Do changes in climate patterns in wintering areas affect the timing of the spring arrival of trans‐Saharan migrant birds?

The life cycles of plants and animals are changing around the world in line with the predictions originated from hypotheses concerning the impact of global warming and climate change on biological systems. Commonly, the search for ecological mechanisms behind the observed changes in bird phenology has focused on the analysis of climatic patterns from the species breeding grounds. However, the ecology of bird migration suggests that the spring arrival of long‐distance migrants (such as trans‐Saharan birds) is more likely to be influenced by climate conditions in wintering areas given their direct impact on the onset of migration and its progression. We tested this hypothesis by analysing the first arrival dates (FADs) of six trans‐Saharan migrants (cuckoo Cuculus canorus, swift Apus apus, hoopoe Upupa epops, swallow Hirundo rustica, house martin Delichon urbica and nightingale Luscinia megarhynchos), in a western Mediterranean area since from 1952 to 2003. By means of multiple regression analyses, FADs were analysed in relation to the monthly temperature and precipitation patterns of five African climatic regions south of the Sahara where species are thought to overwinter and from the European site from where FADs were collected. We obtained significant models for five species explaining 9–41% of the variation in FADs. The interpretation of the models suggests that: (1) The climate in wintering quarters, especially the precipitation, has a stronger influence on FADs than that in the species' potential European breeding grounds. (2) The accumulative effects of climate patterns prior to migration onset may be of considerable importance since those climate variables that served to summarize climate patterns 12 months prior to the onset of migration were selected by final models. (3) Temperature and precipitation in African regions are likely to affect departure decision in the species studied through their indirect effects on food availability and the build‐up of reserves for migration. Our results concerning the factors that affect the arrival times of trans‐Saharan migrants indicate that the effects of climate change are more complex than previously suggested, and that these effects might have an interacting impact on species ecology, for example by reversing ecological pressures during species' life cycles.     

Land-use trends in Endemic Bird Areas: global expansion of agriculture in areas of high conservation value

The impacts of humans on biodiversity tend to be exacerbated by the coincidence of human settlement with areas of high biological value, as demonstrated by regional, continental and global analyses. We present a global analysis, intersecting Endemic Bird Areas (EBAs) with fine‐scale data on changes in agricultural land use for the past 300 years and for four scenarios projecting land use up to 2050. The proportion of land in agricultural use is currently greater in EBAs than in the rest of the world (42.0% vs. 37.0%, respectively), has been historically (in 1700: 9.1% vs. 5.7%, through to 1900: 43.4% vs. 32.1%) and looks set to remain so in the future (44.6–56.1% vs. 37.0–43.2%; depending on scenario). However, the future course of agricultural expansion is more scenario‐dependent in EBAs than in the rest of the world, indicating that development policies have considerable potential to either ease or exacerbate the disproportionate impact of agriculture on areas of highest biological value.     

新疆黄鹀冬季的生物学资料

调查资料表明,黄鹀(Emberiza citronella erythrogenys)在中国境内新疆北部越冬,并非是偶见冬候鸟或迷鸟。     

Isolation of polymorphic tetranucleotide microsatellite markers for the little greenbul (Andropadus virens)

Thirteen polymorphic microsatellite markers have been developed for the little greenbul, Andropadus virens. The number of alleles range from two to 15 per locus with the observed heterozygosity ranging from 0.15 to 0.92. Eight sets of primers also amplify in closely related species, Andropadus laterostris and Andropadus tephrolaemus. These markers will be useful for analysis of questions concerning population genetic structure and models of speciation.     

Organization of Synaptic Inputs to Rubro-Spinal Neurons in the Cat: Interaction of the Effects of Stimulation of the Cerebellar Nucl. Interpositus and Thalamic Nucl. Ventrolateralis

We studied the interaction of synaptic effects in efferent (rubro-spinal) neurons (RSN) of the red nucleus (NR) of the cat brain using intracellular recording and different variants of stimulation of the cerebellar nucl. interpositus (NI) and nucl. ventrolateralis (VL) of the thalamus. Combined simultaneous or consequent stimulation of the above two inputs allowed us to use collision of the impulses in pre-synaptic pathways for estimation of the peculiarities of summation of post-synaptic potentials; it was taken into consideration that cerebello-rubral fibers are collaterals of the cerebello-thalamic axons. In the case of relatively low intensities of stimulation of the VL and NI, EPSP evoked by these stimulations in RSN could demonstrate linear summation, which is indicative of the absence of common fibers excited by stimulation of both the thalamic and cerebellar structures and of the absence of interaction of synaptic effects on the membrane of the postsynaptic unit (an RSN). With increased stimulation intensity and definite time relations between the stimuli applied to the above structures, the second EPSP evoked by the two stimuli was significantly suppressed; this resulted from a decrease of the afferent drive coming to the NR due to collision of afferent impulses in presynaptic pathways. When an interstimulus interval was increased, the second EPSP could be facilitated (probably due to generation of repetitive impulses in common presynaptic fibers). Our experiments show that the statement concerning the nature of cerebello-rubral inputs (all these inputs are formed by collaterals of the cerebello-(interposito)-thalamic pathways) should be considered with reservation.     

Immune challenge mediates vocal communication in a passerine bird: an experiment

Secondary sexual characters may have evolved in part to signalresistance to parasites. Avian song has been hypothesized tobe involved in this process, but the role of parasites in modulatingacoustic communication systems in birds remains largely unknown,owing to lack of experiments. We studied the relationship betweenparasitism, testosterone, song performance, and mating successin male collared flycatchers (Ficedula albicollis) by experimentallychallenging their immune system with a novel antigen. We predictedthat a challenge of the immune system would reduce song performance,and that this reduction would be conditional on the size ofa visual sexual signal, the forehead patch that was previouslyfound to reflect resistance. An antagonistic linkage betweentestosterone and immune function would predict that a challengeof the immune system should suppress testosterone level. Animmunological treatment by sheep red blood cells (SRBCs) triggereda decrease in body mass, testosterone level, and song rate,but other song traits were not significantly affected by theantigen challenge. Initial testosterone level was associatedwith forehead patch size and all song traits except song rate.SRBC injection caused stronger reduction in song rate amongmales with smaller forehead patches, and the change in songrate was also predictable by song features such as strophe complexityand length. We show that song rate and other song characteristicsmay be important cues in male-male competition and female choice.These results suggest that parasite-mediated sexual selectionhas contributed in shaping a complex acoustic communicationsystem in the collared flycatcher, and that testosterone mayplay an important role in this process. Parasitism may drivea multiple signaling mechanism involving acoustic and visualtraits with different signal function.     

Protandry and sexual dimorphism in trans-Saharan migratory birds

Earlier arrival to reproductive sites of males relative to females(protandry) is widespread among migratory organisms. Diversemechanisms have been proposed that may select for protandry,including competition for limiting resources (e.g., territories)or mates. In species with large variation in male reproductivesuccess, such as polygamous species and those with intense spermcompetition, early arriving males may accrue a fitness advantagebecause they acquire more mates or have larger chances of paternity.Comparative studies of birds have shown that sexual size dimorphism(SSD) is positively associated with the level of polygyny, whereasintense sperm competition is associated with sexual dichromatism(SD). Positive correlations between protandry and SSD or SDcan therefore be expected to exist across avian species. Becauselarge males are predicted to be better able to cope with adverseecological conditions early in the breeding season, selectionfor protandry, in turn, may have a correlated response on SSDamong migratory species breeding in boreal latitudes. Althoughprevious studies of birds have analyzed the association betweenSSD and protandry, none has analyzed SD in relation to protandry.Here we analyze the association between protandry during springmigration, SSD, and SD in 21 trans-Saharan monogamous migratorybird species. The difference in median migration dates betweenfemales and males, reflecting protandry, was positively associatedwith SD but not with SSD. Because dichromatism is positivelyrelated to sperm competition across species, present resultsare consistent with predictions derived from sexual selectionhypotheses for the evolution of protandry mediated by spermcompetition.     

Area and the latitudinal diversity gradient for terrestrial birds

We tested the hypothesis that area represents the primary explanation for the latitudinal diversity gradient using breeding terrestrial birds of North America, the northern Palearctic, Australia and the Afrotropics as our focal group. We tested two propositions inherent to the area hypothesis: (1) tropical biomes are larger than extra-tropical biomes, and (2) there is a significant species-area relationship for birds at the biome scale of resolution. Using a more realistic definition of biomes which incorporates the effects of both energy and water, we find no support for either proposition, leading us to conclude that the area per se does not explain terrestrial latitudinal diversity gradients.     

Evidence for long-distance dispersal in a sedentary passerine, Gymnorhina tibicen (Artamidae)

Australian magpies (Gymnorhina tibicen) are group-living birds found across much of mainland Australia. Adults commonly remain in a breeding territory until death. Young of the year either remain on the natal (birth) site or are forced by their parents to disperse. Observational studies in south-eastern Australia suggest that most dispersing juveniles settle within 7 km of their natal territory. Therefore, despite potential for considerable gene flow (via flight), social organization predisposes magpies towards local population structuring. In this study, we measured genetic variation at both nuclear (allozyme) and mitochondrial loci and found evidence of substantial gene flow over very large distances (up to 1599 km). Thus, some juvenile magpies may disperse much greater distances than was previously thought. For mtDNA, geographic and genetic distance were strongly correlated, consistent with a pattern of isolation by distance. Therefore, although female gene flow is substantial it is apparently geographically restricted over large distances, in approximately a stepping-stone fashion. We conclude that a strong relationship between gene flow and geographic distance can develop even over large distances if populations have experienced no major historical disturbances to gene flow.