Crossbills Research Articles

Geographical variation in cone traits of Pinus nigra as result of crossbill predation: implications for assisted migration

The interaction between Spanish Black pine (Pinus nigra subsp. salzmannii) and common crossbill (Loxia curvirostra) could have resulted in a geographic mosaic of coevolution in the Iberian Peninsula. In turn, this coevolutionary interaction might limit the future applicability of assisted migration as a tool to adapt forests of Spanish Black pine to ongoing climate change. Several cone and seed traits were measured in 740 cones collected at six stands distributed across the range of Spanish Black pine. Data were analysed by means of linear-mixed effects models, canonical analysis of principal coordinates and random-forest analysis. Results showed that cones from the northern pine populations exhibited more defensive traits against crossbill predation than cones from the central and southern populations, resulting in a geographic mosaic of selection. Assisted migration of P. nigra would involve moving southern populations toward the north of the species’ range and would result in introducing the genotypes of pines with poorly defended cones into areas where crossbills are comparatively more abundant. The resulting risks for the regeneration prospects of the translocated trees are discussed.

Postjuvenile Moult in the Common Crossbill (Loxia curvirostra curvirostra): Photoperiodic Regulation and Its Role in Synchronization of the Annual Cycle

Captures of Common Crossbills on the southeastern shore of Lake Ladoga and in the St. Petersburg suburbs (1482 individuals from 1968 to 2015) show that the postjuvenile moult is preceded by migration and the overwhelming majority of migrating young birds have plumage that consists solely of juvenile feathers. The postjuvenile moult is recorded from the end of the first ten days of August to the middle of November, the timing of the onset of moult varies within one and a half months with different individuals being observed to have significant distinctions in the number of replaced feathers. The experiments with photoperiodic regulation of the postjuvenile moult were made on 48 individuals captured in nature in the second half of summer and six young birds from one pair of Crossbills, which bred in captivity. The experimental groups were kept in the conditions of a natural decrease in the day (60° N), decrease in the daylength after the transfer from a long day to a short daylength, increasing daylength, constant long daylength, and constant short daylength. The results of the experiments show that the species-specific features of moult in the Common Crossbill are its start being regulated in a wide age range (from 50 to 180 days) and a rather narrow photoperiodic interval of moult with short daylengths (14.5–9 h of daylight). As long as there is more than 14.5 h of daylight, moult begins under the influence of the endogenous rhythm, but not earlier than the age of 4–6 months. The individuals that moult within the photoperiodic interval replace plumage at high rates. After the daylength gets below the lower threshold of the photoperiodic interval, an inhibiting role of the photoperiodic response is activated, terminating moult in the birds that started moult too late, and their plumage mainly retains juvenile generation feathers. Due to the regulation of moult, intrapopulation differences in the timing of annual cycles that are more than seven months at the time of birth of young Common Crossbills decrease almost five times by its start and become even smaller as it ends. It is assumed that this not only makes it possible to implement moult under optimal conditions but also makes first-year birds ready to start breeding in a timely manner if they find themselves in an area with abundantly fruiting spruce trees.

Resource stability and geographic isolation are associated with genome divergence in western Palearctic crossbills.

While many conifers produce annually variable seed crops, serotinous species (which hold seeds in cones for multiple years) represent unusually stable food resources for seed predators. Such stability is conducive to residency and potentially population divergence of consumers as exemplified by the Cassia crossbill (Loxia sinesciuris) in North America. We used genotyping by sequencing (GBS) to test whether three Mediterranean subspecies of common crossbills (L.curvirostra) associated with the serotinous Aleppo pine (Pinus halepensis) were more genetically distinct than European crossbills associated with nonserotinous conifers. We assembled a Cassia crossbill draft genome as a reference for mapping GBS reads and as a first step towards a more contiguous genome assembly. We found clear patterns of genetic divergence for each of the P.halepensis-associated subspecies. Geographic isolation, as promoted by resource stability and residency, is associated with genetic divergence of two of these subspecies. However, geographic isolation cannot account for divergence of L.c.hispana. Instead, resource stability likely contributed to divergence by reducing dispersal and increasing resource competition that may limit breeding by immigrants. In contrast, we found no differentiation among common crossbills associated with less stable resources, and only slight differentiation between common crossbills and parrot crossbills (L.pytyopsittacus). The substantial morphological divergence between common and parrot crossbills has likely originated or been maintained by selection despite gene flow generated by spatiotemporal resource fluctuation. Our results indicate that phenological as well as morphological characteristics of conifers have influenced crossbill diversification, and suggest a possible link between resource stability and population divergence.

Composition et structure avifaunistique dans une steppe arborée de pin d’Alep a chêne vert à Sehary Guebli (Djelfa, Algérie)

The counting of birds was conducted in a forest area of Aleppo Pine and Holm Oak Trees. A total of 35 species of birdswas recorded in this forest area. These species are distributed over 6 orders and 15 families. The Order Passeriformes was the most represented with 25 species and 9 families. The red Crossbill Loxia curvirostra wasthe most observed by means of progressive frequential sampling method with a percentage of 54.1% and the Greenfinch Fringilla coelebs wasthe most counted by the point count abundance indices with an IPA of 4.43.

Innate immunity and environmental correlates of Haemoproteus prevalence and intensity in an opportunistic breeder.

While parasite infection can have substantial fitness consequences in organisms, the predictors of parasite prevalence and intensity are often complex and vary depending on the host species. Here, we examined correlates of Haemoproteus (a common malaria parasite) prevalence and intensity in an opportunistically breeding songbird, the red crossbill (Loxia curvirostra). Specifically, we quantified Haemoproteus prevalence and intensity in crossbills caught in the Grand Teton National Park from 2010 to 2013. We found that parasite prevalence varies seasonally and across years, with the highest number of infected individuals occurring in the summer, although there was variation across summers sampled, and that prevalence was positively related to annual mean cone crop sizes (a measure of crossbill food abundance) and daily ambient temperature (a correlate of vector abundance). Parasite intensity was significantly and positively related to one measure of innate immunity, leucocyte counts per blood volume. Finally, neither crossbill age, ecomorph, nor sex had significant effects on parasite infection intensity; however, parasite prevalence did significantly vary among ecomorph and age classes. These results support the interpretation that a combination of physiological (specifically immune activity) and environmental factors affects parasite prevalence and infection intensity in this opportunistically breeding avian species.

Foraging patterns of common crossbills (Loxia curvirostra) on spruces (Picea spp.) in Scotland

Common crossbills forage on Sitka spruce and Norway spruce when the cones reach full size in late summer until the seeds have shed in the following spring. Sitka spruce start shedding seed in autumn, thereby reducing the food supply for crossbills through autumn to spring, whereas Norway spruce retain their seeds until spring. Crossbills forage on cones that are attached to the tree (more so for Norway spruces) or are removed from the tree by the crossbills before feeding. The latter cones are then dropped after seed extraction. The mean length of dropped Sitka spruce cones was 72 mm, close to the average length in a widespread survey. This suggests little size selection. The mean length of dropped Norway spruce cones was 90 mm, which was much smaller than the average length in the survey. Although used, large cones are probably left attached to trees because they are too heavy to handle if cut from the tree. The average percentage of seeds extracted before a cone was dropped was 45% for Sitka spruce and 42% for Norway spruce. There was a trend for fewer Sitka spruce seeds to be taken per cone across the period between autumn and spring. Incomplete extraction of seeds suggests that cones become unprofitable as the seed number is depleted in cones and that the threshold for switching cones changes as the number of seeds per cone declines.

Range extension of the threatened Red Crossbill (Loxia curvirostra percna) in Canada: new insights from Anticosti Island, Québec

Tremblay, J. A., M. Robert, D. P. Hynes, M. A. Young, and B. Drolet. 2018. Range extension of the threatened Red Crossbill (Loxia curvirostra percna) in Canada: new insights from Anticosti Island, Québec. Avian Conservation and Ecology 13(1):10. https://doi.org/10.5751/ACE-01175-130110

Social information changes stress hormone receptor expression in the songbird brain

Social information is used by many vertebrate taxa to inform decision-making, including resource-mediated movements, yet the mechanisms whereby social information is integrated physiologically to affect such decisions remain unknown. Social information is known to influence the physiological response to food reduction in captive songbirds. Red crossbills (Loxia curvirostra) that were food reduced for several days showed significant elevations in circulating corticosterone (a “stress” hormone often responsive to food limitation) only if their neighbors were similarly food restricted. Physiological responses to glucocorticoid hormones are enacted through two receptors that may be expressed differentially in target tissues. Therefore, we investigated the influence of social information on the expression of the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA in captive red crossbill brains. Although the role of MR and GR in the response to social information may be highly complex, we specifically predicted social information from food-restricted individuals would reduce MR and GR expression in two brain regions known to regulate hypothalamic-pituitary-adrenal (HPA) activity - given that reduced receptor expression may lessen the efficacy of negative feedback and release inhibitory tone on the HPA. Our results support these predictions - offering one potential mechanism whereby social cues could increase or sustain HPA-activity during stress. The data further suggest different mechanisms by which metabolic stress versus social information influence HPA activity and behavioral outcomes.

Two new feather mites of the genus Proctophyllodes Robin, 1868 (Acari: Proctophyllodidae) from European passerines (Aves: Passeriformes)

Two new species of the feather mite genus Proctophyllodes Robin, 1868 (Analgoidea: Proctophyllodidae) are described from two passerine birds (Passeriformes) in Europe: Proctophyllodes markovetsi n. sp. from the tawny pipit Anthus campestris (L.) (Motacillidae) and P. loxiae n. sp. from the red crossbill Loxia curvirostra (L.) (Fringillidae). Males of P. markovetsi are most clearly distinguished from the closely related P. tchagrae Atyeo & Braasch, 1966 by having greater terminal lamellae (30-40×20-25µm), the tips of genital arch curved medially, and the corolla of the anal sucker with 14-15 denticles; females of this species are characterised by the terminal appendages distinctly longer than the lobar region width. Males of P. loxiae differ from the closest species, P. fuchsi Mironov, 1997, by having smaller terminal lamellae (45-50×22-28μm), the genital organ extending beyond the posterior margin of lamellae by half their length; females can be distinguished by having the terminal cleft noticeably wider than long (28-30×35-40μm).

Nest sites and seasonality of breeding behavior in the Common Crossbill population of Shimokita Peninsula, Northern Japan

Nest sites and seasonality of breeding behavior in the Common Crossbill population of Shimokita Peninsula, Northern Japan

Matching habitat choice in nomadic crossbills appears most pronounced when food is most limiting.

Of the various forms of nonrandom dispersal, matching habitat choice, whereby individuals preferentially reside in habitats where they are best adapted, has relatively little empirical support. Here, I use mark-recapture data to test for matching habitat choice in two nomadic ecotypes of North American Red Crossbills (Loxia curvirostra complex) that exist in the lodgepole pine (Pinus contorta) forests in the South Hills, Idaho, every summer. Crossbills are adapted for foraging on seeds in conifer cones, and in the South Hills the cones are distinctive, favoring a relatively large bill. During a period when seed was most limiting, only the largest individuals approximating the average size of the locally adapted ecotype remained for a year or more. During a period when seed was less limiting, proportionately more individuals remained and the trend for larger individuals to remain was weaker. Although matching habitat choice is difficult to demonstrate, it likely contributed to the observed patterns. Otherwise, nearly unprecedented intensities of natural selection would be needed. Given the nomadic behavior of most crossbill ecotypes and the heterogeneous nature of conifer seed crops, matching habitat choice should be favored and likely contributes to their adaptation to alternative conifers and rapid diversification.

Bird ringing in Slovenia in 2015 and the occurrence of Parrot Crossbills Loxia pytyopsittacus

Abstract In 2015, 170 bird species were recorded during bird ringing activities in Slovenia. We ringed 73,371 birds belonging to 162 species, there were 132 foreign recoveries of birds ringed in Slovenia, 120 recoveries of birds ringed abroad and found in Slovenia, as well as 1964 local recoveries. The most frequently ringed species were Blackcap Sylvia atricapilla and Great Tit Parus major. In ringed nestlings, Great Tits and Tree Sparrows Passer montanus predominated. In 2015, the first preliminary ringing of Scops Owls Otus scops during migration took place, resulting in the highest number of Scops Owls ringed so far. Concerning recoveries of birds ringed in Slovenia and later recorded abroad and birds ringed abroad and later recorded in Slovenia, the commonest were Mute Swans Cygnus olor and Black-headed Gulls Chroicocephalus ridibundus. The longest-distance recovery concerned a Reed Bunting Emberiza schoeniculus found in Sweden (2,144 km away). Among the interesting finds were also the first finds of ringed Pygmy Cormorants Microcarbo pygmeus so far from breeding sites in Hungary. Among rare species, Yellow-browed Warbler Phylloscopus inornatus, Spanish Sparrow Passer hispaniolensis and a pair of Parrot Crossbills Loxia pytyopsittacus were caught and ringed, the latter for the very first time in Slovenia after more than 100 years. An overview of records of the Parrot Crossbill is given herein, as well as analysis of irruptive years of the Red Crossbills Loxia curvirostra between 1980 and 2015, when the probability of boreal Crossbill species occurrence is the highest. According to the ringers’ data, the irruptive years of Red Crossbills in Slovenia were 1984, 1985, 2007, 2008, 2010, 2011 and 2012. The article points to the probability that Parrot Crossbills have been overlooked in the past, since larger specimens of Crossbills were ringed mostly in irruptive years, but no specific bill measurements important for distinguishing between Parrot and Red Crossbill had been taken.

The Natural History of the South Hills Crossbill in Relation to Its Impending Extinction.

Increasingly, the species that we discover will be uncommon, area restricted, and vulnerable to extinction. I describe the natural history of a newly discovered seed-eating finch from the Rocky Mountain region, the South Hills crossbill (Loxia curvirostra complex). It relies on seeds in the closed cones of the fire-adapted Rocky Mountain lodgepole pine (Pinus contorta latifolia) and is found only in the higher elevations of two small mountain ranges in southern Idaho. Here crossbills and pine are engaged in a coevolutionary arms race. Although most of the seeds remain secured within the cones for decades until the heat of a stand-replacing fire causes the cone scales to separate, seeds become accessible to crossbills slowly as cones weather and gaps form between some of the scales. However, hot days (≥32°C), especially four or more hot days, seem to mimic the effect of fire, apparently causing the immediate release of a fraction of the seeds. Such events caused a 20% annual decline in crossbills that lasted up to 4 years and an 80% decline in the population between 2003 and 2011. This is an example of a novel trophic mismatch between a consumer and its resource caused by a shift in the phenology of the resource arising from climate change. Not only do these phenological shifts have the potential to cause seed consumers to decline, these shifts are also likely to cause reduced recruitment of the plants. The South Hills crossbill is especially vulnerable and will likely go extinct this century before lodgepole pine is extirpated from the South Hills.

Genome divergence and diversification within a geographic mosaic of coevolution.

Despite substantial interest in coevolution's role in diversification, examples of coevolution contributing to speciation have been elusive. Here, we build upon past studies that have shown both coevolution between South Hills crossbills and lodgepole pine (Pinus contorta), and high levels of reproductive isolation between South Hills crossbills and other ecotypes in the North American red crossbill (Loxia curvirostra) complex. We used genotyping by sequencing to generate population genomic data and applied phylogenetic and population genetic analyses to characterize the genetic structure within and among nine of the ecotypes. Although genome-wide divergence was slight between ecotypes (FST =0.011-0.035), we found evidence of relative genetic differentiation (as measured by FST ) between and genetic cohesiveness within many of them. As expected for nomadic and opportunistic breeders, we detected no evidence of isolation by distance. The one sedentary ecotype, the South Hills crossbill, was genetically most distinct because of elevated divergence at a small number of loci rather than pronounced overall genome-wide divergence. These findings suggest that mechanisms related to recent local coevolution between South Hills crossbills and lodgepole pine (e.g. strong resource-based density dependence limiting gene flow) have been associated with genome divergence in the face of gene flow. Our results further characterize a striking example of coevolution driving speciation within perhaps as little as 6000years.

Light-level geolocators confirm resident status of a Southern European Common Crossbill population

Common Crossbill (Loxia curvirostra) populations are dependent on specific key conifer species for their primary food supply, but many of these conifers standardly show irregular cone crop production. Consequently, the species has evolved a nomadic behavior, breeding in areas with a high crop production in given years. Northern European crossbills mostly forage on Norway Spruce (Picea abies) and migrate along a northeast–southwest gradient across Europe. In contrast, crossbills from Spain were considered to be resident until recent studies on crossbill populations in the Pyrenees showed that a fraction of the population may also migrate. The type of movements of these Spanish birds, however, remains virtually unknown. The aim of our study was to resolve the question of whether these birds displace on a small local scale or whether they actually move to a distinct non-breeding area for part of the annual cycle. We tracked 14 male Common Crossbills from the Pyrenees with light-level geolocators for an entire year. Our results suggest that these birds were resident; only one bird may have shown a west–east movement of up to 200 km along the Pyrenean axis. We conclude that movement of the Common Crossbill from the Pyrenees may predominantly consist of relocation to nearby mountain ranges in Iberia or vertically in altitude. We expect that such small-scale movements have implications for population dynamics, and we recommend further research with telemetry to resolve the details of this small-scale movement.

Mortality and pathology in birds due to Plasmodium (Giovannolaia) homocircumflexum infection, with emphasis on the exoerythrocytic development of avian malaria parasites.

BackgroundSpecies of avian malaria parasites (Plasmodium) are widespread, but their virulence has been insufficiently investigated, particularly in wild birds. During avian malaria, several cycles of tissue merogony occur, and many Plasmodium spp. produce secondary exoerythrocytic meronts (phanerozoites), which are induced by merozoites developing in erythrocytic meronts. Phanerozoites markedly damage organs, but remain insufficiently investigated in the majority of described Plasmodium spp. Avian malaria parasite Plasmodium (Giovannolaia) homocircumflexum (lineage pCOLL4) is virulent and produces phanerozoites in domestic canaries Serinus canaria, but its pathogenicity in wild birds remains unknown. The aim of this study was to investigate the pathology caused by this infection in species of common European birds.MethodsOne individual of Eurasian siskin Carduelis spinus, common crossbill Loxia curvirostra and common starling Sturnus vulgaris were exposed to P. homocircumflexum infection by intramuscular sub-inoculation of infected blood. The birds were maintained in captivity and parasitaemia was monitored until their death due to malaria. Brain, heart, lungs, liver, spleen, kidney, and a piece of breast muscle were examined using histology and chromogenic in situ hybridization (ISH) methods.ResultsAll exposed birds developed malaria infection, survived the peak of parasitaemia, but suddenly died between 30 and 38 days post exposure when parasitaemia markedly decreased. Numerous phanerozoites were visible in histological sections of all organs and were particularly easily visualized after ISH processing. Blockage of brain capillaries with phanerozoites may have led to cerebral ischaemia, causing cerebral paralysis and is most likely the main reason of sudden death of all infected individuals. Inflammatory response was not visible around the brain, heart and muscle phanerozoites, and it was mild in parenchymal organs. The endothelial damage likely causes dysfunction and failure of parenchymal organs.ConclusionPlasmodium homocircumflexum caused death of experimental passerine birds due to marked damage of organs by phanerozoites. Patterns of phanerozoites development and pathology were similar in all exposed birds. Mortality was reported when parasitaemia decreased or even turned into chronic stage, indicating that the light parasitaemia is not always indication of improved health during avian malaria. Application of traditional histological and ISH methods in parallel simplifies investigation of exoerythrocytic development and is recommended in avian malaria research.

Photoperiod but not food restriction modulates innate immunity in an opportunistic breeder, Loxia curvirostra.

An organism's investment in immune function often varies seasonally but understanding of how fluctuations in environmental conditions directly modulate investment remains limited. This experiment investigated how changes in photoperiod and food availability affect investment in constitutive innate immunity and the acute phase response induced by lipopolysaccharide (LPS) injections in captive red crossbills (Loxia curvirostra). Crossbills are reproductively flexible songbirds that specialize on an unpredictably available food resource and display temporal variation in immunity in the wild. Birds were separated into four treatments and exposed to long or short day lengths for 6weeks before continuing on an ad libitum diet or experiencing a 20% food reduction for 10 days. Birds were un-injected or injected with LPS both before and after diet change. Innate immunity was quantified throughout the experiment to assess effects of photoperiod, food availability and their interactions on hemolysis-hemagglutination, haptoglobin, bacterial killing ability and leukocyte counts. Overall, increasing day length significantly increased both bacterial killing ability and leukocyte counts. Surprisingly, food restriction had little effect on the immune parameters, potentially owing to the 'low-cost' environment of captivity and suggesting that investment in innate immunity is prioritized and maintained whenever possible. LPS injections induced stereotypical sickness behaviors and increased bacterial killing ability in short day birds and complement activity (hemolysis) both before and after food restriction. These results demonstrate robust seasonal modulation of immune investment and an ability to maintain innate immunity in the face of limited resources in these temporally flexible songbirds.

Reproductive isolation and the notion of species in birds

Biological diversity is continuous as a result of evolutionary processes, whereas the language for its description is symbolic and, therefore, discrete. Thus, the main question of the “species problem” is as follows: do species really exist in nature or not? The answer of this question depends on the “system of coordinates” that is used for the description of species. Species inhabiting the same territory (“one-dimensional species”) are usually discrete. However, when we begin to describe closely related forms within their ranges (“two-dimensional species”), the determination of the interspecific border becomes problematic. Therefore, speciation can be defined as the process of establishing the sympatry between diverging taxa, and species can be defined as morphologically distinguishable groups of organisms that can coexist in the sympatry zone for a long time. The diversity of the existing species concepts can be reduced to the two main ones—biological and phylogenetic. The latter has a disadvantage compared to the former because it does not deal with the theoretical substantiation of the species reality. But within the framework of the concepts of biological species, the theoretical substantiation of species reality (the hypothesis of the reinforcement of isolating mechanisms in a hybrid zone) has no reliable empirical support too. Another substantial disadvantage is that the use of the biological concept in practice may lead to misinterpretation of the taxonomic status of forms at different stages of the speciation process. At the initial stages of divergence, taxa can be regarded as independent species (for example, ecological races of the red crossbill (Loxia curvirostra), whereas at the final stage of speciation, forms are regarded as conspecific due to their hybridization in the sympatry zone (the yellowhammer Emberiza citrinella and the pine bunting E. leucocephala). The “species problem” seems to be solvable using a synthesis of the biological and phylogenetic concepts of species.

Phenotypic Selection Exerted by a Seed Predator Is Replicated in Space and Time and among Prey Species.

Although consistent phenotypic selection arising from biotic interactions is thought to be the primary cause of adaptive diversification, studies documenting such selection are relatively few. Here we analyze 12 episodes of phenotypic selection exerted by a predispersal seed predator, the red crossbill (Loxia curvirostra complex), on five species of pines (Pinus). We find that even though the intensity of selection for some traits increased with the strength of the interaction (i.e., proportion of seeds eaten), the relative strength of selection exerted by crossbills on cone and seed traits is replicated across space and time and among species. Such selection (1) can account for repeated patterns of conifer cone evolution and escalation in seed defenses with time and (2) suggests that variation in selection is less the result of variation intrinsic to pairwise biotic interactions than, for example, variation in relative densities of the interacting species, community context, and abiotic factors.

The evidence for rapid gametocyte viability changes in the course of parasitemia in Haemoproteus parasites.

Avian haemosporidian parasites of the genus Haemoproteus (Haemoproteidae, Haemosporida) are widespread, and some species cause diseases both in vertebrate hosts and blood-sucking insects. Parasitemia of Haemoproteus species usually is long-lasting, with gametocytes present in the circulation for several months. However, the viability of gametocytes and their ability to produce sexual cells have been insufficiently understood in the course of parasitemia. We initiated the sexual development in vitro conditions and calculated proportions of normal and anomalous ookinetes, which developed in two species of Haemoproteus. Mature gametocytes of the parasites were obtained from naturally infected avian hosts at different days of parasitemia. Haemoproteus (Parahaemoproteus) lanii (cytochrome b lineage hRB1) was isolated from one red-backed shrike Lanius collurio. Two isolates of Haemoproteus (Parahaemoproteus) tartakovskyi (cytochrome b lineage hSISKIN1) were used: one was obtained from a siskin Carduelis spinus and one from a common crossbill Loxia curvirostra. The wild-caught birds were kept indoors under controlled conditions, and blood was taken from them every 1 or 2 days during 10-14 days. After each blood sampling, the sexual process and ookinete development were initiated in vitro by exposure of infected blood containing mature gametocytes to air. Smears were prepared at intervals of 15 min, 3 h, and 12 h after the exposure; they were examined microscopically. In all, 25 experiments were performed; each experiment was repeated two times. The ratios of macro- and microgametocytes did not change in all experimental infections during this study. Sexual process occurred, and both normal and anomalous ookinetes developed in all parasites. The proportion of normal ookinetes did not change significantly in both isolates of H. tartakovskyi. Between 8 and 10 days of observation, the proportion of normal ookinetes of H. lanii decreased 6 times compared to the beginning of the experiment. That was accompanied with the rapid decrease of parasitemia and the inability of the majority of mature gametocytes to escape from erythrocytes and produce gametes, indicating disorder of the gametogenesis. There was clear difference in the gametogenesis between H. tartakovskyi and H. lanii from this point of view. This study shows that the viability of Haemoproteus gametocytes might change dramatically in the course of parasitemia within 1-2 days, and the presence of mature gametocytes in the circulation does not necessarily indicate their ability to exflagellate and produce ookinetes. We predict that this finding is important epidemiologically due to relationship with sporogony success.