Parasite assemblages distinguish populations of a migratory passerine on its breeding grounds

We attempted to establish migratory connectivity patterns for American redstarts Setophaga ruticilla between their breeding and wintering grounds by characterizing the composition of their haematozoan parasite assemblages in different parts of their range. We detected significant but limited geographic structuring of haematozoan parasite lineages across the breeding range of the redstart. We found that redstarts from the south-eastern (SE) region of the breeding range had a significantly different haematozoan parasite assemblage compared with populations sampled throughout the rest of the breeding range. Evidence using stable isotopes from feathers previously demonstrated that redstarts from the SE of the breeding range also have a unique and separate wintering range. Thus, although two methods of estimating migratory connectivity have now both shown the SE US breeding sub-population of redstarts to be distinct from other populations on both the breeding and wintering grounds, conclusive migratory connectivity for this species as a whole could not be established.     

Corticosterone levels as indicators of habitat quality: effects of habitat segregation in a migratory bird during the non-breeding season

During the non-breeding season, many species of territorial migratory birds exhibit a non-random pattern of habitat distribution, with males and females occupying different habitats. In this study, we examined possible physiological consequences arising from such habitat segregation in one migrant passerine species, the American redstart (Setophaga ruticilla), on its non-breeding grounds in Jamaica, West Indies. For 2 years, we measured concentrations of corticosterone, at the time of capture (baseline) and 30 min after capture (profile of acute corticosterone secretion), in redstarts in two distinct habitats, one occupied predominately by males and one mostly by females. All redstarts in both habitat types exhibited similar concentrations of baseline corticosterone levels in fall (October), whereas in spring (March–April), redstarts in female-biased habitat exhibited significantly higher baseline levels regardless of age or sex. In fall, all individuals in both habitats exhibited significant increases in corticosterone concentration with capture and handling, but in spring only redstarts (both sexes) in male-biased habitat continued to exhibit acute corticosterone secretion. Redstarts in female-biased habitat had elevated baseline corticosterone levels and reduced acute corticosterone secretion. In spring, baseline corticosterone concentration was negatively correlated with body mass, suggesting muscle catabolism associated with high corticosterone concentrations or possibly that birds are leaner as a result of increased foraging effort. These results indicate that redstarts (primarily females) in female-biased habitats suffered a decline in physiological condition, which could in turn influence their departure schedules, migration patterns and even their condition and arrival schedules on the breeding grounds. Thus, segregation of populations into habitats of different quality during the non-breeding period may have ramifications throughout the annual cycle of such migratory species. Furthermore, these results show the usefulness of plasma corticosterone levels as indicators of physiological condition and thus habitat quality for birds during the non-breeding period. Received: 14 November 1997 / Accepted: 9 March 1998     

Host activity and the risk of nest parasitism by brown-headed cowbirds

Proportions of nests parasitized by brown-headed cowbirds (Molothrus ater) vary greatly among host species, but factors underlyingthis variation remain poorly understood. Cowbirds are believedto find nests by watching host behavior. We tested the hypothesisthat the activity of hosts during nest building correlateswith the probability of parasitism among and within four sympatrichosts: dusky flycatchers (Empidonax oberholseri), warblingvireos (Vireo gilvus), yellow warblers (Dendroica petechia),and American redstarts (Setophaga ruticilla). Daily probabilityof parasitism varied substantially among these species, from3% for dusky flycatchers to more than four times that for warblingvireos. The four species did not differ in the proportion ofcowbirds fledged from their nests. Differences in nest placementdid not explain differences in probability of parasitism amongor within species. Parasitism frequencies increased among speciesthat made longer nest-building visits, had a greater propensityto perch during nest approach, spent more time near their nests,and had males that vocalized more often near nests. Within species, females that visited their nests less often, spent more timeon the nest per visit, and males that sang more and were activein a smaller area around their nests were more likely to beparasitized by cowbirds. These data support the hypothesisthat cowbirds use the activity of hosts during nest buildingto locate nests.     

中国侯鸟环志的研究

环志是研究鸟类迁徙最简单有效的科学方法。中国从１９８２年开始建立全国鸟类环志中心以来,在林业部的领导下至１９９０年先后建立了候鸟环志站、点６０处,共计环志了候鸟１８６种６２７５５只,同期回收到国内外环志鸟４１３只。回收环志鸟提供了东亚地区候鸟迁徙的宝贵信息,证实了：１．候鸟迁徙可自喜马拉雅山脉飞越;２．中国候鸟迁徙路线和推论是正确的;３．中国东北繁殖的白枕鹤飞往日本九洲南部越冬,丹顶鹤等迁往东部沿海、长江中下游几处湿地越冬,与来自俄罗斯西伯利亚的部分鹤在相同地区越冬;４．某些鸟种迁徙路线在与日本同种候鸟迁徙路线比较后,表明在西太平洋地区,通过中国和日本存在着两条平行的自南向北迁徙的路线。其他信息也指出了更多的情况,同时也表明中国环志研究在西太平洋迁徙候鸟研究中处于关键性的地位。     

The role of behavioral dominance in structuring patterns of habitat occupancy in a migrant bird during the nonbreeding season

Several species of territorial migratory birds exhibit sexualhabitat segregation on their wintering grounds, with some habitatscontaining mostly males and others mostly females. The objectiveof this study was to determine if in the American redstart(Setophaga ruticilla) in Jamaica habitat segregation is dueto social mechanisms or due to sex-specific habitat specialization.I used habitat-specific patterns of arrival by young males andfemales, observations of territorial displacements, removalexperiments, and simulations of territorial intrusions to differentiatebetween these two mechanisms. Redstarts were studied in twohabitat types, a male-biased mangrove forest and a female-biasedscrub habitat. In autumn, male and female hatch-year redstartsinitially settled in equal numbers in each habitat, and segregationof the sexes occurred gradually and mostly later in the arrivalperiod. This shift corresponded with an increase in densityof older birds and an increase in territorial displacements.Removal experiments showed that vacancies in male-biased habitatwere filled more rapidly and with greater frequency than thosein female-biased habitat and that vacated male territoriesin mangrove were replaced more often by females than by males.Simulations of territorial intrusions and analyses of body sizeindicated that levels of aggression and body size of both malesand females were greater in mangrove habitat, suggesting thatthese factors may be important in determining the outcomesof dominance interactions. I conclude that patterns of sexualhabitat segregation in redstarts are structured by the dominancebehavior of older and more dominant individuals, and these aremostly males.     

吉林珲春2002～2005年鸟类环志监测报告

2002～2005年在吉林省珲春市马川子乡依力南沟开展了鸟类环志研究工作。这里为长白山低山丘陵区,是候鸟经长白山脉、乌苏里江迁徙途中重要的停歇地和食物补给站。4年共环志鸟类126种63386只,其中春季103种9761只,秋季113种53625只,隶属13目37科。春季以黄喉鸦（Emberiza elegans）为迁徙鸟类的优势种,环志2467只,占春季环志数量的25．3％;秋季以黄喉鸦、红胁蓝尾鸲（Tarsiger cyanurus）、黄眉柳莺（Phylloscopus inornatus）、大山雀（Parus major）、白眉鸦（E.tristrami）、极北柳莺（P.borealis）等6种为迁徙鸟类的优势种,累计33586只,占秋季环志数量的62．6％;通过环志研究发现,被认为是留鸟的大山雀、银喉长尾山雀（Aeghhalos caudatus）、沼泽山雀（P.palustris）、长尾雀（Uragus sibiricus）具有定期的迁徙行为。     

Feather mites and birds: an interaction mediated by uropygial gland size?

Feather mites (Arachnida: Acari: Astigmata) feed mainly on secretions of the uropygial gland of birds. Here, we use analyses corrected for phylogeny and body size to show that there is a positive correlation between the size of this gland and mite abundance in passerine birds at an interspecific level during the breeding season, suggesting that the gland mediates interactions between mites and birds. As predicted on the basis of hypothesized waterproofing and antibiotic functions of uropygial gland secretions, riparian/marsh bird species had larger glands and higher mite loads than birds living in less mesic terrestrial environments. An unexpected pattern was a steeper relationship between mite load and gland size in migratory birds than in residents. If moderate mite loads are beneficial to a host but high loads detrimental, this could create complex selection regimes in which gland size influences mite load and vice versa. Mites may exert selective pressures on gland size of their hosts that has resulted in smaller glands among migratory bird species, suggesting that smaller glands may have evolved in these birds to attenuate a possible detrimental effect of feather mites when present in large numbers.     

Variable shifts in spring and autumn migration phenology in North American songbirds associated with climate change

Monitoring studies find that the timing of spring bird migration has advanced in recent decades, especially in Europe. Results for autumn migration have been mixed. Using data from Powdermill Nature Reserve, a banding station in western Pennsylvania, USA, we report an analysis of migratory timing in 78 songbird species from 1961 to 2006. Spring migration became significantly earlier over the 46-year period, and autumn migration showed no overall change. There was much variation among species in phenological change, especially in autumn. Change in timing was unrelated to summer range (local vs. northern breeders) or the number of broods per year, but autumn migration became earlier in neotropical migrants and later in short-distance migrants. The migratory period for many species lengthened because late phases of migration remained unchanged or grew later as early phases became earlier. There was a negative correlation between spring and autumn in long-term change, and this caused dramatic adjustments in the amount of time between migrations: the intermigratory periods of 10 species increased or decreased by > 15 days. Year-to-year changes in timing were correlated with local temperature (detrended) and, in autumn, with a regional climate index (detrended North Atlantic Oscillation). These results illustrate a complex and dynamic annual cycle in songbirds, with responses to climate change differing among species and migration seasons.     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.