Prevalence of hematozoa in overwintering American redstarts (Setophaga ruticilla): no evidence for local transmission

We examined American redstarts (Setophaga ruticilla) for protozoan blood parasites on their wintering grounds to determine whether transmission of these parasites occurs prior to spring migration. A total of 73 blood smears from 37 birds were examined for presence and intensity of infection. Thirty-six birds were sampled in the fall, soon after arriving from northern breeding grounds, and the spring prior to departure. Two (5%) of the samples collected in the fall were positive for Haemoproteus fringillae and one (3%) had detectable infections of Trypanosoma avium. Individuals infected with H. fringillae were hatching year redstarts sampled in September and October. Intensity of infection was 78 and < 1 infected erythrocytes per 10,000 erythrocytes, respectively. None of the birds had detectable infections when resampled prior to spring migration the following March.     

Temporal patterns of occurrence and transmission of the blood parasite Haemoproteus payevskyi in the great reed warbler Acrocephalus arundinaceus

We studied the prevalence and intensity of the haemosporidian blood parasite Haemoproteus payevskyi in great reed warblers at Lake Kvismaren (6 years) and Lake Segersj? (3 years) in Sweden. Based on microscopic inspection of slides from 282 adult birds, 20.6% showed infection of H. payevskyi in circulating red blood cells in at least 1 year. For parasite prevalence, there was no difference between years, sex, and age classes. However, parasite intensity was higher in females than in males, and this was most pronounced in 1-year-old birds. Individuals scored to carry parasites in year _n were more likely to show parasite infection year _n + 1 than birds scored to be parasite-free in year _n . None of 99 juvenile birds examined at the breeding site in late summer, 4–9 weeks after hatching, showed infection of H. payevskyi. Parasite intensity in infected adult birds decreased in the course of the breeding season and no new or relapse infections were observed during this period. Thus, our data imply that in the great reed warbler, a long-distance migrant to tropical Africa, transmission of H. payevskyi occurs on wintering sites or at stopover sites during migration.     

Seroprevalence of eastern equine encephalomyelitis virus in birds and larval survey of Culiseta melanura Coquillett during an interepizootic period in central Ohio.

From June through August in 1999 and 2000, we conducted an avian serosurvey for eastern equine encephalomyelitis (EEE) virus at Killbuck Marsh Wildlife Area (KMWA), a focus of infection in central Ohio. We also monitored abundance of the suspected enzootic vector, Culiseta melanura Coquillett, in Brown's Lake Bog, an adjacent wetland. Of the 363 birds of 30 species sampled in 1999, three gray catbirds (Dumetella carolinensis) were positive for antibodies to EEE virus, representing 1.2% of the avian samples and 4.2% of the gray catbirds sampled. Given these results and the abundance of gray catbirds at this site, this species became the focus of our sampling efforts in 2000. However, none of the 109 samples collected from 98 catbirds in 2000 was positive for the virus. Culiseta melanura adults were monitored using resting boxes and CDC CO, light traps at both sites in 1999. Culiseta melanura larvae were monitored in 1999 and 2000 at Brown's Lake Bog, the closest known source of this species, approximately 5km from the avian serosurvey site. We suggest that dry conditions reduced the breeding and abundance of Cs. melanura in 2000 and possibly the transmission of EEE virus at KMWA.     

Hematozoa of waterfowl from Michigan

Two hundred eighteen and 127 wild waterfowl (Anatidae) of five species were sampled from the Kellogg Biological Station area (Michigan, USA) during the summer (1 June to 24 August 1995) and fall (9 September to 8 October 1995), respectively. Twelve (6%) of those sampled in summer and 13 (11%) sampled in the fall were infected with hemosporids. Haemoproteus nettionis, Haemoproteus greineri, and Leucocytozoon simondi infected both summer and fall birds, with H. nettionis the most common (4% summer; 7% fall). Mean intensities were low; the highest mean intensity was 4.6+/-1.1 gametocytes per 5,000 uninfected erythrocytes for H. nettionis in summer. Of 123 local waterfowl, none were infected with any blood parasite. Thirty-five captive year-round resident waterfowl also were sampled and no blood parasites were found.     

Seasonal and age-related changes in blood parasite prevalence in Dark-eyed Juncos (Junco hyemalis, Aves, Passeriformes)

We determined seasonal changes in blood parasite infections in a free-living population of Dark-eyed Juncos (Junco hyemalis) breeding in interior Alaska (65 degrees N; 148 degrees W). The common parasites found in blood smears were Leucocytozoon fringillinarum (56%), Trypanosoma avium (33%), and Haemoproteus fringillae (9%). In males, parasite prevalences were relatively high at arrival on breeding grounds and increased during the breeding season. Intensity of infection with Leucocytozoon also increased between spring and summer, and then decreased at the time of migration (September). This decrease did not occur in adult females. Elevated prevalences during the breeding season probably reflected the addition of new cases via vector activity to positive status resulting from spring relapse. We observed neither an association between parasite species nor a consistent relationship between parasite intensity and body condition. To further study relationships between reproductive system activity and parasite infections, we compared prevalences in adult males that were undergoing their first cycle of gonadal development and regression (males in their second calendar year, or SY) with those of older males (males in their third or more calendar year, i.e., after-second-year males or ASY). Circulating testosterone concentrations declined in both groups between arrival on breeding grounds (end of April-early May) and the end of the reproductive period (July), and they were higher in May in ASY than in SY males. At the peak of the breeding season (June), ASY males also had a higher parasite prevalence than SY males. This difference may have resulted from immunosuppressive effects of gonadal hormones and/or from behavioral differences between SY and ASY males such that older males were exposed to more insect vectors than younger males. .     

Population dynamics of Gyrodactylus sp. (Monogenea) infecting the sand goby in the Oslo Fjord, Norway

Prevalence and abundance of Gyrodactylus sp. on the 1993 year-class of sand gobies Pomatoschistus minutus in the Oslo Fjord, Norway, decreased slightly during the cold months, increased as temperature increased in spring, reaching a peak in June, then decreased significantly, corresponding with a decline in the number of hosts from August. Abundance and, especially, prevalence increased again in September, and decreased in late autumn. Death of the most heavily infected hosts, and/or host resistance might be responsible for the decline in parasite numbers on post-spawners in summer. The young of the year (1994 year-class) were probably infected shortly after they commenced benthic life in July, and prevalence and abundance increased significantly throughout late summer and autumn. Parasite abundance on males was significantly higher than on females at the height of the breeding season in June, but significantly lower at the end of the breeding season in July. Two-thirds of the parasites infected the gills, oral cavity and pharynx. The proportion of parasites on the body, head and fins increased on both sexes, but significantly more so on males, during the breeding season of the host, when parasite intensity was highest. Possible routes of transmission of the parasite are discussed.     

Demographic and Spatiotemporal Patterns of Avian Influenza Infection at the Continental Scale,and in Relation to Annual Life Cycle of a Migratory Host

Since the spread of highly pathogenic avian influenza (HPAI) H5N1 in the eastern hemisphere, numerous surveillance programs and studies have been undertaken to detect the occurrence, distribution, or spread of avian influenza viruses (AIV) in wild bird populations worldwide. To identify demographic determinants and spatiotemporal patterns of AIV infection in long distance migratory waterfowl in North America, we fitted generalized linear models with binominal distribution to analyze results from 13,574 blue-winged teal (Anas discors, BWTE) sampled in 2007 to 2010 year round during AIV surveillance programs in Canada and the United States. Our analyses revealed that during late summer staging (July-August) and fall migration (September-October), hatch year (HY) birds were more likely to be infected than after hatch year (AHY) birds, however there was no difference between age categories for the remainder of the year (winter, spring migration, and breeding period), likely due to maturing immune systems and newly acquired immunity of HY birds. Probability of infection increased non-linearly with latitude, and was highest in late summer prior to fall migration when densities of birds and the proportion of susceptible HY birds in the population are highest. Birds in the Central and Mississippi flyways were more likely to be infected compared to those in the Atlantic flyway. Seasonal cycles and spatial variation of AIV infection were largely driven by the dynamics of AIV infection in HY birds, which had more prominent cycles and spatial variation in infection compared to AHY birds. Our results demonstrate demographic as well as seasonal, latitudinal and flyway trends across Canada and the US, while illustrating the importance of migratory host life cycle and age in driving cyclical patterns of prevalence.     

Interspecific differences in hematozoan infection in Sonoran desert Aimophila sparrows

Numerous studies have identified factors that control avian hematozoan infections, but the mechanisms that account for host differences in parasitemia remain largely speculative. To address this issue, we compared the prevalence of these parasites in stained blood smears from four conspecific Sonoran desert Aimophila sparrow species sampled during their breeding season: rufous-winged (Aimophila carpalis; RWSP), rufous-crowned (Aimophila ruficeps; RCSP), Cassin's (Aimophila cassinii, CASP), and Botteri's (Aimophila botterii; BOSP) sparrows. Blood smears contained Haemoproteus fringillae (RWSP), Trypanosoma everetti (RWSP, RCSP, BOSP), Trypanosoma avium (CASP), and microfilariae (all species). Most (92.5%) RWSP (n=40) were infected with Haemoproteus, but this parasite was not detected in RCSP (n=20) or BOSP (n=20) and was found only in one (2.5%) CASP (n=40). Trypanosoma spp. and microfilariae were detected in all species, but prevalence differed between these four sparrow species. Species differences in parasite prevalence were not due to difference in sex, age, adult body mass, incubation period, breeding habitat, or plumage colorfulness. However, differences in Haemoproteus sp. prevalence correlated with preferred nesting height, as RWSP generally nest above ground, whereas the other species nest on or close to the ground. Elevated H. fringillae prevalence in breeding-condition RWSP presumably does not result from a seasonal relapse associated with breeding or require new infection because 1) this prevalence did not differ in males sampled during and outside (n=21) the breeding season, and 2) all male RWSP (n=25) that we held in captivity and shielded from new infections and influence of natural photoperiod for 1 yr had viable blood H. fringillae gametocytes. H. fringillae prevalence in fall-sampled hatch-year male RWSP (n=11) was 63.6%, demonstrating that this parasite can be transmitted on the breeding grounds and during the first months of life. T. everetti prevalence in RWSP was lower in winter than in summer and also in long-term captive than in free-ranging adults. Presence of this parasite in the blood of breeding males may depend on recrudescence of existing infections or new infections.     

Disease‐limited distributions? Contrasts in the prevalence of avian malaria in shorebird species using marine and freshwater habitats

Migratory shorebirds show strong dichotomies in habitat choice during both the breeding and nonbreeding season. Whereas High Arctic breeding species are restricted to coastal marine and saline habitats during the nonbreeding season, more southerly breeding species tend to use freshwater habitats away from coasts. It has been proposed that this co-variation in habitat use is a consequence of a single axis of adaptation to pathogens and parasites, which are hypothesized to be relatively scarce in High Arctic, marine, and saline habitats and relatively common at lower latitudes and in freshwater habitats. Here we examine this contrast by comparing the prevalence of avian malaria infections in shorebirds occupying different habitats. We used a PCR-based assay on 1319 individuals from 31 shorebird species sampled in the Arctic, in temperate Europe and in inland and marine habitats in West Africa. Infections mainly occurred in tropical wetlands, with the shorebirds in freshwater inland habitats having significantly higher prevalence of malaria than birds in marine coastal habitats. Infections were not found in birds migrating through Europe even though conspecifics did show infections in tropical Africa. Adults should resist infection better than juveniles, but showed higher malaria prevalence, suggesting that infection probability increases with cumulative exposure. We argue that exposure to vectors is the main factor explaining the habitat-related differences in malaria prevalence.     

Interspecific variability of prevalence in blood parasites of adult passerine birds during the breeding season in Alaska

Blood parasite prevalence based on microscopic examination of stained blood smears was determined in adults of 11 passerine bird species sampled during their breeding season (May and June 1997-98) in interior Alaska (USA). These species included primarily Nearctic migratory species such as the dark-eyed junco (Junco hyemalis) and neotropical migratory species such as the blackpoll warbler (Dendroica striata), alder flycatcher (Empidonax alnorum), Swainson's thrush (Catharus ustulatus), northern waterthrush (Seiurus noveboracensis), and bank swallow (Riparia riparia) as well as one long-distance palearctic migrant, the arctic warbler (Phylloscopus borealis). The more prevalent parasites were Leucocytozoon dubreuili (73% of the sampled turdinids), L. fringillinarum (42% of the sampled fringillids and parulids), and Trypanosoma avium (39% of the sampled hosts). Other parasites (H. fallisi: 18% of the sampled turdinids; Haemoproteus paruli: 14% of the sampled parulids; H. fringillae: 5% of the sampled fringillids; microfilariae: 4% of the sampled hosts) were observed less frequently. Plasmodium vaughani was found only in two yellow warblers (Dendroica petechia). Overall parasite prevalence varied between 0% in the alder flycatcher to >80% in Swainson's thrush, arctic warbler, and Townsend's warbler (Dendroica townsendi). Prevalence of various hematozoa also was bird species-dependent. No relationship was observed between prevalence and either foraging (aerial versus trees/shrubs) or nesting habits (ground versus arboreal) or general location of the wintering area of the different species examined. Prevalence also was unrelated to average dates of arrival on breeding grounds and, therefore, to potential duration of exposure to local insect vectors before capture. Differences in blood parasite prevalence among species breeding in a same region and in the same type of habitat may result from differences in host specificity such as immunological resistance to infection or blood meal preference by potential vectors and/or in behavioral adjustments/physiological traits that alter exposure to vectors.     

Hantavirus infections in fluctuating host populations: the role of maternal antibodies

Infected females may transfer maternal antibodies (MatAbs) to their offspring, which may then be transiently protected against infections the mother has encountered. However, the role of maternal protection in infectious disease dynamics in wildlife has largely been neglected. Here, we investigate the effects of Puumala hantavirus (PUUV)-specific MatAbs on PUUV dynamics, using 7 years'' data from a cyclic bank vole population in Finland. For the first time to our knowledge, we partition seropositivity data from a natural population into separate dynamic patterns for MatAbs and infection. The likelihood of young of the year carrying PUUV-specific MatAbs during the breeding season correlated positively with infection prevalence in the overwintered parent population in the preceding spring. The probability of PUUV infection varied between seasons (highest in spring, lowest in late summer) and depended on population structure, but was also, in late autumn, notably, negatively related to summer MatAb prevalence, as well as to infection prevalence earlier in the breeding season. Hence, our results suggest that high infection prevalence in the early breeding season leads to a high proportion of transiently immune young individuals, which causes delays in transmission. This suggests, in turn, that MatAb protection has the potential to affect infection dynamics in natural populations.     

甘肃黑河内陆河湿地自然保护区候鸟多样性

甘肃黑河为我国第二大内陆河,位于其中游的黑河湿地自然保护区为内陆河流湿地生态系统自然保护区。2008年分季节采用样线法和样点法调查该保护区湿地、农田村庄、人工林和荒漠4种生境的鸟类种类和数量。调查共记录保护区分布的鸟类17目35科116种,其中夏候鸟73种(占鸟类种类的62.93%),迁徙过路鸟20种(占17.24%),留鸟17种(占14.66%),冬候鸟6种(占5.17%)。其中,属于《湿地公约》的水禽56种。在湿地生境共记录鸟类70种,占保护区鸟类种数的60.34%,其中繁殖期在湿地生境栖息的鸟类有50种,绝大部分为夏候鸟(47种),留鸟只有3种;迁徙季节分布有44种鸟类,其中迁徙过路鸟(只在迁徙季节见到)有17种,占迁徙季节鸟类种类数的38.64%。村庄农田、人工林以及荒漠生境中,繁殖期和迁飞期共记录鸟类57种,夏候鸟有33种,留鸟有17种,迁徙过路鸟只有3种。甘肃张掖黑河湿地保护区是众多水禽在我国西北地区的重要繁殖地和迁徙停歇地,是我国候鸟迁徙西部路线上的关键区域。     

Haemosporidian parasitism in the blackcap Sylvia atricapilla in relation to spring arrival and body condition

Parasites can exert strong selection on hosts. Throughout the year migrants are exposed to different sets of parasites, which may affect life history traits such as migratory schedules. Here, we studied the relationship between parasite infection and arrival date of blackcaps Sylvia atricapilla to their breeding grounds in Germany throughout a period of six years (2007–2012). We used two data sets, one that included all blackcaps and one that included only recaptured birds. We assesed whether parasites influence spring arrival to breeding grounds, and for the recaptured data set, we analysed temporal variation in parasitism (i.e. infection status and parasitaemia) throughout the breeding season. We used both microscopy and PCR (a fragment of ? 479 bp of the mtDNA cyt b) to determine haemosporidian infection. Blackcaps were mostly infected with Haemoproteus parabelopolskyi (lineages SYAT01 and SYAT02). Infection status, but not parasitaemia, was constant through time for individual birds; meaning that once a bird is infected, it most likely will retain the infection for life. We found that infection by haemosporidian parasites has no relationship to arrival date in this blackcap population; however, infection by H. parabelopolskyi has a marginally significant effect on arrival date of recaptured blackcaps, somewhat delaying their arrival to breeding grounds. Birds captured later in the season were more likely to be infected than those from early spring, and parasitaemia was frequently lower in birds captured earlier in the season compared to those captured later (summer).     

The prevalence of avian haemosporidian parasites in an invasive bird is lower in urban than in non-urban environments

Urbanization affects the ecology of wildlife diseases and although it has been suggested that there are lower risks of infection in urban areas, there have been no experiments to support this conclusion. We assessed haemosporidian prevalence and intensity in House Sparrows Passer domesticus using field and experimental data under contrasting conditions (i.e. urban vs. non-urban). For experimental data, we kept 32 male House Sparrows in captivity as a proxy of stress, and for field data we sampled 49 House Sparrows (17 females). We made use of microscopy to determine the relative intensity and used the polymerase chain reaction to estimate infection prevalence. We obtained total leucocyte counts, leucocyte differentials, heterophil/lymphocyte ratio (H/L) as a measure of stress, and the Polychromatic Index as a measure of physiological condition (erythropoiesis). We identified a total of 10 haemosporidian lineages. For field samples (both males and females), we found a significantly higher prevalence of infection in non-urban House Sparrows than in urban ones. Under experimental conditions, non-urban House Sparrows showed a higher prevalence than urban ones both before and after captivity, with a significant increase in parasite intensity. The number of infected birds increased after captivity for both urban (~ 32%) and non-urban House Sparrows (~ 19%), indicating either a recrudescence of chronic and relapses of latent infections or the appearance of infections that had been acquired earlier. The H/L ratio was significantly higher for non-urban than for urban male House Sparrows before captivity. No difference in H/L was found for urban House Sparrows before and after captivity, indicating tolerance to city stressors. Our results showed a significant decrease in H/L for non-urban birds after captivity, suggesting higher stress in the non-urban agricultural environment. Haemosporidian infections were not associated with the H/L ratio. Our study provides evidence that highly urbanized areas within cities represent lower haemosporidian infection risks than do non-urban areas for House Sparrows.     

Molecular Detection of Hematozoa Infections in Tundra Swans Relative to Migration Patterns and Ecological Conditions at Breeding Grounds

Tundra swans (Cygnus columbianus) are broadly distributed in North America, use a wide variety of habitats, and exhibit diverse migration strategies. We investigated patterns of hematozoa infection in three populations of tundra swans that breed in Alaska using satellite tracking to infer host movement and molecular techniques to assess the prevalence and genetic diversity of parasites. We evaluated whether migratory patterns and environmental conditions at breeding areas explain the prevalence of blood parasites in migratory birds by contrasting the fit of competing models formulated in an occupancy modeling framework and calculating the detection probability of the top model using Akaike Information Criterion (AIC). We described genetic diversity of blood parasites in each population of swans by calculating the number of unique parasite haplotypes observed. Blood parasite infection was significantly different between populations of Alaska tundra swans, with the highest estimated prevalence occurring among birds occupying breeding areas with lower mean daily wind speeds and higher daily summer temperatures. Models including covariates of wind speed and temperature during summer months at breeding grounds better predicted hematozoa prevalence than those that included annual migration distance or duration. Genetic diversity of blood parasites in populations of tundra swans appeared to be relative to hematozoa prevalence. Our results suggest ecological conditions at breeding grounds may explain differences of hematozoa infection among populations of tundra swans that breed in Alaska.     

Seasonal changes in thyroid-gonadal interactions in the edible dormouse,Glis glis

Summary This study was conducted to determine changes in thyroid-gonadal interaction in the edible dormouse during the phase of the annual cycle that corresponds to the end of the breeding season (from June to September). We evaluated intra-hypothalamic luteinizing hormone-releasing hormone (LHRH) content, and plasma concentrations of luteinizing hormone (LH), testosterone, thyroid-stimulating hormone (TSH) and thyroxine (T4) in three groups of dormice: (1) controls; (2) dormice receiving sufficient T4 supplementation to maintain June levels in control animals until September, thus counteracting the seasonal reduction of T4 that normally begins in July; and (3) thyroidectomized dormice. The effect of thyroidectomy was only detectable in June, when plasma T4 concentration in the control group was maximal, and consisted of a significant decrease in plasma testosterone levels. This provides strong support for the hypothesis that thyroid function positively influences gonadal function during the breeding season. The T4 supplementation resulted in a decrease in hypothalamic LHRH concentration, suggesting that an increased LHRH release led to the observed stimulated hypophyseal secretion of LH in June and September and the increased circulating testosterone levels in September. There was no detectable effect in July and August. These results show that thyroid axis activation of the hypothalamic-pituitary-gonadal system is only possible during certain phases of the annual cycle, particularly evidenced here during the breeding season. They also reinforce our conclusions drawn from the thyroidectomy results. Conversely, the summer testicular regression which normally occurs after the breeding season is no longer controlled by plasma T4 levels. Even though the sensitivity of the gonadal axis to the thyroid axis appears to reappear at the end of the summer, results of previous studies indicate that this resumption is only temporary.Abbreviations LH luteinizing hormone - LHRH luteinizing hormone-releasing hormone - RIA radioimmunoassay - T4 thyroxine - TSH thyroid-stimulating hormone     

The blood parasite Haemoproteus reduces survival in a wild bird: a medication experiment

While avian chronic haemoparasite infections induce reproductive costs, infection has not previously been shown to affect survival. Here, we experimentally reduced, through medication, the intensity of infection by Haemoproteus parasites in wild-breeding female blue tits Cyanistes caeruleus. However, this treatment did not reduce the intensity of infection in males or the intensity of infection by Leucocytozoon. Medicated females, but not males, showed increased local survival until the next breeding season compared with control birds. To our knowledge, this is the first empirical evidence showing long-term direct survival costs of chronic Haemoproteus infections in wild birds.     

Blood parasites in sage-grouse from Nevada and Oregon

Peripheral blood smears from 196 adult and yearling female greater sage-grouse (Centrocercus urophasianus) were examined for blood parasites (167 from the breeding and 29 from the brood-rearing season) to determine prevalence of blood parasites, to attempt to correlate infection with chick survival, and to establish base-line values of prevalence in sage-grouse from Nevada and Oregon (USA). Birds were captured and released on two study areas during 1999-2001; Sheldon National Wildlife Refuge (SNWR) in northwestern Nevada, and Hart Mountain National Antelope Refuge (HMNAR) in southeastern Oregon. Birds from a third study area, Beaty's Butte grazing allotment (BB) in southeastern Oregon, were sampled in 2000 and 2001. Overall, 19 birds (10%) were positive for Leucocytozoon lovati (= L. bonasae), 1 (0.5%) for Plasmodium pedioecetii, and 2 (1%) for microfilariae. Although prevalence of L. lovati on HMNAR was 39% during the breeding season in 1999 and 100% during the brood-rearing season in 2000, statistically, prevalence of L. lovati among study areas and years was not different. However, there were statistical differences between capture periods. Overall, 31% of the hens were positive for L. lovati during the brood-rearing season compared to 6% during the breeding season. There was no difference in packed cell volume between infected and non-infected birds and no difference between age-classes. However, mean sage-grouse productivity on HMNAR was higher (1.6 chicks/hen) for non-infected (n = 10) compared to infected hens (0.7 chicks/hen; n = 7), during 1999. Based on these limited observations on HMNAR in 1999, the possible effects that L. lovati may have on young sage-grouse could be detrimental to sage-grouse populations in Nevada and Oregon.     

Hormone levels and infection of Haemoproteus danilewskyi in free-ranging blue jays (Cyanocitta cristata)

Annual spring relapse of blood parasite infections in birds is believed to be the result of hormonal changes associated with breeding. As part of a larger study on the epizootiology of Haemoproteus danilewskyi in blue jays in south-central Florida, we studied the relationship between H. danilewskyi infections and levels of luteinizing hormone, prolactin, progesterone, testosterone, estradiol, and corticosterone. We found a positive association between intensity of H. danilewskyi infection and corticosterone levels in females but not in males. We also found no association between infection and levels of prolactin, luteinizing hormone, progesterone, testosterone, or estradiol in males or females. In addition, we found a positive relationship between levels of corticosterone and handling time and between corticosterone and testosterone levels. We suggest a possible influence of corticosterone on spring relapse of Haemoproteus spp. infections in birds but provide no support for the influence of breeding hormones on relapse of these parasites.     

The development of photorefractoriness in termination of the breeding season in the tropical brahminy myna: role of photoperiod

Gonads of brahminy myna (Sturnus pagodarum) spontaneously regress in July/August when the daylength is still stimulatory. Experiments were conducted to investigate if photoperiod was involved in the timing of gonadal regression and if photorefractoriness terminated the breeding season in this species. The observations obtained in the present study clearly show that: i) increasing photoperiods of spring/summer programmed for eventual gonadal regression in the late summer; ii) the birds developed photorefractoriness to all stimulatory daylengths and consequently the breeding season could not be extended by providing more stimulatory photoperiods; and iii) exposure to short daylength treatment failed to overcome the onset of refractoriness in birds after they had attained full gonadal growth and development. These results suggest that refractoriness is a process used by the brahminy myna to terminate the breeding season, and that this species becomes totally photorefractory.