tit (Parus major) Nests

Although interest in the relationship between birds and microorganisms is increasing, few studies have compared nest microbial assemblages in wild passerines to determine variation within and between species. Culturing microorganisms from blue tit (Cyanistes caeruleus) and great tit (Parus major) nests from the same study site demonstrated diverse microbial communities with 32 bacterial and 13 fungal species being isolated. Dominant bacteria were Pseudomonas fluorescens, Pseudomonas putida, and Staphylococcus hyicus. Also common in the nests were the keratinolytic bacteria Pseudomonas stutzeri and Bacillus subtilis. Dominant fungi were Cladosporium herbarum and Epicoccum purpurascens. Aspergillus flavous, Microsporum gallinae, and Candida albicans (causative agents of avian aspergillosis, favus, and candidiasis, respectively) were present in 30%, 25%, and 10% of nests, respectively. Although there were no differences in nest mass or materials, bacterial (but not fungal) loads were significantly higher in blue tit nests. Microbial species also differed interspecifically. As regards potential pathogens, the prevalence of Enterobacter cloacae was higher in blue tit nests, while Pseudomonas aeruginosa—present in 30% of blue tit nests—was absent from great tit nests. The allergenic fungus Cladosporium cladosporioides was both more prevalent and abundant in great tit nests. Using discriminant function analysis (DFA), nests were classified to avian species with 100% accuracy using the complete microbial community. Partial DFA models were created using a reduced number of variables and compared using Akaike’s information criterion on the basis of model fit and parsimony. The best models classified unknown nests with 72.5–95% accuracy using a small subset of microbes (n = 1–8), which always included Pseudomonas agarici. This suggests that despite substantial intraspecific variation in nest microflora, there are significant interspecific differences—both in terms of individual microbes and the overall microbial community—even when host species are closely related, ecologically similar, sympatric, and construct very similar nests.     

Bird predation by tawny owls (Strix aluco L.) and its effect on the reproductive performance of tits

The density of great tit Parus major L. and blue tit Parus caeruleus L. was artificially increased by placing nest-box colonies for these species in the vicinity of the nests of breeding tawny owls during 1993–1997. Bird prey composition in the owl nests, the proportion of parents disappearing from the breeding tit populations and the reproductive performance of the widowed parents were analysed. The frequency of predation on tits by tawny owls was greater in areas where tit density had been artificially increased. Owls preyed more on tits during the feeding period of owlets than during the incubation period and more in years when snow covered the ground during the incubation period than when it did not. Mortality due to predation was male biased and more females lost their mates in populations breeding near tawny owl nests. Reproductive performance of the widowed parents was lower and their body weights were lighter at the end of the nestling period than those found in birds rearing youngs with their mates. Predation by owls increased the between-year turnover in the breeding tit population: widowed parents did not return to the nesting site for the next breeding season.     

Experimental manipulation of temperature reduce ectoparasites in nests of blue tits Cyanistes caeruleus

Several models predict changes in the distributions and incidences of diseases associated with climate change. However, studies that investigate how microclimatic changes may affect host–parasite relationships are scarce. Here, we experimentally increased the temperature in blue tit Cyanistes caeruleus nest boxes during their breeding season to determine its effects on the parasitic abundance (i.e. of nest‐dwelling ectoparasites, blood‐sucking flying insects and hemoparasites) in nests and the host condition of nestlings and adults. The temperature was increased using heat mats placed underneath the nest material, which resulted in an average temperature increase of 3ºC and a reduction in relative humidity of about six units. The abundance of mites Dermanyssus gallinoides and blowfly pupae Protocalliphora azurea was significantly reduced in heated nest boxes. Although not statistically significant, a lower prevalence of flea larvae Ceratophyllus gallinae was also found in heated nests. However, heat treatment did not affect hemoparasite infection of adult blue tits or the body condition of adult and nestling blue tits. In conclusion, heat treatment in blue tit nests reduced nest‐dwelling ectoparasites yet without any apparent benefit for the host.     

Does the temporal mismatch hypothesis match in boreal populations?

The temporal mismatch hypothesis suggests that fitness is related to the degree of temporal synchrony between the energetic needs of the offspring and their food supply. The hypothesis has been a basis in studying the influence of climate warming on nature. This study enhances the knowledge on prevalence of temporal mismatches and their consequences in boreal populations, and questions the role of the temporal mismatch hypothesis as the principal explanation for the evolution of timing of breeding. To test this, we examined if synchrony with caterpillar prey or timing of breeding per se better explains reproductive output in North European parid populations. We compared responses of temperate-origin species, the great tit (Parus major) and the blue tit (Cyanistes caeruleus), and a boreal species, the willow tit (Poecile montanus). We found that phenologies of caterpillars and great tits, but not of blue tits, have advanced during the past decades. Phenologies correlated with spring temperatures that may function as cues about the timing of the food peak for great and blue tits. The breeding of great and blue tits and their caterpillar food remained synchronous. Synchrony explained breeding success better than timing of breeding alone. However, the synchrony effect arose only in certain conditions, such as with high caterpillar abundances or high breeding densities. Breeding before good synchrony seems advantageous at high latitudes, especially in the willow tit. Thus, the temporal mismatch hypothesis appears insufficient in explaining the evolution of timing of breeding.     

Snake-like calls in breeding tits

Hole-nesting tits belonging to the family Paridae produce a hissing display that resembles the exhalatory hiss of a snake. When a predatory animal enters the nest hole of a tit, tits often hiss vigorously, while lunging their head forward and shaking their wings and tail, until the intruder retreats. We assessed the acoustic similarity between such hiss calls from 6 species of tits, snake hisses, and tit syllables used in alarm vocalizations, as well as white noise as a control. Tit hiss calls showed a high degree of similarity with snake hisses from 3 different snake families. Tit hisses had lower similarity to syllable alarm calls, suggesting convergence of tit hisses in their spectral structure. Hiss calls would only be effective in protecting nest boxes if nest predators responded to these calls. In order to test this hypothesis, we trained individual Swinhoe’s striped squirrels, Tamiops swinhoei hainanus, a common predator of egg and nestling tits, to feed at feeders in proximity to nest boxes. We compared the aversive response of squirrels to tit’s hiss calls and white noise, presented in random order. Squirrels showed a higher degree of avoidance of feeders when hiss calls were played back than when white noise was presented. In conclusion, our study suggests that hole-nesting birds have evolved convergent snake-like hiss calls, and that predators avoid to prey on the contents of nest boxes from which snake-like hisses emerge.     

Nestling detectability affects parental feeding preferences in a cavity-nesting bird

In many avian species, nestlings have evolved striking plumage, behaviours and mouth colours to obtain a greater share of parental investment. Studies revealing parental feeding preferences for nestlings with red gapes have proposed that red mouth colour in songbirds can act as a signal of nestling need or condition. Alternative hypotheses suggest that bright nestling mouths in cavity-nesting birds evolved to increase nestling detectability by the parents. We tested whether nestling mouth colour affects parental feeding preferences in great tits, Parus major L. In broods of six young, we experimentally painted mouth gapes and flanges either red or yellow and tested the effect of mouth colour on nestlings' mass gain under two lighting conditions. In nests with high luminosity, there was no significant effect of mouth colour on mass gain. In nests with low luminosity, nestlings with red gapes and flanges gained less mass than nestlings with red gapes and yellow flanges or both yellow gapes and flanges. Our results suggest that, in nests with low luminosity, red mouths decreased nestling detectability to the feeding parents and support the hypothesis that poor luminosity in nesting cavities can select for pale mouths. Overall, our results do not support the hypothesis that red mouth colour signals nestling need or condition to parent great tits.     

Sexual imprinting and the origin of obligate brood parasitism in birds

We discuss two pathways along which obligate brood parasitism (OBP) may evolve and examine some of the critical steps that must be passed by letting great tits Parus major be reared by blue tits Parus caeruleus in a field experiment. The cross-fostered chicks survived well in blue tit nests, but their local recruitment and reproductive success was much lower than that of controls. The effect was strongest when great tits grew up with siblings of the host species rather than with conspecific siblings in blue tit nests. The low success seemed to be caused by misimprinting because the cross-fostered birds behaved like blue tits in several aspects (species association, alarm calls, and aggressive response by resident females to caged intruders). Some birds of both sexes were apparently so strongly imprinted that they did not attract or accept a social mate of their own species. We conclude that imprinting may be necessary for OBP to evolve in birds because the parasite must be attracted to the nests of the host species to add eggs and thereby continue the parasitic life cycle. However, strong imprinting may also prevent OBP from occurring if parasitic offspring seek a mate from the host species.