| the thyroid and the hypothalamus-pituitary-ovarian axis in american tree sparrows (spizella arborea). | prompted by evidence of a linkage between the thyroid gland and seasonal reproduction in obligately photoperiodic american tree sparrows (spizella arborea), we measured circulating t4 (l-thyroxine), hypothalamic cgnrh-i (chicken gonadotropin-releasing hormone, variant i), pituitary and plasma lh (luteinizing hormone), and ovarian mass in euthyroid females moved from short to long days. our purpose was to correlate temporal changes in t4 and cgnrh-i with each other and with pituitary and plasma l ... | 1996 | 8812334 |
| thyroid dysfunction and thyroxine-dependent programming of photoinduced ovarian growth in american tree sparrows (spizella arborea). | the time course of thyroid dysfunction after injecting 0.30 mci na131i was charted in female american tree sparrows (spizella arborea) transferred to long days on day 0 and challenged with 30 micrograms bovine thyroid-stimulating hormone on postinjection days 4, 7, 46, and 105. serum t4 (l-thyroxine) was not detectable in thyroidectomized birds, indicating complete thyroid dysfunction by day 4 and no restoration of thyroid function by day 105. by contrast, serum t4 concentrations in similarly ch ... | 1996 | 8812336 |
| the timing of thyroid-dependent programming in seasonally breeding male american tree sparrows (spizella arborea). | there is convincing evidence that euthyroid male american tree sparrows are already programmed for seasonal reproduction and postnuptial molt by week 4 of photostimulation. to explore more precisely when, during early photostimulation, thyroid-dependent programming of seasonal events occurs, photosensitive male tree sparrows were radiothyroidectomized or sham thyroidectomized on the first day of photostimulation (week 0) or at weeks 1 or 3 thereafter. birds were monitored for testicular growth a ... | 1996 | 8812339 |
| effects of thyroxine (t4) or triiodothyronine (t3) replacement therapy on the programming of seasonal reproduction and postnuptial molt in thyroidectomized male american tree sparrows (spizella arborea) exposed to long days. | this study tested the hypothesis that t3 (triiodothyronine) is the tissue-active "seasonality" hormone by determining whether t3 could mimic t4 (thyroxine) and program photostimulated thyroidectomized (thx) male american tree sparrows (spizella arborea) for three components of seasonality (i.e., full-blown testicular growth, photorefractoriness, and postnuptial molt). photosensitive males were radiothyroidectomized, transferred to long days 4 weeks later, and administered 14 daily injections (s. ... | 1997 | 9360316 |
| long days and thyroxine program american tree sparrows for seasonality: evidence for temporal flexibility of the breeding season of euthyroid females. | to explore the role of the thyroid in the control of seasonality, photosensitive female american tree sparrows (spizella arborea) were thyroidectomized (thx), moved to long days, and given daily injections of thyroxine (t4) for 3 weeks; thx and thyroid-intact (thi) controls received daily injections of alkaline vehicle. birds were retained on long days 4 additional weeks and then moved to constant light and given t4 in drinking water for 5 weeks in order to test for photorefractoriness. endpoint ... | 1999 | 9882552 |
| thyroid hormone acts centrally to programme photostimulated male american tree sparrows (spizella arborea) for vernal and autumnal components of seasonality. | thyroid hormone and long days interact to programme american tree sparrows (spizella arborea) for seasonality (i.e. thyroid hormone-dependent photoperiodic gonadal growth, photorefractoriness, and postnuptial moult). this study explored in radiothyroidectomized (thx) males given thyroid hormone replacement therapy whether thyroid hormone acts within the brain and, additionally, the identity of the putative tissue-active thyroid hormone. the minimum dose (30 ng) of l-thyroxine (t4) that restored ... | 2000 | 10692147 |
| a test of the hypothesis that t3 is the "seasonality" thyroid hormone in american tree sparrows (spizella arborea): intracerebroventricular infusion of iopanoic acid, an inhibitor of t3 synthesis and degradation. | this study tested the hypothesis that l-3,5,3'-triiodothyronine (t3) is the bioactive "seasonality" thyroid hormone in american tree sparrows (spizella (arborea). the experimental approach coupled thyroid hormone replacement therapy after radiothyroidectomy with photostimulation and intracerebroventricular infusion of iopanoic acid, an inhibitor of l-3,5,3'-triiodothyronine synthesis and degradation. endpoints were testis length, molt score, and hypothalamic content of chicken gonadotropin-relea ... | 2001 | 11302527 |
| thyroid hormone-dependent seasonality in american tree sparrows (spizella arborea): effects of gc-1, a thyroid receptor beta-selective agonist, and of iopanoic acid, a deiodinase inhibitor. | to explore the role of th in the control of seasonality [i.e., photoperiodic testicular growth, photorefractoriness, and postnuptial (prebasic) molt] in american tree sparrows (spizella arborea), we performed experiments in which thx males were simultaneously photostimulated and given th replacement therapy. in the first experiment, equimolar concentrations (1x = 1.3 nmol) of t4, t3, or gc-1, an iodine-free trbeta agonist, were administered s.c. daily during the first 21 days of photostimulation ... | 2004 | 15235810 |
| arsenic speciation in terrestrial birds from yellowknife, northwest territories, canada: the unexpected finding of arsenobetaine. | the surrounding area of yellowknife, northwest territories, canada, is known for naturally and anthropogenically elevated concentrations of arsenic. five bird species (gray jay [perisoreus canadensis], american tree sparrow [spizella arborea], dark-eyed junco [junco hyemalis], yellow-rumped warbler [dendroica coronata], and spruce grouse [dendragapus canadensis]) were collected from this area. their tissues were analyzed for total arsenic and for arsenic species, allowing us to report, to our kn ... | 2005 | 16117124 |
| an investigation of arsenic compounds in fur and feathers using x-ray absorption spectroscopy speciation and imaging. | the accumulation of arsenic in fur and feathers has been used as an indicator of environmental quality and animal health. however, difficulties remain in distinguishing between arsenic present from external sources versus ingestion. in addition, low extraction efficiencies limit the complete characterization of arsenic compounds in such tissues by conventional analytical techniques (e.g. high performance liquid chromatography inductively coupled plasma mass spectrometry, hplc-icp-ms). x-ray abso ... | 2008 | 17988717 |
| west nile virus antibodies in permanent resident and overwintering migrant birds in south-central kansas. | we conducted serological studies, using epitope-blocking elisas directed at west nile virus (wnv) and flavivirus antibodies, of wild birds in south-central kansas, the first for this state, in the winters of 2003-04 through 2005-06. overwintering migratory species (primarily the american tree sparrow and dark-eyed junco) consistently showed significantly lower seropositivity than permanent residents (primarily the northern cardinal). the cardinal showed annual variation in seropositivity between ... | 2008 | 18471059 |
| on control of spontaneous testicular regression in tree sparrows (spizella arborea). | | 2015 | 4649163 |
| hypothalamic neurosecretion and photoinduced testicular growth in the tree sparrow, spizella arborea. | | 2014 | 4177450 |
| avian seed preference and weight loss experiments: the effect of fungal endophyte-infected tall fescue seeds. | the impact of endophytic fungus-infected seeds on seed predators is poorly understood. in this multiple trophic level investigation, seed preference experiments were conducted to determine whether five species of passerines (dark-eyed juncos, junco hyemalis; american tree sparrows, spizella arborea; song sparrows, melospiza melodia; chipping sparrows, spizella pusilla; and house sparrows, passer domesticus) recognize and preferentially consume noninfected (ni) over infected (i) seeds of tall fes ... | 1991 | 28312146 |
| the relationship of plasma indicators of lipid metabolism and muscle damage to overnight temperature in winter-acclimatized small birds. | plasma glycerol and triglyceride levels and creatine kinase (ck) activity may increase during long-distance flights in migratory birds, but plasma profiles of these metabolites have not previously been reported for small birds during thermoregulation in cold climates. we measured early morning levels of plasma glycerol, triglycerides and ck activity in four species of small birds overwintering in south dakota, junco hyemalis, spizella arborea, passer domesticus, and carduelis tristis. we hypothe ... | 2007 | 17049895 |
| are summit metabolism and thermogenic endurance correlated in winter-acclimatized passerine birds? | small birds exhibiting marked winter improvement of cold tolerance also show elevated summit metabolic rates (maximum cold-induced metabolic rate) in winter relative to summer. however, relatively large increases in cold tolerance can occur with only minor increments of maximum cold-induced metabolic rate and geographic variation in cold tolerance is not always positively correlated with variation in maximum cold-induced metabolic rate. thus, it is uncertain whether maximum cold-induced metaboli ... | 2001 | 11585259 |
| evidence for a proximate influence of winter temperature on metabolism in passerine birds. | the roles of ultimate and proximate factors in regulating basal and summit metabolic rates of passerine birds during winter have received little study, and the extent to which winter temperatures affect these variables is unknown. to address this question, we measured basal and summit (maximum cold-induced) metabolic rates in black-capped chickadees (poecile atricapillus), dark-eyed juncos (junco hyemalis), and american tree sparrows (spizella arborea) during winters from 1991/1992 to 1997 in so ... | 2008 | 10521324 |
| a new genus for the american tree sparrow (aves: passeriformes: passerellidae). | the genus spizella (bonaparte) contains seven species of north american sparrows in the recently resurrected family passerellidae (bock 1994; barker et al. 2013), formerly placed in the emberizidae, and includes a few of the region's most common and familiar bird species. spizella sparrows occupy more or less open habitats; most species are at least partially migratory and form small flocks when not breeding. on the basis of their similar morphology and behavior, they have long been treated as a ... | 2014 | 24989754 |
| a comprehensive multilocus assessment of sparrow (aves: passerellidae) relationships. | the new world sparrows (emberizidae) are among the best known of songbird groups and have long-been recognized as one of the prominent components of the new world nine-primaried oscine assemblage. despite receiving much attention from taxonomists over the years, and only recently using molecular methods, was a "core" sparrow clade established allowing the reconstruction of a phylogenetic hypothesis that includes the full sampling of sparrow species diversity. in this paper, we use mitochondrial ... | 2014 | 24792084 |
| increased sensitivity of the serotonergic system during the breeding season in free-living american tree sparrows. | in order to understand the physiological role of serotonin in regulating aggressive behaviour it is important to understand how this neuromodulator acts within the context of a naturally fluctuating social and physical environment. to accomplish this, we examined the effect of the selective serotonin reuptake inhibitor fluoxetine during the breeding season in free-living male american tree sparrows (spizella arborea) in northern alaska. during this time period males are maximally aggressive towa ... | 2005 | 15617778 |
| corticosterone treatment has no effect on reproductive hormones or aggressive behavior in free-living male tree sparrows, spizella arborea. | we examined the effect of corticosterone on plasma levels of reproductive hormones (testosterone, dihydrotestosterone, and luteinizing hormone) and territorial defense behavior in male tree sparrows, spizella arborea. birds receiving silastic implants filled with corticosterone (b) had significantly higher plasma levels of b than control birds, which received empty implants, and exhibited pectoral muscle wastage and a decrease in body mass. we evaluated the hormonal and agonistic responses of th ... | 2000 | 10712856 |
| time of thyroidectomy variably affects seasonality in female american tree sparrows (spizella arborea). | female american tree sparrows (spizella arborea) were injected with na131i before, at, or after the onset of photostimulation in order to study the effect of time of thyroidectomy on three components of seasonality: thyroid-dependent photoperiodic ovarian growth, photorefractoriness, and postnuptial (prebasic) molt. thyroidectomy before or at the onset of photostimulation abolished all components of seasonality; birds exhibited only minor thyroid-independent photoperiodic ovarian growth. thyroid ... | 1999 | 10336830 |
| effect of withdrawing long days from male american tree sparrows (spizella arborea): implications for understanding thyroid-dependent programming of seasonal reproduction and postnuptial molt. | in previous studies, we withdrew thyroid hormones by thyroidectomy before, at, or after the onset of photostimulation and showed that male american tree sparrows (spizella arborea) are programmed for seasonal reproduction and postnuptial molt by or before week 3 on long days. in this corollary study, we withdrew long days before or after the control circuits had been programmed. after 1 day to 4 wk on long days, groups of thyroid-intact males were returned to short days until week 7, when they w ... | 1998 | 9472917 |
| testis-dependent and -independent effects of photoperiod on volumes of song control nuclei in american tree sparrows (spizella arborea). | songbirds exhibit seasonal changes in the volumes of song control nuclei. birds on long, spring-like days have larger nuclei than do birds on short, winter-like days. the mechanisms mediating volumetric changes have not been determined unequivocally, but testosterone (t) is probably involved. this study examined whether testicular factors are uniquely responsible for seasonal changes in the song system, or whether photoperiod has testis-independent effects. male american tree sparrows were expos ... | 1997 | 9237531 |
| the photoperiodic control circuit in euthyroid american tree sparrows (spizella arborea) is already programmed for photorefractoriness by week 4 under long days. | the aim of this investigation was to determine whether spontaneous testicular regression in male american tree sparrows (spizella arborea) that were thyroidectomized at week 4 of photostimulation manifests photorefractoriness, as it does in chronically photostimulated euthyroid controls. on the basis of our demonstration that exogenous thyroxine stimulates the gonads only when recipient birds are photosensitive, male tree sparrows were thyroidectomized at week 4 of photostimulation (20 h light:4 ... | 1995 | 7616501 |
| the thyroid and photoperiodic control of seasonal reproduction in american tree sparrows (spizella arborea). | to explore the role of the thyroid gland in the control of seasonal reproduction in obligately photoperiodic american tree sparrows (spizella arborea), the effects of (1) thyroxine administered in drinking water to thyroid-intact photosensitive or photorefractory birds, and (2) radiothyroidectomy before and after photostimulation and during photorefractoriness were examined. chronic administration of pharmacological doses of thyroxine induced testicular growth and usually regression in initially ... | 1993 | 8151015 |
| on the recovery of photosensitivity in two passerine species, american tree sparrows (spizella arborea) and harris' sparrows (zonotrichia querula). | to test the hypothesis that a spontaneous increase in plasma luteinizing hormone (lh) signals recovery of photosensitivity in castrated passerine birds, lh concentrations were measured weekly in intact and in castrated photorefractory tree sparrows and harris' sparrows transferred to short days. after 7 weeks on short days (experiment 1) or after 1, 3, 5, 7, and 10 weeks (experiment 2) were challenged with long days (1 week) to determine if photosensitivity had been restored. as evidenced by a s ... | 1990 | 2391029 |
| the drive on luteinizing hormone secretion in castrated tree sparrows (spizella arborea) exposed to short days is daylength independent. | for many, if not most, photoperiodic species of birds, short days are nongonadostimulatory. the tacit assumption that short days are also nonphotostimulatory was tested by determining whether plasma concentrations of luteinizing hormone (lh) in castrated tree sparrows exposed to short daily photoperiods (8 hr or less) are daylength dependent or independent. castration of tree sparrows held on an 8-hr daily photoperiod evoked, within 2 weeks, a fivefold elevation in plasma lh concentration. over ... | 1990 | 2338227 |
| extraocular control of seasonal reproduction in female tree sparrows (spizella arborea). | the work reported here explored extraocular control of seasonal reproduction in a photoperiodic species. photosensitive female tree sparrows (spizella arborea) were subjected to bilateral or unilateral ocular enucleation or to sham operation and exposed to a photoregimen designed to stimulate luteinizing hormone (lh) secretion, to induce photorefractoriness, and to restore photosensitivity. as revealed by plasma lh profiles constructed from measurements taken over 181 days, neither bilateral nor ... | 1990 | 2338219 |
| extraocular control of photorefractoriness in american tree sparrows (spizella arborea). | photorefractoriness, a reversible state of unresponsiveness to daylengths of gonadostimulatory duration, terminates seasonal breeding in many photoperiodic species of birds. whether the eyes are components of the mechanism that triggers photorefractoriness is an important, but heretofore unresolved, question. although a role for extraocular photoreception in the mechanism of photoinduced gonadal growth is well documented, the eyes may be important in the mechanism of photorefractoriness if, as s ... | 1989 | 2804201 |
| a testosterone-independent reduction in net photoperiodic drive triggers photorefractoriness in male tree sparrows (spizella arborea). | an experiment was performed to determine whether photorefractoriness in male tree sparrows is triggered by a testosterone-independent reduction in net photoperiodic drive or by a photoperiod-induced hypersensitivity of the hypothalamic-pituitary axis to testosterone negative feedback. photosensitive male tree sparrows were transferred from 8 h light:16 h darkness (8l:16d) to 20l:4d. birds were castrated bilaterally on day 28 of photostimulation. beginning on day 33 and weekly thereafter until da ... | 1986 | 3701241 |
| testosterone sensitivity of the seminal sacs of tree sparrows (spizella arborea) in different reproductive states. | testosterone sensitivity of the seminal sacs of castrated tree sparrows from each of three reproductive states was evaluated by measuring the change in seminal-sac mass per unit change in the logarithm of replacement or plasma testosterone. birds were exposed to exogenous testosterone for 38 days. replacement doses less than 0.17 mumol or plasma concentrations less than about 0.7 nmol/l did not induce seminal-sac growth in photosensitive castrated birds held on short days, in photosensitive cast ... | 1986 | 3701240 |
| an androgen-independent mechanism maintains photorefractoriness in male tree sparrows (spizella arborea). | a series of experiments was performed to clarify whether photorefractoriness in male tree sparrows is maintained by an androgen-dependent mechanism. castration did not raise plasma lh in photorefractory males held under a daily photoperiod of 20 h light:4 h darkness (20l:4d). castrated photorefractory males were implanted with the antiandrogen cyproterone or injected s.c. with the antiandrogen flutamide to determine whether androgens which may be resistant to castration inhibit lh secretion. nei ... | 1985 | 4045352 |
| androgen feedback-dependent and -independent control of photoinduced lh secretion in male tree sparrows (spizella arborea). | photoperiodic control of gonadotrophin secretion in male tree sparrows was studied by examining changes in plasma lh in castrated birds retained on short daylengths and in castrated birds transferred to long daylengths. plasma lh concentrations were markedly higher in photostimulated birds than in non-photostimulated birds throughout the 25-day experiment, and implantation of the antiandrogen cyproterone (free alcohol), which should have blocked the action of castration-resistant androgens, did ... | 1985 | 3989422 |
| dissimilar effects of hemicastration on plasma lh and fsh in photostimulated tree sparrows (spizella arborea). | | 1978 | 631546 |
| testicular inhibition of gonadotropin secretion in photosensitive tree sparrows (spizella arborea) exposed to a winter-like day length. | | 1977 | 902978 |
| plasma and pituitary luteinizing hormone in intact and castrated tree sparrows (spizella arborea) during a photoinduced gonadal cycle. | | 1974 | 4828883 |