Tit Species Research Articles

Individual consistency of hissing displays across night and day in a free-living female songbird

Birds have evolved a variety of antipredator strategies, which have been extensively studied during day-time. Yet, how diurnal birds directly respond to nocturnal predation threats remains largely elusive, despite that predation risk can be high during both night- and day-time. One form of antipredator behaviour found in several tit species when confronted with a predator at the nest is the hissing display. As for many forms of antipredator behaviour, studies on hissing displays have so far focussed on the day-time. Here, we exposed cavity-nesting free-living female great tits (Parus major) to simulated predator intrusions inside their nest box during both night- and day-time. We showed that 28 % of females uttered at least one hissing call during night-time, while the occurrence of hissing calls was higher during day-time (84 %). Hissing females at night, compared to non-hissing females, produced more hissing calls during day-time, providing evidence for individual cross-context consistency. Night-time hissing behaviour did not predict lay date, clutch size, breeding or nest success, indicating the absence of consequences in terms of current reproduction. Together, we reveal the hitherto undescribed occurrence of hissing displays at night in a cavity-nesting bird, while simultaneously strengthening the evidence for the existence of hissing behavioural types.

Nest structure and breeding success in two tit species: a long-term study

AbstractOne of the most critical functions of nests in parids is thermal insulation, particularly during egg incubation by females and during the first week of the hatchlings’ life when they are poikilothermic. Several avian studies reported associations between aspects of breeding success and nest parameters. In this study, we present results regarding long-term (eleven breeding seasons) impact of nest parameters on breeding characteristics in Great Tits (Parus major) and Eurasian Blue Tits (Cyanistes caeruleus) in a deciduous forest and an urban parkland study area. Our findings indicate that in Great Tits and Eurasian Blue Tits the number of fledglings (and in Eurasian Blue Tits also clutch size tended to be) was positively associated with lining mass and was influenced by the study area, with higher values observed in the forest. Additionally, there was a relationship between lining mass and higher hatching success in both tit species. We also demonstrated that both clutch size and number of fledglings were higher in Great Tits in the forest and in Eurasian Blue Tits the number of fledglings was higher in the forest. The study site also impacted hatching success, with Great Tits showing higher rates in the forest, and fledging success for Eurasian Blue Tits being higher in the forest. The number of fledglings differed between years in Great Tits and hatching success and fledging success differed between years in both Great and Eurasian Blue Tit species. We conclude that avian nests play an important role during reproduction, and the materials used to construct nests contribute to various functional properties. However, further studies are needed to establish clear relationships between nest parameters and breeding performance.

The influence of climate change on brood size and breeding time in three tit species in Sweden, 1962–2019

Climate change is expected to affect many biological systems, including the timing of seasonal events such as breeding in birds. In this study, I investigated how brood size and timing of reproduction (measured as median date for ringing of broods) changed for three tit species in Sweden 1962–2019 using data reported to the Swedish Bird Ringing Centre. The brood size for the Coal Tit Periparus ater increased from 7.74 between 1962–2001 to 7.98 young between 2002–2019, while no change was detected for Crested Tit Lophophanes cristatus or Willow Tit Poecile montanus. The largest biological effects were seen for timing of reproduction, with Coal Tits and the Crested Tits initiating breeding about seven days earlier at the end of the study period compared to the 1960s. The Willow Tit data also suggested earlier breeding, but only by about two days across the study period.

Nestling Diet of Two Sympatric Insectivorous Passerines in Different Habitats—A Metabarcoding Study

Increasing landscape transformations and urbanisation affect insectivorous bird populations in various ways such as food availability, breeding phenology, or reproductive success. Especially during the breeding season, many passerine birds rely on the availability of caterpillars as the main prey for their nestlings. Previous studies suggested that similar diet preferences of sympatric species may result in interspecific competition, as demonstrated for Blue and Great Tits in forest habitats. However, nestling diet and prey preferences in other habitats are not fully understood. Prey availability, especially caterpillars, is lower in cities than in forests, thus influencing prey choice and interspecific competition. Here we used faecal DNA metabarcoding to investigate if nestling diet composition of the two sympatric species Blue Cyanistes caeruleus and Great Tits Parus major varied among species and different habitats (forest, traditional orchards, and urban parks). Furthermore, we examined food availability by DNA barcoding of the arboreal arthropod communities among habitats and compared them to the nestling diet to infer parental prey selectivity. The study was carried out in central Germany from 2018 to 2019. Blue and Great Tits showed a diverse diet which was dominated by Lepidoptera in all habitats. Lepidopteran diet components were most similar between forest and orchard sites, as were the components with other arthropods between orchard and urban sites. Both tit species showed selectivity for the lepidopteran families Geometridae and Tortricidae in all habitats, and for Noctuidae (Lepidoptera), Tenthredinidae and Braconidae (Hymenoptera) in forest and orchard sites. As the tits showed preferences for mainly families of Lepidoptera, and Hymenoptera, our approach provides a baseline to support monitoring of these groups.

The intensity of forest management affects the nest cavity production of woodpeckers and tits in mature boreal forests

Cavities made by birds are an important microhabitat for many taxa in forests. Long-term dynamics of cavity patterns and the effect of forest management on cavities are, however, largely unknown. We studied cavity production, measured as nest cavity production rates (CPR = no. of new cavities/km2/year), of woodpeckers and tits in forests with different management intensity in southern Finland, based on a data from 37 years. Forests were divided into managed, seminatural and natural stands. The data covered 56 forest stands with the total area of 1690 ha. Stands were inventoried annually for new cavities. The total numbers of woodpecker and tit cavities were 2238 and 329, respectively. There were large differences in CPRs between forest stands with different management intensity. For woodpeckers, the CPR was highest in natural forests (5.7) and lowest in managed forests (1.5). For the tit species, the respective numbers were 0.9 and 0.3. The CPRs of different cavity-making bird species and cavity tree characteristics (e.g. tree condition and species) were consistent, suggesting that different cavity-makers benefit from similar forest and tree characteristics. The results also suggest that forests managed with currently prevailing methods limit the production of cavities. To promote cavities, the results from this and other studies suggest that managed forests should include more features of natural forests, such as more diverse tree species and within-stand structural variability distribution (tree-level heterogeneity), larger amount of decayed wood, more retention trees and snags and longer rotation periods.

Nest Box Bacterial Loads Are Affected by Cavity Use by Secondary Hole Nesters.

Among the environmental factors that affect bird nesting in nest boxes, the influence of microbial communities is relatively poorly understood. In this study, nest boxes used for breeding by secondary cavity nesters were sampled before the start of the breeding season to assess the bacterial loads of the nest box in relation to their previous year status. Different parts of the wooden nest box offer variable conditions for the development of bacteria. During the breeding season, the nest box entrance hole is wiped out by birds, delivering bacteria to their bodies, but during winter, it is exposed to unfavourable external conditions. The interior of the nest box, in turn, is also wiped by birds, but the conditions during winter are more stable there. Therefore, samples from the entrance hole and the interior of the nest box were taken at two different study sites: an urban parkland and a natural forest. We predicted that both the occupancy of the nest boxes during the previous breeding season by birds and the nesting sites would influence the bacterial load of the nest box. To verify this prediction, two categories of nest boxes were sampled at both study sites: nest boxes occupied by any of the two tit species (Great Tit or Blue Tit) in the previous season for breeding and nest boxes that had remained empty that year. The interior bacterial load of the nest box was higher in the nest boxes occupied in the previous breeding season, but only in the forest area. Furthermore, the bacterial load of both the entrance hole of the nest box and the interior was significantly higher in the forest study area in both occupied and unoccupied nest boxes. Our results show that the bacterial load of the nest box is positively related to the presence of nests in the previous breeding season and can vary between different sites.

Nest size parameters of Great Tits and Blue Tits: a long-term study

Nest construction behaviour is widespread among bird species. Causes for the occurrence and great variation in nest characteristics between and within populations are still poorly understood. In this study, we present results concerning nest parameters of Great Tits Parus major and Blue Tits Cyanistes caeruleus over a period of 11 breeding seasons (2012–2022) in two structurally and floristically contrasting study areas in central Poland. The nest depth differed significantly between young (yearlings) and older females (≥ 2 years after hatching) in Blue Tits (but not in Great Tits): younger females tended to build deeper nests. The size and mass of the nest were very variable in both tit species. Blue Tits tended to build deeper and heavier nests than Great Tits. The depth of the nest was positively correlated with nest mass in Great and Blue Tits. In Great Tits, the nest mass (but not nest depth) differed between study sites, with nests being heavier in the forest and the nest depth differed between years; in Blue Tits, there was an interaction between year and study site that affected nest depth. The nest mass (but not depth) from the same nestbox tended to be consistently similar within species in Great Tits and Blue Tits. We argue that the large amount of variation in nest parameters between and within populations of both tit species may be a multi-factorial result of female age, breeding area, breeding season, individual predispositions and the size of the nestbox/natural hole.

Eggshell spots are an important cue for the egg retrieval behavior in two tit species.

It is a common occurrence for incubating female ground- or cavity-nesting birds to accidentally roll their own eggs out of the nest cup. To correctly roll eggs that are not in the nest cup back to the nest, birds must be able to discriminate between their eggs and things around their nests that could be easily confused for their eggs (e.g., egg-shaped stones or other birds' eggs). Moreover, there may be a strong interaction between egg retrieval and egg rejection behaviors in the context of avian brood parasitism where recognition and rejection of alien eggs is an effective means for hosts to defend against cuckoo parasitism. It has been shown that green-backed tits (Parus monticolus) and Japanese tits (P. minor) in China have strong egg recognition ability and are able to reject nonmimetic eggs in the nest. Eggshell spots play an essential role in the egg rejection behavior of these two tit hosts. This study investigated the egg retrieval behavior of green-backed tits and Japanese tits by adding one experimental egg to the nest corner to explore whether eggshell spots also play a role in the process of egg retrieval. The results revealed significant differences in the retrieval rates of white-rumped munia (Lonchura striata) eggs painted with spots, Japanese tits' own true eggs, and unpainted, pure white-white-rumped munia eggs. The retrieval rate of white-white-rumped munia eggs was significantly lower than that of spotted white-rumped munia eggs and Japanese tits' own spotted eggs. For green-backed tits, the retrieval rate of spotted white-rumped munia eggs in the nest corner was significantly higher than that of pure white-white-rumped munia eggs, while the rejection rate of spotted white-rumped munia eggs was significantly lower than that of pure white-white-rumped munia eggs. These findings indicate that eggshell spots play a key role in the egg retrieval of green-backed tits and Japanese tits.

Host specificity of passerine Lankesterella (Apicomplexa: Coccidia)

Lankesterella parasites are blood coccidians that have recently gained attention as their records in common passerine species emerge. To date, their occurrence has been molecularly confirmed in several passerine genera, mainly among members of the families Paridae and Acrocephalidae. Despite their relatively high prevalence in some host populations, their life cycles remain unclear, mosquitoes or mites being the proposed vectors. The aim of this study was to reveal Lankesterella host specificity, focusing mainly on parasites of tit and warbler species (families Paridae and Acrocephalidae). We have determined the 18S rRNA gene sequences of Lankesterella from 35 individuals belonging to eight different host species. Phylogenetic analysis revealed that passerine Lankesterella are host-specific, with specificity at the host genus or species level. Besides Lankesterella, Isospora sequences were obtained from avian blood as well, pointing out the need for barcoding.

Annual captures and low apparent survival rates in two tit species in western Hungary

AbstractAdult and juvenile survival are important factors affecting the population dynamics of small passerines. Understanding variation in the population dynamics and survival rates is critical for ecological studies and nature conservation. The aim of this study was to investigate the annual capture-recapture, apparent survival and capture probabilities of the Blue TitCyanistes caeruleusand the Great TitParus majoroccurring in western Hungary. Data from 8,628 Blue Tits and 7,727 Great Tits came from a constant-effort ringing scheme, using three ringing periods, spanning 24 years (1998 to 2021). The annual captures did not show a significant linear trend from 1998 to 2021 in the study site for both tit species. The temporal variation of annual captures and the annual capture-recapture proportions of different ages and sexes of the tit species were similar. This indicated that the migration strategies of these two partial migrant species did not differ significantly. According to the best standard Cormack-Jolly-Seber model, apparent survival of first-year birds was lower than that for adults. The CJS model selection for the dataset indicated that the time and sex had no effect on apparent survival probabilities for both tit species. Capture probability in the juvenile groups was not significantly higher than that in the adult groups for both species.

Season does not influence the response of great tits (Parus major) to allopatric mobbing calls

Many species of birds emit mobbing calls to recruit prey to join mobbing events. This anti-predator strategy often involves several species and, therefore, implies heterospecific communication. Some species of tit exhibit a sensitivity to allopatric mobbing calls, suggesting that heterospecific recognition is based on an innate component. To date, however, we have no information on whether the perception of allopatric calls varies with season, despite seasonality playing an important role in the perception of heterospecific call in some species. In this study, I investigate the responses of European great tits (Parus major) to the calls of a North American bird species, the black-capped chickadee (Poecile atricapillus), during two seasons: spring and in autumn (breeding and non-breeding seasons, respectively). Great tits approached the sound source during both seasons, with no significant difference in response between seasons. These findings indicate that season does not influence the response of birds to allopatric calls, and will help to shed light on the evolution of interspecific communication.

Graded‐risk sensitivity in northern European mixed‐species flocks of tit and nuthatch species

AbstractAvian species often use anti‐predator calls such that the costs and benefits of vigilance are distributed within the group. Some species respond differentially to graded risk by attending to relevant predator cues, such as head orientation and gaze direction. One benefit of graded‐risk sensitivity is fewer missed foraging opportunities. It is not known how the makeup of risk response behaviors in mixed‐species flocks may relate to the relative nuclearity of each species in the flock. In the current study, predator models were presented to two nuclear and two satellite species of passerines that frequently occur in natural mixed flocks. Predator models either faced toward or away from a nearby stocked feeder to simulate high and low risk of predation, and calling and seed‐taking rates of the present flock were recorded. The nuclear species, great tits (Parus major) and crested tits (Lophophanes cristatus), took more seeds when the predator faced away from the feeder than toward it. The satellite species, Eurasian nuthatches (Sitta europaea) and willow tits (Poecile montanus), did not show an effect of predator orientation. No species showed consistent differences in calling behavior relative to predator orientation, although insufficient calling data for great tits prevented analysis for this species. The results of this study suggest that one aspect of nuclearity in mixed‐species flocks is a tendency for graded‐risk sensitivity, or alternatively, that satellite species are more sensitive to mere predator presence rather than to predator orientation cues.

Year-round multi-scale habitat selection by Crested Tit (Lophophanes cristatus) in lowland mixed forests (northern Italy)

Determining how animals respond to resource availability across spatial and temporal extents is crucial to understand ecological processes underpinning habitat selection. Here, we used a multi-scale approach to study the year-round habitat selection of the Crested Tit (Lophophanes cristatus) in a semi-natural lowland woodland of northern Italy, analysing different habitat features at each scale. We performed Crested Tit censuses at three different spatial scales. At the macrohabitat scale, we used geolocalized observations of individuals to compute Manly's habitat selection index, based on a detailed land-use map of the study area. At the microhabitat scale, the trees features were compared between presence and absence locations. At the foraging habitat scale, individual foraging birds and their specific position on trees were recorded using focal animal sampling. Censuses were performed during both the breeding (March to May) and wintering (December to January) seasons. At the macrohabitat scale, the Crested Tits significantly selected pure and mixed pine forests and avoided woods of alien plant species, farmlands and urban areas. At the microhabitat scale, old pine woods with dense cover were selected, with no significant difference in the features of tree selection between the two phenological phases. At the foraging habitat scale, the species was observed spending more time foraging in the canopies than in the understorey, using mostly the portion of Scots Pine (Pinus sylvestris) canopies closer to the trunk in winter, while during the breeding period, the whole canopy was visited. Overall, breeding and wintering habitats largely overlapped in the Crested Tit. Based on our findings, lowland Crested Tits can be well defined as true habitat specialists: they are strictly related to some specific coniferous woodland features. Noteworthily, compared to other tit species, which normally show generalist habits during winter, the Crested Tit behaves as a habitat specialist also out of the breeding season. Our study stressed the importance of considering multi-scale (both spatial and phenological) habitat selection in birds.

Sharing detection heterogeneity information among species in community models of occupancy and abundance can strengthen inference.

The estimation of abundance and distribution and factors governing patterns in these parameters is central to the field of ecology. The continued development of hierarchical models that best utilize available information to inform these processes is a key goal of quantitative ecologists. However, much remains to be learned about simultaneously modeling true abundance, presence, and trajectories of ecological communities.Simultaneous modeling of the population dynamics of multiple species provides an interesting mechanism to examine patterns in community processes and, as we emphasize herein, to improve species‐specific estimates by leveraging detection information among species. Here, we demonstrate a simple but effective approach to share information about observation parameters among species in hierarchical community abundance and occupancy models, where we use shared random effects among species to account for spatiotemporal heterogeneity in detection probability.We demonstrate the efficacy of our modeling approach using simulated abundance data, where we recover well our simulated parameters using N‐mixture models. Our approach substantially increases precision in estimates of abundance compared with models that do not share detection information among species. We then expand this model and apply it to repeated detection/non‐detection data collected on six species of tits (Paridae) breeding at 119 1 km2 sampling sites across a P. montanus hybrid zone in northern Switzerland (2004–2020). We find strong impacts of forest cover and elevation on population persistence and colonization in all species. We also demonstrate evidence for interspecific competition on population persistence and colonization probabilities, where the presence of marsh tits reduces population persistence and colonization probability of sympatric willow tits, potentially decreasing gene flow among willow tit subspecies.While conceptually simple, our results have important implications for the future modeling of population abundance, colonization, persistence, and trajectories in community frameworks. We suggest potential extensions of our modeling in this paper and discuss how leveraging data from multiple species can improve model performance and sharpen ecological inference.

Biological conclusions about importance of order in mobbing calls vary with the reproductive context in Great Tits (Parus major)

Currently, there is considerable debate surrounding the presence of some human language‐specific characteristics in non‐human animals, such as the use of compositional syntax (i.e. meaning of a sequence determined both by meaning of its individual parts and in the way they are combined). Compositional syntax has been investigated in mobbing calls of two closely related tit species, the Japanese Tit Parus minor and the Great Tit Parus major, but with one contrasting result: hearing calls in the reversed order diminished the behavioural responses of Japanese Tits but only partially those of Great Tits. This difference may have been due to an external factor such as the season in which the experiment was undertaken, as the Japanese Tits were tested in winter and Great Tits in spring. Here, we studied the responses of Great Tits towards natural and reversed mobbing sequences during spring and winter by investigating two behaviours: approaching and vigilance behaviours. We found that sensitivity to syntax reversal was impacted by the season. The birds were vigilant but less likely to approach reversed calls in winter. However, the opposite occurred in spring, with the birds scanning less but still approaching. This study suggests that the perception of combinatorial calls in Great Tits is influenced by the season, emphasizing the importance of context in studies investigating complex cognitive processing in animals.

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.

Enhancing ecosystem services in apple orchards: Nest boxes increase pest control by insectivorous birds

Abstract Ecological intensification in croplands aims to enhance biodiversity‐based ecosystem services, helping to increase yield while reducing agricultural environmental impacts. Identifying ecological intensification tools of wide applicability and easily implemented by farmers is, therefore, an imperative. Here, we verify the efficiency of provisioning artificial nest boxes for insectivorous birds to reinforce pest biological control in apple orchards. The study was conducted in 24 cider‐apple orchards in Asturias (NW Spain) over 3 years. We compared the effect of insectivorous birds between orchards with and without nest boxes occupied by different bird species, through insectivory estimates based on attack on a sentinel pest and measurements of arthropod abundance in apple trees. We also identified preys that birds of different species captured to feed nestlings. Bird occupancy of nest boxes was widespread, ranging 25.0%–33.3% each year. Great tit was the dominant species, followed by blue tit and, occasionally, common redstart. Predation pressure on apple pests increased in orchards with nest boxes, as judged by the increased proportion of sentinel models attacked by birds (34.9% increase in 2018 and 41.1% in 2019), decreased biomass of tree‐dwelling arthropods (−51.7%) and reduced probability of apple pest occurrence (from 57% to 40%), compared to orchards without nest boxes. Nesting species showed different predatory roles in apple orchards. Fewer attacks on sentinel pests but lower arthropod biomass was associated with blue tit rather than great tit. Besides, blue tit fed nestlings at a faster rate and included in their diet a higher proportion of apple pests than great tit, which preyed mostly on other herbivorous insects. Synthesis and applications. We demonstrated the usefulness of nest boxes for insectivorous birds in enhancing biological control of apple pests at a regional scale, identifying tit species as complementary predators of apple pests and herbivores. From the farmers' perspective, providing nest boxes in orchards may represent an efficient, easy to implement, cheap and attractive measure of ecological intensification, compatible with other actions fostering biodiversity in croplands.

Three Decades of Crimes and Misdemeanours in the Nest Box Life of European Pied Flycatchers Ficedula hypoleuca

Pied Flycatchers Ficedula hypoleuca are known to be victims of nest killings in contexts of competition for nest boxes. However, there is only anecdotal information on their opposite role as perpetrators of nest takeovers and occasional killings of other songbirds. Over 31 years we examined whether competition with Great Tits Parus major over nest box ownership is a significant source of mortality for Pied Flycatchers and whether the increase in Pied Flycatcher populations affected the use of nest boxes by the smallest tit species, the Blue Tit Cyanistes caeruleus and Coal Tit Periparus ater, in two forests in the central Iberian Mountain Range. We found 31 Pied Flycatchers killed inside nest boxes. The Great Tit was the most frequent species to which the killings were attributed. Followed by Pied Flycatchers themselves and Nuthatches Sitta europaea. We confirmed the killing by Pied Flycatchers of at least two conspecific males and one incubating female Coal Tit, with one killer male identified. Large increases in population densities of flycatchers after nest box deployment in the two study areas seem to have triggered an intensification of agonistic interactions among their potential occupants, resulting in an increase of takeovers by Pied Flycatchers of nest boxes initially owned by the smallest tit species. Great Tits are not a serious threat for Pied Flycatchers breeding in the study area, most likely due to their preference for natural holes over the nest box types most frequently installed. The interactions of Pied Flycatchers with Blue and Coal Tits for the ownership of nest boxes do not seem to cause significant mortality in the species involved. However, aggressive usurpations of nest boxes by Pied Flycatchers surely have negative impacts on the reproductive success of the victims through their eviction from suitable nesting sites.—Potti, J., Camacho, C., Canal, D. & Martínez-Padilla, J. (2021). Three decades of crimes and misdemeanours in the nest box life of European Pied Flycatchers Ficedula hypoleuca. Ardeola, 68: 315-333.

Differences in use of bryophyte species in tit nests between two contrasting habitats: an urban park and a forest

A considerable number of avian species tend to use bryophytes as nest construction material, but the selectivity of birds in their bryophyte use in nest construction in relation to the availability of particular mosses in individual territories remains largely unexplored. We studied the bryophyte composition of nests in two passerine species: the Blue Tit Cyanistes caeruleus and the Great Tit Parus major in two floristically and structurally contrasting study areas (a mature deciduous forest and an urban parkland). We also studied territories within a radius of 10 m from each occupied nest box, listing all bryophyte species and checking to what extent the moss composition of the nest reflected what was available in the surrounding of the nest box. Both tit species appeared to be selective. The tits used a total of 31 bryophyte species in their nests (27 found in Blue Tits and 19 in Great Tits), whereas 25 additional bryophyte species were found around (10 m radius) the studied nests, but not in the nests. The number of bryophyte species found in individual nests varied in the urban parkland between 1 and 6 and in the forest between 1 and 11. The average number of bryophytes in the nest ranged from 2.31 in Great Tit from the urban parkland to 3.52 in Blue Tit in the urban parkland. Only a few species were used in a higher proportion than 5% of the volume within a single nest and, considering only these most abundant bryophyte species, the mean number ranged from 1.28 in Great Tits in the forest to 1.57 in Blue Tits in the urban parkland. Our study also showed that, in general, the bryophyte species composition of the nests seems to be affected by the site (the urban park vs the forest) rather than the parid species (Blue Tit vs Great Tit).

Perfluoroalkyl acid (PFAA) profile and concentrations in two co-occurring tit species: distinct differences indicate non-generalizable results across passerines

Eggs of terrestrial bird species have often been used to biomonitor both legacy and emerging anthropogenic contaminants, such as perfluoroalkyl acids (PFAAs). However, few, if any, studies have examined whether results obtained in a given model species can be generalized across bird species. Therefore, we compared potential differences in egg PFAA profile and concentrations between two widely studied passerine species, great tit (Parus major) and blue tit (Cyanistes caeruleus), which are similar in many aspects of their ecology and life history. Whole clutches of both species were collected from the same breeding season and at the same place (Antwerp, Belgium), enabling us to study laying order effects. Additionally, we evaluated how egg PFAA concentrations for both species changed along a distance gradient from a PFAA point source. Although the sum PFAA concentrations did not significantly differ between great tits and blue tits, large differences in PFAA profile and laying order effects were observed. Great tits showed a more diverse PFAA detection profile, including perfluorooctane sulfonic acid (PFOS) and various long-chain perfluorocarboxylic acids (PFCAs) but no short-chain compounds. Contrarily, short-chain PFCAs (perfluorobutanoic acid (PFBA) and perfluorohexanoic acid (PFHxA)) were only detected in blue tit eggs. The variation of perfluorooctanoic acid (PFOA) concentrations within clutches was large in both species, although laying order effects on PFOA concentrations were only found in blue tits. Although egg PFOA concentrations of both species decreased similarly from the fluorochemical point source onwards, more variation in egg PFOA concentrations could be explained by distance from the fluorochemical plant in great tits (60%) than in blue tits (15%). Results showed that both species markedly differed in terms of egg PFAA profile and concentrations, most likely reflecting differences in diet, foraging habits and egg protein composition. Finally, biomonitoring results of PFAAs in eggs are likely not generalizable across bird species.