Academic literature on the topic 'Migratory change'

Aim: This thesis aims to investigate the potential impacts of climatic change on Afro-Palaearctic migratory birds by investigating simulated changes in breeding and non-breeding distribution. Methods: Generalised Additive Models were used to determine those climatic variables that produced the most robust species distribution models. Tests on the performance of three regression-based techniques were undertaken and consensus modelling framework was subsequently chosen. This framework was used in conjunction with three general circulation models and two emission scenarios to model the future distributions of Afro-Palaearctic migratory birds. Changes in both breeding and non-breeding range and migratory distance were examined for groups of species. A vulnerability index was created to indicate those species that were most vulnerable to climate change. Finally, changes in recent population trends observed on the European breeding grounds were related to simulated climatic suitability to investigate the role of climate in recent population changes and determine the vulnerability of populations to climate change. This analysis also enabled a partial validation of species distribution models. Results: The results indicate differential change on the breeding and non-breeding grounds for many species. For many migratory birds a progressive separation of the two ranges is projected, potentially increasing migratory distances in future. However, for some species newly suitable climatic areas may provide non-breeding areas closer to the breeding range, enabling species to adapt to climatic change. Trans-Saharan migrants, species residing in dry environments as well as montane and coastal species are projected to be most vulnerable to climatic change. Although a link between population trends and climatic suitability could be found, the results indicated, as might be expected, that climate is only one of a number of factors potentially contributing to population changes Conclusion: This thesis gives the first broad analysis of the likely direction and magnitude of change of the distribution of migratory birds to climate change, when only climate is considered. The challenge ahead is to refine these coarse scale models to include habitat and demographic data so as to provide more realistic estimates of change and improve conservation strategies that aim to support species under climate change.

Recent observed changes in bird distributions provide an unprecedented opportunity to gain a deeper understanding of the processes that influence species' persistence. By modelling presence-absence data from the North American Breeding Bird Survey, we found evidence that the breeding range of the western burrowing owl has contracted at its northern, western, and eastern boundaries since 1967. We suggest that the species' breeding distribution is also expanding southwards to former wintering grounds into northern Mexico, facilitated by the appearance of new breeding habitat created by irrigated agriculture in the arid areas of southwestern United States and northwestern Mexico. This dissertation explores the hypothesis that burrowing owls from northern migratory populations have become resident breeders in areas of northwestern Mexico that were formerly used only by migratory owls during winter, contributing to both population declines near the northern extent of the species' breeding range and population increases in the southern half of the species' range. We used novel DNA microsatellite markers to test patterns of gene flow predicted by this migration-mediated range-shift hypothesis. We genotyped 1,560 owls from 36 study locations in Canada, Mexico, and the United States. Analyses of molecular variance provided evidence that burrowing owl populations in both northwestern Mexico and Canada are genetically different from the rest of the populations in the breeding range, lending some support to the migration-mediated range-shift hypothesis. We found evidence of subtle genetic differentiation associated with subtropical irrigated agricultural areas in southern Sonora and Sinaloa, demonstrating that land use can produce location-specific population dynamics leading to genetic structure even in the absence of dispersal barriers. We also used stable isotopes 2/H, 13/C, and 15/N in feathers to test philopatry and breeding dispersal patterns predicted by this migration-mediated range-shift hypothesis. Burrowing owl populations near the northern edge of the species' breeding range had a high proportion of immigrants compared to interior populations, while other populations had high levels of philopatry. Stable isotopes also provided evidence of breeding dispersal events from Canadian populations to northwestern Mexico in support of the migration-mediated range-shift hypothesis, but similar isotope signatures in nestling feathers between these two regions prevent stronger inferences.

Recent global climate change is influencing the behaviour and ecology of species worldwide. Birds are typical systems to study in this context, as they are often migratory and thus subjected to a variety of environmental effects. This thesis employs the use of long-term ringing records, field observations, historical maps and historical volunteer observations with the aim of describing behavioural and ecological responses of birds to the current environmental change. An investigation into the spring arrival, reproduction and autumn departure in willow warblers (Phylloscopus trochilus) breeding at a southern study site in Sweden (65°N 18°E) showed that all three phenological events had advanced in parallel. Thus birds arrive earlier, start breeding earlier and leave Sweden earlier, with the breeding period staying the same in length. By teasing apart the migratory responses of different individuals, it became clear that particularly early arriving males and early departing juveniles had advanced migration. However, willow warblers migrating past a northern study site in Sweden (65°N 23°E) displayed no change in autumn departure. When migration in the two regionally separate populations were analyzed in relation to climatic variables, the results indicated that foremost a combined effect of growing season onset and the North Atlantic Oscillation influenced migratory timing, and only in individuals that had advanced migration. As growing season onset had advanced at both regions, but only elicited migratory change in southern willow warblers, it is proposed that intra-specific difference between populations prepare them differently to climate change. Willow warblers breeding at northern latitudes were also displaying absence of an otherwise common behaviour of the species: philopatry. It is suggested that the climate induced change in onset of the growing season, coupled with an increase in available territories, could have enabled a southern influx of dispersal-prone birds adopting a less philopatric breeding behaviour. Availability of territories was also studied in southern Sweden, in relation to 100 years of land use change and future climate change effects on forestry. The mass-conversion of grazed forest into coniferous sylvicultures that has occurred in Sweden 1900-2013 was shown to have negatively affected territory availability for willow warblers. The second most common bird species in Sweden, the chaffinch (Fringilla coelebs), was however shown to be largely unaffected. In a future scenario where rising temperatures will increase growth rates of trees, harvest rotation will be faster and both sylvicultures and logged areas will increase in coverage, favouring both species. Thus commonness in terms of landscape and species occurrence has altered historically and is dynamically linked. Historic perspectives were also applied to observations of spring arrival of 14 migratory bird species. A relative comparison of two data sets, collected over 140 years, revealed that short-distance migrants have changed their spring arrival more than long-distance migrants in southern Sweden. In conclusion, the results of this thesis provide insights into climate change effects on avian behaviour and ecology, document unique observations and contribute with a great spectrum of knowledge, from exact details on responses by individual birds, through long-term changes in populations to historical perspectives on shifts in entire landscapes<br><p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

This thesis develops a conceptual and methodological approach to understanding how future climate change is likely to affect migration, and then applies this approach to explore the likely effects of climate change on different migration flows in and from Mexico. Scientific and policy interest in the climate change-migration nexus has been growing over the last decade, yet empirical results remain inconclusive. Existing approaches are often conceptually and methodologically unconvincing as they assume a linear relationship between climate change and migration, or try to separate climate stressors from other factors involved in migration decisions. Furthermore, most current research into the climate-migration nexus has focused on a relatively simple framing of localised environmental pressures forcing people to migrate. In contrast, this thesis acknowledges the complexity of migration and suggests that climate change is likely to affect factors involved in migration decisions at the local and the global level. It develops a more realistic understanding of the potential effect of climate change on migration by examining the impact of the local and global consequences of climate change on livelihood stressors and other factors involved in migration decisions. This thesis adopts a qualitative and comparative approach to illustrate this concept, based on fieldwork in Zacatecas and Veracruz, two Mexican states with different migration profiles and different local climate stressors. It analyses the factors involved in migration decisions, which include livelihood stressors but also networks, recruiters and individual agency. A risk matrix is then developed to explore the climate sensitivity of the various factors that influence internal and international migration flows. It analyses the extent to which each factor is likely to be affected by climate change in combination with the relevance of this factor for the migration decision-making process. This approach allows identifying those factors that, affected by future climate change, have the highest potential to impact on existing migration patterns. It also allows a comparison between different migration flows. Results suggest that climate change is likely to have moderate effects on migration, mainly on internal rural flows. Alarmist predictions of large numbers of 'climate change refugees' are thus inappropriate and policies should instead focus on the factors projected to impact most on migration under scenarios of future climate change. Policies should also aim at mitigating the negative effects of climate change on people's livelihoods and at protecting migrants and non-migrants.

Nous avons utilisé la télédétection pour examiner comment l’abondance du caribou migrateur pouvait influencer la quantité de ressources alimentaires, et comment ces changements pouvaient affecter la dynamique de population et les patrons d’utilisation de l’espace des caribous. Nous avons évalué les relations entre le caribou et ses ressources alimentaires pour l’aire de mise bas et l’aire d’estivage du troupeau Rivière-George (TRG) du nord du Québec et du Labrador (Canada) entre 1991 et 2011. Nous avons modélisé les relations entre la productivité primaire et des variables climatiques, nous permettant d’isoler les effets d’autres facteurs, comme la pression de broutement des caribous. Nous avons trouvé une relation négative entre la densité de caribous et la productivité primaire à grande échelle, suggérant que la pression de broutement par les caribous pouvait réduire l’abondance des ressources alimentaires et contribuer à la dégradation de l’habitat. Une forte tendance au réchauffement durant la période d’étude, couplée avec un déclin de la taille de population du TRG, a cependant entrainé une productivité primaire plus élevée. Cette hausse de la productivité primaire pourrait représenter un rétablissement de la végétation suite à la réduction de la pression de broutement et/ou un effet du réchauffement climatique.<br>This thesis used remote sensing to examine how changes in caribou abundance can impact forage availability, and how these changes might in turn affect the population dynamics and space use patterns of migratory caribou. We investigated these relationships for the Rivière-George caribou herd (RGH) and its calving grounds and summer range in Northern Quebec and Labrador (Canada) from 1991-2011. We modelled the relationships between primary productivity and various climatic variables, allowing us to isolate the effects of non-climatic factors, such as caribou herbivory, on primary productivity. We found a negative relationship between caribou density and primary productivity at the range-scale, suggesting that caribou herbivory can reduce forage abundance and contribute to habitat degradation. However, a strong warming trend over the study period, coupled with a decline in RGH population size, meant that we observed a trend towards higher primary productivity. This greening trend may represent vegetation recovery following the reduction in caribou herbivory and/or an effect of climate warming.

Migrant birds may be vulnerable to climate change at different stages of their annual cycles especially on the breeding grounds, where changes in phenology may affect their ability to synchronise breeding with the peak of resources availability. Understanding how phenology of breeding, survival and productivity varies between and within years is therefore crucial to understand migrant population dynamics. This thesis describes this variation in the Cyprus Wheatear Oenanthe cypriaca, with particular emphasis on a colour-ringed population at Troodos, Cyprus, 2010-2012. Our results suggest that the phenology of breeding of Cyprus Wheatear is variable with breeding onset and number of breeding attempts probably varying with annual temperature variation. Minimum true survival rates were very high for a small passerine migrant, although they were probably sufficiently annually variable to profoundly affect annual population dynamics. For productivity, nest survival was very high and did not vary between years, or nesting attempts, or with clutch initiation date but it was significantly higher in the chick stage versus the egg stage. Post-fledging survival in the first 4 weeks was very high. Renesting probability was significantly different in all years, yet total productivity per pair was the same in each of three years. Cyprus Wheatears at Troodos showed such high productivity and survival that the population must be a major source population and this was reflected in the very high density of breeding pairs at the study site. Finally we used altitude as a proxy for variation in temperature and investigated how abundance, productivity and phenology in Cyprus Wheatears varied between and within years, from sea level to 1952m, using transect surveys to record breeding birds across Cyprus. Cyprus Wheatears were common in all habitats and altitudes; altitudinal temperature variation probably affected the occurrence of double brooding and so the timing of chick production, but not the onset of breeding. The results suggest that Cyprus Wheatears are already very well adapted to high variation in temperature within and between seasons, changing investment accordingly.

Climate change threatens to disrupt biological systems around the globe, sparking debate over natural capacity for adaptation in a fragmented landscape. Marine turtles are evolutionarily ancient and have survived millions of years of prehistoric climate change, but are threatened by the rapidity of modern warming and a history of severe overexploitation that has left most populations depleted. This thesis explores a nesting aggregation of the green turtle (Chelonia mydas) in northern Cyprus, where a longitudinal programme of both intensive and extensive monitoring enables insight into individual and population level parameters and processes. Nesting on the two coastlines covered by this project is in the early stages of recovery, possibly in response to exhaustive nest protection efforts over the last twenty years. Saturation tagging at one key site allows us to confirm that recruitment of new breeders is an important driver of this trend, and that average clutch frequency has remained stable around three nests per female per year, validating nest-count derived abundance estimates at a regional scale. Concern has been raised, however, regarding recent changes in fishing practices which are impacting the local juvenile neritic phase, which may have a lagged effect on the recovery of this nesting population. A collaborative tracking effort including all other countries with major nesting in the Mediterranean allows us to identify major foraging grounds for this species, with two hotspots accounting for >50% of tracked individuals, as well as coastal and pelagic seasonal corridors of high use. Bycatch levels and mortality rates for turtles in these key areas are largely unknown and should be prioritised for investigation. Hatchling sex ratios from the main study beach are extremely female-biased (estimated 97% female for the twenty year period 1993-2012). A 1oC rise in average incubation temperatures threatens near complete hatchling feminisation on this beach, whilst a 2oC rise could reduce hatch success to less than 50%. Thermal effects on hatchling morphometrics are evident, with a 1oC rise in temperature reducing average length, width and weight by 1%, 2% and 3% respectively. More favourable incubation conditions were found early in the season, in deeper nests laid by larger females, and on beaches of lighter sand. In contrast, adult sex ratios at the main site are male-biased, posing questions regarding sex-specific survival rates and optimal hatchling sex ratios. A phenological shift towards earlier nesting is demonstrated for the first time in this species, and could potentially ameliorate warming effects. Carry-over climate forcing effects from the foraging ground influence the breeding frequency of individuals, driving population level responses in annual magnitude of nesting. This work emphasises the utility and necessity of long-term individual-based monitoring programmes in elucidating population trends and climate responses in iteroparous species with non-annual breeding.