| 1. |
- Bianco, Giuseppe, et al.
(author)
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Emlen funnel experiments revisited : methods update for studying compass orientation in songbirds
- 2016
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 6:19, s. 6930-6942
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Journal article (peer-reviewed)abstract
- Migratory songbirds carry an inherited capacity to migrate several thousand kilometers each year crossing continental landmasses and barriers between distant breeding sites and wintering areas. How individual songbirds manage with extreme precision to find their way is still largely unknown. The functional characteristics of biological compasses used by songbird migrants has mainly been investigated by recording the birds directed migratory activity in circular cages, so-called Emlen funnels. This method is 50 years old and has not received major updates over the past decades. The aim of this work was to compare the results from newly developed digital methods with the established manual methods to evaluate songbird migratory activity and orientation in circular cages. We performed orientation experiments using the European robin (Erithacus rubecula) using modified Emlen funnels equipped with thermal paper and simultaneously recorded the songbird movements from above. We evaluated and compared the results obtained with five different methods. Two methods have been commonly used in songbirds’ orientation experiments; the other three methods were developed for this study and were based either on evaluation of the thermal paper using automated image analysis, or on the analysis of videos recorded during the experiment. The methods used to evaluate scratches produced by the claws of birds on the thermal papers presented some differences compared with the video analyses. These differences were caused mainly by differences in scatter, as any movement of the bird along the sloping walls of the funnel was recorded on the thermal paper, whereas video evaluations allowed us to detect single takeoff attempts by the birds and to consider only this behavior in the orientation analyses. Using computer vision, we were also able to identify and separately evaluate different behaviors that were impossible to record by the thermal paper. The traditional Emlen funnel is still the most used method to investigate compass orientation in songbirds under controlled conditions. However, new numerical image analysis techniques provide a much higher level of detail of songbirds’ migratory behavior and will provide an increasing number of possibilities to evaluate and quantify specific behaviors as new algorithms will be developed.
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| 2. |
- Bianco, Giuseppe, et al.
(author)
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Magnetic body alignment in migratory songbirds : a computer vision approach
- 2019
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In: The Journal of experimental biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 222
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Journal article (peer-reviewed)abstract
- Several invertebrate and vertebrate species have been shown to align their body relative to the geomagnetic field. Many hypotheses have been proposed to explain the adaptive significance of magnetic body alignment outside the context of navigation. However, experimental evidence to investigate alternative hypotheses is still limited. We present a new setup to track the preferential body alignment relative to the geomagnetic field in captive animals using computer vision. We tested our method on three species of migratory songbirds and provide evidence that they align their body with the geomagnetic field. We suggest that this behaviour is involved in the underlying mechanism for compass orientation and calibration, which may occur near to sunrise and sunset periods. Our method could easily be extended to other species and used to test a large set of hypotheses to explain the mechanisms behind the magnetic body alignment and the magnetic sense in general.
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| 3. |
- Bianco, Giuseppe, et al.
(author)
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Magnetic storms disrupt nocturnal migratory activity in songbirds
- 2019
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In: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 15:3
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Journal article (peer-reviewed)abstract
- Birds possess a magnetic sense and rely on the Earth's magnetic field for orientation during migration. However, the geomagnetic field can be altered by solar activity at relative unpredictable intervals. How birds cope with the temporal geomagnetic variations caused by solar storms during migration is still unclear. We addressed this question by reproducing the effect of a solar storm on the geomagnetic field and monitoring the activity of three songbird species during autumn migration. We found that only the European robin reduced nocturnal migratory restlessness in response to simulated solar storms. At the same time, robins increased activity during early morning. We suggest that robins reduced activity at night when the perception of magnetic information would be strongly disrupted by temporal variations of the magnetic field, to extend their migration during daytime when several visual cues become available for orientation. The other two species, chiffchaff and dunnock, showing low or no nocturnal migratory activity, did not respond to the solar storm by changing activity.
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| 4. |
- Bianco, Giuseppe, et al.
(author)
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The importance of time of day for magnetic body alignment in songbirds
- 2022
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In: Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology. - : Springer Science and Business Media LLC. - 0340-7594. ; 208:1, s. 135-144
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Journal article (peer-reviewed)abstract
- Spontaneous magnetic alignment is the simplest known directional response to the geomagnetic field that animals perform. Magnetic alignment is not a goal directed response and its relevance in the context of orientation and navigation has received little attention. Migratory songbirds, long-standing model organisms for studying magnetosensation, have recently been reported to align their body with the geomagnetic field. To explore whether the magnetic alignment behaviour in songbirds is involved in the underlying mechanism for compass calibration, which have been suggested to occur near to sunset, we studied juvenile Eurasian reed warblers (Acrocephalus scirpaceus) captured at stopover during their first autumn migration. We kept one group of birds in local daylight conditions and an experimental group under a 2 h delayed sunset. We used an ad hoc machine learning algorithm to track the birds’ body alignment over a 2-week period. Our results show that magnetic body alignment occurs prior to sunset, but shifts to a more northeast–southwest alignment afterwards. Our findings support the hypothesis that body alignment could be associated with how directional celestial and magnetic cues are integrated in the compass of migratory birds.
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| 5. |
- Bobeva, Aneliya, et al.
(author)
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Degree of associations among vectors of the genus Culicoides (Diptera: Ceratopogonidae) and host bird species with respect to haemosporidian parasites in NE Bulgaria
- 2014
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In: Parasitology Reseach. - : Springer Science and Business Media LLC. - 1432-1955 .- 0932-0113. ; 113:12, s. 4505-4511
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Journal article (peer-reviewed)abstract
- The occurrence of haemosporidians in biting midges of the genus Culicoides is examined in North-East Bulgaria in order to reveal their potential role for parasite transmission. A PCR-based technique amplifying part of the mitochondrial cytochrome b gene of the parasite is applied on naturally infected biting midges. Totally, 640 parous individuals of four species and 95 blood-fed individuals of six species of Culicoides are examined for the presence of DNA of haemosporidians. Haemosporidian genetic lineages are identified in individuals of three insect species: Culicoides alazanicus (12 lineages, nine lineages of Haemoproteus and three lineages of Plasmodium), Culicoides festivipennis and Culicoides circumscriptus (with two and one lineages of Haemoproteus, respectively). Two genetic lineages of Haemoproteus are recorded in more than one vector species. These results demonstrate variations in the specificity of Haemoproteus genetic lineages to their potential vectors, since some lineages are recorded in a single vector species and others occur in two or more vector species.
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| 6. |
- Bobeva, A., et al.
(author)
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Host preferences of ornithophilic biting midges of the genus Culicoides in the Eastern Balkans
- 2015
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In: Medical and Veterinary Entomology. - : Wiley. - 0269-283X. ; 29:3, s. 290-296
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Journal article (peer-reviewed)abstract
- Many biting midges of the genus CulicoidesLatreille, 1809 (Diptera: Ceratopogonidae) are competent vectors of a diverse number of pathogens. The identification of their feeding behaviour and of vector-host associations is essential for understanding their transmission capacity. By applying two different nested polymerase chain reaction (PCR) assays, of which one targeted the avian cyt b gene and the other targeted the COI gene of a wide range of vertebrates, we identified the blood hosts of six biting midge species including Culicoides circumscriptus, Culicoides festivipennis, Culicoides punctatus, Culicoides pictipennis, Culicoides alazanicus and Culicoides cf. griseidorsum, the latter two of which are reported in Bulgaria for the first time. Bird DNA was found in 50.6% of 95 investigated bloodmeals, whereas mammalian DNA was identified in 13.7%. Two Culicoides species were found to feed on both birds and mammals. There was remarkable diversity in the range of avian hosts: 23 species from four orders were identified in the abdomens of four Culicoides species. The most common bird species identified was the magpie, Pica pica (n=7), which was registered in all four ornithophilic biting midge species. Six bloodmeals from the great tit, Parus major, were recorded only in C.alazanicus. None of the studied species of Culicoides appeared to be restricted to a single avian host.
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| 7. |
- Dimitrov, Dimitar, et al.
(author)
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Molecular characterization of haemosporidian parasites (Haemosporida) in yellow wagtail (Motacilla flava), with description of in vitro ookinetes of Haemoproteus motacillae
- 2013
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In: Zootaxa. - : Magnolia Press. - 1175-5334 .- 1175-5326. ; 3666:3, s. 369-381
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Journal article (peer-reviewed)abstract
- In studies of haemosporidian systematics and taxonomy, a combination of microscopic examination and molecular identification has been recommended. The yellow wagtail (Motacilla flava) is a frequently used species in studies of host-parasite interactions; blood parasites of this bird have been well studied using microscopic examination of blood films, but data on molecular characterization of the parasites are scattered. Here we present the first study linking several haemosporidian cyt b sequences with their morphospecies parasitizing the yellow wagtail, combining light microscopy and nested PCR methods. The lineage hYWT1 of Haemoproteus motacillae was the most prevalent parasite; it was recorded in 38% of the birds. The latter lineage and the lineages hYWT2, hYWT3, hYWT5 and hYWT6 form a well-supported clade on the phylogenetic tree and likely represent intraspecific genetic variation of H. motacillae, with genetic divergence of 0.3-1.5 % among these lineages. Microscopic examination of smears prepared during an in vitro experiment, which was designed for observation of developing ookinetes, showed that H. motacillae ookinetes were present 5 hours after exposure of blood to air at 18-20 degrees C. Ookinetes of this parasite belong to a group of large Haemoproteus spp. ookinetes (19.9 mu m in length on average). Illustrations of the parasites are given. Two of reported Plasmodium lineages, pCOLL1 and pYWT4 are phylogenetically closely related to the widespread host generalist parasites Plasmodium relictum (cyt b lineages pSGS1, pGRW4 and pGRW11), but it was not possible to establish this morphologically. This study contributes to the molecular identification of avian haemosporidian parasites and provides information on morphology of H. motacillae ookinetes, which is additional information assisting the microscopic identification of this species.
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| 8. |
- Dimitrov, Dimitar, et al.
(author)
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Plasmodium spp.: An experimental study on vertebrate host susceptibility to avian malaria.
- 2015
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In: Experimental Parasitology. - : Elsevier BV. - 0014-4894. ; 148, s. 1-16
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Journal article (peer-reviewed)abstract
- The interest in experimental studies on avian malaria caused by Plasmodium species has increased recently due to the need of direct information about host-parasite interactions. Numerous important issues (host susceptibility, development of infection, the resistance and tolerance to avian malaria) can be answered using experimental infections. However, specificity of genetically different lineages of malaria parasites and their isolates is largely unknown. This study reviews recent experimental studies and offers additional data about susceptibility of birds to several widespread cytochrome b (cyt b) lineages of Plasmodium species belonging to four subgenera. We exposed two domesticated avian hosts (canaries Serinus canaria and ducklings Anas platyrhynchos) and also 16 species of common wild European birds to malaria infections by intramuscular injection of infected blood and then tested them by microscopic examination and PCR-based methods. Our study confirms former field and experimental observations about low specificity and wide host-range of Plasmodium relictum (lineages SGS1 and GRW11) and P. circumflexum (lineage TURDUS1) belonging to the subgenera Haemamoeba and Giovannolaia, respectively. However, the specificity of different lineages and isolates of the same parasite lineage differed between species of exposed hosts. Several tested Novyella lineages were species specific, with a few cases of successful development in experimentally exposed birds. The majority of reported cases of mortality and high parasitaemia were observed during parasite co-infections. Canaries were susceptible mainly for the species of Haemamoeba and Giovannolaia, but were refractory to the majority of Novyella isolates. Ducklings were susceptible to three malaria infections (SGS1, TURDUS1 and COLL4), but parasitaemia was light (<0.01%) and transient in all exposed birds. This study provides novel information about susceptibility of avian hosts to a wide array of malaria parasite lineages, outlining directions for future experimental research on various aspects of biology and epidemiology of avian malaria.
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| 9. |
- Ilieva, Mihaela, et al.
(author)
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Autumn migratory orientation and displacement responses of two willow warbler subspecies (Phylloscopus trochilus trochilus and P. t. acredula) in South Sweden.
- 2012
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In: Behavioural Processes. - : Elsevier BV. - 0376-6357. ; 91:3, s. 253-261
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Journal article (peer-reviewed)abstract
- Topography and historical range expansion has formed a so-called migratory divide between two subspecies of willow warbler (Phylloscopus trochilus) in central Scandinavia. The autumn migratory directions of individuals assigned molecularly to both subspecies and possible hybrids were recorded using orientation cage experiments in southwest and southeast Sweden. We found pronounced differences in willow warblers' orientation in respect to genotype. The mean directions registered in the control experiments were in accordance with the ringing recoveries and analyses of stable isotopes for Scandinavian willow warblers. With the same individuals we performed displacement experiments between both sites. They resulted in non-significant orientation, which could be explained by the intermediate distance of the displacement or reactions to housing, transportation and location. On a separate set of birds we tested whether stress following transportation could explain the disorientation and found that orientation before and after transport was unchanged. Experimental studies of effects of intermediate displacements across longitudes and studies of orientation of hybrid individuals in the zones of migratory divides are crucial for understanding the mechanisms underlying orientation behaviour. Our work further stresses the importance of knowing the migration genotype of a particular bird under study, in order to correctly evaluate expected migration routes.
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| 10. |
- Ilieva, Mihaela, et al.
(author)
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Does migratory distance affect fuelling in a medium-distance passerine migrant?: results from direct and step-wise simulated magnetic displacements.
- 2016
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In: Biology Open. - : The Company of Biologists. - 2046-6390. ; 5, s. 272-278
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Journal article (peer-reviewed)abstract
- In birds, fat accumulation before and during migration has been shown to be endogenously controlled and tuned by, among other factors, the Earth's magnetic field. However, our knowledge about the influence of the geomagnetic field on the fuelling in migrating birds is still limited to just a few nocturnally migrating passerine species. In order to study if variations of the magnetic field can also influence the fuelling of both day- and night-migrating passerines, we caught first-year dunnocks (Prunella modularis) and subjected them to three magnetic field conditions simulated by a system of magnetic coils: (1) local geomagnetic field of southern Sweden, (2) magnetic field corresponding to the centre of the expected wintering area, and (3) magnetic field met at the northern limit of the species' breeding distribution. We did not find a difference in mass increase between the birds kept in a local magnetic field and a field resembling their wintering area, irrespectively of the mode of magnetic displacement, i.e. direct or step-wise. However, the dunnocks magnetically displaced north showed a lower rate of fuelling in comparison to the control group, probably due to elevated activity. Compared with previous studies, our results suggest that the fuelling response to magnetic displacements during the migration period is specific to the eco-physiological situation. Future studies need to address if there is an effect of magnetic field manipulation on the level of migratory activity in dunnocks and how widespread the influence of local geomagnetic field parameters is on fuelling decisions in different bird species, which have different migratory strategies, distances and migration history.
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