The effect of water availability on fuel deposition of two staging Sylvia warblers

In order to succeed in crossing extensive ecological barriers, migratory birds usually deposit fuel en route. High rates of fuel deposition may enable birds to shorten their total migration time and are therefore advantageous for time-minimizing migrants. Several studies have suggested that water provision may increase food utilization in non-migratory birds. The goal of this study was to test the influence of water availability on the fuel deposition of en route migratory passerines. We studied fuel deposition of blackcaps Sylvia atricapilla and lesser whitethroats S. curruca staging in a plantation of Mount Atlas gum-tree Pistacia atlantica in the northern Negev desert, Israel, during the autumns of 2000 and 2002. We manipulated water availability at the site and measured the effect of water supplementation on fuel deposition of birds of both species. We found that when water was available, blackcaps had higher fuel loads and higher fuel deposition rates than during control trials. However, water availability had no effect on fuel deposition of lesser whitethroats. Species-specific differences in adaptations to arid conditions, reflected in the species' winter habitat preferences, may be responsible for the between-species dissimilarity in responding to water provision. We suggest that water availability may have strong ecological and evolutionary consequences for birds migrating through arid environments, by its possible effect on bird behavior and physiology.     

The effect of water availability on fuel deposition of two staging Sylvia warblers

In order to succeed in crossing extensive ecological barriers, migratory birds usually deposit fuel en route. High rates of fuel deposition may enable birds to shorten their total migration time and are therefore advantageous for time‐minimizing migrants. Several studies have suggested that water provision may increase food utilization in non‐migratory birds. The goal of this study was to test the influence of water availability on the fuel deposition of en route migratory passerines. We studied fuel deposition of blackcaps Sylvia atricapilla and lesser whitethroats S. curruca staging in a plantation of Mount Atlas gum‐tree Pistacia atlantica in the northern Negev desert, Israel, during the autumns of 2000 and 2002. We manipulated water availability at the site and measured the effect of water supplementation on fuel deposition of birds of both species. We found that when water was available, blackcaps had higher fuel loads and higher fuel deposition rates than during control trials. However, water availability had no effect on fuel deposition of lesser whitethroats. Species‐specific differences in adaptations to arid conditions, reflected in the species’ winter habitat preferences, may be responsible for the between‐species dissimilarity in responding to water provision. We suggest that water availability may have strong ecological and evolutionary consequences for birds migrating through arid environments, by its possible effect on bird behavior and physiology.     

Recognizability of different food types in faeces and in alimentary flushes of Sylvia warblers

The efficiency of the analysis of faeces and flushes of the digestive tract was examined by feeding captive Garden Warblers Sylvia borin and Blackcaps S. atricapilla with different food types (arthropods, fruits). Faecal analysis underestimated aphids; the analysis of flushes overestimated beetles and underestimated aphids and fruits. Correction factors to remove these biases are given. Flushing free-living birds showed no noticeable effect on recapture rates and body mass. Methods of calculating the number of prey items from different fragments are evaluated.     

Basal and stress-induced corticosterone levels of garden warblers,Sylvia borin,during migration

Summary Plasma levels of the metabolically and behaviorally active corticosteroid hormone, corticosterone, were studied in garden warblers in the laboratory and in the field during the autumnal migratory phase. Garden warblers showing nocturnal migratory activity in the laboratory had elevated levels of corticosterone at the end of the dark phase and low levels during daytime. When nocturnal migratory activity was experimentally disrupted by food deprivation and subsequent refeeding or after spontaneous termination of migratory activity this rhythm was absent. Garden warblers stopping over in the Sahara desert during autumnal migration had low levels of corticosterone. Levels were negatively correlated with fat stores and body mass in birds sampled throughout the day. These levels were generally lower than those associated with stress in response to repeated handling and blood sampling. The results suggest (1) the existence of diel changes in adrenocortical hormonal activity that could be involved in regulation of migration, and (2) that garden warblers carrying large fat depots are not stressed by prolonged flight or lack of appropiate feeding areas during migration over the desert.Abbreviations ACTH adrenocorticotrope hormone - cpm counts per minute - EtOH ethanol - RIA radioimmunoassay     

Effects of experience and object complexity on exploration in garden warblers (Sylvia borin)

Animals are increasingly exposed to novel environmental conditions because of human activities. An organism's ability to cope with these challenges is critical to its survival. The decision of whether or not an animal should investigate environmental changes involves a trade-off between the risk and the potential benefit of a novel resource. Novelty often elicits approach (exploratory) as well as avoidance behaviour in animals, and the extent of each of these behaviours may influence learning about the environment. We formulated and tested several hypotheses to determine how external factors (complexity of a novel stimulus) and internal factors (experience with objects) might influence exploration latencies to touch a novel object based on either cost or benefit considerations. Garden warblers were confronted with a simple and a complex novel object in their familiar cages, and latencies until first touch were measured. Additionally, corticosterone levels before and after the experiment were measured to assess whether differences in baseline levels might explain variations in latency to approach and whether presentation of novel objects is stressful. The complex object was touched significantly later than the simple object. Experienced birds investigated both types of objects later than inexperienced birds. Although birds showed marked approach–avoidance behaviour with the complex object, none of the objects elicited a corticosterone stress response. The results indicate that garden warblers consider both costs and benefits when exploring novel objects, and that the relative influence of costs and benefits varies with external and internal factors.     

Molecular phylogeny and the historical biogeography of the warblers of the genus Sylvia (Aves)

A molecular phylogeny based on DNA/DNA hybridization revealed that the Sylvia-Parisoma complex is monophyletic and includes three main groups of species, the “mid-European” warblers, the genus Parisoma, and the “eu-Mediterranean” Sylvia species sensu stricto. The latter can be assigned to three main clusters, a “West-Mediterranean” group, a “Central-Mediterranean group”, and an “East-Mediterranean” group. The radiation of the whole complex is much more ancient than formerly believed. It started ca 12–13 Ma ago and the ancestors of the main extant groups differentiated during the Pliocene. Only speciation events within the “eu-Mediterranean” lineages occurred during the Pleistocene. The paleoclimatical and paleoecological history of the Mediterranean region is too complicated to provide any evidence for direct relationships between past events and evolutionary steps of these taxa which did not leave any reliable fossil record. However, some major speciation events may be related to well documented climatical crises as well as paleobotanical data. The largely man-induced extension of matorrals over several millenia presumably extended the range of several species that were formerly much more restricted, which complicates reconstruction of the spatio-temporal course of speciation.     

Nest predation is little affected by parental behaviour and nest site in two African Sylvia warblers

Parental behaviour and nest site are supposed to affect nest predation in birds. Few nest visits and high nest attentiveness are assumed to lead to low predation rates. Poorly concealed nests are thought to be more likely to be preyed upon than well concealed nests. Studies on the relationship between parental behaviour, nest site, and nest predation are rare and none have, so far, been conducted in the Afrotropics. We studied the effect of nest site, nest visitation rate, and nest attentiveness on the nest predation rate of the two tropical warblers Sylvia boehmi and Sylvia lugens in Kenya. Parental behaviour and predation on nests of 13 breeding pairs of both species were observed daily in two consecutive breeding seasons. In both species, parental activity at the nest was low [0.9 trips to the nest in 30 min during incubation, maximum 4.6 (S. boehmi) and 5.8 (S. lugens) trips to the nest in the nestling stage]. Predation rates in both species were high (Mayfield nest success 19.4 and 33.2%). Our analysis revealed only weak evidence for an effect of nest site, nest visitation rate, and nest attentiveness on the predation rate. It is suggested that smaller clutches of tropical in comparison to northern temperate birds result from lower feeding rates in tropical ecosystems with high predation rates (Skutchs hypothesis). The underlying mechanism could not be proven in this study.     

Evaluation of African annual clovers to moisture stress in two Ethiopian highland soils

Five annual clover species from Ethiopia and Kenya were evaluated in greenhouse studies for biomass production, water use efficiency, and total nitrogen (N) accumulation when grown under different moisture conditions. Two Ethiopian highland soils (Nitosol and Vertisol) were maintained under either high or low soil moisture conditions until maturity. The largest biomass yields and N accumulations occurred in the high moisture treatment on both soils. One species (Trifolium tembense) was superior to the other four in biomass production over all soil and moisture treatments. Two species (T. decorum and T. quartinianum) were intermediate in performance, and two species (T. rueppellianum and T. steudneri) demonstrated low productivity over treatments. The results imply that at least three of the clovers evaluated may be capable of substantial biomass production and N accumulation on two Ethiopian soils that are commonly found in the central African highlands. These clovers should be evaluated in field trials in Africa to determine their use as pasture legumes to support livestock production.     

Life-history of ascomycetes: two new species ofChaetosphaeria withChloridium andChloridium-Dictyochaeta anamorphs

Two new species ofChaetosphaeria, Chaet. dilabens andChaet. hebetiseta, withChloridium andChloridium-Dictyochaeta anamorphs, are described and illustrated on material from Japan and Ukraine, respectively. The lifehistories of both species were confirmed by cultural studies.     

Genetic and phenotypic associations in morphological traits: a long term study of great reed warblers Acrocephalus arundinaceus

We present estimates of standardized selection (directional and quadratic) differentials via reproductive success on eight morphological traits in a newly founded long-term study population of great reed warblers Acrocephalus arundinaceus in Sweden. In order to predict the evolutionary response to selection in these traits we present estimates of heritabilities (h²), phenotypic (r_P) and genetic (r_A) correlations among the same traits. We also examined the extent of parental effects in the expression of the phenotypic traits. Overall, the population is subject to low levels of directional selection and higher levels of stabilizing selection. This makes us predict that the population is changing very little if anything, even though h² in many cases are considerable. Midparent-midoffspring h² ranged from 0.14 and 0.94 (mean 0.58) and were significant for seven of eight traits. We found indications of positive maternal effects in tarsus length. Phenotypic correlations between traits ranged from 0.02 to 0.43 (mean 0.15) and showed generally much lower values than the corresponding genetic correlations that ranged between 0.08 and 1.04 (mean 0.46). Overall, the correlation between r_P and r_A was significant, although moderate, but they tended to differ in magnitude, possibly due to overestimation of additive covariance between traits.     

Biometry and phenology of two sibling Phylloscopus warblers on their circum-Mediterranean migrations

The Mediterranean Sea is known as an ecological barrier for numerous migratory birds flying from European breeding grounds to African wintering sites. Birds generally avoid migration over open sea and fly over land. In the Mediterranean Basin, few land bridges or bottlenecks for migratory birds exist. The narrowest are at the western and eastern extremes: the Strait of Gibraltar and Israel. Comparative studies between these locations are extremely rare to date. Therefore, in order to elucidate the differences between the two flyways, we compared data collected simultaneously for two sister leaf warbler species, the Bonelli’s Warbler complex, Phylloscopus bonelli and Phylloscopus orientalis, at ringing stations in the western Mediterranean Basin Gibraltar, and the eastern Eilat, Israel. Data on biometrics and passage dates of individuals trapped at Gibraltar and Eilat were used, and it was found that mean arrival date of Western Bonelli’s Warblers at Gibraltar was 15 days later than Eastern Bonelli’s Warblers at Eilat. Furthermore, Western Bonelli’s Warblers had shorter wings than Eastern Bonelli’s Warblers. On the other hand, birds in Eilat were in poorer body condition than individuals in Gibraltar. The comparison between geographically distant stop-over sites contributes to furthering our understanding of the development of migration strategies across ecological barriers in sibling species. Our study showed that populations that breed in southwestern Europe migrate through Gibraltar and winter in West Africa are able to accomplish migration in comparatively good body condition. This is in contrast to those that winter in East Africa, migrate through Israel and have to endure the combined challenge of crossing the Sahel, Sahara and Sinai deserts before reaching their breeding grounds across southeast Europe and southwest Asia. Hence, the discrepancies described between the western and the eastern flyway suggest that individuals in the west, in general, migrate shorter distances, have a physiologically less demanding crossing of the North African deserts and appear to stage before their crossing the Strait of Gibraltar, a privilege unavailable to the migrants of the eastern flyway.     

Determinants of parental care and offspring survival during the post-fledging period: males care more in a species with partially reversed sex roles

Sexual conflict is magnified during the post-fledging period of birds when the sexes face different trade-offs between continuing parental care or investing in self maintenance or other mating opportunities. Species with reversed sex roles provide a unique opportunity to study the relationship between mating systems and investment in parental care. Here, we provide the first detailed study of the length of care by males versus females (n = 24 pairs) during the post-fledging period, assessing factors that may promote care within and between the sexes. In the northern flicker Colaptes auratus, a species with partly reversed sex roles, males cared longer than females (average 16 versus 12 days, respectively). Overall, 36 % of females but no males deserted the brood prior to fledgling independence. Parents that provisioned nestlings at a high rate also spent more days feeding fledglings. Among males, age and nestling feeding rates were positively associated with the length of care. Among females, a low level of feather corticosterone (CORT_f) was associated with a longer length of care. About 45 % of fledglings died within the first week, but fledglings with intermediate body mass had the highest survival suggesting stabilizing selection on mass. Fledgling survival was also higher in individuals with larger broods and lower levels of CORT_f. We demonstrate that because females can be polyandrous they often desert the brood before males, and that the sexes respond to different cues relating to their energy balance when deciding the length of care given to their offspring.     

Cave breeding by African Penguins near the northern extreme of their range: Sylvia Hill,Namibia

Only three mainland sites are known among the total 27 breeding colonies of the African Penguin, Spheniscus demersus: two in South Africa and one in Namibia. The latter is a unique cave site near the northern extreme of the species' range on the edge of the Namib Desert. To determine the colony size, long-term viability and any difference in breeding ecology relative to more southern sites we combined data from previous visits to the site with four visits in 2001. We found that about 240 to 300 birds use the Sylvia Hill cave, and about 90 nests are active with a laying peak in January. Eggs are laid on top of guano mounds not in burrows as is usual for this species. Smaller clutches (1.68 eggs/nest) but larger broods (x = 1.31 chicks/nest) were apparent in this colony than those farther south. Larger mean clutches farther south suggest a latitudinal trend in clutch size for Namibia's penguins. We found no evidence for a population decline over 17 years, and thus no evidence that birds at the periphery of their range moved southwards into core areas. We conclude that the colony is healthy and thriving despite a general decline in penguin numbers in southern Africa.     

Influence of mating duration on fecundity and fertility in two aphidophagous ladybirds

Abstract:  The influence of different mating durations on fecundity and fertility has been studied in two aphidophagous ladybirds, Cheilomenes sexmaculata and Coelophora saucia . Pre-oviposition period decreased while fecundity and fertility increased with increase in mating duration in both the ladybird species. The increase in fecundity with longer mating durations is probably due to the female response because of cryptic female choice. Mating of 10-s duration resulted in oviposition but of unviable eggs probably because of lack of sperm transfer. A minimum duration of 1 min of mating was probably essential for fertilization of the eggs. Absence of spermatophore in the reproductive tract of females is indicative of direct sperm transfer in both the ladybird species. Trend of fertility (similar fertility at 1 and 5 min followed by increase at 60 min which was again similar to that at complete mating) indicates probable sperm transfer in spurts in C. sexmaculata while continuous transfer in C. saucia is indicated by continuous increase in fertility with increase in mating duration.     

Marcescent corollas as functional structures: effects on the fecundity of two insect-pollinated plants

Background and aims

Persistence of withered corollas after anthesis (‘corolla marcescence’) is widespread in angiosperms, yet its functional significance does not seem to have been explored for any species. This note reports the results of experiments assessing the fecundity effects of marcescent corollas in two southern Spanish insect-pollinated plants, Lavandula latifolia (Lamiaceae) and Viola cazorlensis (Violaceae).

Methods

The effect of marcescent corollas on seed production was evaluated experimentally on wild-growing plants. Newly open flowers were randomly assigned to either control or treatment groups in experimental plants. After anthesis, withered corollas of treatment flowers were removed and those in control flowers were left in place. Fruits produced by treatment and control flowers were collected shortly before dehiscence and the number of seeds counted.

Key Results

In V. cazorlensis, removal of withered corollas had no effect on percentage of fruit set, but mean seeds per fruit increased from 9·5 to 11·4. In L. latifolia, corolla removal had no effect on the number of seeds per fruit, but reduced the proportion of flowers ripening fruit from 60 % to 40 %. The detrimental effect of corolla removal on L. latifolia fecundity resulted from the drastic increase in fruit infestation by seed-predatory cecidomyiid larvae, which occurred in 4 % and 34 % of control and treatment fruits, respectively.

Conclusions

Because of their potential effects on plant fecundity, marcescent corollas should not be dismissed a priori as biologically irrelevant leftovers from past floral functions. The simplicity of the experimental layout required to test for short-term fecundity effects of corolla marcescence should help to achieve a better understanding of the ecological and evolutionary correlates of this widespread but poorly understood trait.