Dave I. Leech

Climatic effects on breeding grounds are more important drivers of breeding phenology in migrant birds than carry- over effects from wintering grounds

Long-distance migrants may be particularly vulnerable to climate change on both wintering and breeding grounds. However, the relative importance of climatic variables at different stages of the annual cycle is poorly understood, even in well-studied Palaearctic migrant species. Using a national dataset spanning 46 years, we investigate the impact of wintering ground precipitation and breeding ground temperature on breeding phenology and clutch size of 19 UK migrants. Although both spring temperature and arid zone precipitation were significantly correlated with laying date, the former accounted for 3.5 times more inter-annual variation. Neither climate variable strongly affected clutch size. Thus, although carry-over effects had some impact, they were weaker drivers of reproductive traits than conditions on the breeding grounds.

Carry-over effects from passage regions are more important than breeding climate in determining the breeding phenology and performance of three avian migrants of conservation concern

Long distance migrants are declining more rapidly than residents, with birds that breed in Europe and winter in tropical Africa providing particularly clear examples. Causal mechanisms may include climate change, but are poorly understood partly because carry-over effects from non-breeding ranges can influence breeding performance. Using long-term data spanning four decades we assess how climatic variation in migrants’ winter, passage and breeding ranges determine timing of breeding and reproductive success. We do so for three Afro-European avian migrants of regional conservation concern (redstart, spotted flycatcher and wood warbler). We find that carry-over effects from passage regions consistently had stronger impacts on breeding phenology than breeding climate. Warm Mediterranean passage conditions promoted earlier breeding in all species, and redstarts also bred earlier following higher Sahel rainfall. Warmer springs on the breeding grounds promoted slightly earlier breeding in redstart and wood warbler, but not spotted flycatcher. Carry-over effects also typically influenced breeding performance to a greater extent than weather on the breeding grounds. Greater rainfall in the Sahel increased redstart brood size, warmer Mediterranean passage conditions increased spotted flycatcher brood size and, to a lesser extent, the number of wood warbler fledglings. In contrast to the concern regarding climate change impacts on migrants’ breeding grounds we found no evidence that warmer temperatures on the breeding grounds were associated with reduced reproductive performance. We thus find that climatic variation on the non-breeding grounds, especially passage regions, typically influenced migrants’ breeding phenology and demography more strongly than equivalent variation on the breeding sites. Such carry-over effects should be considered when assessing the causes of migrants’ marked population declines.

Using citizen science to investigate the role of productivity in House Sparrow Passer domesticus population trends

Capsule Seasonal variation in garden House Sparrow numbers provides a tool to examine overall annual productivity, measuring the combined success of multiple breeding attempts and post-fledging survival. Aims To develop a metric to use British Trust for Ornithology (BTO) Garden BirdWatch (GBW) data to measure annual productivity in House Sparrows across regions and habitats exhibiting contrasting population trends. Methods We examine variation in annual productivity by quantifying the height of the seasonal peak of garden House Sparrows relative to pre-breeding numbers. We use BTO Nest Record Scheme (NRS) data to explore the demographic drivers of variation in this metric and relate differences to BTO/Joint Nature Conservation Committee/Royal Society for Protection of Birds Breeding Bird Survey regional population trends. Results GBW annual productivity was similar between rural and urban gardens but was lower in the south and the east of Britain (1.32 fledglings per adult), where populations are declining, than in the north and west where populations are stable (1.37 fledglings per adult). Analysis of NRS data showed similar regional variation in clutch and broods sizes. Conclusion The intensity of effort required to measure breeding success directly through nest monitoring has limited the scale of data collection but these results suggest that Garden BirdWatch (GBW) data can provide a measure of annual productivity across multiple sites. Regional variation in annual productivity (primarily driven by reduced clutch sizes) mirrors population trends, suggesting that reduced breeding success may be influencing House Sparrow population recovery.

Does variation in demographic parameters account for regional variation in Northern Lapwing Vanellus vanellus population declines across Great Britain

Capsule Variations in regional nest survival rates, natal philopatry, first-year and adult survival cannot explain regional Northern Lapwing population declines. Aims To assess whether regional nest survival rates, natal dispersal, and first-year and adult survival rates could explain regional variations in population declines. Methods Nest monitoring data from the period 1962–2003 were analysed to see if any differences in nest failure rates existed among regions. Estimates of nesting success were used in conjunction with aspects of Lapwing dispersal extracted from ring recovery data, to identify regional source and sink populations. Ring recovery data were also analysed to see if variation in regional population declines could be explained by variation in first-year and/or adult Lapwing survival rates. Results There was no evidence to indicate the existence of source–sink dynamics at the regional level. Nest failure rates have increased since the 1960s, and nest failure rates were highest in grassland habitats. Nest failure rates did vary among regions and regional increases in nest failure rates were associated with an increasing proportion of birds nesting on grassland habitats. There was no association between regional nest failure rates or adult and first-year survival rates and regional population declines. Conclusions Although recent increases in nest failure rates may have influenced British population declines, it is not possible to explain variation in population decline among regions through source–sink dynamics, nest failure rates or adult/first-year survival rates. It is more likely that chick mortality is the main determinant of poor Lapwing productivity and population decline.

Season-long consequences of shifts in timing of breeding for productivity in Willow Warblers, Phylloscopus trochilus

Capsule Breeding Willow Warblers, Phylloscopus trochilus, in the UK have advanced in timing of breeding but with little impact on overall productivity. Aims To quantify the impact of shifts in timing of breeding on changes in Willow Warbler productivity across the UK. Methods Using records of ∼7000 nests from the British Trust for Ornithology Nest Record Scheme, we quantify shifts in timing of breeding and seasonal variation in productivity and timing of breeding, and explore their relative contribution to changes in overall productivity. As population trajectories vary across Britain (south-east declining, north-west stable), analyses were conducted regionally. Results In both regions, nesting dates have advanced and early-season productivity is highest. However, while the proportion of early-season nests has increased, the seasonal decline in productivity in the north-west has lessened, and overall (season-long) productivity is stable. In the south-east, however, the seasonal decline in productivity has strengthened and, despite the advance in timing of breeding, overall productivity has declined. Conclusions Advances in timing of breeding have not led to increased Willow Warbler productivity in the UK, because the population-level impact of advances depends on seasonal patterns in both productivity and the distribution of nesting dates within a population.

Playback survey trial for the Little Owl Athene noctua in the UK

ABSTRACT Capsule: Playback is effective at improving detectability of Little Owls. Aims: To trial a playback survey methodology for Little Owls in the UK to determine detectability and practicalities which could inform potential future national monitoring efforts. Methods: Nocturnal playback surveys were carried out in an open landscape in the east of England in spring 2015. Twelve 2 × 2 km survey squares were each visited four times. Little Owl calls were broadcast from three locations within each square along a linear transect and spaced 500 m apart. The responses of owls of any species were recorded. Little Owl occupancy was later confirmed through existing nest monitoring efforts. Results: Little Owls were detected responding to playback in all survey squares and were confirmed to be breeding in 8 of the 12. Detection and response rates were greater when combining data from multiple broadcast locations. The likelihood of Little Owls responding decreased with greater distance of broadcast location to known nest site, but no relationships were identified with time of evening or the presence of other owl species. Conclusion: Playback methodology proved to be effective at increasing detectability of Little Owls and this study provides an estimated response rate to inform future efforts.

Bird ringing in Britain and Ireland in 2009

This is the 73rd annual report of the British Trust for Ornithologys Ringing Scheme, covering data received and work carried out in 2009. Much of the research carried out during the year looked at ways to improve the analysis of ringing data to understand population change. This included producing survival rates from the Constant Effort Sites (CES) scheme for the first time and further developing methods of analysing our demographic data sets in an integrated manner. Research was also undertaken on the biometric data to investigate how individual condition responds to long‐term environmental change. CES data suggested that the low productivity in 2007 and 2008, combined with one of the coldest winters since 1995/96 for residents, contributed to reduced adult numbers in 2009 in many species. There were significant decreases in Wren Troglodytes troglodytes, Sedge Warbler Acrocephalus schoenobaenus, Reed Warbler A. scirpaceus, Blackcap Sylvia atricapilla, Lesser Whitethroat S. curruca, Willow Warbler Phylloscopus trochilus, Long‐tailed Tit Aegithalos caudatus, Blue Tit Cyanistes caeruleus, Great Tit Parus major, Treecreeper Certhia familiaris, Chaffinch Fringilla coelebs, Greenfinch Carduelis chloris and Reed Bunting Emberiza schoeniclus. However, a good breeding season, for both residents and migrants, resulted in significantly higher productivity for 15 species, but significantly lower for Willow Tit Poecile montana, compared to the long‐term mean (1983–2007). Data for 104 Retrapping Adults for Survival studies were submitted, covering 39 species, three quarters of which are Birds of Conservation Concern. The total number of birds ringed (935,867) was the highest ever recorded, and was over 10% higher than the mean of the previous five years. However, the total number of pulli ringed in 2009 (179,712) was only 5% higher than the preceding five‐year mean, while that of fully grown birds (756,155) was over 13% higher. The recovery total (14,643) was also high. However, this is partly due to changes in the way that records of colour‐ringed and other specially marked birds are stored. The number of recoveries of foreign‐ringed birds (1,314) was higher than the mean of the preceding five years, although this figure is influenced by varying response times of different ringing schemes. Recovery details for 250 individual birds are given in the final section of the report. They include movements that confirm suspected or known migration patterns, unexpected movements and longevity records.

Bird ringing and nest recording in Britain and Ireland in 2013

This is the 77th annual report of the British Trust for Ornithologys Ringing Scheme, incorporating the report of the Nest Record Scheme and covering work carried out and data processed in 2013. In recent years the schemes have focused on the collection of demographic data as part of our Integrated Population Monitoring programme. We expanded (from 10 to 17) the number of species for which we were able to construct integrated models and identified differences in the relative contributions of recruitment and adult survival to population change between increasing and decreasing species. Recruitment of young into the breeding population can be difficult to estimate. We investigated the use of proportions of birds in their second calendar year, or older, caught in the early summer using Blackbird Turdus merula as a model. Results showed that recruitment was a more important determinant of population change than survival. Changes in phenology are being documented widely and we carried out analyses looking at the timing of moult and reproduction in selected passerine species. Patterns in timing and duration of moult varied between resident species but were more aligned within migrant species, which also moulted faster. Temperature on spring breeding grounds accounts for more variation between years in breeding phenology than precipitation rates on the wintering grounds in 19 migrant species but neither climate variable affected clutch size. We continued to emphasise the value of targeted ringing and nest recording; increased participation in our structured ringing schemes has provided additional opportunities to improve the quality of demographic monitoring. Long-term (1984–2012) population trends derived from the Constant Effort Sites (CES) data have changed little in the past year. Three of the eight migrant species monitored by CES showed significant increases in productivity compared to the five-year average, although Sedge Warbler Acrocephalus schoenobaenus recorded its second-lowest productivity since CES began in 1983. Breeding performance of residents was mixed, with juvenile:adult ratios for some early breeders significantly lower than during the preceding five years, but significantly higher for some late breeders; one late-breeding resident species, Bullfinch Pyrrhula pyrrhula, had its highest productivity since CES began. Data were submitted for 124 sites. The number of active RAS projects in 2013 was 154, with 22 new projects, 13 of which involved RAS target species. The total number of birds ringed in 2013 decreased slightly (952,750) compared to 2012 and comprised 424,401 first-year birds, 355,278 adults (birds in their second calendar year or older), 19,776 unaged birds and 153,295 nestlings. In addition, there were 241,111 recaptures of ringed birds at or near the ringing site. The reduction in numbers ringed compared to 2012 was probably a result of weather events in 2013. In 2013, there were 465 colour-marking projects registered, covering a total of 110 species; 65 new projects were registered during the year. There were 21,275 recoveries of BTO-ringed birds: the highest total ever. A selection of recoveries that have extended our knowledge of movements is presented, as well as longevity records established during the year. In total, 40,384 nest records were submitted. Of these, 82% originated from England, 8% from Wales and 9% from Scotland, the remaining 1% divided between Northern Ireland and the Republic of Ireland. This was a reduction on the 2012 totals and probably reflected the poor start to the breeding season caused by the exceptionally cold weather in early spring. Long-term trends in nest productivity (fledglings per breeding attempt) were significant for 44 of the 72 species monitored. Of these, thirteen trends were negative, indicating a decline in breeding success over time.

Bird ringing in Britain and Ireland in 2008

This is the 72nd annual report of the British Trust for Ornithologys Ringing Scheme, covering work carried out, and data received, in 2008. Research carried out in 2008 included developing methods to combine ringing data with data from other monitoring schemes to detect the causes of population change. This approach was used for Song Thrush Turdus philomelos data, confirming the findings of previous analyses that the population decline observed over the last thirty years is primarily related to first‐year survival. Constant Effort Site data suggested that low productivity in 2007 contributed to reduced adult numbers during 2008 for many species, including significant decreases in Blackcap Sylvia atricapilla, Willow Warbler Phylloscopus trochilus, Blue Tit Cyanistes caeruleus and Bullfinch Pyrrhula pyrrhula. However, there were significant increases in numbers of adult Long‐tailed Tits Aegithalos caudatus and Chiffchaffs Phylloscopus collybita. As in 2007, the 2008 breeding season was poor, with 11 of the 25 core species monitored by the Scheme showing significantly lower productivity compared to the long‐term average (1983–2007). In contrast to 2007, many of the species faring worst were residents, including Blackbird Turdus merula, Song Thrush and Great Tit Parus major. Data for 92 Retrapping Adults for Survival studies were submitted, covering 34 species, more than half of which are of conservation concern. The total number of birds ringed (835,326) was 2% lower than the mean of the previous five years. This reduction may have been influenced by the poor breeding season in 2008; the total number of pulli ringed in 2008 (161,846) was 6% lower than the preceding five‐year mean, while that of fully grown birds (673,480) showed no change. The recovery total (15,164) was the highest in over 15 years; however, this is partly due to changes in the way that records of colour‐ringed and other specially marked birds are stored, which led to an inflation of the 2008 total. The number of recoveries of foreign‐ringed birds (1,192) was higher than the mean of the preceding five years, although this figure is influenced by response times of different ringing schemes, which vary from year to year. Recoveries of 230 individual birds are presented in the final section of the report. They include unexpected movements, movements that confirm suspected or known migration patterns, and longevity records.

Tritrophic phenological match–mismatch in space and time

Increasing temperatures associated with climate change may generate phenological mismatches that disrupt previously synchronous trophic interactions. Most work on mismatch has focused on temporal trends, whereas spatial variation in the degree of trophic synchrony has largely been neglected, even though the degree to which mismatch varies in space has implications for meso-scale population dynamics and evolution. Here we quantify latitudinal trends in phenological mismatch, using phenological data on an oak–caterpillar–bird system from across the UK. Increasing latitude delays phenology of all species, but more so for oak, resulting in a shorter interval between leaf emergence and peak caterpillar biomass at northern locations. Asynchrony found between peak caterpillar biomass and peak nestling demand of blue tits, great tits and pied flycatchers increases in earlier (warm) springs. There is no evidence of spatial variation in the timing of peak nestling demand relative to peak caterpillar biomass for any species. Phenological mismatch alone is thus unlikely to explain spatial variation in population trends. Given projections of continued spring warming, we predict that temperate forest birds will become increasingly mismatched with peak caterpillar timing. Latitudinal invariance in the direction of mismatch may act as a double-edged sword that presents no opportunities for spatial buffering from the effects of mismatch on population size, but generates spatially consistent directional selection on timing, which could facilitate rapid evolutionary change.Most work on phenological mismatch has focused on temporal trends only. Here, the authors analyse trends in spatial and temporal mismatch between trees, caterpillars and birds in the UK, and find delayed phenology of all species with increasing latitude and little spatial variation in the magnitude of mismatch between caterpillars and birds.