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PubMed1975

Chromosomes and cellular radiosensitivity. IV. A new radiotaxon represented by the ferns.

Survival curves were constructed and D0 values determined after X-irradiation of single-celled germinating spores of 14 species of ferns, which had a wide variation in interphase chromosome and nuclear volumes and in DNA content per chromosome and per nucleus. A good fit to a line of slope equal to -1 is given on a log-log plot relating D0 to interphase chromosome volume. In a previous publication (Sparrow, Underbrink and Sparrow 1967), ferns fell into radiotaxon VIII, but the new data suggest that they should be assigned to a new group (VIIa) falling midway between radiotaxa VII and VIII. The calculated energy absorption per chromosome at D0 for VIIa is also intermediate between those for VII and VIII. If the value of this parameter is set at 1 for radiotaxon V, that for VIIa is approximately 32 times greater and the radiotaxa V, VI, VII and VIIa form a series 1 : 4 : 14 : 32. The new results indicate that radiotaxon VIII may have to be abandoned unless some other radiobiologically unexplored group (e.g. algae) fills the gap.

Cell Survival↗
PubMed2006

Morphological adaptation influences the evolution of a mating signal.

Theory predicts that forces of natural selection can reduce the intensity of sexually selected traits. In this study, I investigate how morphological adaptation to feeding ecology influences a mating signal. In birds, changes in feeding ecology can cause rapid divergence in bill morphology. Because bills are also important for song production, feeding ecology may influence song divergence. During song, birds can rapidly change vocal tract resonance using bill movement, yet are constrained in rate and magnitude of bill movements resulting in a trade-off between trill rate and frequency bandwidth. Male swamp sparrows vary in their ability to produce rapid, broad-band trills and females prefer more physically demanding songs. Populations of swamp sparrows adapted to the feeding ecology of tidal marshes have larger bills than inland populations. Larger bills should increase the constraints of producing rapid, broad-band trills allowing for a test of how changes in feeding ecology affect a feature of song used in mate choice. I found significant differences in acoustic features of song consistent with the hypothesis that coastal males are less able to meet the physical demands of song production because of the constraints of having larger bills. As possible compensation for decreases in song performance, coastal populations exhibit an increase in song complexity. These changes support the current model of how motor constraints influence song production and suggest a mechanism by which feeding ecology can influence signal evolution.

Adaptation, Physiological↗
PubMed1996

Identification, distribution, and developmental changes of a melatonin binding site in the song control system of the zebra finch.

In many avian species, singing is a circadian or seasonal behavior that appears to be widely dependent on gonadal steroid hormones. To explore the possibility of a further hormone-dependent vocal control mechanism driven by the action of melatonin, we examined the binding of iodinated melatonin (IMEL) in the vocal control network of adult and juvenile (22- and 40-day-old) zebra finches. IMEL binding areas of the zebra finch brain were localized and characterized by using quantitative in vitro autoradiography. In the vocal control system, dense IMEL binding sites were restricted to the nucleus hyperstriatalis ventrale, pars caudalis (HVC). The binding of IMEL to the HVC and to visual areas, e.g., the ectostriatum and the optic tectum, was saturable and showed a single class of high-affinity binding sites with binding affinities (Kds) in the range of 5-20 pM. Competition experiments with various indols and IMEL showed that the IMEL binding site in the zebra finch brain has properties similar to the high-affinity melatonin receptor described in the chicken, in the house sparrow, and in the mammalian brain and retina. Similar to the zebra finch HVC, the HVC of other songbirds, e.g., male canaries and male house sparrows, has the most intense IMEL binding of all areas of the vocal control network. The IMEL binding in the forebrain vocal control areas of the zebra finch, but not that in the visual processing areas, was sexually dimorphic in correlation with the sexually dimorphic neuroanatomy of the forebrain vocal control areas. In the HVC, there is a developmental increase in the maximal number of binding sites for IMEL and in the protein content, so that the adult phenotype of dense IMEL binding develops between day 40 and day 80. The distribution and developmental pattern of IMEL binding in the song system suggests that melatonin has a role in the motor control of singing. Melatonin binding sites in HVC could link HVC-based song control to circadian and circannual changes in the photoperiod independent of gonadal steroids.

Animals↗
PubMed1999

A field study of seasonal neuronal incorporation into the song control system of a songbird that lacks adult song learning.

Adult songbirds can incorporate new neurons into HVc, a telencephalic song control nucleus. Neuronal incorporation into HVc is greater in the fall than in the spring in adult canaries (open-ended song learners) and is temporally related to seasonal song modification. We used the western song sparrow, a species that does not modify its adult song, to test the hypothesis that neuronal incorporation into adult HVc is not seasonally variable in age-limited song learners. Wild song sparrows were captured during the fall and the spring, implanted with osmotic pumps containing [3H]thymidine, released onto their territories, and recaptured after 30 days. The density, proportion, and number of new HVc neurons were all significantly greater in the fall than in the spring. There was also a seasonal change in the incorporation of new neurons into the adjacent neostriatum that was less pronounced than the change in HVc. This is the first study of neuronal recruitment into the song control system of freely ranging wild songbirds. These results indicate that seasonal changes in HVc neuronal incorporation are not restricted to open-ended song learners. The functional significance of neuronal recruitment into HVc therefore remains elusive.

Age Factors↗
PubMed1997

Bird song learning as an adaptive strategy.

Parallels are often drawn between bird song learning and human language learning. The analogies include an early sensitive period for learning, separation of sensory and motor phases of learning, 'innate knowledge' of language or song, and specialized neural systems. Nevertheless, in distinction to human language learning, song learning is usually viewed as a purely auditory process. This view is implied in the typical experimental paradigm for studying song learning, in which the bird is isolated in a sound-proof chamber and exposed only to tape-recorded song. This paradigm remains the major method of studying song learning despite recent demonstrations of the importance of social variables, and it contains the implicit assumption that non-auditory variables, especially social and ecological variables, play only a minor role in this process. I will argue here that understanding the functions of song learning requires that we investigate it in the field, where social and ecological variables have full play. We have done just this for the song sparrow, and when viewed in this perspective song learning in the song sparrow takes on the clear outlines of an adaptive strategy.

Adaptation, Psychological↗
PubMed1995

Testosterone-induced shortening of the storage phase of song development in birds interferes with vocal learning.

Bird song is a complex, learned behavior. Vocal learning in sparrows involves several different processes that occur in a distinct temporal pattern over the course of the first year of life. Songs are acquired without practice during a sensitive period within the first 3 months of life and rehearsal of the acquired song does not begin until 7 or 8 months of age. The function of the storage period between song acquisition and production is not known. We set out to investigate its significance by administering testosterone, known to stimulate production of adult song, to birds at 100 days of age after song acquisition was completed but some 5 months prior to normal song onset. Most testosterone-treated birds produced abnormal songs resembling those of males raised in acoustic isolation suggesting that, in sparrows, events occurring during the storage phase play a significant role in vocal learning.

Animals↗
PubMed2003

Androgens and estrogens induce seasonal-like growth of song nuclei in the adult songbird brain.

In seasonally breeding songbirds, the brain regions that control song behavior undergo dramatic structural changes at the onset of each annual breeding season. As spring approaches and days get longer, gonadal testosterone (T) secretion increases and triggers the growth of several song control nuclei. T can be converted to androgenic and estrogenic metabolites by enzymes expressed in the brain. This opens the possibility that the effects of T may be mediated via the androgen receptor, the estrogen receptor, or both. To test this hypothesis, we examined the effects of two bioactive T metabolites on song nucleus growth and song behavior in adult male white-crowned sparrows. Castrated sparrows with regressed song control nuclei were implanted with silastic capsules containing either crystalline T, 5alpha-dihydrotestosterone (DHT), estradiol (E(2)), or a combination of DHT+E(2). Control animals received empty implants. Song production was highly variable within treatment groups. Only one of seven birds treated with E(2) alone was observed singing, whereas a majority of birds with T or DHT sang. After 37 days of exposure to sex steroids, we measured the volumes of the forebrain song nucleus HVc, the robust nucleus of the archistriatum (RA), and a basal ganglia homolog (area X). All three steroid treatments increased the volumes of these three song nuclei when compared to blank-implanted controls. These data demonstrate that androgen and estrogen receptor binding are sufficient to trigger seasonal song nucleus growth. These data also suggest that T's effects on seasonal song nucleus growth may depend, in part, upon enzymatic conversion of T to bioactive metabolites.

Androgens↗
PubMed1997

Host responses to cowbirds near the nest: cues for recognition

Two cues (bill shape and vocalizations) that yellow warblers, Dendroica petechiamay use to recognize brown-headed cowbirds, Molothrus aterwere examined experimentally. Female yellow warblers responded more intensely to a control cowbird than one with a longer, thinner bill, which suggests that bill shape was an important cue in recognition. Responses involved close approaches, 'seet' alarm calls and sitting in the nest. Female yellow warblers distinguished between vocalizations of male and female cowbirds and those of a song sparrow, Melospiza melodia (control). They responded most intensely to female cowbird 'chatter calls' and least intensely to the sparrow song; responses to male cowbird 'perched song' were intermediate in intensity. The results suggest that female yellow warblers recognize cowbirds on the basis of bill shape and vocalizations. Furthermore, these results, coupled with previous findings, suggest that female yellow warblers distinguish between male and female cowbirds by vocalizations but not appearance.

Journal Article↗
PubMed1998

External validity and experimental design: the sensitive phase for song learning.

In the past decade there has been widespread acceptance of the idea that the use of live, socially interactive tutors in song learning experiments produces results that differ dramatically from, and are more valid than, results obtained with tape tutors. The influential series of experiments by Baptista & Petrinovich (1984, Animal Behaviour, 32, 172-181, 1986, Animal Behaviour, 34, 1359-1371; Petrinovich & Baptista 1987, Animal Behaviour, 35, 961-974) have promoted this view, and their results have been widely accepted. Baptista & Petrinovich's results have led them and others to question whether there are age-limited sensitive phases for song learning, as Marler's (1970, Journal of Comparative Physiology and Psychology Monographs, 711-25) early studies on the white-crowned sparrow, Zonotrichia leucophrys, suggested, and led them to argue that interactive tutoring produces essentially open-ended learning. I argue here that this view is mistaken, and that the sensitive phase for song learning in the white-crowned sparrow is identical for live and tape tutors and is restricted to the first few months of life. Baptista & Petrinovich presented live and tape tutors for different periods to their subjects. Type of tutor (live versus tape) is confounded with duration of exposure to tutors. As a consequence, their experiments confound two different forms of song learning that occur at different ages, and give the mistaken appearance of an extended sensitive phase when live tutors are used. Copyright 1998 The Association for the Study of Animal Behaviour

Journal Article↗
PubMed1996

A probabilistic model for deriving soil quality criteria based on secondary poisoning of top predators. II. Calculations for dichlorodiphenyltrichloroethane (DDT) and cadmium.

A simplified food web with three trophic levels is designed: plants and invertebrates at the first, small birds and mammals at the second, and birds and beasts of prey at the third trophic level. Exposure of top predators via separate food chains is analyzed. However, most top predator species are exposed via more than one food chain (food web). Therefore, a species-specific approach is followed too, for which four bird of prey species and two beast of prey species with different food choices are selected: sparrow hawk, kestrel, barn owl, little owl, badger, and weasel. The most critical food chains for secondary poisoning of top predators are soil --> worm/insect --> bird --> bird of prey for dichlorodiphenyltrichloroethane (DDT), and soil --> worm --> bird/mammal --> bird of prey for cadmium (Cd). The risk for the selected top predator species is much lower than the risk based on these critical food chains because the critical food chains constitute a minor part of their food webs. Species feeding on birds (sparrow hawk) and small carnivorous mammals (barn owl) are exposed to DDT and Cd to a much higher extent than species mainly feeding on small herbivorous mammals (kestrel and weasel). It is recommended to include exposure via the pathways soil --> worm/insect --> bird/mammal --> top predator in procedures for derivation of environmental quality objectives for persistent and highly lipophilic compounds.

Animal Feed↗
PubMed1994

Gender and seasonal differences in the adrenocortical response to ACTH challenge in an arctic passerine, Zonotrichia leucophrys gambelii.

We evaluated the adrenocortical response to acute stress in free-living Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) using a standardized capture stress protocol in which five serial blood samples (70 microliters) were taken for measurement of plasma corticosterone (B) over the course of an hour of captivity (at 1, 5, 10, 30, and 60 min). In field-captured birds, male plasma B levels rose two to four times higher than those of females under capture stress during the breeding season, but were no different during winter (nonbreeding). We investigated the basis of this pattern by conducting dexamethasone (DEX) suppression tests on breeding and nonbreeding sparrows of both genders. This test involves pretreatment with subcutaneous DEX implants (a potent synthetic glucocorticoid) and challenge with intrajugular injections of either corticotropin (ACTH) or saline, followed by collection of a series of blood samples for evaluation of plasma B levels over a 2-hr period. ACTH injections in DEX-treated birds resulted in elevated B in both genders, with nonbreeding B profiles consistently lower than those of breeding birds. All DEX-treated, saline-injected birds, except breeding males, maintained low B levels for the entire 2-hr post-challenge period. This result indicates effective negative feedback by DEX on the hypothalamic-pituitary-adrenal axis, thus inhibiting endogenous B secretion. The apparent reduction in glucocorticoid feedback inhibition in breeding males may be related to an uncoupling of adrenal effects on reproductive behavior.

Adrenal Cortex↗
PubMed1998

Molecular phylogenetics of the avian genus Pipilo and a biogeographic argument for taxonomic uncertainty.

We sequenced 1709 base pairs (bp) of mitochondrial DNA including parts of cytochrome b, ND 2, and the control region (CR I, II) for seven members of the avian genus Pipilo (towhees), Melozone kieneri (rusty-crowned ground-sparrow), and Arremonops rufivirgatus (olive sparrow). A total of 457 bp was variable and 257 bp were potentially phylogenetically informative. All gene regions were similarly variable (20.2 to 28.4%) except for CR II (38.4%); third position transitions were as common as substitutions in the CR. Tree topology was sensitive to choice of outgroup(s) and individual sequences used as exemplars. Six trees were considered viable phylogenetic hypotheses based on maximum parsimony and maximum likelihood analyses. These trees generally supported two groups of towhees (rufous-sided group, brown towhee group), a sister taxon relationship for P. aberti and P. crissalis, and a sister taxon relationship for P. ocai and P. maculatus. The occurrence of M. kiernei within Pipilo in three trees challenges the monophyly of the latter; the other species of Melozone and other outgroups require study to resolve Pipilo monophyly. The relationships of P. albicollis and P. fuscus were ambiguous, as they were with previous data sets (allozymes, mtDNA restriction sites); they could be sister species or either one could be the basal species in the brown towhee group. We suggest that this taxonomic uncertainty obtains from the contemporaneous origin of P. fuscus, P. albicollis, and the ancestor of P. aberti/P. crissalis. We favor a "star" phylogeny because species in unrelated lineages found in the same region as P. albicollis are similarly difficult to resolve phylogenetically. Synapomorphies from coding genes and the CR did not preferentially support basal and terminal nodes, and hence did not provide different windows of taxonomic resolution, which might be expected from the apparent rapid rate of CR evolution. Phylogenetic trees inferred from allozymes, restriction sites, and mtDNA sequences were congruent, suggesting that each is a useful source of phylogenetic information.

Animals↗
PubMed1991

The effect of corticosterone on standard metabolic rates of small passerine birds.

Resting metabolic rates of Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) and pine siskins (Carduelis pinus) were evaluated at thermoneutral temperatures before and after administration of corticosterone (B) at physiological doses. There was no effect of B on basal metabolic rate of either species, but nocturnal metabolic rate varied significantly less over the 3-h period of measurement in B-treated sparrows and siskins than in control birds. These results, coupled with observations of caged birds, suggest that corticosterone has no direct effect on avian resting metabolism but does reduce the responsiveness of birds to external stimuli and thus promotes nocturnal restfulness.

Animals↗
PubMed1981

Changes in lipid content during the post-hatching development of the brain of altricial birds.

The post-hatching development of the brain was studied in three altricial birds (those whose development is completed after hatching), namely, the domestic pigeon, house swift and house sparrow, to assess the state of maturity of the brain at the time that the fledglings leave the nest. Maturity is related to the process of myelination and, therefore, Sudan Black was chosen as it is a sensitive indicator of myelin lipids. On hatching, it was found that sudanophilia was very low in all three birds, indicating a lack of maturation. However, between 15 to 25 days in the pigeon and swift and between 8 and 14 days in the sparrow, there was a steady increase in Sudan Black staining. By the time the birds left their nests, the staining was similar to that of adults, thus indicating that the process of myelination was complete and that the brains were mature.

Animals↗
PubMed2002

Platinum group elements in the feathers of raptors and their prey.

Platinum (Pt), palladium (Pd), and rhodium (Rh) concentrations were determined in the feathers of three raptor species in Sweden, the sparrowhawk ( Accipiter nisus), the peregrine falcon ( Falco peregrinus), and the gyrfalcon ( Falco rusticolus), as well as the main prey of the sparrowhawk (the house sparrow, Passer domesticus) and the gyrfalcon (the willow grouse, Lagopus lagopus). The analysis of feathers from 1917-1999 revealed a clear temporal trend, with significantly higher Rh concentrations in sparrowhawk and peregrine falcon after 1986. There is evidence for increasing platinum group element (PGE) concentrations from 1917 to 1999 in peregrine falcon and sparrowhawk. This suggests that feathers reflect increased PGE concentrations in the environment over this time period. Mean concentrations of PGE in feathers of raptors after 1986 ranged from 0.3 to 1.8 ng x g(-1) for Pt, 0.6 to 2.1 ng x g(-1) for Pd (indicative values), and 0.1 to 0.6 ng x g(-1) for Rh. House sparrows in urban areas had significantly higher Pt and Pd concentrations than urban sparrowhawks. The higher Pd concentrations in relation to Pt and Rh may indicate the greater mobility of Pd in the environment. Although PGE concentrations are generally higher in birds living in urban areas, no significant spatial trend could be established. This is partly due to the widespread distribution of automobiles and partly because birds forage and integrate PGE exposure over large areas. Laser ablation analysis demonstrates that PGE contamination of feathers is predominantly external, consisting of small particles in the nanometer size range. Other indications of external contamination are that Pt and Pd levels are significantly higher in the vane than in the shaft and that PGE relative ratios (except Pd) reflect urban particles.

Animals↗
PubMed2004

Comparative tissue distribution of metals in birds in Sweden using ICP-MS and laser ablation ICP-MS.

Cadmium, copper, lead, palladium, platinum, rhodium, and zinc profiles were investigated along feather shafts of raptor and other bird species by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The distribution of external versus internal metal contamination of feathers was investigated. The species examined were peregrine falcon (Falco peregrinus), sparrowhawk ( Accipiter nisus), willow grouse (Lagopus lagopus), and house sparrow (Passer domesticus) in Sweden. For habitat comparisons, total Cu, Pb, Zn, and Cd concentrations were analyzed by ICP-MS in feathers of the examined species as well as captive peregrine falcon. For investigation of metal distribution and correlation in different biological materials of raptors, total concentrations of Cu, Pb, Cd, and Zn were also investigated by ICP-MS in feathers, eggs, blood, feces, liver, and kidney of wild peregrine falcon from southwestern Sweden. Laser ablation of feathers revealed that Pb contamination is both external and internal, Zn contamination is internal, and Cd and Cu contamination is predominantly internal, with a few externally attached particles of high concentration. Pb, Cu, and Cd signal intensities were highest in urban habitats and contamination was mainly external in feathers. The background signal intensity of Zn was also higher in birds from urban habitats. The laser ablation profile of PGE (Pt, Pd, Rh) demonstrated that PGE contamination of feathers consists almost exclusively of externally attached PGE-containing particles, with little evidence of internally deposited PGE.Generally, total metal concentrations in feathers were highest in sparrowhawk and house sparrow due to their urban habitat. Total Cu, Zn, and Cd concentrations were highest in liver and kidney due to binding to metallothionein, while the total Pb concentration was highest in feces due to the high excretion rate of Pb. A decreasing temporal trend for Pb in feathers, showing that Pb levels in feathers have decreased since the introduction of nonleaded petrol, is also discussed.

Animals↗
PubMed2001

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 metabolic rate and cold tolerance are phenotypically correlated in small birds and no previous study has directly examined this relationship. I measured maximum cold-induced metabolic rate and cold tolerance (i.e., thermogenic endurance) over three winters in black-capped chickadees Poecile atricapillus, American tree sparrows Spizella arborea, and dark-eyed juncos Junco hyemalis. For raw thermogenic endurance data, residuals of maximum cold-induced metabolic rate and thermogenic endurance from mass regressions were significantly and positively correlated in juncos and tree sparrows, and their correlation approached significance for chickadees. Log10 transformation of thermogenic endurance and mass data gave similar results. These data provide the first direct evidence for a phenotypic correlation between maximum cold-induced metabolic rate and thermogenic endurance in small birds, although much of the variance in thermogenic endurance is explained by factors other than maximum cold-induced metabolic rate and the degree of correlation differs among species. Nevertheless, these data suggest that physiological adjustments producing elevated thermogenic endurance also produce elevated maximum cold-induced metabolic rate in small birds.

Acclimatization↗
PubMed2005

Variable effects of climate change on six species of North American birds.

Many recent studies have shown that birds are advancing their laying date in response to long-term increases in spring temperatures. These studies have been conducted primarily in Europe and at local scales. If climate change is a large-scale phenomenon, then we should see responses at larger scales and in other regions. We examined the effects of long-term temperature change on the laying dates and clutch sizes of six ecologically diverse species of North American birds using 50 years of nest record data. As predicted, laying dates for most (four of six) species were earlier when spring temperatures were warmer. Over the long-term, laying dates advanced over time for two species (red-winged blackbirds, Agelaius phoeniceus and eastern bluebirds, Sialia sialis). Laying date of song sparrows (Melospiza melodia) also advanced with increasing temperature when the analysis was restricted to eastern populations. Neither laying date nor clutch sizes changed significantly over time in the remaining species (American coot, Fulica americana, killdeer, Charadrius vociferous, and American robin, Turdus migratorius), an unsurprising result given the lack of increase in temperatures over time at nest locations of these species. This study indicates that the relationship between climate change and breeding in birds is variable within and among species. In large-scale analyses of North American birds, four of seven species have shown advances in laying dates with increasing temperature (including song sparrows in the east). These variable responses within and among species highlight the need for more detailed studies across large spatial scales.

Animal Migration↗