La migration des cellules souches / progénitrices neurales (CSPN) dans le cerveau adulte est cruciale pour la réparation cérébrale. Reeline (Rln) est une protéine de la matrice extracellulaire, régulant le positionnement des neurones pendant la croticogénèse. Nous révélons un rôle nouveau de Rln chez l'adulte. In vitro, Rln est chémocinétique mais pas chémoattractante. In vivo, Rln induit le détachement et la dispersion des CSNP de la zone sousventriculaire (SVZ) hors du courant rostral de migration (RMS) où elles sont sinon confinées. Rln potentialise le recrutement spontané des CSPN vers les lésions démyélinisantes où un tiers deviennent oligodendrocytaires. L'expression endogène de Rln est stimulée après lésion. Les animaux sans voie de signalisation Rln ont un recrutement réduit des CSPN vers les lésions.Ces résultats révèlent que Rln est un arbitre clef de la migration post-lésionnelle des CSPN et que permettre au CSPN de sortir du RMS est une stratégie thérapeutique prometteuse. / Neural stem/ progenitor cell (NSPC) migration in the adult brain is crucial for brain repair. Reelin (Rln) is an extracellular matrix protein regulating neuron positioning during coricogenesis. We reveal new roles of Rln in adult NSPC migration. In vitro, Rln promotes detachment, is chemokinetic but not chemoattractant. After Rln ectopic overexpression in the healthly brain, subventricular zone (SVZ) NSPC detach from the rostal migratory stream (RMS) in which they are normally restricted, and disperse in adjacent fiber tracts. Rln over-expression potentiates spontaneous cell recruitment to demyelinated lesion and one third of the NSPC recruited adopt an oligodendrocytic phenotype. Rln expression is spontaneously upregulated after lesion, and disruption of its signaling pathway results in reduced NSPC recruitment toward lesion. Our study reveals that Rln is a key player of post-lesional NSPC migration and that allowing NSPC to escape from RMS is a promising therapeutic approach

Le plateado ou dorado - Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) est un grand poisson-chat Amazonien d’intérêt commercial, qui présente un des cycles de vie les plus surprenants et énigmatiques, avec la plus grande migration connue en eaux douces, entre l’estuaire de l'Amazone et les têtes de fleuves en Amazonie occidentale. Le but de ce travail était de déterminer, au niveau moléculaire, la position phylogénétique du plateado dans la famille Pimelodidae ainsi que sa structure génétique dans le Haut Madera (Villa Bella–VB, Cachuella Esperanza–CE, Puerto Maldonado–PM, Rurrenabaque–RU, Puerto Villarroel–PV) et ouest de l'Amazonie (Iquitos–IQ) bassins (Bolivie et Pérou). Les relations phylogénétiques ont été définies par une analyse du maximum de vraisemblance (ML) des séquences nucléotidiques de deux gènes mitochondriaux (Région de Contrôle–RC, ~ 900 pb, 32 taxons; Cytochrome Oxydase 1-CO1, ~ 650 pb, 61 taxons), et d’un gène nucléaire (F-reticulon4–RTN4, ~ 1700 pb, 38 taxons). La structure génétique des populations a été évaluée par le polymorphisme de longueur de neuf microsatellites (284 inds) et par les variations de séquence de la RC (461 inds + 45 en provenance du Brésil, disponibles dans GenBank). Les variations de fréquences des microsatellites ont été utilisées pour identifier les unités panmictiques (clusters) les plus probables dans l'ensemble des données, à travers une approche bayésienne (BAPS), après avoir démontré une déviation significative à l'équilibre de Hardy-Weinberg (HWE) quand l’ensemble des données étaient analysé comme faisant partie d’une seule unité.L’analyse phylogénétique concaténée (ML) a montré que la famille Pimelodidae était un groupe monophylétique. Les résultats les plus notables de la phylogénie sont la monophylie peu soutenue (77%) de la tribu Brachyplatystomatini et la non-monophylie des Brachyplatystoma. Seul le sous-genre Malacobagrus (B. rousseauxii + (B. filamentosum + B. capapretum)), défini morphologiquement, s’est avéré monophylétique. Ces résultats suggèrent que le genre Brachyplatystoma pourrait contenir Platynematichthys ou pourrait être limité au sous-genre Malacobagrus.L'analyse des microsatellites sur l'ensemble des échantillons (ouest Amazone + haut Madera) a montré un écart significatif á la panmixia, ainsi que sur l'ensemble des échantillons du haut Madera. A la lumière de ces résultats, l’approche bayésienne a été développée, montrant qu'au moins trois clusters (1, 2, 3) sont présents dans les bassins du haut Madera et de l'ouest de l'Amazone, avec des répartitions qui se chevauchent partiellement. En parallèle á l'identification des clusters, il a été mis en évidence une différence significative au sein de B. rousseauxii entre l’ouest de l'Amazonie et le haut Madera bassin.L'analyse généalogique (ML) des séquences de la RC a montré une topologie en peigne, sans groupe d'haplotypes montrant une histoire commune. En revanche, l'analyse des fréquences haplotypiques a révélé l’existence de 4 haplogroupes, liés à la géographie. Un haplogroupe a été identifié le long de l'axe principal de l’Amazonas-Solimões (Belem-Brésil et Iquitos-Pérou) et 3 autres dans le haut Madera (VB; CE+MD; RU+PV), organisés selon une tendance aval - amont. Ainsi, nous observons d’un coté 3 populations (clusters) avec une distribution géographique partiellement chevauchante, et de l’autre quatre haplogroupes positionnés selon une logique géographique. Le scenario le plus probable implique un comportement de homing des individus du cluster 1 (homing à l’échelle des grands sous-bassins), qui préfèrent ou tendent à retourner dans le sous-bassin du Madera. Les 3 populations coexisteraient alors dans le haut Madera en se reproduisant à des périodes (phénologie) ou à des endroits différents (ségrégation spatiale). Enfin, les résultats sont discutés à la lumière des résultats précédemment publiés dans le bassin de l'Amazone et des menaces qui pèsent sur l'espèce dans le bassin du Madera. / The Plateado or Dorado - Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) is a commercial migratory catfish species with one of the most surprising and enigmatic life histories in the Amazon basin, involving the largest migration known for a freshwater species, between the estuary and the head waters in the Andean piedmont. The aim of the present work was to determine the molecular phylogenetic position of the Plateado in the Pimelodidae family and its population genetic structure in the Upper Madera (Villa Bella – VB, Cachuella Esperanza – CE, Puerto Maldonado – PM, Rurrenabaque – RU, Puerto Villarroel - PV) and Western Amazon (Iquitos - IQ) basins (Bolivia and Peru). The phylogenetic relationships were defined through a Maximum Likelihood (ML) analysis of nucleotide sequences of two mitochondrial (Control Region – CR, ~ 900 pb, 32 taxa; Cytochrome Oxidase 1 – CO1, ~ 650 bp, 61 taxa), and a nuclear fragment (F-reticulon4 - RTN4, ~1700 bp, 38 taxa). The population genetic structure was evaluated through the length polymorphism of nine microsatellites (284 inds) and CR sequence variations (461 inds + 45 from Brazil available in GenBank). Microsatellites frequencies variations were used to identify through a Bayesian approach (BAPS) the most probable panmictic units (clusters) in the whole data, after previous demonstration of a deviation to Hardy-Weinberg Equilibrium (HWE). The ML phylogenetic concatenated analysis showed the Pimelodidae family as a monophyletic group, with the genera Phractocephalus and Leiarius as basal lineages. The most notable results in the phylogeny were the not well-supported monophyly (77%) of the tribe Brachyplatystomatini and the non-monophyly of Brachyplatystoma. Only the morfologically defined subgenus Malacobagrus (B. rousseauxii + (B. filamentosum + B. capapretum)) was recovered as monophyletic. These results suggest that Brachyplatystoma could contain Platynematichthys or be restricted to the subgenus Malacobagrus, and the other species be related to distinct (earliest) genera, in agreement with another study carried out in parallel with other markers.Microsatellite analysis of the whole data (Western Amazon + Upper Madera) showed a significant departure of the HWE expectations, as well as the analysis of the whole data from the Upper Madera region. In the light of these results, the Bayesian approach has been implemented, showing that at least three clusters (1, 2, 3) are present in the Upper Madera and Western Amazon basins with partial overlapping distribution.To the margin of the cluster identification, it was evident the significant difference between Western Amazon (Iquitos region) and the Upper Madera basin.The genealogical analysis (ML) of the CR sequences showed a generalized comb-like topology without group of haplotypes with common ancestry. On the other hand, CR frequency analysis showed the conformation of four haplogroups associated to geography. One haplogroup was identified along the main axis of the Amazonas-Solimões, from Belem (Brazil) to Iquitos (Peru), and three other haplogroups were observed in the Upper Madera basin (VB; CE+PM; RU+PV), positioned in a downstream - upstream pattern.Hence, we observed on the one hand three genetic populations (clusters), distributed in partially overlapping geographical areas, and on the other hand four haplogroups, positioned according to a geographical pattern. The most probable scenario involves a homing behavior of individuals from cluster 1 (homing at the scale of large watersheds), which prefer or tend to return to the Madera basin, with the three populations coexisting within the upper Madera because they reproduce at different moments (phenology) or different places (spatial segregation). Finally, the results are discussed in the light of previous results in the Amazon basin and the threats to the species in the Madera basin (p.e. fragmentation by dams, overfishing, climate variability, among other).

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Anseriformes mantidos em lagos de zôos e parques estão sob constante risco de exposição às doenças presentes nas populações de aves migratórias, que dividem com eles o mesmo local durante um determinado período todos os anos. São doenças que podem ter implicações para as aves cativas, para a população humana que tem contato com essas aves e para os plantéis de produção. Assim, ações de vigilância, com o objetivo de detectar rapidamente determinadas doenças, representam alternativas interessantes para se fazer gestão de risco. O objetivo do presente estudo foi pesquisar a presença de agentes etiológicos selecionados na população de Cisnes Negros (Cygnus atratus), mantida nos lagos da FPZSP, visto que essa população tem contato com as seguintes aves migrantes que visitam a FPZSP todos os anos: irerês (Dendrocygna viduata), marreca caneleira (Dendrocygna bicolor) e marreca asa de seda (Amazoneta brasiliensis). Assim, foram colhidos suabes de traquéia e cloaca de uma amostra capaz de detectar doença com prevalência estimada em 1% para um nível de confiança de 95%. Além disso, foi realizado um estudo retrospectivo (2001 a 2006) das principais causas de morte nessa população. As principais causas de mortalidade registradas em 184 registros analisados foram: desvio de tendão extensor tarso-metatarsiano (37, 20,1%), desnutrição (20, 10,9%), problemas hepáticos (17, 9,2%), traumas (15, 8,2%), problemas respiratórios (8, 4,3%), septicemias (6, 3,3%), intoxicações (5, 2,7%) e problemas gastrointestinais (3, 1,6%). Um terço das carcaças (62, 33,7%) foi encontrado em estado de putrefação. A taxa de mortalidade foi decrescente de 2001 a 2006 e apresentou sazonalidade, sendo maior entre os meses de novembro a maio. No momento das coletas, não houve nenhuma evidência clínica ou laboratorial da presença dos seguintes agentes: Pasteurella multocida., Salmonella sp., Chlamydophila psittaci, Orthomixovírus (Influenza Aviária), Paramixovirus (Doença de Newcastle) e Coronavirus (Bronquite Infecciosa). / Waterfowls housed in ponds of zoos and parks are under constant risk of exposure to pathogens of migratory birds that visit these places every year. Some of them involving zoo animals and humans. The spread of particular diseases may also become a serious threat for domestic poultry. So, surveillance, focused in early detection of some diseases, can be an interesting tool to do risk management. The goal of the present work was to search the presence of some select pathogens in the captive black swan population (Cygnus atratus) present in the ponds of the Fundação Parque Zoológico de São Paulo (FPZSP), because these animals have contact with the following free-living waterfowls: white-faced whistling-duck (Dendrocygna viduata), fulvous whistling-duck (Dendrocygna bicolor) e brasilian teal (Amazoneta brasiliensis). Swabs of trachea and cloaca were sampled from 239 animals, the sample size required for detecting disease present in at least 1% of the animals (CI = 95%). Moreover, a retrospective study was done about the causes of death to the period from 2001 to 2006. The mainly causes of black swan death in FPZSP were: slipped tendon (37/184, 20,1%), malnutrition (20/184, 10,9%), hepatic problem (17/184, 9,2%), trauma (15/184, 8,2%), respiratory problem (8/184, 4,3%), septicemias (6/184, 3,3%), intoxication (5/184, 2,7%) e gastro-intestinal problems(3/184, 1,6%). One third of the carcass (62/184, 33,7%) was in autolysis. The mortality presented peaks of occurrence from november to may and a decreasing trend from 2001 to 2006. At the moment of the sampling, there was no clinical or laboratorial evidence of the infection by the following pathogens: Pasteurella multocida., Salmonella sp., Chlamydophila psittaci, Orthomixovírus (Avian Influenza), Paramixovirus (Newcastle Disease) e Coronavirus (Infectious Bronchitis).

As migrações constituem um dos pilares da relação entre Brasil e Portugal. Com esta premissa este estudo tem por objetivo compreender a formação, a sustentação no tempo e a configuração atual do sistema migratório luso-brasileiro. Partindo da Geografia da População, dialoga-se tanto com os demais campos da própria ciência geográfica, especialmente a Geografia Política e a Geografia Econômica, como com as demais ciências humanas e sociais, dentre outras a Sociologia e a Antropologia. Adota- se uma periodização que busca articular as migrações e as imaginações geográficas produzidas e produtoras das ordens geopolíticas. Esta perspectiva diacrônica tem como ponto de partida a formação do estado territorial português e, posteriormente, do estado territorial brasileiro. Enfatiza-se, em especial, como homens e mulheres imigrantes brasileiros e portugueses participam das transformações recentes de Portugal e do Brasil, respectivamente. Desde o final da década de 2000 há uma situação em que fluxos e contrafluxos migratórios praticamente se equivalem. Dados quantitativos e qualitativos foram utilizados para demonstrar que portugueses no Brasil e brasileiros em Portugal imigrados a partir de 2000 possuem perfis diferentes quanto à idade, sexo, nível de instrução e inserção no mercado laboral. A análise das semelhanças e divergências entre estes grupos de imigrantes levou à consideração de que enfrentam barreiras e desafios distintos, mas têm em comum sua contribuição para ressignificação de uma relação pretérita e assimétrica, marcada pelo compartilhar de uma população luso-brasileira. / Migration is one of the pillars of the relationship between Brazil and Portugal. Over this assumption, this study aims to understand the formation, the maintenance over time and current configuration of Luso-Brazilian immigration system. Starting from Population Geography, the thesis dialogues with the main disciplines of geographical science, notably Political Geography and Economic Geography, as well as other human sciences like Sociology and Anthropology. A periodization is adopted in an effort to articulate the migration and geographical imaginations seen as result and an inductive process of geopolitical orders. This diachronic perspective takes as bottom line the formation of portuguese territorial state and, later, the formation of brazilian territorial state. The research seeks to emphasize, particularly, how brazilian and portuguese immigrants, men and women, participates on the recent transformations of Brazil and Portugal. Since the end of this decade, there is a situation in which migration flows and counterflows are virtually equivalent. Quantitative and qualitative data were used to demonstrate that portugueses in Brazil and brazilians in Portugal, those whom emigrated from 2000 until now, have different profiles in terms of age, sex, educational level and labour market insertion. The analysis of the similarities and differences between these groups of immigrants led to the consideration that they do face barriers and different challenges, but combine a contribution to a redefinition of a historical and asymmetrical relationship, strongly marked by the sharing of a Luso-Brazilian population.

[pt] Este trabalho tem como foco analisar a experiência migratória de jovens peruanos que se dirigem ao Brasil como estudantes universitários. Entendendo a experiência migratória como um conjunto de vivências proporcionadas pelo deslocamento por diferentes espaços geográficos e simbólicos concomitantemente, a tese examina os significados que preenchem de sentido a mobilidade estudantil internacional. Baseando-se no método etnográfico, que tem na intersubjetividade uma condição para produção de conhecimento, a presente pesquisa analisa como os estudantes se apropriam das condições oferecidas pela sociedade peruana e brasileira para a realização deste tipo particular de mobilidade. Quando ainda estão no Peru, os jovens descobrem através de suas redes as oportunidades de estudar no Brasil, um país próximo geograficamente, mas distante culturalmente. No país de destino, as redes apoiam a adaptação dos jovens à vida cotidiana no Rio de Janeiro. Se tornar um estudante no exterior é a estratégia que os jovens peruanos elaboram para se integrar ao fluxo internacional de pessoas de forma mais socialmente prestigiada, lidando com as hierarquias de poder da sociedade peruana, que atribuem um maior valor àqueles que já viveram no exterior. Negociando com as condições estruturais dentro e fora do seu país, estes jovens encontram na mobilidade estudantil uma oportunidade para almejar novos horizontes. Neste processo, os jovens peruanos encontram um terreno fértil para (re)pensar a si mesmos, seu país de origem, o destino e o mundo. / [en] This work aims to analyze the migratory experience of Peruvian young people who go to Brazil as university students. Understanding the migratory experience as a set of experiences provided by displacement towards different geographical, and symbolic space concomitantly, this thesis examines the meanings that give a sense to international student mobility. Through ethnographic method, which consider intersubjectivity as inherent to knowledge production, the present study examines how peruvian students appropriate the conditions that Brazilian and Peruvian society offers to make this specific kind of mobility possible. Still in Peru, their network inform them about oportunities to study in Brazil, a country that is geographic close, but cultural distant from them. Once peruvian students arrive there, network in Brazil uphold their adaption to everyday life in Rio de Janeiro. To become an international student is a strategy that Peruvian young people ellaborate to be integrated into international people flow in a more prestigious way. In this process, they deal with power hierarchy of Peruvian society, that attribute greater valeu to those who have lived abroad. Negotiating against structural conditions in and outside their homecountry, these young people find in student mobility an opportunity to crave new horizons. In such process, they find a fruitful terrain to (re)think themselves, their homeland, the destination and the world.

Européenne, (Anguilla anguilla) a conduit à une diminution du nombre d’anguille jaune dans les bassins versants. En 2007, le règlement (CE) instaure que 60% des civelles pêchées (<12 cm de long) doivent être dédiés à des opérations de repeuplement. Cependant, pour migrer et coloniser un nouvel environnement, les civelles doivent avoir une bonne condition énergétique. Or, les civelles ne s’alimentent pas ou peu durant leur migration estuarienne et la vitesse d’utilisation de leurs réserves dépend de divers facteurs (température, contaminants etc.). Dans l’estuaire de l’Adour, différents travaux ont mis en évidence de fortes concentrations en methylmercure (MeHg) dans les sédiments et une bioaccumulation de ce composé chez l’anguille jaune. L’exposition au MeHg entraîne la mise en place de processus de détoxication qui pourraient être couteux en énergie ce qui, chez des organismes jeûnant comme les civelles, conduirait à une perte de poids pouvant affecter leurs capacités de migration. Pour étudier l’impact du méthylmercure sur le potentiel de migration des civelles, nous avons tout d’abord (1) effectuer un état des lieux des concentrations en MeHg des civelles de l’estuaire de l’Adour, (2) évaluer l’effet du MeHg sur deux synchroniseurs de la migration estuarienne: le signal crépusculaire et l’alternance des marées chez les civelles grâce à l’utilisation de traceurs isotopiques et (3) étudier dans le milieu naturel (Adour) le comportement de migration, les taux de contamination au mercure et les mécanismes de détoxication des civelles. Nos résultats montrent des fluctuations temporelles et saisonnières de la concentration en MeHg des civelles prélevées en entrée et en milieu de l’estuaire. Par ailleurs, l’exposition au MeHg, en milieu contrôlé, a augmenté l'activité des civelles mais pas leur comportement de migration. Cependant, suite à la contamination, la structure mitochondriale et le métabolisme ont été modifiés suggérant un plus fort stress oxydant et une activation des défenses antioxydantes notamment des civelles ayant un faible potentiel de migration (non migrantes).En complément, l’étude en milieu naturel a mis en évidence une plus forte demande énergétique pour les civelles non migrantes entrainant une augmentation du fonctionnement des mitochondries et pouvant conduire à un plus fort stress oxydant. / Over the last three decades, the arrival of Anguilla anguilla glass eels has markedly declined which has lead to a decrease in the number of yellow eels in the watersheds. In 2007, the Regulation (EC) indicated that 60% of glass eels (<12cm long) caught by fisheries should be used for restocking. To migrate and colonize a new environment, glass eels must have a good energetic condition. However, during their estuarine migration, glass eels either feed very little or more likely not at all. The speed at which they expend their energy stores depends on various factors (temperature, contaminants etc.). In the Adour estuary, many studies have reported relatively high methylmercury (MeHg) concentrations in the sediments, and bioaccumulation in yellow eels. Exposure to MeHg requires energy for detoxification which, in starving organisms such as glass eels, might lead to weight loss, decreasing their ability to migrate up the estuary. To study the impact of MeHg on migratory behaviour in glass eels, we first conducted an inventory of MeHg concentrations of glass eels in the estuary of the Adour, (2) evaluate the effect of MeHg on two synchronizers of estuarine migration: dusk and tide on glass eels through the use of isotopic tracers and (3) to study the natural environment (Adour) migratory behavior, mercury contamination levels and detoxification mechanisms of glass eels. Our results show temporal and seasonal fluctuations in the concentration of MeHg glass eels collected input and middle of the estuary. Moreover, MeHg exposure, in a controlled environment, increased the activity of glass eels but not in response to migratory behavior. However, due to contamination, mitochondrial structure and metabolism have been modified suggesting a stronger oxidative stress and activation of antioxidant defences of glass eels, particularly those with low migration potential (non-migrant). In addition, the wild study showed a higher energy demand for non-migrating glass eels causing an increase in mitochondrial function which may lead to higher oxidative stress.

For migrant birds, the non-breeding season can greatly influence survival and future reproductive success. Knowledge of annual and overwinter survival, the degree of site fidelity and habitat use in the non-breeding season, migration ecology, routes and stopovers, and whether these differ with age or sex is fundamental to understanding population dynamics, vulnerability to anthropogenic habitat degradation, and consequently for understanding the severe widespread declines of migrant bird species. The degree to which a migrant is a winter specialist or generalist is likely to be central to understanding population dynamics. I studied survival rates and the wintering and migration ecology of a declining Palearctic migrant, the whinchat Saxicola rubetra, wintering in West Africa, to establish how the non-breeding season may influence migrant population dynamics. Whinchats were extremely site faithful to both within and between years, holding distinct winter territories and returning to those territories in subsequent winters, despite the opportunity to relocate. Overwinter survival was very high and annual survival was comparable to or higher than that reported on the breeding grounds. Because our power to detect resident and dispersing birds was high, survival rates likely estimated true survival well. Habitat characteristics varied widely across territories and territories were smaller if more perching shrubs and maize were present. Most individuals showed a tolerance or even preference for human modified habitats. Some individuals may have multiple wintering sites. There was no evidence of dominance-based habitat occupancy or any differences in winter ecology, site fidelity, survival and most aspects of migratory behaviour between age and sex classes. Migratory connectivity occurred only on a large-scale and individual migratory behaviour was also varied. Fundamentally, the results suggest a generalist strategy in the non-breeding season within their wintering habitat of open savannah, most likely as an adaption to stochastic site selection within the wintering range for juveniles undertaking their first migration plus changing and unpredictable conditions both within and between years. Consequently, wintering conditions may not significantly limit whinchat populations and mortality is probably highest during active migration. Notably, non-specialist migrants such as whinchats may have some resilience at the population-level to the increasing anthropogenic habitat modification occurring in Africa, suggesting that conditions during migration and in Europe may be driving declines; yet establishing the currently unknown thresholds of any resilience is likely to be fundamental for the future conservation migrants.

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Animal populations are limited by their environment and interactions with one another, the latter proportional to density. How density-dependent mechanisms regulate populations is poorly understood, particularly for migratory animals. Winter, or non-breeding, mechanisms remain particularly poorly understood for almost all migratory bird species. This dissertation tested the hypothesis that American Redstarts (Setophaga ruticilla) are regulated both within and between habitats in the winter by two mechanisms, a crowding effect and a buffer effect. As population size increases, crowding increases competition for space and resources and more individuals are relegated to lower quality habitats and forced into a transient behavioral strategy, which buffers high quality habitats from negative feedback of density. My study was carried out in Jamaica, where redstarts occupy diverse habitats. I found that population size varied among habitats, but accounting for both territorial and transient individuals was critical for accurate assessment of this variation. Ecological conditions drive differences in habitat suitability and redstart density at multiple spatial scales. Regionally, redstart survival, density, and numbers of transient individuals distinguish inland from coastal populations, consistent with differences in ecological conditions (e.g. rainfall). Locally, timing of spring departure, as well as age and sex structure distinguish neighboring habitats, consistent with increased competition for food. When population size increased over the years of this study, changes in local density were similar among habitats, and thus not the result of a buffer effect. However, increasing densities decreased food availability, which corresponded with negative feedback on departure timing and territorial behavior, i.e. more transients, in poorer habitats. This supported a crowding effect on spatial behavior (territoriality) and late-winter condition of individuals relegated to low suitability habitats. High quality inland habitats appear to buffer individuals from the effects of changing population abundance, as well as ecological conditions, evidence of a regional buffer effect. / acase@tulane.edu