Photoperiod-induced testicular apoptosis in European starlings (Sturnus vulgaris)

To determine the extent to which testicular regression involves apoptotic cell death, photosensitive adult starlings were photostimulated for up to 9 wk by exposure to long-day (18 h of light) photoperiods. Apoptotic activity in recrudescing and regressing testes was assessed by in situ TUNEL labeling. Absolute testis mass in male starlings increased after 2 wk of photostimulation and subsequently decreased with continued long-day exposure. Seminiferous tubule diameter also increased after 1-3 wk of photostimulation, then decreased as photorefractoriness developed. Testosterone concentrations increased significantly by Week 2 of photostimulation and declined with further light exposure. TUNEL labeling was significantly elevated in germ cells with 4 wk of photostimulation. An approximate 7-fold increase in the degree of apoptotic cell death was observed over the course of gonadal regression. Incidences of TUNEL labeling in somatic Sertoli cells also increased. Light and electron microscopy examination confirmed that these somatic cells displayed morphological characteristics of apoptotic death. In rodents, Sertoli cells have not been previously reported to die during gonadal regression. These results suggest that seasonal testicular regression in European starlings is mediated by apoptosis.     

Thyroxine treatment prevents the development of photosensitivity in european starlings (Sturnus vulgaris)

Summary In starlings, the breeding season is terminated by a state of photorefractoriness. Birds remain completely reproductively inactive as long as long days are maintained, and only exposure to short days restores photosensitivity. Two experiments investigated the role of different doses of thyroxine in the development of photosensitivity in castrated starlings. First, photorefractory castrated male starlings were moved from long (18L:6D) to short (8L:16D) days, and received in the drinking water either 1 or 10 mg · 1^-1 thyroxine for the first 7 weeks of a 14-week observation period. Control birds regained photosensitivity after 5 weeks of short days, as signaled by a spontaneous increase in plasma LH, whereas the return to photosensitivity was delayed until weeks 7 and 9 in the 1- and 10-mg · 1^-1 thyroxine-treated birds, respectively. In the second experiment, the effect of different doses of thyroxine was explored at the level of the hypothalamic Gn-RH neurosecretory neurones. The acquisition of photosensitivity in control birds transferred from long to short days was characterized by a marked increase in hypothalamic Gn-RH content (while long-day controls maintained low Gn-RH content). Doses of 10 and 20 mg · 1^-1 of thyroxine completely prevented the return to photosensitivity, as seen through changes in either plasma LH concentrations or hypothalamic Gn-RH content, while a dose of 1 mg · 1^-1 allowed a partial recovery of photosensitivity, as hypothalamic Gn-RH content increased to an intermediate level and the spontaneous rise in plasma LH occurred slowly but steadily.Abbreviations Gn-RH gonadotrophin-releasing hormone - LH luteinizing hormone - LHRH-I luteinizing hormone releasing hormone     

Song predicts immunocompetence in male European starlings (Sturnus vulgaris)

According to the immunocompetence handicap hypothesis, sexually selected characteristics predict immune function and this relationship is mediated by testosterone. In the present study, we investigated whether bird song could predict immunity in European starlings (Sturnus vulgaris). We recorded the singing and reproductive behaviours of 16 adult male starlings in an outdoor aviary and then assessed their cell-mediated and humoral immunity in vivo. The males were observed in groups of four for 2 h each day over a 4-day period. For each male, the number of songs produced was recorded and the average song-bout length was computed. Next, cell-mediated and humoral immunity were assessed via cutaneous swelling responses to the T-cell mitogen phytohaemagglutinin and antibody responses to a novel antigen, keyhole limpet haemocyanin. Song rate and song-bout length were positively correlated with cell-mediated and humoral immunity, respectively. Additionally, a negative relationship between plasma testosterone concentration and antibody response was observed. These data demonstrate that male starling song can be used as a predictor of immunocompetence, with more robust singers exhibiting enhanced immunity. Whether this relationship is mediated directly by testosterone requires further investigation.     

Innervation of the parathyroid in the european starling (Sturnus vulgaris)

Anatomical studies were conducted to characterize the source, type, and distribution of parathyroid gland innervation in European starlings. Denervation experiments demonstrated that the parathyroid glands and adjacent carotid bodies are innervated by nerve fibers originating in the nodose ganglion of the vagus nerve. In the parathyroid parenchyma, these fibers terminate adjacent to chief cells or near vascular smooth muscle. Vagal fibers also form synapses with catecholamine-containing glomus cells of the carotid body. Blood that first perfuses the carotid body subsequently perfuses the parathyroid parenchyma. These observations suggest that vagal innervation may influence parathyroid function in starlings either through direct chief cell innervation or through alteration of vascular perfusion. A neurohemal relationship also may exist between the carotid body and parathyroids.     

Intrasexual competition among polygynously mated female starlings (Sturnus vulgaris)

In southern Sweden, the starling (Slurnus vulgaris) has a variablemating system with some males mating monogamously and othersattracting several females. Mating status affected the reproductivesuccess of females: monogamous and primary females laid largerclutches and fledged more and heavier young than secondary females.This pattern was explained by female competition for male help,with the male primarily helping the offspring of highest value(i.e., the oldest brood). However, when the nesting attemptof the primary female failed, the success of the secondary femaleincreased to the same level as that for primary and monogamousfemales. The success of the secondary female in terms of fledgingsuccess and fledgling size was higher when the secondary femalehatched her eggs soon after the primary female. This was dueto the fact that a male divided his effort between his broodswhen the age difference between broods was small.     

Embryonic modulation of maternal steroids in European starlings (Sturnus vulgaris)

In birds, maternally derived yolk steroids are a proposed mechanism by which females can adjust individual offspring phenotype to prevailing conditions. However, when interests of mother and offspring differ, parent–offspring conflict will arise and embryonic interests, not those of the mother, should drive offspring response to maternal steroids in eggs. Because of this potential conflict, we investigated the ability of developing bird embryos to process maternally derived yolk steroids. We examined how progesterone, testosterone and oestradiol levels changed in both the yolk/albumen (YA) and the embryo of European starling eggs during the first 10 days of development. Next, we injected tritiated testosterone into eggs at oviposition to characterize potential metabolic pathways during development. Ether extractions separated organic and aqueous metabolites in both the embryo and YA homogenate, after which major steroid metabolites were identified. Results indicate that the concentrations of all three steroids declined during development in the YA homogenate. Exogenous testosterone was primarily metabolized to an aqueous form of etiocholanolone that remained in the YA. These results clearly demonstrate that embryos can modulate their local steroid environment, setting up the potential for parent–offspring conflict. Embryonic regulation must be considered when addressing the evolutionary consequences of maternal steroids in eggs.     

Breeding of starlings (Sturnus vulgaris) in nest boxes of various types

Abstract

The reproductive success of starlings (Sturnus vulgaris) using nest boxes in Hawke's Bay, New Zealand, differed significantly according to the type of box, but this may reflect the competence of the parents as well as the quality of the site. The most young fledged from boxes of 310 cm² internal basal area, significantly fewer from boxes of 520 cm² or more, and insignificantly fewer from boxes of 180 cm². Success increased with the depth of the nest box up to at least 200 mm. Sites with large entrance holes were little used, suggesting that starlings prefer minimal access clearance (perhaps to exclude predators) and the nest bowl to be dark. The box material (wood, concrete, or PVC) had no significant effect on use or success.     

Post-hatching dynamics of plasma biochemistry in free-living European starlings (Sturnus vulgaris)

This is the first study of plasma biochemical parameters in free-living altricial birds during an entire developmental period in a nest, represented by European starling (Sturnus vulgaris). Dynamics of postnatal changes from hatching until close to fledging (days 1 to 15) were registered. Parameters of protein metabolism represented by total proteins, albumin and globulin concentrations increased continuously during the observed developmental period. There were two peaks in uric acid concentration on days 5 and 11. To the contrary, the creatinine content did not change throughout the observed period and increased only on day 15. Creatine kinase activity gradually increased until day 11 and then fell before fledging. Parameters of lipid metabolism (concentration of total lipids, triacylglycerols and nonesterified fatty acids) in plasma increased gradually reaching a plateau between days 8 and 11 and then declined on day 15. The cholesterol concentration pattern was similar to maximum value on day 11, then consecutively decreased. Concentration of glucose increased until day 8 and remained unchanged until fledging. Whereas calcium reached the highest concentration during days 8 and 11, phosphorus peaked earlier on day 5. The activity of alkaline phosphatase was similar to the pattern found in calcium concentration. Presented data showed an increase in both protein and lipid metabolism during the phase of rapid growth. A remarkable decrease in parameters of lipid metabolism before fledging may reflect increased physical activity and changes in nutrition.     

Searching in patches by European starlings,Sturnus vulgaris

Despite the importance of within-patch search for predicting optimal patch-leaving strategy, little experimental effort has been devoted to the study of this foraging behaviour. In addition, predators' strategic responses to variability in features like the within-patch distribution of prey can have important consequences for their dietary decisions. We therefore analyse the search paths of European starlings, Sturnus vulgaris, foraging individually in artificial patches that vary in the spatial distribution of buried prey in an outdoor aviary. The results demonstrate that the birds are searching differently depending on the order in which the experimental patch-types are experienced. We speculate that where the spatial predictability of prey is initially high the birds adopt a fixed search rule that results in area-concentrated search once a prey item is found, and performs well for both distributions encountered. However, where the predictability is initially low a more flexible strategy is adopted that results in increased area-concentrated search with experience of a patch type, independent of the actual within-patch distribution of prey. These findings suggest that starlings can use distinct strategies for different prey types, but they are classifying these types on subjective criteria that are difficult to predict from a priori reasoning.     

Occurrence and attempted transmission of Toxoplasma gondii in European starlings (Sturnus vulgaris)

Serums of 563 fledgling starlings (Sturnus vulgaris) trapped during a 14 month period near Lodi, California were examined for antibodies to Toxoplasma gondii using the microtiter indirect hemagglutination method. Titers ranging from 1:64 to 1:512 were found in 4.8% of the birds. Starlings collected during May through October had a higher prevalence of antibody than those collected during November through April. Rats inoculated with individual heart and brain suspensions from 10 seropositive starlings remained seronegative for T. gondii antibodies when tested at 22 and 82 days post-inoculation. Peritoneal smears made from these rats at post-inoculation day 82 were negative for T. gondii.     

Ahemeral light regimens test the photoperiodic threshold of the european starling(Sturnus vulgaris)

Male European starlings(Sturnus vulgaris) were held for three consecutive photoperiod oscillations (ahemeral years) composed of 30-h day lengths, i.e., the daily light and dark each lasted three hours longer than under the natural daily photoperiod at latitude 38°N. These starlings had no gonad metamorphosis during the 45 actual months necessary to complete the three ahemeral photoperiod oscillations; nor did subsequent exposure to continuous illumination elicit gonad response. It is concluded that the daily duration of light and darkness (although certainly operant in controlling starling sexual cycles under temperate-zone photoperiod oscillations) is not the critical factor establishing a sexual cycle under the ahemeral regimen. Rather, it appears that this species must experience a daily duration of light of 12 hours or less (a definitive photoperiodic threshold) before photo-induction of a sexual cycle is possible.Presented at the Eighth International Congress of Biometeorology, 9–14 September 1979, Shefayim, Israel.     

Thyroidectomy results in termination of photorefractoriness in starlings (Sturnus vulgaris) kept in long daylengths

Four groups of 10 male starlings were transferred from short daylengths (8 h light/day) to long daylengths (18 h light/day), which caused the tests to develop rapidly to maximum size and then to decrease to minimal size as birds became photorefractory. Birds were surgically thyroidectomized at 8, 16 or 28 weeks. A fourth group was left intact. Testicular volume and plasma FSH and prolactin concentrations were measured. After 42 weeks all birds were castrated and plasma FSH was measured during the next 6 weeks. Testicular growth began in all thyroidectomized birds between 4 and 8 weeks after thyroidectomy. By 42 weeks, the testes of all thyroidectomized birds were large, whereas those of intact birds were still of minimal size. Plasma FSH concentrations remained low in all birds and plasma prolactin values, originally elevated by long daylengths, decreased at a similar rate in thyroidectomized and intact birds. After castration at 42 weeks, plasma FSH values increased rapidly in all thyroidectomized birds but remained low in non-thyroidectomized birds. The results demonstrate that thyroidectomy of photorefractory starlings does not induce immediate testicular growth but may initiate a process which eventually terminates photorefractoriness in a way similar to that caused by return to short daylengths.     

Castration does not decrease nonreproductive aggression in yearling male European starlings (Sturnus vulgaris)

In the nonbreeding season, some bird species express high levels of aggression despite basal plasma testosterone (T) concentrations. Consequently, nonreproductive aggression is believed to be independent of plasma T. In the present study, we investigated the effect of castration on nonreproductive aggressive behavior in yearling male European starlings (Sturnus vulgaris). We paired castrated (Cx) with control (C) males in dyadic trials during three test periods (December, January-February, and March-April), and by using an infrared camera, we defined which male was the most aggressive one when both males were competing over access to a nest box to roost in. During each of the three periods, Cx males behaved more aggressively than C males but differences between groups did not reach significance. When analyzing the results of the three periods together, Cx males were found to be significantly more aggressive than C males. Likewise, when considering only the second and third period (when plasma T levels of C males were significantly higher than those of Cx males) the same result was obtained. Furthermore, in the third period, aggression tended to be lower than in the first and second period, although T concentrations of C males were highest in this period. Our data thus clearly show that nonreproductive aggression in yearling male starlings is independent of gonadal sex steroids and suggest it even increases by castration.     

Circannual variations in plasma luteinizing hormone levels in castrated male European starlings (Sturnus vulgaris)

Intact and castrated male European starlings were held for about 2 years in a constant 12-hr photoperiod and constant temperature conditions. At 1- to 2-month intervals, testicular width was measured by laparotomy, and blood samples were taken for analysis of plasma luteinizing hormone (LH). Most of the control birds went through at least one circannual cycle of testicular width and plasma LH concentration. In the castrates, a similar proportion of birds went through circannual LH cycles with periods indistinguishable from those of the controls. It is concluded that the testes and their hormones are not essential components of the mechanism that generates circannual gonadal cycles in male European starlings.     

Contrasting mitochondrial diversity of European starlings (Sturnus vulgaris) across three invasive continental distributions

European starlings (Sturnus vulgaris) represent one of the most widespread and problematic avian invasive species in the world. Understanding their unique population history and current population dynamics can contribute to conservation efforts and clarify evolutionary processes over short timescales. European starlings were introduced to Central Park, New York in 1890, and from a founding group of about 100 birds, they have expanded across North America with a current population of approximately 200 million. There were also multiple introductions in Australia in the mid‐19th century and at least one introduction in South Africa in the late 19th century. Independent introductions on these three continents provide a robust system to investigate invasion genetics. In this study, we compare mitochondrial diversity in European starlings from North America, Australia, and South Africa, and a portion of the native range in the United Kingdom. Of the three invasive ranges, the North American population shows the highest haplotype diversity and evidence of both sudden demographic and spatial expansion. Comparatively, the Australian population shows the lowest haplotype diversity, but also shows evidence for sudden demographic and spatial expansion. South Africa is intermediate to the other invasive populations in genetic diversity but does not show evidence of demographic expansion. In previous studies, population genetic structure was found in Australia, but not in South Africa. Here we find no evidence of population structure in North America. Although all invasive populations share haplotypes with the native range, only one haplotype is shared between invasive populations. This suggests these three invasive populations represent independent subsamples of the native range. The structure of the haplotype network implies that the native‐range sampling does not comprehensively characterize the genetic diversity there. This study represents the most geographically widespread analysis of European starling population genetics to date.     

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

Keratinophilic fungi associated with starlings Sturnus vulgaris in Brittany,France

The occurrence of keratinophilic fungi on the feathers of 110 starlings (Sturnus vulgaris) was investigated in order to assess the part that these birds may have in spreading of fungi of medical interest. Thirty eight birds (26%) yielded keratinophilic fungi, primarily Chrysosporium species, but also Scopulariopsis brevicaulis and Trichophyton terrestre. We reviewed the pathogenicity of the isolated fungi. Starlings may spread the propagules of keratinophilic fungi but it is difficult to determine if their increasing numbers in cities can be of significance in the epidemiology of today's rare mycoses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hand-rearing reduces fear of humans in European starlings, Sturnus vulgaris

Pending changes in European legislation ban the use of wild-caught animals in research. This change is partly justified on the assumption that captive-breeding (or hand-rearing) increases welfare of captive animals because these practices result in animals with reduced fear of humans. However, there are few actual data on the long-term behavioural effects of captive-breeding in non-domestic species, and these are urgently needed in order to understand the welfare and scientific consequences of adopting this practice. We compared the response of hand-reared and wild-caught starlings to the presence of a human in the laboratory. During human presence, all birds increased their general locomotor activity but the wild-caught birds moved away from the human and were less active than the hand-reared birds. After the human departed, the wild-caught birds were slower to decrease their activity back towards baseline levels, and showed a dramatic increase in time at the periphery of the cage compared with the hand-reared birds. We interpret these data as showing evidence of a greater fear response in wild-caught birds with initial withdrawal followed by a subsequent rebound of prolonged attempts to escape the cage. We found no effects of environmental enrichment. However, birds in cages on low shelves were less active than birds on upper shelves, and showed a greater increase in the time spent at the periphery of their cages after the human departed, perhaps indicating that the lower cages were more stressful. In demonstrating reduced fear of humans in hand-reared birds, our results support one of the proposed welfare benefits of this practice, but without further data on the possible welfare costs of hand-rearing, it is not yet possible to reach a general conclusion about its net welfare impact. However, our results confirm a clear scientific impact of both hand-rearing and cage position at the behavioural level.