Food availability during migratory stopover affects testis growth and reproductive behaviour in a migratory passerine

Long-distance migratory passerines initiate testicular recrudescence during spring migration to meet the demands of timely reproduction upon immediate arrival on the breeding grounds. The degree of testicular development is known to depend on environmental factors like stopover habitat quality; reproductive performance may be strongly impacted by testicular maturation upon arrival on the breeding grounds. We investigated the effect of stopover food availability on subsequent reproductive performance in garden warblers (Sylvia borin). Spring migration was simulated by repeated food deprivation and re-feeding to imitate the alternation of flight and stopover periods. During the two final stopover periods, males were either kept under ad libitum food (ad libitum males) or under limited food conditions (limited males). After simulated arrival in the breeding area, manipulation of previous stopover food availability resulted in significantly slower testicular recrudescence (p < 0.001) and decreased plasma testosterone (p < 0.01) in limited males compared to ad libitum males. Body mass change was not significantly different between the two groups (p = 0.38). Limited males also exhibited reduced performance in reproductive behaviours employed in territorial and sexual contexts. Limited males had a longer ‘freezing’ interval (p < 0.05) and decreased activity (p < 0.01) when challenged with a live male decoy. In direct confrontation between limited and ad libitum males in the presence of a female, limited males exhibited significantly fewer behavioural traits in sexual context, i.e. directed to the female (p < 0.001). Therefore, we suggest that conditions encountered during previous migratory stopover may affect subsequent annual reproductive success by influencing key reproductive behaviours.     

Extraordinary high natal philopatry in a migratory passerine

Natal dispersal is a key component of population dynamics in birds. It guarantees the genetic exchange of populations, favours range expansions and reduces intraspecific competition. In general, natal philopatry of migratory passerines is quite low (0–13.5%). In this study, we give evidence that, under specific conditions, migratory populations of passerine birds may show a considerably elevated natal philopatry. In a Linnet Carduelis cannabina population on the remote island of Helgoland in the North Sea, we found an extraordinary high return rate of yearlings (38%), which corresponds exactly to the annual survival rate of the species. Despite being completely migratory, the Linnets of Helgoland apparently return to a large extent to their native area and consequently might support the population maintenance on the island. Further studies are needed to reveal if this high natal philopatry is only an unusual 1-year event or a general characteristic of this partially isolated island population.     

Antioxidants and condition-dependence of arrival date in a migratory passerine

Early arrival at the breeding area after spring migration determines several fitness benefits to migratory birds, including an early start of reproduction and a greater seasonal reproductive success. Environmental conditions determine the onset of migration at the population level, while physiological costs associated with migration and imposed on individuals determine the level of asynchrony in the pattern of arrival. These costs include several physiological changes, suppression of immune response, and an increased risk of oxidation by production of free radicals due to energetically expensive activities. According to the condition-dependent hypothesis of arrival date, only healthy individuals in prime condition can afford to arrive and thus reproduce early in the season.
We investigated condition-dependence of arrival date in male barn swallow ( Hirundo rustica L.), a migratory passerine, in two years that differed in environmental condition, and the role of carotenoids in mediating arrival date. We show that male tail length, the main secondary sexual character, body condition, and hematocrit were negatively correlated with arrival date in the first year, indicating better quality of early arriving males. In the second year, better environmental conditions advanced arrival of the entire population by weeks. In this season we could show no relationship between arrival and tail length or body condition. Moreover, a lower value of sedimentation rate and a brighter colour of the red throat feathers indicated better health status of the population. Arrival date is a condition-dependent character in barn swallows, since we found high repeatability of arrival date, lower values of carotenoids in blood and a lower depletion of carotenoids in blood shortly after arrival in early arriving males. This suggests that early arriving males either use fewer antioxidants for free radical scavenging, or they have differential access to antioxidants.     

Maladaptive habitat selection of a migratory passerine bird in a human-modified landscape

In human-altered environments, organisms may preferentially settle in poor-quality habitats where fitness returns are lower relative to available higher-quality habitats. Such ecological trapping is due to a mismatch between the cues used during habitat selection and the habitat quality. Maladaptive settlement decisions may occur when organisms are time-constrained and have to rapidly evaluate habitat quality based on incomplete knowledge of the resources and conditions that will be available later in the season. During a three-year study, we examined settlement decision-making in the long-distance migratory, open-habitat bird, the Red-backed shrike (Lanius collurio), as a response to recent land-use changes. In Northwest Europe, the shrikes typically breed in open areas under a management regime of extensive farming. In recent decades, Spruce forests have been increasingly managed with large-size cutblocks in even-aged plantations, thereby producing early-successional vegetation areas that are also colonised by the species. Farmland and open areas in forests create mosaics of two different types of habitats that are now occupied by the shrikes. We examined redundant measures of habitat preference (order of settlement after migration and distribution of dominant individuals) and several reproductive performance parameters in both habitat types to investigate whether habitat preference is in line with habitat quality. Territorial males exhibited a clear preference for the recently created open areas in forests with higher-quality males settling in this habitat type earlier. Reproductive performance was, however, higher in farmland, with higher nest success, offspring quantity, and quality compared to open areas in forests. The results showed strong among-year consistency and we can therefore exclude a transient situation. This study demonstrates a case of maladaptive habitat selection in a farmland bird expanding its breeding range to human-created open habitats in plantations. We discuss the reasons that could explain this decision-making and the possible consequences for the population dynamics and persistence.     

Reverse turning and angle compensation in a migratory passerine,passerculus sandwichensis

Reverse turning behaviour was revealed in the savannah sparrow (Passerculus sandwichensis), a migratory passerine, using a T-shaped runway system. Compensatory reverse turns were recorded for experimental birds which were forced to make 90° turns either to the left or right before proceeding to a choice point. Controls ran a straight runway from start to choice point and were as likely to turn left as right. A second experiment revealed an ability to compensate for angular deviations in course. Experimentals were forced to make turns of less than 90° before entering a semi-circular arena. They responded with a compensatory turn of the appropriate sign (left or right) and magnitude. An idiothetic mechanism is probably involved in the observed angle sense (Winkelsinn). The results are broadly relevant to animal orientation.     

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.     

Impact of density and environmental factors on population fluctuations in a migratory passerine

1. Populations of plants and animals typically fluctuate because of the combined effects of density-dependent and density-independent processes. The study of these processes is complicated by the fact that population sizes are typically not known exactly, because population counts are subject to sampling variance. Although the existence of sampling variance is broadly acknowledged, relatively few studies on time-series data have accounted for it, which can result in wrong inferences about population processes. 2. To increase our understanding of population dynamics, we analysed time series from six Central European populations of the migratory red-backed shrike Lanius collurio by simultaneously assessing the strength of density dependence, process and sampling variance. In addition, we evaluated hypotheses predicting effects of factors presumed to operate on the breeding grounds, at stopover sites in eastern Africa during fall and spring migration and in the wintering grounds in southern Africa. We used both simple and state-space formulations of the Gompertz equation to model population size. 3. Across populations and modelling approaches, we found consistent evidence for negative density-dependent population regulation. Further, process variance contributed substantially to variation in population size, while sampling variance did not. Environmental conditions in eastern and southern Africa appear to influence breeding population size, as rainfall in the Sahel during fall migration and in the south African wintering areas were positively related to population size in the following spring in four of six populations. In contrast, environmental conditions in the breeding grounds were not related to population size. 4. Our findings suggest negative density-dependent regulation of red-backed shrike breeding populations and are consistent with the long-standing hypothesis that conditions in the African staging and wintering areas influence population numbers of species breeding in Europe. 5. This study highlights the importance of jointly investigating density-dependent and density-independent processes to improve our understanding of factors influencing population fluctuations in space and time.     

Demographic response to environmental variation in breeding,stopover and non-breeding areas in a migratory passerine

Demographic rates of migratory species passing through several areas during their annual cycle may be affected by environmental conditions at each of these areas. Recent studies provide evidence that their impact is not necessarily immediate, but can be delayed. We studied survival, reproductive success and arrival date at the breeding grounds of red-backed shrikes Lanius collurio, a trans-Saharan migrant, in relation to weather and vegetation on the breeding grounds, the stopover sites during migration and in the wintering areas. These environmental factors are used as proxy of the shrike’s food supply. We analysed detailed demographic data of some 4,600 individuals from 25 years with multistate capture–recapture and mixed models. Survival probabilities of juveniles and breeders of both sexes varied in parallel across time, suggesting that all cohorts were sensitive to similar causes of mortality. Reproductive performance increased with temperature and decreased with rainfall on the breeding area. Moreover, it increased with vegetation cover in the Sahelian stopover area used on autumn migration suggesting a carry-over effect. Arrival date was negatively affected by spring temperatures in the breeding area. Hence, demographic rates were affected by environmental factors on the breeding grounds, but also outside and elsewhere. This suggests that the shrike’s population dynamics are driven by environmental factors operating at various scales of space and time. However, only a small amount of the temporal variation in demographic rates is explained by the environmental factors considered, suggesting that additional factors, such as those operating during migration, might be important.     

Plasma metabolite profiles: effects of dietary phospholipids in a migratory passerine (Zonotrichia leucophrys gambelii)

Plasma metabolites, including triglycerides, beta -hydroxybutyrate, and glycerol, can be used to estimate mass change in birds. Although dietary fatty acids can be ingested and absorbed as phospholipids, they have been largely overlooked as a potential indicator of mass change. The plasma ratio of triglyceride to phospholipid could also provide insight into diet quality because a high ratio in food items indicates high relative energy content. Variability in dietary phospholipid content and triglyceride : phospholipid may also affect the relationships between metabolites and mass change. We fed Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) diets differing in phospholipid content and triglyceride : phospholipid and measured metabolites during mass loss and mass gain. Plasma phospholipids were higher and triglyceride : phospholipid was lower in birds fed a diet higher in phospholipid content and lower in triglyceride : phospholipid. Contrary to our expectations, plasma phospholipids were negatively related to mass change. Plasma triglyceride levels were positively related to mass change and unaffected by diet. The relationships between mass change and both plasma beta -hydroxybutyrate and glycerol were affected by diet. Plasma triglyceride appears to be the most reliable metabolite predicting body mass changes, but inclusion of plasma phospholipids and triglyceride : phospholipid into metabolite profiles may provide additional information on diet quality.     

Patchiness and compensatory growth in a fungus-Collembola system

The compensatory growth potential of a grazed fungal biomass was mathematically expressed as a function of patchiness in its distribution and demonstrated in an experiment using the fungivorous collembolan Onychiurus armatus and the soil fungi Verticillium bulbillosum and Penicillium spinulosum. The model addresses the regrowth potential in relation to patch fragmentation, travelling time and consumption rate of the collembolan and the mean relative growth rate of the fungus. It suggests that the mean relative growth rate required for regrowth decreases with patch fragmentation and increases with the mean growth rate of the fungus. The experiments were performed with a system of soil-filled vials provided with fungi and collembolans. The size of the vials and the length of the tubes connecting them were varied to give different patch sizes and travelling times. The respiratory activity of fungi after grazing increased as a unit of mycelium was distributed into smaller connected vials. The slow growing species V. bulbillosum showed a greater but delayed response to grazing in comparison with the fast growing P. spinulosum. An increased travelling time delayed the growth response in both species.     

谈谈鱼类的补偿生长

简要介绍了鱼类的补偿生长现象,并根据补偿量的大小将鱼类的补偿生长划分为超补偿生长,完全补偿生长,部分补偿生长和不能补偿生长四类,同时根据饥饿或限食以及重喂时间的不同介绍了目前鱼类补偿生长实验设计的一般思路,最后对鱼类补偿生长在水产养殖和环境保护等方面的应用前景作了展望。     

Adaptive sex differences in growth of pre-ovulation oocytes in a passerine bird

Maternal modification of offspring sex in birds has strong fitness consequences, however the mechanisms by which female birds can bias sex of their progeny in close concordance with the environment of breeding are not known. In recently established populations of house finches (Carpodacus mexicanus), breeding females lay a sex-biased sequence of eggs when ambient temperature causes early onset of incubation. We studied the mechanisms behind close association of incubation and sex-determination strategies in this species and discovered that pre-ovulation oocytes that produce males and females differed strongly in the temporal patterns of proliferation and growth. In turn, sex-specific exposure of oocytes to maternal secretion of prolactin and androgens produced distinct accumulation of maternal steroids in oocyte yolks in relation to oocyte proliferation order. These findings suggest that sex difference in oocyte growth and egg-laying sequence is an adaptive outcome of hormonal constraints imposed by the overlap of early incubation and oogenesis in this population, and that the close integration of maternal incubation, oocytes' sex-determination and growth might be under control of the same hormonal mechanism. We further document that population establishment and the evolution of these maternal strategies is facilitated by their strong effects on female and offspring fitness in a recently established part of the species range.     

Transition between moult and migration in a long-distance migratory passerine: organ flexibility in the African wintering area

Phenotypic flexibility of organs in migratory birds has been documented for a variety of species of different genera during the migratory period. However, very little is known about phenotypic mass changes of organs with respect to other events within the annual cycle. This seems particularly interesting when birds face different physiological challenges in quick succession. We investigated mass changes of 13 organs from garden warblers (Sylvia borin) during the transition from moult to migration. These long-distance migratory birds perform a complete moult within their wintering area just shortly before the onset of spring migration. Birds were sampled in three successive stages according to their moult status: group I consisted of birds with growing primary or secondary wing feathers, group II consisted of birds with completed wing moult but with still moulting body feathers, and group III consisted of birds that had completed wing moult and body moult. Size-corrected flight muscle, kidney mass, and pancreas mass differed significantly among the three groups. Flight muscle was heaviest in birds that were about to leave their wintering area (group III) compared with birds still in body moult (group II). Kidney and pancreas showed a pattern similar to each other, with the heaviest mass occurring in birds with moulting wing feathers (group I) and significantly reduced mass in birds that had completed wing moult (group II) or both wing and body moult (group III). Mass reductions of kidney and pancreas during the transition from moult to migration are considered to be related to the demands of moult, while increased flight muscle may be due to moult, migration, or both. Phenotypic mass changes of organs in birds occur during their migration, but they also occur during the transition between other phases of the annual cycle such as moult and migration and are not restricted to the flight muscle.     

Structure in avian growth patterns: a multivariate study of passerine development

A series of four principal component analyses was applied to data on the nestling development of three passerines, the Blue tit Parus caeruleus , House martin Delichon urbica and House sparrow Passer domesticus. The pattern of weight development in the tit and sparrow was largely controlled by selection for growth rate and for final size but in the martin final size was due to the prevailing levels of nestling food. Development in all three species was primarily through size increase in all growth measures but the differential development of individual organs or body constituents nevertheless accounted for 15% or more of the variance in developmental pattern. Blue tit young in broods of above average size sacrificed differential development to maintain size increase. Species specific differences in the integration of weight and plumage development and their sensitivity to hatching weight and hatching order were explicable as adaptive modifications of developmental pattern to the nature of each species' food supply. The value of such individual measures of development as weight and feather growth is assessed in the light of multivariate analysis of arrays of such variables.     

Carrying capacity of wetlands for massive migratory waterfowl

Although it has been documented that waterfowl can cause water quality problems when their populations are large relative to the size or volume of the water body, the question as to how many waterbirds a wetland or a lake can support remains unanswered. A method to quantify the carrying capacity of a water body with regard to massive waterfowl was developed through the study of five wetlands that are used as the wintering ground by a large number of waterfowl in Japan. It takes into consideration water depth, retention time, and in-lake phosphorus concentration. For one of the sites, Sakata Lagoon, which is a registered Ramsar wetland in Japan, the assessment of its carrying capacity suggests that the number of waterfowl should be reduced by half to sustain the water quality of this wetland. Based on the comparison among the five wetlands, a simple indicator was proposed for quick diagnosis. Moreover, a general plot of permissible loading of phosphorus (kg/ha/year) by waterfowl was presented. Besides, this study shed some new light on potential toxicity and accumulation of waterfowl feces at lakebed. Finally, a proposal to increase the carrying capacity of Sakata Lagoon is discussed.     

Reduced DNA-repair capacity in cells originating from a progeria patient

A Chinese boy was identified to be suffering from progeria (Hutchinson-Gilford syndrome), the first case of the disease ever reported in China. Cells originating from the patient had a reduced amount of unscheduled DNA synthesis after irradiation with ultraviolet light (UV). The fractions of the progeria cells surviving against UV irradiation measured by colony-forming ability, and the host-cell reactivation capacity of the progeria cells, measured by the plaque formation of UV-irradiated herpes simplex virus were lower than those measured in normal cells. The progeria cells appear to have a reduced capacity to repair UV excision damage.