Morphological and genetic sex identification of white-tailed eagle Haliaeetus albicilla nestlings

Identifying the sex of bird nestlings is relevant to studies of behaviour and ecology and is often a central issue in the management of endangered or captive populations. The white-tailed eagle Haliaeetus albicilla is a formerly threatened Eurasian raptor which is closely monitored in many countries due to its high exposure to environmental pollutants in the food chain. The aim of this study was to evaluate the reliability of sex identification methods for white-tailed eagle nestlings based on morphological measurements that can be recorded at the nest by a single person and with minimum disturbance. The sex of each bird was independently determined using molecular (genetic) methods. One measure of tarsus width allowed the correct identification of sex for 96% of the nestlings from southern and central Sweden. However, we found that the criteria for sex identification were not directly applicable to the population in Swedish Lapland, where nestlings are typically thinner, probably due to a limited food supply. These results show that sexing in the field of white-tailed eagle nestlings can be feasible with high accuracy based on a limited number of measurements. However, the criteria employed to separate sexes may have to be adjusted for each population.     

Population dynamics and evolutionary processes: the manifold roles of habitat selection

Summary Any character that has a substantial effect on a species' distribution and abundance can exert a variety of indirect effects on evolutionary processes. It is suggested that an organism's capacity for habitat selection is just such a character. Habitat selection can constrain the selective environment experienced by a population. Habitat selection can also indirectly influence the relative importance of natural selection, drift, and gene flow, through its effect on population size and growth rate. In many circumstances (but not all), habitat selection increases population size and growth rate, and thereby makes selection in a local environment more effective than drift and gene flow.     

Spawning habitat selection and suitability for Japanese dace, Tribolodon hakonensis

We have investigated the effects of three current velocities and three substrate sizes (gravel to cobble) on the spawning behavior of Japanese dace, Tribolodon hakonensis, in spawning-induction and habitat-selection experiments. In the spawning-induction experiment under laboratory conditions the number of females induced to spawn was significantly fewer at low current velocity (ca. 5 cm s^–1) than at medium (ca. 30 cm s^–1) or high (ca. 50 cm s^–1) current velocity. Females spawned independently of substrate size in the experimental tank, and did not bury their eggs in the substrate bed. In the habitat-selection experiment under field conditions, females selected the substrate microhabitat and spawned more frequently at a site with medium substrate size (very coarse gravel; major axis ca. 40 mm) than at sites with small (fine gravel; ca. 8 mm) or large (cobble; ca. 70 mm) substrate size. We conclude that Japanese dace select spawning sites at least partly on the basis of current velocity and substrate size, which affects the survival rate of eggs.     

Origin and genetic structure of white-tailed sea eagles (<Emphasis Type="Italic">Haliaeetus albicilla</Emphasis>) in the Czech Republic: an analysis of breeding distribution,ringing data and DNA microsatellites

The population of white-tailed sea eagles (Haliaeetus albicilla) in the Czech Republic declined dramatically during the twentieth century. None were observed in the area for more than 60 years until population recoveries were observed beginning in the 1980s. It is currently estimated that 25–30 breeding pairs of white-tailed sea eagles nest in the Czech Republic. This article analyses surveillance data from three periods between 1973 and 2003 on the occurrence and nesting of white-tailed sea eagles in the Czech Republic. We investigated recolonization of European white-tailed sea eagles in the Czech Republic in terms of migration patterns and population structures. Bird ringing data suggest the Czech population may be recovered from various areas encompassing northern Europe. Using data collected by DNA microsatellite, no population structure was revealed through Bayesian and cluster analyses with an existing Hardy–Weinberg equilibrium, which suggests mixed panmictic populations of white-tailed sea eagles in the Czech Republic and Slovakia. While analysis of genetic diversity showed no difference between recovered populations in the southeastern Czech Republic and those persisting in Slovakia, there was genetic diversity between eagles of the southeastern subpopulation and eagles in other parts of the Czech Republic. Taken together, these observations on the population structure of white-tailed sea eagles in the Czech Republic imply that other European birds contributed to the recovery of the Czech population, likely through breeding mixture with an identifiable centre in the southeastern Czech Republic.     

Population size,habitat fragmentation,and the nature of adaptive variation in a stream fish

Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to increase variability within and among habitats as population size decreases. Such variability might instead favour the maintenance of adaptive polymorphisms and/or generate more variability in adaptive differentiation at smaller population size. We investigated these alternative hypotheses by analysing coding-gene, single-nucleotide polymorphisms associated with different biological functions in fragmented brook trout populations of variable sizes. Putative adaptive differentiation was greater between small and large populations or among small populations than among large populations. These trends were stronger for genetic population size measures than demographic ones and were present despite pronounced drift in small populations. Our results suggest that fragmentation affects natural selection and that the changes elicited in the adaptive genetic composition and differentiation of fragmented populations vary with population size. By generating more variable evolutionary responses, the alteration of selective pressures during habitat fragmentation may affect future population persistence independently of, and perhaps long before, the effects of demographic and genetic stochasticity are manifest.     

Environmental networks,compensating life histories and habitat selection by white-footed mice

Summary Analysis of 6 years' data on a population of free-living white-footed mice documents both phenotypic and environmental control of litter size. Litter size was positively correlated with maternal body size. Maternal size depended upon both seasonal and annual variation. Paradoxically, the proportion of small versus large litters varied among habitats independently of the effects of body size. The result is an influence of habitat on life history that yields patterns of reproduction and survival opposite to the predictions of demographic theory. The habitat producing the largest litters had a relatively high ratio of adult/juvenile survival. Litter size was small in the habitat where the adult/juvenile survival ratio was smallest. All of these anomalous patterns can be explained through density-dependent habitat selection by female white-footed mice. Life-history studies that ignore habitat and habitat selection may find spurious correlations among traits that result in serious misinterpretations about life history and its evolution.     

Nestling characteristics and identification of the lesser spotted eagle Aquila pomarina, greater spotted eagle A. clanga, and their hybrids

The lesser spotted eagle Aquila pomarina and the greater spotted eagle A. clanga are closely related endangered raptors whose taxonomic status, field identification, and ultimately conservation, have been complicated due to morphological similarity. However, the partial overlap in morphological features may also involve hybrids, which are known to exist, but which have so far been poorly described. This study investigated spotted eagle nestlings in Estonia, pre-identifying them according to mitochondrial DNA, nape patch and the appearance of their parents. Relative size of bill and toes (corrected for nestling growth) enabled us to separate the smaller A. pomarina, but hybrids were as large as A. clanga. All three groups had distinct plumages with hybrids being intermediate; the separation was clearest using both size and plumage indices. In all, 164 of 168 birds were correctly identified using a three-step procedure, separating: (1) A. clanga, having no nape patch; (2) 9 of 13 hybrids according to plumage index; and (3) the remaining hybrids by their large size (at least two features over the mean+2 SD values of A. pomarina). Knowing the sex helped to interpret size, but not plumage, characteristics, and its overall value for assisting identification was not high. The results support the view that spotted eagles with intermediate characters are usually hybrids which can be recognised by their appearance.Communicated by F. Bairlein     

Aspects of habitat selection in the mosquitofish gambusia affinis

Laboratory experiments were performed to determine behavioral preferences of Gambusia affinis for habitat variables in partitioned aquaria. The fish preferred calm water, dark-colored substrates and subsurface vegetation providing lateral concealment. Floating cover, which obstructed access to the surface, was avoided. Lack of preference for real over plastic plant cover indicates that visual rather than chemical cues are involved. These laboratory preferences correspond to the reported microhabitat distribution of G. affinis in nature and indicate the presence of an active habitat preference, as opposed to passive habitat correlation, in this species. Species-specific habitat preferences, which may be narrower where a species occurs sympatrically with its congeners, probably form part of a reproductive isolating mechanism.     

Habitat selection of the Tibetan Snow Cock Tetraogallus tibetanus in the spring in Lhasa

The habitat selection of Tibetan Snow Cocks in shrub vegetation was investigated in Lhasa, Tibet, China, between March and April, 2005. Fourteen parameters were measured. These include altitude, slope, slope aspect, slope position, vegetation cover, plant type and other environmental parameters. Results show that Snow Cocks favor foraging in areas where vegetation cover was small and close to the residents’ houses. Supplementary food supplied by humans has caused Snow Cocks to decrease their foraging range. Snow Cocks also favor roosting in areas with low vegetation, sparse grass, short grass, large rocks and close to houses. The Snow Cocks’ activity in the study areas show a close relationship with human activities. __________ Translated from Zoological Research, 2006, 27(5): 513–517 [译自: 动物学研究]     

Factors affecting breeding habitat selection in a cliff-nesting peregrine Falco peregrinus population

We studied factors affecting breeding habitat selection in a population of cliff-nesting peregrines Falco peregrinus across multiple spatial levels (cliff site, cliff context and land-use of the surrounding landscape), over a 2,100 km² study area in the Alps (Italy and Switzerland). We detected 30 breeding pairs (density: 1.43 territorial pairs/100 km²), whose territories were uniformly distributed over the study area. We compared 15 habitat features characterising occupied cliffs and 30 randomly selected unoccupied cliffs by means of stepwise forward logistic regression and hierarchical partitioning. The logistic regression analysis showed that occupied cliffs were longer (horizontal length), steeper, and had a greater extension of urban areas in the surrounding landscape compared to non-occupied cliffs. The model had a discrimination ability of 0.95. Hierarchical partitioning indicated that the logistic regression model was appropriate. Neither the distance of cliffs to the nearest site occupied by a potential competitor and predator, the eagle owl Bubo bubo, which occurred at a low density (0.67 pairs/100 km²), nor the distance to the nearest site occupied by peregrines had any effect on the cliff suitability model. Therefore, habitat selection in cliff-nesting peregrines was mainly influenced by cliff site features and surrounding landscape characteristics, whereas the proximity to conspecifics and to an intraguild predator had no apparent effects on peregrine settlement in our study population.     

Contrasting patterns of body size for Daphnia species that segregate by habitat

Summary We investigate how body size of two coexisting Daphnia species varies among 7 lakes that represent a gradient of predation risk. The two species segregate vertically in stratified lakes; D. galeata mendotae is typically smaller and more eplimnetic than D. pulicaria. The extent of vertical habitat partitioning, however, varies seasonally within and among lakes in apparent response to predation intensity by epilimnetic planktivorous fishes. Daphnia pulicaria uses the epilimnion at low levels of fish predation but is restricted to the hypolimnion under high fish predation, whereas D. galaeta mendotae always utilizes the epilimnion. The species display contrasting patterns of genetic variation in neonate size and size at maturity. D. pulicaria is larger in lakes with higher fish and Chaoborus densities whereas D. galeata mendotae is smaller. This contrast in body size in lakes with high predation is associated with greater habitat segregation in those lakes. In lakes with low predation risk, the two species are similar in body size at birth and maturity.Authorship order alphabetical     

Nest-site habitat selection by Lesser Rheas ( Rhea pennata pennata ) in northwestern Patagonia, Argentina

Selection of nest-site habitat by a population of wild Lesser Rheas (Rhea pennata pennata) was studied in the northwestern Patagonia steppe, Argentina, during two reproductive seasons (2004/2005 and 2005/2006). Nest spatial distribution was compared with randomly selected points in the study area. Contrary to observations in other ratite species, nest distribution showed an aggregate pattern associated with “mallín” (meadow) areas, which are habitats of higher productivity in the Patagonia steppe. Moreover, similar to observations made on the Greater Rhea (Rhea americana), vegetation cover was higher in nest sites than in randomly selected sites, probably because higher vegetation provides concealment from predators and protection from the strong westerly winds that frequent in this region. Our results reinforce the importance of “mallín” areas for the reproduction and conservation of this threatened ratite species.     

Spacing behaviour and habitat use of rock ptarmigan (Lagopus mutus) at low density in the Italian Alps

Studies of rock ptarmigan Lagopus mutus in northern latitudes have shown that, in the breeding season, the majority of cocks pair monogamously and defend small territories, whilst in most populations, a small proportion of cocks are polygynous or remain unmated. Little is known, however, on spacing behaviour and habitat use of alpine rock ptarmigan populations occurring at low densities at the southern edge of the species’ range. From 1995 to 1997, we trapped, radio-tracked and observed birds in the Central Italian Alps (elevation 2,000–3,000 m) in order to investigate spacing behaviour and habitat use in alpine landscapes where habitats offering rich food and cover are patchy. Both sexes were selective in their habitat use, and cocks did not establish territories on bare ground, artificial or nutrient rich grasslands or bogs. In the breeding season, cocks had larger home ranges than hens (cocks 99 ± 57 ha, hens 50 ± 25 ha) that overlapped with the ranges of neighbouring cocks and hens. Cocks were monogamous and defended relatively large territories (core areas of home ranges: cocks 37 ± 26 ha, hens 24 ± 12 ha), which corresponded with low spring densities (0.47–2.29 cocks km⁻² and 0.35–1.60 pairs km⁻²). Territory size of individual cocks was negatively correlated with the amount of high quality habitat in the core-area. Our results suggest increased home ranges and large breeding territories in low density alpine rock ptarmigan populations, compared to populations occurring at higher densities in the central and northern alps, and on subarctic and arctic grounds at northern latitudes, confirming the predictions of models on food-based territoriality.     

Not only size matters: Acorn selection by the European jay (Garrulus glandarius)

A strong selection for acorn characteristics is expected to have evolved in the mutualistic relationship between the European jay (Garrulus glandarius) and the oak (Quercus spp.). Bossema's pioneer work suggested that jays do not select acorns randomly, but rather they preferentially select some size and species. Preference for some seeds over others may have implications on plant community dynamics by conferring advantages (or disadvantages) on the selected (avoided) seed characteristics. In this paper we test to what extent jays select acorns by species and/or by size and the relation between these two traits in Mediterranean oak species. The experiments consist of a set of field tests in which acorns from four different coexisting Mediterranean oak species (Quercus ilex, Quercus faginea, Quercus suber, and Quercus coccifera) were placed in artificial feeders accessible to wild jays. The acorns were previously measured to control individual acorn characteristics. Using video-recording techniques, we followed jay activity and the fate of each acorn (sequence of acorn selection and method of transport). Q. ilex acorns were preferred over other acorns, and Q. coccifera acorns were avoided when other acorns were available. Preference for Q. faginea and Q. suber acorns was intermediate, that is, they were preferred over Q. coccifera acorns but not over Q. ilex acorns. Large acorns were also preferred although acorn species selection was stronger than size selection. Jays selected species and size both by visual means and by using acorn area as an indicator of size. Acorns wider than 17–19 mm were carried in the bill because of throat limitation. Our results confirm Bossema's study on temperate oaks and extend it to Mediterranean oak species, revealing implications on mixed oak forest dynamics.     

Genetic structure, habitat fragmentation and bottlenecks in Danish bank voles (Clethrionomys glareolus)

Tissue-samples from 161 bank voles (Clethrionomys glareolus) collected in three forests (five sampling localities) situated in eastern Jutland (Denmark) were analysed by nine microsatellite loci. The genetic diversity found within the populations was high (H_e=0.753–0.806).Bank voles have specific habitat requirements favouring woodlots, hedgerows and deciduous forests as their prime living area. Hence, a natural or human-induced fragmentation of the forest may cause a sub-structuring of the populations and thereby a restriction of dispersal among populations. The sub-structuring indicated by the observed significant genetic differentiation among the five geographically distinct localities (F_st =0.033, P<0.05) could either result from habitat fragmentation or a combination of home range behaviour and different tree composition in the forests. A road situated between two adjacent forests was not found to exert any barrier effect to the gene flow of bank voles. In one out of five localities investigated, genetic evidence for a recent bottleneck-like situation was found. Bank voles are known to exhibit sometimes huge density fluctuations not only from year to year but also from season to season. The bottleneck-like situation found could therefore be due to the low number of individuals during the low-density phase.     

The cost of habitat selection in prairie voles: an empirical assessment using isodar analysis

The ideal free distribution assumes that habitat selection is without cost and predicts that fitness should be equal in different habitats. If habitat selection has a cost, then individuals should only move to another habitat when potential fitness in the new habitat exceeds that in the source habitat by an amount greater than the cost of habitat selection. We used isodar techniques to assess the cost of habitat selection. In an experimental landscape, we monitored density, movement, and reproductive success of adult female prairie voles, Microtus ochrogaster, in adjacent paired habitats with low and high cover. We tested the following hypotheses: (1) adult female prairie voles exhibited density-dependent habitat selection; (2) the cost of habitat selection was density-independent. Habitat quality based on population density and fitness of adult females was higher in high cover habitats. Net movement was from low cover to high cover habitats. The results indicated that adult female prairie voles exhibited density-dependent habitat selection. Furthermore, there was a significant cost of habitat selection, and the cost was density-independent.     

Age and host effects on clutch size in the Mexican fruit fly, Anastrepha ludens

We document individual and age-specific variation in reproductive output and clutch size of Anastrepha ludens Loew. (Diptera: Tephritidae). The influence of host size, color, and density on clutch size are also examined. Individual and groups of flies were offered artificial hosts composed of agar spheres wrapped in Parafilm. The gross reproduction rate of individual flies was 1000 eggs/female and 165 clutches/female with a range of 1 to 40 eggs/clutch. Mean clutch sizes for these females ranged from 4.5 to 10.6 eggs/clutch. The number of eggs/clutch laid by females held in groups was highly correlated with host size, ranging from about 4.4 eggs/clutch in 2 cm diameter hosts to 12.7 eggs/clutch in 11 cm hosts. Host color, host density, fly density, and fly age did not affect clutch size. This study suggests that variation among females and host size are the principal determinants of clutch size in A. ludens.

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Résumé L'examen a porté sur l'influence du polymorphisme et des modifications dues à l'âge des mouches sur la fécondité et la taille des pontes de A. ludens Loew (Dipt. Tephritidae). L'étude a concerné aussi l'influence de la dimension, de la couleur et de la densité des hôtes sur la taille des pontes. Des mouches isolées ou par groupes ont reçu des hôtes artificiels formés de sphères d'agar enveloppées dans du parafilm. La fécondité brute de femelles isolées a été de 1000 oeufs/femelle et de 165 pontes/femelle, avec une variation de 1 à 40 oeufs/ponte. La taille moyenne des pontes des différentes femelles isolées s'étalait de 4,5 à 10,6 oeufs/ponte. Le nombre d'oeufs/ponte des femelles groupées était fortement liée à la dimension de l'hôte, s'étalant de 4,4 oeufs/ponte pour des hôtes de 2 cm de diamètre à 12,7 oeufs/ponte pour ceux de 11 cm de diamètre. Ni la couleur et la densité des hôtes, ni la densité et l'âge des mouches n'ont influé sur la taille des pontes. Ces résultats suggèrent que les variabilités du comportement des femelles et de la dimension des hôtes déterminent par priorité la taille des pontes de A. ludens.

     

Monoterpenes governing host selection in the bark beetles Hylurgops palliatus and Tomicus piniperda

Under field conditions, both bark beetles, Hylurgops palliatus Gyll. and Tomicus piniperda L. (Col., Scolytidae) preferred flight barrier traps baited with ethanol and oleoresin of their favoured host, Picea abies L., and Pinus sylvestris L., respectively, compared to traps baited with ethanol and various monoterpenes. However, replacing the host-specific oleoresin with -pinene and the pine-characteristic terpinolene enhanced trap catches of both species. Response of H. palliatus increased with myrtenol, but decreased with (+)-trans-verbenol, while T. piniperda was attracted by both terpene alcohols.

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Zusammenfassung Die Lockwirkung wirtsspezifischer Terpenmuster auf die sekundären Rindenbrüter Hylurgops palliatus und Tomicus piniperda wird im Freiland untersucht. Beide Arten fliegen bevorzugt Fallen an, die mit Ethanol und dem Rohharz ihrer Wirtsbäume, Picea abies bzw. Pinus sylvestris, beködert sind. Der Ersatz der Rohharze durch eine Mischung aus -Pinen und dem für Kiefernharz charakteristischen Terpinolen erhöht die Fangzahlen beider Arten deutlich. Die Präferenzen für Monoterpene deuten unterschiedlich enge Wirtsbindungen an: Bei breitem Wirtsspektrum bevorzugt H. palliatus wenig spezifische Terpene und hohe Ethanol-Konzentrationen, der zur Monophagie an Frischholz neigende Waldgärtner T. piniperda jedoch geringe Ethanol-Konzentrationen und spezifische Terpenkombinationen. H. palliatus wird von dem Terpenalkohol (-)-Myrtenol deutlich angelockt, während das von aggressiven Scolytiden bekannte Pheromon (+)-trans-Verbenol seinen Anflug im Gegensatz zu T. piniperda zu hemmen scheint.