Populations Of Migratory Species Research Articles

Disentangling the relative roles of climate and land cover change in driving the long‐term population trends of European migratory birds

AbstractAimGlobal declines in the populations of migratory species have been attributed largely to climate change and anthropogenic habitat change. However, the relative contribution of these factors on species’ breeding and non‐breeding ranges is unclear. Here, we present the first large‐scale assessment of the relative importance of climatic conditions and land cover on both the breeding and non‐breeding grounds in driving the long‐term population trends of migratory species.LocationEurope and Africa.MethodsWe use data on the long‐term population trends of 61 short‐ and 39 long‐distance migratory species of European breeding birds. We analyse these population trends in relation to changes in climate and land cover across species’ breeding and non‐breeding ranges over a 36‐year period, along with species’ migratory behaviour.ResultsThe population trends of European migratory birds appear to be more closely related to changes in climate than changes in land cover on their breeding grounds, but the converse is true on their non‐breeding grounds. While improvements in climate suitability across the breeding ranges of short‐distance migrants led to increasing population trends, the same was not true for long‐distance migrants. The combined effects of changes in climate and land cover account for approximately 40% of the variation in migratory species’ population trends, suggesting that factors other than climate and land cover as we have measured them, such as habitat quality, also affect the population trends of migrant birds.Main ConclusionsOver recent decades, population trends of most migrant species are most strongly related to climatic conditions on the breeding grounds but land cover change on the non‐breeding grounds. This suggests that management to stem the declines of migrant birds requires an integrated approach that considers all processes affecting migrant birds across their dynamic distributions throughout the year.

Range‐wide migration corridors and non‐breeding areas of a northward expanding Afro‐Palaearctic migrant, the European Bee‐eater Merops apiaster

Across their ranges, different populations of migratory species often use separate routes to migrate between breeding and non‐breeding grounds. Recent changes in climate and land‐use have led to breeding range expansions in many species but it is unclear whether these populations also establish new migratory routes, non‐breeding sites and migration phenology. Thus, we compared the migration patterns of European Bee‐eaters Merops apiaster from two established western (n = 5) and eastern (n = 6) breeding populations in Europe, with those from a newly founded northern population (n = 19). We aimed to relate the breeding populations to the two known non‐breeding clusters in Africa, and to test for similarities of migration routes and timing between the old and new populations. Western Bee‐eaters used the western flyway to destinations in West Africa; the eastern birds uniformly headed south to southern African non‐breeding sites, confirming a complete separation in time and space between these long‐established populations. The recently founded northern population, however, also used a western corridor, but crossed the Mediterranean further east than the western population and overwintered mainly in a new non‐breeding area in southern Congo/northern Angola. The migration routes and the new non‐breeding range overlapped only slightly with the western, but not with the eastern, population. In contrast, migration phenology appeared to differ between the western and both the northern and the eastern populations, with tracked birds from the western population migrating 2–4 weeks earlier. The northern population thus shares some spatial traits with western Bee‐eaters, but similar phenology only with eastern population. This divergence highlights the adjustments in the timing of migration to local environmental conditions in newly founded populations, and a parallel establishment of new breeding and non‐breeding sites.

Population monitoring and annual population fluctuation of migratory and resident species of vultures in and around Jodhpur, Rajasthan

Vultures are important scavengers that play a vital role in clearing animal carcasses and municipal dumps. In the past decade, a sharp decline has been observed in vulture population. For the present work, Jodhpur district of Thar Desert, India, the natural habitat of resident and migratory species of vultures, was investigated. Intensive surveys of the study area were undertaken from 2007 to 2015 to determine the annual population fluctuations in various vulture species in and around Jodhpur (26°19′N and 73°08′E). The data obtained regarding the population fluctuation of different vultures species in the study area are of great significance. Comparative analysis of data obtained with regard to the population dynamics of the various species of vultures in this region has suggested that there has been a drastic decline in the population of migratory as well as resident vulture species in this region. A comparative study suggests that the population of migratory species has reached very low relative abundance in 2015 as compared to 2007. Neophron percnopterus has the highest and Gyps bengalensis has the lowest population during the entire 9-year study. The finding suggests that the reason for this population fluctuation is climate change as well as change in temperature fluctuation over a period of time, particularly during the breeding season.

The importance of hunting pressure, habitat preference and life history for population trends of breeding waterbirds in Finland

Populations of migratory species have undergone dramatic changes in recent decades, but little is known about the factors actually driving those changes. Of particular concern are quarry species such as migratory ducks (Anatidae), many of which have an unfavourable conservation status in Europe. By including both quarry and non-quarry species, as well as habitat preference and life history characteristics of the species, we investigated the relative importance of hunting pressure, both in Finland and at the European level, in explaining population changes of 16 species of migratory waterbirds in Finland during 1986–2011. Ban of lead shot in 1996 resulted in considerably lower annual hunting bags in Finland thereafter. Species which had the highest hunting pressure had the most negative slopes in population trends from 1986 up to 1997, suggesting that hunting probably limited those populations. However, in general population trends of the species were not strongly associated with hunting pressure in Finland or in Europe. Nor were basic life history characteristics (body mass and clutch size) associated with population trends of the species. In contrast, recent population declines were associated with habitat preferences of the species: those breeding mainly in eutrophic lakes had more negative population trends than those breeding in oligotrophic lakes or generalist species. Reasons for the relatively poor status of species preferring eutrophic lakes probably include over-eutrophication of nutrient-rich lakes, resulting in less abundant food resources, and increased nest depredation.

Dams and the fish fauna of the Neotropical region: impacts and management related to diversity and fisheries

Reservoirs have been built in almost all of the hydrographic basins of Brazil. Their purposes include water supply for cities, irrigation and mainly, generation of electricity. There are more than 700 large dams and associated reservoirs in the large rivers of the country. These reservoirs favor local and regional economic development, but they also bring serious and irreversible alterations in the natural hydrologic regime of rivers, affecting habitat quality and the dynamics of the biota. In the impounded area, the main impact is the change from lotic to lentic water, which influences aquatic fauna, including fishes. Impacts of reservoirs present relevant spatiotemporal variations. Immediately after reservoir formation, fish species richness usually increases due to incorporation of surrounding habitats, but richness decreases as reservoirs age. However, impacts downstream of dams appear to be similar or stronger than those that occur within the reservoir. Dams promote discharge control, altering the seasonal cycles of floods. These effects are augmented when dams are constructed in cascades. Therefore, dams profoundly influence composition and structure of fish assemblages. Most affected species are the rheophilics and long distance migratory that require distinct habitats to fulfill their life cycles. Populations of migratory species may collapse or even disappear in intensely regulated stretches. Management actions taken to minimize impacts of dams in Brazil historically considered construction of fish passages, fishery control and stocking. The results of these actions are questionable and/or with clear failures. In this paper, we give emphasis to the Paraná River basin, the most affected by dams in Brazil. We describe some patterns in the alteration and decline in fish diversity in areas influenced by dams. We also discuss negative consequences in the fishery and ecosystems functioning. Finally, we argue the relevance and the success of the management actions taken and present some suggestions to improve conservation of the ichthyofauna in South American basins influenced by dams.

Seeing in the dark: molecular approaches to the study of bat populations.

Whilst the use of molecular genetic techniques is widespread in the fields of population and evolutionary biology, their application within the mammalian order Chiroptera neither reflects the species richness nor the ecological and behavioural diversity of the order. This is despite the fact that the Chiroptera are problematic to study using more direct observational techniques. Here, we standardize and synthesise the current data, assess the contribution of molecular research to the study of bat species and highlight the importance of its continued and expanded use. At an inter-population level, molecular studies have demonstrated a great diversity of population genetic structure within the order. Among populations of migratory species, genetic structure appears universally low, and hence seasonal movement is likely to be the prevailing influence. However, for sedentary species an array of factors including dispersal ability, extrinsic barriers to gene flow and historical events may determine the extent of genetic partitioning among populations. Intrinsic factors such as wing morphology or roost requirements may also influence population genetic structure in sedentary bat species, a proposal which requires further research. Molecular studies have also made important contributions towards an understanding of social organisation in bats. Evidence indicates that in many polygynous species male mating success does not translate directly into reproductive success, perhaps as a result of multiple mating by females. Estimates of relatedness within and genetic structure among colonies are, in general, very low; a finding which has important implications regarding theories concerning the formation and persistence of bat social groups. Molecular studies have provided new and important insights into the ecology of bats, and have opened up exciting and previously unexplored avenues of research. The data from these studies suggest not only a predictive framework for future studies, but also the use of genetic data in the management and conservation of bat species.

The effect of local change in habitat quality on populations of migratory species

1. Habitat deterioration is a major problem world‐wide as a result of processes such as change in land use, introduced species, human disturbance and exploitation of food supplies. Many studies have shown that habitat change can have considerable effect on the numbers of individuals using a site. For migratory species, however, the consequences for the total population cannot be deduced from local studies. 2. For a migratory species, the change in total population size ΔN, as a consequence of habitat change in the wintering area, can be calculated from ΔN = LMγd′/(b′ + d′), where γ is the expected proportional change in the number of birds using a site as a result of the habitat change, L is the area affected, M is the density of individuals using the site prior to habitat change, b′ is the strength of the per capita density‐dependent breeding output, and d′ is the strength of the per capita density‐dependent winter mortality. Similarly the consequences of habitat change in the breeding area can be calculated from ΔN = LMγb′/(b′ + d′). 3. The same approach can be used for predicting the consequences of improvements in habitat quality. 4. A worked example is given to illustrate how this approach could be used to predict the consequences for the total population of changes in the food supply of oystercatchers within one estuary. 5. There is a need for more measures of γ, the expected proportional change in the number of birds using a site as a result of various forms of habitat deterioration, and the strengths of density dependence.