Aromatic plants in nests of the blue tit <Emphasis Type="Italic">Cyanistes caeruleus</Emphasis> protect chicks from bacteria

Several bird species add fresh fragments of plants which are rich in volatile secondary compounds to their nests. It has been suggested, although never tested, that birds use fresh plants to limit the growth of nest microorganisms. On Corsica, blue tits (Cyanistes caeruleus) incorporate fresh fragments of aromatic plants into their nests. These plants do not reduce infestation by nest ectoparasites, but have been shown to improve growth and condition of chicks at fledging. To understand the mechanisms underlying such benefits, we experimentally tested the effects of these plants on the bacteria living on blue tits. Aromatic plants significantly affected the structure of bacterial communities, in particular reducing bacterial richness on nestlings. In addition, in this population where there is a strong association between bacterial density and infestation by blood-sucking Protocalliphora blow fly larvae, these plants reduced bacterial density on the most infested chicks. Aromatic plants had no significant effect on the bacteria living on adult blue tits. This study provides the first evidence that fresh plants brought to the nests by adult birds limit bacterial richness and density on their chicks.     

Interacting effects of aromatic plants and female age on nest-dwelling ectoparasites and blood-sucking flies in avian nests

Some avian species incorporate aromatic plants to their nests. The "nest protection hypothesis", which posits that volatile secondary compounds contained in these plants may have antiparasite properties, has not received full support. All previous tests of this hypothesis have only considered effects on nest-dwelling ectoparasites, but not on blood-sucking flies. The "drug hypothesis" posits that aromatic plants may stimulate nestling immune system, development, or condition. We tested these hypotheses experimentally in wild blue tits, Cyanistes caeruleus, a species that adds aromatic plants to their nests. We supplemented aromatic plants to half of a sample of nests, while adding grass to the other half of nests. We quantified abundance of two groups of blood-sucking flies (blackflies and biting midges) at two different stages of the reproductive period, and abundance of three nest-dwelling ectoparasites (fleas, mites, and blowflies). Experimental supplementation of aromatic plants reduced abundance of fleas only in nests of yearling females and not in nests of older females. Blackflies and biting midges were both more numerous in nests of yearling females than in nests of older females. Mass of aromatic plants added by females was negatively related with abundance of fleas in control nests but not in experimental nests supplied with aromatic plants. Mass of plants added by females was also positively related with abundance of blackflies during the nestling stage. Finally, aromatic plants did not affect nestling growth or immune responses. We conclude that several factors such as female experience and their ability to add plants to the nest interact to explain effects of aromatic plants on different parasites.     

Tree swallows (Tachycineta bicolor) nesting on wetlands impacted by oil sands mining are highly parasitized by the bird blow fly Protocalliphora spp

Oil sands mining is steadily expanding in Alberta, Canada. Major companies are planning reclamation strategies for mine tailings, in which wetlands will be used for the bioremediation of water and sediments contaminated with polycyclic aromatic hydrocarbons and naphthenic acids during the extraction process. A series of experimental wetlands were built on companies' leases to assess the feasibility of this approach, and tree swallows (Tachycineta bicolor) were designated as upper trophic biological sentinels. From May to July 2004, prevalence and intensity of infestation with bird blow flies Protocalliphora spp. (Diptera: Calliphoridae) were measured in nests on oil sands reclaimed wetlands and compared with those on a reference site. Nestling growth and survival also were monitored. Prevalence of infestation was surprisingly high for a small cavity nester; 100% of the 38 nests examined were infested. Nests on wetlands containing oil sands waste materials harbored on average from 60% to 72% more blow fly larvae than those on the reference site. Nestlings on reclaimed sites suffered mean parasitic burdens about twice that of those on the reference site; and for comparable parasitic load, they exhibited greater pathologic effects (e.g., decreased body mass) than control nestlings. The heavy blow fly infestation on oil sands-impacted wetlands suggests that oil sands mining disturbs several components of the local ecosystem, including habitat characteristics, blow fly predators, and host resistance to parasites.     

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.     

Within-brood distribution of ectoparasite attacks on nestling blue tits: a test of the tasty chick hypothesis using inulin as a tracer

Blow fly ( Protocalliphora spp.) larvae are nest ectoparasites that compete with nestlings for resources by feeding on blood. Their main direct consequences on nestlings are a reduction in growth, blood parameters, and physiological performance. The impact of Protocalliphora larvae on nestling development can be extremely variable between nests within years and between years due to varying food availability. However, there is also considerable within-nest variation in nestling growth and development which has been attributed to an aggregation of ectoparasites on less resistant chicks; the tasty chick hypothesis. We tested for aggregated attacks of Protocalliphora within broods of nestling blue tits using radio-labelled inulin to trace plasma, and hence blood, turnover. To estimate blood removal by Protocalliphora, we compared inulin turnover in naturally parasitized and experimentally deparasitized nestlings. Inulin turnover, and hence the blood loss attributed to Protocalliphora attacks, was significantly correlated with chick mass and size rank within the brood, with the smallest and lowest-ranking chicks showing greatest inulin turnover. This is the first study demonstrating non-random blood-feeding by Protocalliphora larvae, a phenomenon which can render the statistical detection of their impact problematical by increasing within-brood variance in developmental and physiological measures.     

Determinants of abundance and effects of blood-sucking flying insects in the nest of a hole-nesting bird

Compared to non-flying nest-dwelling ectoparasites, the biology of most species of flying ectoparasites and its potential impact on avian hosts is poorly known and rarely, if ever, reported. In this study we explore for the first time the factors that may affect biting midge (Diptera: Ceratopogonidae) and black fly (Diptera: Simuliidae) abundances in the nest cavity of a bird, the hole-nesting blue tit Cyanistes caeruleus, and report their effects on adults and nestlings during reproduction. The abundance of biting midges was positively associated with nest mass, parental provisioning effort and abundance of blowflies and black flies, while negatively associated with nestling condition. Furthermore, a medication treatment to reduce blood parasitaemias in adult birds revealed that biting midges were more abundant in nests of females whose blood parasitaemias were experimentally reduced. This finding would be in accordance with these insect vectors attacking preferentially uninfected or less infected hosts to increase their own survival. The abundance of black flies in the population was lower than that of biting midges and increased in nests with later hatching dates. No significant effect of black fly abundance on adult or nestling condition was detected. Blood-sucking flying insects may impose specific, particular selection pressures on their hosts and more research is needed to better understand these host–parasite associations.     

Aromatic herbs in Corsican blue tit nests: The ‘Potpourri’ hypothesis

This study reports that Corsican blue tit (Parus caeruleus ogliastrae) nests contain between one to five aromatic herb species between the onset of egg laying till the chicks’ finished growth 13 d after hatching. An herb removal experiment during the chick stage shows that blue tits bring fresh aromatic material 1–5 d after herb removal. Nests with a series of distinct odour classes easily perceived by humans have never been reported in birds. A new ‘Potpourri’ hypothesis is proposed that may explain the functional significance of this behaviour.     

Physiological ecology of Mediterranean blue tits (Parus caeruleus L.): effects of ectoparasites (Protocalliphora spp.) and food abundance on metabolic capacity of nestlings

The consequences of nest ectoparasites, such as Protocalliphora larvae, on nestling birds have been the subject of numerous studies. Despite observed reductions in mass and hematocrit of chicks from parasitized nests, no studies have found any effect of Protocalliphora on nestling survival, suggesting that fitness consequences of Protocalliphora are either weak or occur after fledging. From experiments on the metabolic performance of chicks, we found that parasitized chicks suffer from reduced thermogenic and metabolic capacities as a result of decreased mass and hematocrit. Hence, Protocalliphora may potentially affect nestling survival after fledging, when energetically costly activities such as flight and moult are undertaken. Previous studies have demonstrated an increase in parental feeding rate to compensate for the detrimental consequences of parasite infestation. We tested whether parasite effects on nestling aerobic capacity were dependent on food availability during the feeding period. Measures of caterpillar densities and experimental manipulations of parasite loads allowed us to investigate relationships among host, parasite, and environment. A positive relationship between chick aerobic and thermogenic performances and caterpillar density suggests that negative effects of parasitism may be offset by increased food availability. This study provides the first measurement of the effects of an ectoparasite on metabolic competence in wild birds and documentation of the effect of food availability on ectoparasite virulence using a quantitative measure of food abundance.     

Intensity of nest defence is related to offspring sex ratio in the great tit Parus major

Nest-defence behaviour of passerines is a form of parental investment. Parents are selected, therefore, to vary the intensity of their nest defence with respect to the value of their offspring. Great tit, Parus major, males were tested for their defence response to both a nest predator and playback of a great tit chick distress call. The results from the two trials were similar; males gave more alarm calls and made more perch changes if they had larger broods and if they had a greater proportion of sons in their brood. This is the first evidence for a relationship between nest-defence intensity and offspring sex ratio. Paternal quality, size, age and condition, lay date and chick condition did not significantly influence any of the measured nest-defence parameters.     

Cavity type influences abundance of nest-dwelling avian blow flies: an experiment with tree swallows

1. Diverse assemblages of blood-feeding parasitic arthropods occupy the nests of birds, and nest temperature and humidity can strongly influence the population dynamics of these ectoparasites, with important implications for parasite–host relationships. 2. This study used two types of nest box that differed in internal microclimates, one constructed of plywood and the other constructed of boles of aspen (Populus tremuloides Michx.), more closely replicating natural cavities, to examine how nest microclimate affects the prevalence and abundance of nest-dwelling larval blow flies (Protocalliphora and Trypocalliphora spp.) in nests of tree swallows (Tachycineta bicolor Vieillot, 1808). 3. Based on known microclimatic differences between the box types and responses of larval blow flies to different temperatures, it was predicted that the microclimate of plywood boxes would be more favourable for growth and development of larval blow flies, and therefore have higher abundance, and possibly higher prevalence, of larval blow flies. 4. Plywood nest boxes had higher abundance, but not prevalence, of larval blow flies compared with aspen boxes at two different geographical locations in Canada. Nest composition also differed between box types, particularly at one site, where aspen boxes contained more nesting material (grass and feathers) than did plywood boxes. 5. Although it seems probable that microclimate was driving the differences between box types in abundance of larval blow flies, several additional explanations are discussed. These findings may have implications for conservation efforts, particularly those where nest boxes are used to aid in the recovery of declining bird populations.     

Green plant material versus ectoparasites in nests of Bonelli's eagle

The greenery and arthropod nest composition has been studied in a population of Bonelli's eagle Hieraaetus fasciatus in south-east Spain, relating them to the plant availability within territories and breeding success of pairs. Greenery was invariably from trees and shrubs, with pine and oak species accounting for 78% of the nest composition in weight. All eagle pairs with Pinus pinaster availability in territories actively selected it for nest greenery. This pine species is characterized by a high level of aromatic compounds, particularly β -pinene, highly repellent for insects. The amount of pine greenery in the nest was correlated with a lower presence of ectoparasites in that nest (blow fly larvae, Protocalliphora) , and higher breeding success of pairs. We discuss whether a coevolutionary process between parasites and their hosts has guided a particular nesting strategy of the eagles to improve their breeding success.     

Blue tits use selected plants and olfaction to maintain an aromatic environment for nestlings

Animals use the chemical compounds of plants as a defence mechanism against enemies, and sometimes use olfaction to discriminate and select the chemical plant substances. Some birds bring to the nest plant material that has volatile compounds that protect the host and their offspring against parasitic organisms. Here we show that blue tits on the island of Corsica ( Parus caeruleus ogliastrae ) adorn their nests with fragments of aromatic plants. These plants have chemical compounds that are used by humans to make aromatic house cleaners and herbal medicines. We also show that individual blue tits maintain an aromatic nest environment when offspring are raised, using odour cues to determine the frequency with which they replenish the nest with fresh plant material. We provide an exceptional example of the ecologically relevant use of olfaction by birds under natural conditions. To our knowledge, we present the first experimental demonstration that a free-ranging animal makes use of smell to maintain an aromatic environment for offspring with plants, supporting predictions of the nest protection hypothesis.     

Blue tits (Cyanistes caeruleus) respond to an experimental change in the aromatic plant odour composition of their nest

Although the use of olfaction by birds is now widely recognised, the olfactory abilities of passerine birds remain poorly explored, for historical reasons. Several studies however suggest that passerines can perceive volatile compounds in several biologically relevant contexts. In Corsica, recent findings suggest that cavity-nesting blue tits may use volatile compounds in the context of nest building and maintenance. Although they build their nests mainly from moss, female blue tits also frequently incorporate fragments of several species of aromatic plants in the nest cup. In field experiments, breeding female blue tits altered their nest maintenance behaviour in response to experimental addition of aromatic plants in their nest. In aviary experiments, captive male blue tits could be trained to detect lavender odour from a distance. Here I report results from a field study aimed to test whether adult blue tits altered their chick-feeding behaviour after an experimental change in nest odour composition. I experimentally added fragments of aromatic plant species that differed from those brought in the nests before the start of the experiment in a set of experimental nests and added moss, the basic nest material, in a set of control nests. Both male and female blue tits hesitated significantly longer entering the nest cavity after addition of new aromatic plant fragments, as compared to moss addition. This response was especially observed during the first visit following the experimental change in nest plant composition. Nest composition treatment had no effect on the time spent in the nest. This study demonstrates that free-ranging blue tits detect changes in nest odour from outside the nest cavity.     

On the origin and rarity of interspecific nest parasitism in birds

Interspecific nest parasitism is surprisingly rare in birds given the potential advantages for the parasite of exploiting the parental care of other species. One possibility is that chicks will not thrive with the parental care and food of heterospecifics. I simulated parasitism in nonparasitic congeners by switching eggs between nests of three species of titmice (great tit Parus major, blue tit Parus caeruleus, and coal tit Parus ater). The experiment showed that compatibility of parental care was not a constraint preventing parasitism. I also used the model system to compare fitness consequences of inter- and intraspecific nest parasitism, addressing the problem of which form is ancestral. Fledging success (body mass, survival) was higher when an egg was added to the nest of a smaller species than to the nest of a conspecific and also higher when the parasitic chick hatched early rather than late relative to host chicks. This suggests that interspecific nest parasitism may not require a stage of intraspecific nest parasitism before evolving but may start from a larger species directly exploiting the parental care of a smaller species or a species with shorter incubation period directly exploiting a species with longer incubation period.     

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.     

Effect of the blood-sucking mite

Pathological consequences of the blood-sucking mite Ornithonyssus bursa vary between species, with its impact ranging from no measurable effect, to significant blood loss and chick mortality. In New Zealand, where several bird species are known to be parasitised by O.bursa, the effect of this mite on host fitness is unclear, as few studies have been carried out. During a three-year study of the North Island robin Petroica longipes on Tiritiri Matangi Island, the prevalence of O. bursa in robin nests and on chicks and its impact on robin chick growth and survival was measured. The presence of mites was correlated with both time of the season and humidity of the habitat, with infestation being positively correlated with later nesting attempts and more humid microclimates. Robin chicks in infested nests were significantly smaller and fledged at an earlier age than chicks in nests where no mites were detected. Despite this effect, no significant difference in body size or survival was detected between the two groups at one month post-fledging. This was most likely because chicks from mite- infested nests compensated for their retarded growth once they left the nest environment. On mainland New Zealand, where ground-dwelling mammalian predators are present, chicks forced to leave the nest at an earlier age with less developed flying skills may be at an increased risk of predation.     

Nest excavation does not reduce harmful effects of ectoparasitism: an experiment with a woodpecker, the northern flicker Colaptes auratus

It has been hypothesized that it is adaptive for birds to build new nests annually in order to avoid the accumulation of ectoparasites. Previous studies on costs of ectoparasitism have focused on cavity nesters in nestboxes while largely ignoring reproductive consequences in natural tree cavity nests, the context where nest selection strategies presumably evolved. To see whether ectoparasitism could be a driving selective force in the evolution of nest excavation in a woodpecker, I experimentally fumigated a subset of freshly excavated cavities and a subset of reused cavities of the northern flicker Colaptes auratus and compared reproductive performance with a set of control nests. The main ectoparasite of nestlings, a blood-sucking fly Carnus hemapterus , may have appeared one or two days earlier in reused nests but there was no difference between fresh and reused nests in intensities of flies one week post-hatching. Prevalence of parasitism reached 100% in both reused and freshly-excavated control nests in the second week. Nestlings from control nests had lower body mass residuals than those from fumigated nests after 15 d and fledged at a lower weight, suggesting that ectoparasitism by C. hemapterus was costly. However, fresh nest construction was no benefit, likely because the high dispersal ability of the ectoparasite meant all nests were colonized rapidly. Parents did not adjust provisioning effort according to parasitism as delivery rates did not differ between control and fumigated nests but delivery rates increased with brood size.     

EFFECT OF ECTOPARASITIC MITES ON SEXUAL SELECTION IN A SONORAN DESERT FRUIT FLY

We conducted a field study and a laboratory experiment to test whether ectoparasitic mites, Macrocheles subbadius, generate parasite-mediated sexual selection in the Sonoran desert endemic fruit fly, Drosophila nigrospiracula. Male flies gather on the outer surfaces of necrotic saguaro cacti where they engage in male–male competitive interactions and vigorous female-directed courtship. At these sites, operational sex ratios were significantly skewed toward males. The degree to which mites were aggregated among flies varied across the 25 fly populations sampled. The degree of mite aggregation across fly populations was strongly positively related to the mean number of mites per fly (intensity of infestation). Both the intensity and prevalence of infestation (fraction of flies infested) increased with the age of the cactus necrosis. Infested flies of both sexes were significantly less likely to be found in copula than uninfested flies, and mean intensity of infestation was significantly more pronounced in noncopulating than in copulating flies. The effect of attached mites on copulatory success exhibited dose-dependency, and this effect was more stringent in males: males or females with more than two and four mites, respectively, were never found in copula. The magnitude of parasite-mediated sexual selection was estimated for 12 fly populations by calculating selection differentials for each sex separately. The relation between intensity of infestation and magnitude of parasite-mediated sexual selection was stronger in males but significant for both sexes. We also assayed copulatory success of field-caught males in the laboratory, both during infestation and after experimental removal of mites. Males infested with two mites copulated less frequently than uninfested individuals, and in mating trials after mites had been removed, previously infested males copulated as many times as flies with no history of infestation. These findings, and the lack of difference in the number of mite-induced scars on copulating and single individuals in nature, strongly suggest that the reduced copulatory success of infested flies is attributable to an effect of mites per se, rather than to a character correlated with parasitism or previous parasite infestation.     

红火蚁工蚁受侵扰的行为反应强度与蚁巢大小和侵扰强度之间的关系研究

红火蚁Solenopsis invicta Buren的防御行为是其被认定为社会性昆虫的关键特征之一。红火蚁蚁巢受到侵扰时,工蚁会快速涌出搜寻侵扰物并展开攻击。然而,蚁巢受侵扰后工蚁的行为反应与蚁巢大小和侵扰强度之间的关系有待进一步明确。为此,本研究通过野外视频记录并结合室内统计分析的方法来明确不同大小的红火蚁蚁巢受侵扰后工蚁反侵扰行为的动态过程。结果表明,蚁巢大小和受侵扰强度对蚁巢受侵扰后工蚁的反应速度具有显著影响。同等侵扰强度下,与中、大型蚁巢相比,小型蚁巢的工蚁往往表现出更慢的行为反应。尤其在低侵扰强度时,小蚁巢工蚁的反应时间平均0.8 s,而中蚁巢和大蚁巢均仅为0.34 s。当侵扰强度相同时,蚁巢越大,受侵扰后召集工蚁的数量越多;当蚁巢大小相同时,侵扰强度越高,召集工蚁的数量越多。但无论是蚁巢大小还是侵扰强度的不同,红火蚁蚁巢受侵扰后,召集工蚁的数量到达峰值的时间均为30 s左右。研究结果为进一步了解红火蚁的防御行为,科学预防红火蚁的攻击,以及有效开展红火蚁的防治提供了重要的实验依据。     

High blowfly parasitic loads affect breeding success in a Mediterranean population of blue tits

The detrimental effects of ectoparasites on the breeding success of birds have been especially well demonstrated in the case of ectoparasites that affect both chicks and their parents. Since blowfly larvae of the genus Protocalliphora attack only nestling birds, they represent a good model for testing the consequences of parasitism on nestlings. A Corsican population of blue tit suffers extremely high rates of infestation by blowflies, which are suspected to negatively affect young birds. Comparing experimentally deparasitized (treated) and naturally infested (control) broods, we showed that the attack by Protocalliphora causes anaemia and an important disturbance to the chicks. Therefore, we expected that these effects would have a negative impact on body condition and survival in the infested broods. Although we did not find any effect of treatment on fledging success, our predictions were confirmed by lower growth rate, body mass at fledging and tarsus length at fledging in the control compared with the treated group. This suggests that in this population, blowflies decrease the probability of recruitment of young blue tits. Received: 6 May 1997 / Accepted: 14 July 1997