The strength of migratory connectivity is a measure of the cohesion of populations among phases of the annual cycle, including breeding, migration, and wintering. Many Nearctic-Neotropical species have strong migratory connectivity between breeding and wintering phases of the annual cycle. It is less clear if this strength persists during migration when multiple endogenous and exogenous factors may decrease the cohesion of populations among routes or through time along the same routes. We sampled three bird species, American redstart Setophaga ruticilla, ovenbird Seiurus aurocapilla, and wood thrush Hylocichla mustelina, during spring migration through the Gulf of Mexico region to test if breeding populations differentiate spatially among migration routes or temporally along the same migration routes and the extent to which withinpopulation timing is a function of sex, age, and carry-over from winter habitat, as measured by stable carbon isotope values in claws (δ 13 C). To make quantitative comparisons of migratory connectivity possible, we developed and used new methodology to estimate the strength of migratory connectivity (MC) from probabilistic origin assignments identified using stable hydrogen isotopes in feathers (δ 2 H). We found support for spatial differentiation among routes by American redstarts and ovenbirds and temporal differentiation along routes by American redstarts. After controlling for breeding origin, the timing of American redstart migration differed among ages and sexes and ovenbird migration timing was influenced by carry-over from winter habitat. The strength of migratory connectivity did not differ among the three species, with each showing weak breeding-to-spring migration MC relative to prior assessments of breeding-wintering connectivity. Our work begins to fill an essential gap in methodology and understanding of the extent to which populations remain together during migration, information critical for a full annual cycle perspective on the population dynamics and conservation of migratory animals.

In order to study the interaction between the renin-angiotensin system (RAS) and nitric oxide (NO), we analyzed the activity of aspartyl- (AspAP), glutamyl- (GluAP), alanyl- (AlaAP), and cystinylaminopeptidase (CysAP) enzymes involved in the RAS cascade, in the hypothalamus, and plasma of normotensive adult male rats after the inhibition of NO production with the NO synthase inhibitor L-NAME (L-N (G)-nitroarginine methyl ester). L-NAME treatment produced a significant increase of systolic blood pressure (SBP). In plasma, while GluAP activity decreased significantly, suggesting a lower Ang III formation, the other aminopeptidases did not change after L-NAME treatment. In hypothalamus, the activities of AspAP and CysAP were not affected after L-NAME treatment. In contrast, GluAP and AlaAP increased significantly. These results suggested mainly a higher formation of Ang III, but also higher levels of Ang IV in the hypothalamus of L-NAME treated rats. Both peptides have hypertensive properties at central level. On the contrary, Ang III may counteract the hypertensive action of Ang II at the periphery. Therefore, the increased SBP in L-NAME treated rats may be due in part to the increased activity of GluAP and AlaAP in hypothalamus and to a decreased activity of GluAP in plasma.

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Barrier islands on the north coast of the Gulf of Mexico are an internationally important coastal resource. Each spring hundreds of thousands of Nearctic-Neotropical songbirds crossing the Gulf of Mexico during spring migration use these islands because they provide the first landfall for individuals following a trans-Gulf migratory route. The effects of climate change, particularly sea level rise, may negatively impact habitat availability for migrants on barrier islands. Our objectives were (1) to confirm the use of St. George Island, Florida by trans-Gulf migrants and (2) to determine whether forested stopover habitat will be available for migrants on St. George Island following sea level rise. We used avian transect data, geographic information systems, remote sensing, and simulation modelling to investigate the potential effects of three different sea level rise scenarios (0.28 m, 0.82 m, and 2 m) on habitat availability for trans-Gulf migrants. We found considerable use of the island by spring trans-Gulf migrants. Migrants were most abundant in areas with low elevation, high canopy height, and high coverage of forests and scrub/shrub. A substantial percentage of forest (44%) will be lost by 2100 assuming moderate sea level rise (0.82 m). Thus, as sea level rise progresses, less forests will be available for migrants during stopover. Many migratory bird species’ populations are declining, and degradation of barrier island stopover habitat may further increase the cost of migration for many individuals. To preserve this coastal resource, conservation and wise management of migratory stopover areas, especially near ecological barriers like the Gulf of Mexico, will be essential as sea levels rise.

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