Nuthatches (Sitta europaea: Aves) in forest fragments: demography of a patchy population

Breeding density, local survival and summer recruitment of nuthatches were evaluated in a population scattered over many small (1–30 ha) forest fragments, and compared with study plots inside larger forests. Since most young birds settle outside the fragment in which they were born this population corresponds to the “patchy population” concept implying that patterns in abundance may be better explained by processes at the population level than by metapopulation processes. Mean breeding density was c. 50% lower in fragments and decreased with regional isolation (distance from larger forests) but not with local isolation (distance to nearby fragments). Local survival of adults and established (i.e. territorial) 1st-year birds was not related to forest size or isolation. However, fewer young birds settled in summer in the fragments compared with a large forest. This difference probably reflects high mortality during the sensitive dispersal phase. Moreover, the observed number of recruits and their estimated survival was insufficient to maintain the breeding population, suggesting significant net immigration from larger forests. This “rescue effect” explains why densities are affected by regional, but not local isolation. Received: 14 December 1998 / Accepted: 1 March 1999     

Habitat fragmentation influences nestling growth in Mediterranean blue and great tits

In patchy forest areas, the size of the forest patch where birds breed has a strong influence on their breeding success. However, the proximate effects contributing to lowering the breeding success in small forest patches remain unclear; and a shortage of crucial resources in those forest patches has been suggested to account in some degree for this failure. With the aim to further investigate this issue, we have monitored the breeding cycle of blue and great tits in three ‘large’ forest patches (ranging between 26.5 and 29.6 ha) and twelve ‘small’ forest patches (ranging between 1.1 and 2.1 ha) in a Mediterranean area in central Spain, during three years (2011–2013). We also recorded the nestling diet inside the nest-boxes with the aid of handy-cams. Only males significantly differed between forest patch size categories; being on average younger and with better body condition in small patches for great and blue tits respectively. Reproductive traits did not vary between forest patch size categories, but the body condition of blue tit nestlings and the size of great tit nestlings did, being significantly better and larger respectively in large forest patches. The recruitment rate of blue tit nestlings was also higher in large patches. Regarding nestling diet, blue tits did not differ but great tits did, delivering a larger amount of caterpillars in large forest patches. Most variation in the reproductive traits occurred between years, probably due to annual differences in environmental conditions. This study suggests that food supply could be limiting the breeding success of birds above all in small patches, but also in large patches under particular environmental conditions.     

Behavioural responses to changing landscapes: flock structure and anti-predator strategies of tits wintering in fragmented forests

We analysed the effects of forest fragmentation on the flock structure of insectivorous forest passerines (Parus, Aegithalos, Certhia, Regulus, etc.), and on the anti‐predator behaviour and energy management of blue tits in these flocks. We surveyed flocks in Central Spain during two winters. Flocks in fragments comprised fewer individuals and species than flocks in unfragmented forests. The most abundant species in forest flocks (blue tit, Parus caeruleus, and firecrest, Regulus ignicapillus) were also the most abundant in fragments, while the rarest species in the area never occurred in small woodlots. We investigated how fragmentation and related changes in flock structure affect anti‐predator behaviour of blue tits, a widely distributed species in the area. In fragments but not in forests, blue tits increased scanning rates with decreasing flock size. Vigilance was relaxed when great tits, Parus major, were abundant as flock mates, suggesting that the absence of this dominant species in fragments could intensify anti‐predator behaviour of blue tits. Blue tits enhanced anti‐predator behaviour in the second winter parallel to an increase in the abundance of raptors. This behavioural change was stronger in fragments, where blue tits foraged deeper in the canopy and increased scanning and hopping rates. Under increased predation risk, birds are expected to reduce body mass to improve predator avoidance. On average, blue tits weighed similar in fragments and forests the second winter. However, they accumulated fat along the day in fragments only, and adjusted body mass to body size more closely in that habitat type. This suggests that blue tits perceived fragments as unpredictable habitats where fattening would help avoid starvation, but also as dangerous sites where overweight would further increase the risk of predation. In summary, our results support that fragmentation affects individual behaviour of blue tits, and show the potential of behavioural approaches to unravel how different species face the advancing fragmentation of their habitats.     

Indicators of habitat quality and the reproductive output of a forest songbird in small and large fragments

The distribution of individuals among habitats that vary in quality (i.e. resource availability) may affect reproductive output at a population level. I compared indicators of habitat quality including the breeding experience ratios (inexperienced:experienced birds), turnover rates, pairing success, and densities of a forest songbird, the Eastern Yellow Robin Eopsaltria australis , in two small, food-poor forest fragments, with those in two large, food-rich fragments. I then evaluated the likelihood that the breeding experience ratio affected the reproductive output of populations. Inexperienced males occurred in small fragments eight times as often as in large fragments. Male turnover rates were 1.5 times higher in the small than large fragments, and 20% (10/50) of the male population were unpaired in the small fragments compared to 0% (0/25) in the large. None of these measures differed significantly for females. Experienced birds of both sexes produced almost all of the offspring compared with inexperienced birds. Despite these findings, reproductive output did not vary with fragment size for robins. Thus, while breeding experience clearly influenced the reproductive success of individuals, there were no obvious population consequences of having disproportionately more inexperienced males in the small fragments. I conclude that while male traits may be good indicators of resource levels within fragments (specifically, food availability), they may not be adequate predictors of population performance. Thus, the reproductive output of populations must be measured directly before conclusions concerning population performance can be made. Interestingly, breeding densities were not accurate indicators of either resource levels or population performance. Densities were two times higher in the smaller fragments, and I suggest that this result reflects problems with male dispersal among fragments caused by isolation.     

Sea buckthorn berries Hippophae rhamnoides L. predict size and composition of a great tit population Parus major L

In seasonal environments variation in food abundance in the non‐breeding season is thought to affect songbird population dynamics. In a unique tit‐sea buckthorn berry system we can estimate the berry abundance and both the tit consumption and population dynamics. Six hundred nest boxes were available to great and blue tits Cyanistes caeruleus for breeding in spring and roosting in winter. We followed the dynamics including the recapture histories of individually marked great tits from 2008 to 2014. In each year we estimated 1) the winter sea buckthorn berry availability, 2) an index of berry consumption in December based on the colour of the faeces of roosting birds, 3) the number of breeding great and blue tits, 4) both recapture probability and the return rate of the great tits and 5) immigration rates. December berry abundance positively predicted the number of breeding pairs of both species in the subsequent season and great tit return rates in the second half of the winter. There was support for a sex specific berry effect on the adult return rate in the great tit: female return rate was associated less strongly to berry abundance than male return rate. This skewed the sex ratio of the local breeders in the following breeding season. Intriguingly, annual berry consumption in December was not related to berry abundance, and individuals consuming more berries tended to have slightly lower return rates. Reproductive rate was not related to berry abundance. There was hardly support for a relation between immigration rates of first year breeders and berry abundance. Taken together these results imply that berry stock not only affected population size but also the population composition through sex specific exchange with the surroundings. Since population density covaried with berry abundance, density dependent effects provide an alternative explanation for the patterns observed.     

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.     

Linking individual foraging behavior and population spatial distribution in patchy environments: a field example with Mediterranean blue tits

 In spite of recent theoretical interest, few field studies have addressed the links between individual behavioral decisions and population distribution. This work analyzes the foraging behavior of individuals and the spatial distribution of a population of blue tits (Parus caeruleus) just before the main breeding season, when blue tit foraging was not affected by central-place or flocking behaviors. The study was carried out in open holm oak Quercus ilex woodlands (dehesas) that are patchy for canopy-foraging birds because of the scattered arrangement of trees. Residence time on each tree was not correlated either with previous flight time or with prey abundance in trees. Flight distances between trees were larger than average distances estimated in random samples of holm oaks taken close to foraging birds. Trees were not selected by birds on the basis of their expected energy costs and rewards. Bird abundance was not related to food availability in trees or to tree size across dehesas. However, bird abundance was strongly correlated with tree density and with the availability of tree holes for nesting, to the extent that the proportion of tits matched the proportions of both tree abundance and hole abundance across study plots. Overall, neither the behavior of individuals nor the distribution of the population of blue tits corresponded with food resources, which appeared superabundant; instead, tits appeared to behave and be distributed according to the distribution of structural resources such as trees and tree holes for nesting. Received: 18 August 1996 / Accepted: 14 March 1997     

Spatial and temporal changes in bird assemblages in forest fragments in an eastern Amazonian savannah

We investigated the effects of forest fragmentation on bird assemblages in an Amazonian savannah landscape with forest fragments that have been isolated for more than 100 years. The study was conducted in areas surrounding the village of Alter do Chão (2°31′S, 55°00′W), Santarém, Brazil. Bird surveys and measurements of tree density were undertaken in 25 areas, with 19 plots in forest fragments of different sizes and six in an area of continuous forest. Data on forest‐fragment size, perimeter, and isolation were obtained from a georeferenced satellite image. Variation in number of bird species recorded per plot was not related to vegetation structure (tree density). The number of bird species recorded per plot increased significantly only with fragment area, but was not influenced by fragment shape or degree of isolation, even when considering species from the savannah matrix in the analysis. Fragments had fewer rare species. Multivariate ordination analyses (multiple dimensional scaling, [MDS]) indicated that bird species composition changed along a gradient from small to large forest fragments and continuous‐forest areas. In the Amazonian savannah landscapes of Alter do Chão, the organization and composition of bird assemblages in forest fragments are affected by local long‐term forest‐fragmentation processes. Differences in the number of bird species recorded per plot and assemblage composition between forest fragments and continuous forest were not influenced by forest structure, suggesting that the observed patterns in species composition result from the effects of fragmentation per se rather than from preexisting differences in vegetation structure between sites. Nevertheless, despite their long history of isolation, the forest fragments still preserve a large proportion (on average 80%) of the avifauna found in continuous‐forest areas. The fragments at Alter do Chão are surrounded by natural (rather than planted) grassland, with many trees in the savannah matrix and the landscape has vast areas covered by forest, which may have helped to ameliorate the influences of forest fragmentation.     

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.     

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.     

Repertoire Sharing and Song Similarity between Great Tit Males Decline with Distance between Forest Fragments

Birdsong can play a critical role in establishing a territory and finding a mate among individuals from local and foreign populations. Variation in birdsong among populations can be influenced by habitat fragmentation and might affect successful dispersal among habitat fragments. We studied variation in great tit song in a long‐term study population distributed over nine forest fragments. All individual males recorded had a known dispersal history within the fragmented forest habitat. We found spatial structure of declining song‐type sharing with distance, with a marked drop from an individual’s own forest fragment to another across a habitat gap. We also found decreasing song similarity among increasingly distant fragments in terms of temporal and spectral characteristics of shared song types. The change in acoustic structure was more gradual and seemed less affected by habitat discontinuity but also showed a tight correlation with dispersal index among forest fragments. Immigrant birds shared fewer song types with neighbouring birds that were born within the same forest fragment, but not less compared to birds born in another forest fragment within the study area. Our data provide detailed insight into the relationship between song differentiation and male dispersal and contribute to our understanding of the potential role of song in reproductive exchange and avian speciation. The fact that birds in small forest fragments shared more songs than birds in larger forest fragments confirms that song analysis has potential as a tool for conservation in rare species.     

Changes in patch features may exacerbate or compensate for the effect of habitat loss on forest bird populations

One and a half centuries after Darwin visited Chiloe Island, what he described as "…an island covered by one great forest…" has lost two-thirds of its forested areas. At this biodiversity hotspot, forest surface is becoming increasingly fragmented due to unregulated logging, clearing for pastures and replacement by exotic tree plantations. Decrease in patch size, increased isolation and "edge effects" can influence the persistence of forest species in remnant fragments. We assessed how these variables affect local density for six forest birds, chosen to include the most important seed dispersers (four species) and bird pollinators (two species, one of which acts also as seed disperser), plus the most common insectivore (Aphrastura spinicauda). Based on cue-count point surveys (8 points per fragment), we estimated bird densities for each species in 22 forest fragments of varying size, shape, isolation and internal-habitat structure (e.g. tree size and epiphyte cover). Bird densities varied with fragment connectivity (three species) and shape (three species), but none of the species was significantly affected by patch size. Satellite image analyses revealed that, from 1985 to 2008, forested area decreased by 8.8% and the remaining forest fragments became 16% smaller, 58-73% more isolated and 11-50% more regular. During that period, bird density estimates for the northern part of Chiloé (covering an area of 1214.75 km(2)) decreased for one species (elaenia), increased for another two (chucao and hummingbird) and did not vary for three (rayadito, thrust and blackbird). For the first three species, changes in patch features respectively exacerbated, balanced and overcame the effects of forest loss on bird population size (landscape-level abundance). Hence, changes in patch features can modulate the effect of habitat fragmentation on forest birds, suggesting that spatial planning (guided by spatially-explicit models) can be an effective tool to facilitate their conservation.     

Weak genetic structuring indicates ongoing gene flow across White-ruffed Manakin (<Emphasis Type="Italic">Corapipo altera</Emphasis>) populations in a highly fragmented Costa Rica landscape

We explored the effects of recent forest fragmentation on fine-scale patterns of population structuring and genetic diversity in populations of White-ruffed Manakins (Corapipo altera) inhabiting premontane forest fragments of varying size in southwestern Costa Rica. Habitat fragmentation is a major conservation concern for avian populations worldwide, but studies of the genetic effects of fragmentation on Neotropical birds are limited. We sampled 159 manakins from nine forest fragments of varying size within an 18 km radius, and genotyped these birds at 13 microsatellite loci. Bayesian clustering methods revealed that birds from all fragments comprised a single genetic population, and an MCMC approach showed that the fragments were likely to be at migration-drift equilibrium. F-statistics showed only modest levels of differentiation between forest fragments. We calculated allelic diversity indices for each fragment but found no correlation between genetic diversity and fragment size. These results suggest that manakins may retain substantial connectivity via inter-fragment dispersal despite habitat fragmentation.     

Using genetic diversity and mating system parameters estimated from genetic markers to determine strategies for the conservation of <Emphasis Type="Italic">Araucaria angustifolia</Emphasis> (Bert.) O. Kuntze (Araucariaceae)

In order to understand the impacts of forest fragmentation on Araucaria angustifolia populations, we evaluated the genetic diversity and mating system using SSR markers and open-pollinated seeds from four populations of varying sizes and spatial isolation, in and around one of the best-conserved Araucaria Forest remnants in Southern Brazil. The four population types of A. angustifolia include: (1) a continuous forest; (2) a physically isolated cluster located 2 km from the continuous forest; (3) an open population in a field located between the cluster and continuous forest; and (4) a fragment on a private property located 5 km from the cluster. Approximately 28 seeds were collected from ten reproductive trees in each population. We found higher amounts of alleles (113) and exclusive alleles (25) in the continuous forest than in the other populations. The multilocus paternity correlation was significantly higher and effective number of pollen donors was significantly lower in the private population, decreasing the diversity and consequently the variance effective size of families sampled from that population. However, despite its isolation from the other studied fragments, the private population had the second highest number of alleles as well as unique alleles from the other populations. Therefore, strategies for A. angustifolia conservation should focus not only on larger populations, such as those found in protected areas, but also include smaller and isolated fragments on private properties as these populations are able to maintain high levels of genetic diversity and functional connectivity between isolated stands across a landscape.     

Non-photoperiodic factors and timing of breeding in blue tits: impact of environmental and social influences in semi-natural conditions

The seasonal development of life-history traits is influenced by many environmental factors. The impact of photoperiodic and non-photoperiodic factors on nest building and egg laying has been rarely investigated in non-domesticated avian species for which long term field data sets are available. Former investigations showed that blue tits originating from geographically close populations in the Mediterranean region do not respond in the same way to photoperiodic factors in semi-natural outdoor conditions. Here we show experimentally that nest building and onset of egg laying in captive blue tits is also proximately influenced by non-photoperiodic factors, including aspects related to aviary characteristics and social interactions between birds of the two sexes originating from different local Mediterranean study populations. In two successive experiments, we show that (1) increasing the volume of the aviary advanced the egg laying period of one specific population by almost 1 month, and (2) crossing pairs of birds from different origins strongly reduced the nest building and egg laying behaviours. These results indicate that obtaining biologically relevant breeding results in captivity with wild birds requires the control and experimental manipulation of a wide array of complex environmental cues.     

The rise and fall of local populations of ortolan buntings Emberiza hortulana: importance of movements of adult males

Changes in population size of local populations of birds have usually been interpreted in relation to adult return rate and recruitment of young individuals after natal dispersal. Little is known about the importance of redistribution of adult individuals through breeding dispersal. The small Norwegian population of ortolan buntings Emberiza hortulana has a patchy distribution with about 30 long‐term local populations. During a period of general population decline (29% decrease over 7 years), the population trends of local populations (measured as number of males recorded) were highly variable, with some even increasing four‐fold. Comparisons of demographic parameters showed that adult immigration rate (i.e. dispersal of adult males) explained both yearly changes in male population size and population trends over the whole study period better than adult return rate or adult emigration rate, or a measure of recruitment of young males. Adult immigration rates and recruitment rates were correlated, suggesting that both young and adult males find the same places attractive. In the study area, adult sex ratio was strongly male‐biased, and immigration rate was higher when local sex ratio was less skewed. In addition, less skewed sex ratio was related to higher adult return rate and lower emigration rate. We found no relationships between measures of breeding success and population change. We suggest that conspecific attraction may explain the observed patterns. Some local populations may act as hot‐spots attracting adult males from other populations. Thus, local population changes need not reflect overall population growth rate, but may be a consequence of redistribution of adult birds.     

Adaptive inter-population differences in blue tit life-history traits on Corsica

Few studies of natural populations have investigated how phenotypic variation across populations relates to key factors in the environment and landscape structure. In the blue tits of southern France, inter-population differences in reproductive life-history traits (e.g. laying date and clutch size) are small, whatever the timing of maximum caterpillar availability, a key factor for offspring survival in tits. These small differences are attributed to gene flow between local populations occupying different habitat types. In contrast, in blue tits on the island of Corsica, we noted large differences in reproductive life-history traits between two populations, where each population is synchronized with the peak-date of caterpillar abundance. These occur over a short geographical distance (25km). Considering our study within a framework of long-term population studies in tits, our results support the hypothesis that different blue tit populations on Corsica show adaptive differences in life-history traits, and suggest that landscape structure at a small spatial scale can have profound effects on adaptive between-population differentiation in life-history traits that are closely linked with fitness.     

Experimental evidence for density dependence of reproduction in great tits

1. Density dependence of avian reproduction has often been analysed using correlations between annual mean reproductive output and population density. Experiments are necessary to prove that density is the cause of the observed patterns, but so far, three out of four experimental studies do not support a direct causal effect of density on reproduction.
2. This paper presents experimental evidence that reproductive decisions in great tits, Parus major L., are causally affected by breeding density. The breeding density of great tits was manipulated by providing nest-boxes at different densities in an ecologically homogeneous area.
3. Within years the densities in the high and low density plots differed approximately 8-fold. During the 11 years of the experiment, clutch size, nestling mass and the proportion of birds starting a second brood were all lower in the high density plot. In 5 years with equal breeding densities in both parts, clutch size did not differ between the plots. The patterns found were consistent with the density effects as predicted from the non-experimental data.     

Limited effect of anthropogenic habitat fragmentation on molecular diversity in a rain forest skink, Gnypetoscincus queenslandiae

To examine the effects of recent habitat fragmentation, we assayed genetic diversity in a rain forest endemic lizard, the prickly forest skink (Gnypetoscincus queenslandiae), from seven forest fragments and five sites in continuous forest on the Atherton tableland of northeastern Queensland, Australia. The rain forest in this region was fragmented by logging and clearing for dairy farms in the early 1900s and most forest fragments studied have been isolated for 50-80 years or nine to 12 skink generations. We genotyped 411 individuals at nine microsatellite DNA loci and found fewer alleles per locus in prickly forest skinks from small rain forest fragments and a lower ratio of allele number to allele size range in forest fragments than in continuous forest, indicative of a decrease in effective population size. In contrast, and as expected for populations with small neighbourhood sizes, neither heterozygosity nor variance in allele size differed between fragments and sites in continuous forests. Considering measures of among population differentiation, there was no increase in FST among fragments and a significant isolation by distance pattern was identified across all 12 sites. However, the relationship between genetic (FST) and geographical distance was significantly stronger for continuous forest sites than for fragments, consistent with disruption of gene flow among the latter. The observed changes in genetic diversity within and among populations are small, but in the direction predicted by the theory of genetic erosion in recently fragmented populations. The results also illustrate the inherent difficulty in detecting genetic consequences of recent habitat fragmentation, even in genetically variable species, and especially when effective population size and dispersal rates are low.     

Sex ratio of Parus major and P. caeruleus broods depends on parental condition and habitat quality

Brood sex ratio was studied in 88 families of Parus caeruleus (blue tit) and 95 families of P. major (great tit) in deciduous and mixed forest habitats differing in food availability. As a food specialist, the blue tit is expected to be more sensitive to the nutritional differences between the habitats than a food generalist such as the great tit. A shift of brood sex ratio towards males was detected for great tits in the high quality habitat, but there was no significant impact of parental condition or the number of nestlings. In contrast, brood sex ratio of blue tits was not affected by habitat quality. In blue tits, male condition correlated positively with a male-biased sex ratio. Habitat quality, however, affected the body mass differences of male and female blue tit siblings, and nestlings developed differently. The low quality habitat had a negative effect on the sexual dimorphism of siblings in male-biased broods, and the condition of offspring was bad. Nevertheless, sexual dimorphism cannot explain the differences between great and blue tits with respect to the correlation of sex ratio and individual condition.