Bird populations most exposed to climate change are less sensitive to climatic variation

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species' range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two co-familial European songbirds, the great tit (Parus major) and blue tit (Cyanistes caeruleus), covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity than those in evergreen and mixed habitats. However, populations with higher sensitivity tended to have experienced less rapid change in climate over the past decades, such that populations with high phenological sensitivity will not necessarily exhibit the strongest phenological advancement. Our results show that to effectively assess the impact of climate change on phenology across a species' range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population. Intra-specific variations may contribute to heterogeneous responses to climate change across a species' range. Here, the authors investigate the phenology of two bird species across their breeding ranges, and find that their sensitivity to temperature is uncoupled from exposure to climate change.Peer reviewe

Interaction of climate change with effects of conspecific and heterospecific density on reproduction

We studied the relationship between temperature and the coexistence of great titParus majorand blue titCyanistes caeruleus, breeding in 75 study plots across Europe and North Africa. We expected an advance in laying date and a reduction in clutch size during warmer springs as a general response to climate warming and a delay in laying date and a reduction in clutch size during warmer winters due to density-dependent effects. As expected, as spring temperature increases laying date advances and as winter temperature increases clutch size is reduced in both species. Density of great tit affected the relationship between winter temperature and laying date in great and blue tit. Specifically, as density of great tit increased and temperature in winter increased both species started to reproduce later. Density of blue tit affected the relationship between spring temperature and blue and great tit laying date. Thus, both species start to reproduce earlier with increasing spring temperature as density of blue tit increases, which was not an expected outcome, since we expected that increasing spring temperature should advance laying date, while increasing density should delay it cancelling each other out. Climate warming and its interaction with density affects clutch size of great tits but not of blue tits. As predicted, great tit clutch size is reduced more with density of blue tits as temperature in winter increases. The relationship between spring temperature and density on clutch size of great tits depends on whether the increase is in density of great tit or blue tit. Therefore, an increase in temperature negatively affected the coexistence of blue and great tits differently in both species. Thus, blue tit clutch size was unaffected by the interaction effect of density with temperature, while great tit clutch size was affected in multiple ways by these interactions terms.Peer reviewe

Variation in clutch size in relation to nest size in birds

Peer reviewe

Searching for Density-Dependent Regulation in a Population of Pied Flycatchers (Ficedula hypoleuca Pallas).

(1) Breeding data from a population of pied flycatchers (Ficedula hypoleuca) nesting from 1948 to 1964 in the Forest of Dean, Gloucestershire, U.K. were analysed for density-dependent changes in clutch size, mortality and migration rates. (2) High breeding population densities followed seasons in which many young were fledged, but the increased numbers of breeding birds resulted from high levels of immigration as well as increased recruitment of birds raised in the study area in the previous breeding season. (3) When nestling mortality was high, a smaller proportion of birds breeding in the area in the following year were immigrants. (4) During the first 7 years of the study, high breeding population densities were associated with small clutch sizes. (5) Nestling mortality was not correlated with breeding population densities. (6) The number of birds in the study area at the end of the breeding season accounted for about 76% of the variation in rates of return of first-year birds to breed in the area the following year, with a lower proportion of birds returning following high-density years

Factors Influencing Reproductive Success in the Pied Flycatcher

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Individual variation in Seasonal Breeding Success of Pied Flycatchers (Ficedula hypoleuca).

(1) We present and analyse reproductive success data from a long term study of the pied flycatcher (Ficedula hypoleuca) nesting in the Forest of Dean, Gloucestershire. (2) Our measures of high reproductive success are earlier laying date, larger clutch size and more young fledged. (3) Breeding performances of both sexes inprove with age after breeding experience has been controlled for. (3) Breeding performances of both sexes inprove with age after age has been controlled for. (4) Females that have bred as both 1 and 2 year olds are more likely to survive to breed again than those that bred in their second year but failed to breed in their first year. (5) Females that have bred as both 1 and 2 year olds are more likely to survive to breed again than those that bred in their second year but failed to breed in their first year. (6) A male is more likely to survive to breed again after a breeding season in which its mate laid an early clutch. (7) The data indicate that at least 40% of males and females did not breed in their first year

Breeding Dispersal of the Pied Flycatcher

(1) We present and analyse breeding dispersal data from a long term study of the pied flycatcher (Ficedula hypoleuca Pallas) nesting in the Forest of Dean Gloucestershire. (2) The median breeding dispersal (distance between successive breeding sites) varied from 52 to 133 m. The average distance between occupied nest boxes ranged from 41 m to 55 m depending on the breeding density in each year. (3) Older birds of both sexes were more likely to move shorter distances between breeding seasons than were younger birds. (4) Females were less likely than males to return to their former breeding site after the death of or divorce from their previious partner. (5) The possible influence of migration, interspecific competition for nest-sites, and polygyny on the patterns of breeding dispersal are discussed

Hatching Asynchrony and Brood Reduction in Blue Tits Cyanistes caeruleus may be a Plastic Response to Local Oak Bud Burst and Caterpillar Emergence.

Blue tits exhibit extreme variation in clutch size and hatching asynchrony, which is the focus of this study. This paper reports an in-depth study of breeding blue tits showing that variation in blue tit hatching asynchrony can be explained by a number of phenological variables including particularly, date of bud burst in the local oak tree, which signals caterpillar emergence (34%), also date of first egg (14%) and female weight (8%). Hatching asynchrony explained 9% of the variation in brood mortality in this southern English population. Early incubation relative to clutch completion (incubation asynchrony) in blue tits explained 85% of the variation in hatching asynchrony, differs between years and advanced hatching in early and fledging in late laid eggs. Consequently, because fledging is usually synchronous, hatching asynchrony shortens the total time spent in the nest and explained 28% of the variation in total nesting time from clutch completion to fledging. I present experimental evidence that brood reduction resulting from hatching asynchrony may be particularly adaptive towards the end of the breeding season, with 91% of the variation in the productivity of asynchronously hatched birds being explained by, and increasing with date of hatching. About one fifth of birds delayed daytime incubation until after clutch completion, probably in wait for the caterpillars to appear. Although the delay period was variable, and extended total nesting time it always resulted in synchronous hatching. I propose that blue tits may have evolved plastic responses to environmental cues such as oak bud burst, which causes them to incubate at the optimum time to ensure maximum fledging success and chick fitness

Bird populations most exposed to climate change are less sensitive to climatic variation

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species’ range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two co-familial European songbirds, the great tit (Parus major) and blue tit (Cyanistes caeruleus), covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity than those in evergreen and mixed habitats. However, populations with higher sensitivity tended to have experienced less rapid change in climate over the past decades, such that populations with high phenological sensitivity will not necessarily exhibit the strongest phenological advancement. Our results show that to effectively assess the impact of climate change on phenology across a species’ range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population