Song switching and agonistic stimulation in the song sparrow (Melospiza melodia): five tests

Male song sparrows in southeastern Ontario have repertoires of five to 11 distinct song types. The singer repeats each song type a variable number of times before switching to another type. Analysis of territorial singing suggested that rate of switching song types is positively correlated with intensity of agonistic stimulation, where ‘agonistic’ signifies conflict-related. The song-switching hypothesis was tested with playback experiments which varied stimulus intensity in five different ways: (1) presence or absence of song stimuli; (2) addition of visual to auditory stimuli; (3) location of the song stimulus 20 m inside or outside territory; (4) nesting phases of the subjects; and (5) switching rate and rate of novel song type production of the playback (i.e. stimulus versatility). The subjects' switching rates and flight rates consistently increased with greater stimulation, although song rate tended to remain unaffected. The signalling of response intensity through adjustments in switching rate exemplifies how song repertoires function in agonistic communication.     

Typical versions of learned swamp sparrow song types are more effective signals than are less typical versions

The learned songs of songbirds often cluster into population-wide types. Here, we test the hypothesis that male and female receivers respond differently to songs depending on how typical of those types they are. We used computational methods to cluster a large sample of swamp sparrow (Melospiza georgiana) songs into types and to estimate the degree to which individual song exemplars are typical of these types. We then played exemplars to male and female receivers. Territorial males responded more aggressively and captive females performed more sexual displays in response to songs that are highly typical than to songs that are less typical. Previous studies have demonstrated that songbirds distinguish song types that are typical for their species, or for their population, from those that are not. Our results show that swamp sparrows also discriminate typical from less typical exemplars within learned song-type categories. In addition, our results suggest that more typical versions of song types function better, at least in male–female communication. This finding is consistent with the hypothesis that syllable type typicality serves as a proxy for the assessment of song learning accuracy.     

Hearing in the swamp sparrow,Melospiza georgiana,and the song sparrow,Melospiza melodia

Operant conditioning techniques and a psychophysical tracking procedure were used to measure thresholds for pure tones in two congeneric species of sparrows: swamp sparrows and song sparrows. Thresholds were measured both in quiet conditions and in the presence of white noise. The two species were similar in their gross pattern of auditory sensitivity with most sensitive thresholds in the frequency region of 1·0–8·0 kHz and poor hearing above and below this range. However, the best sensitivity occurred at 2 kHz for the song sparrows and at 4 kHz for the swamp sparrows. This pattern was also observed in song spectra of the two species. The songs of song sparrows had more power in lower frequencies than the songs of swamp sparrows. Masked auditory thresholds for both species were very similar, showing a generally increasing signal-to-noise ratio with increasing frequency. The similarity between swamp and song sparrows in these measures of basic auditory sensitivity suggests that the primary mechanisms underlying selective vocal learning in these sparrows probably reside at higher levels than the peripheral auditory sensitivities.     

Song development in the white-crowned sparrow: modification of learned song

Previous research has shown that laboratory-tutored white-crowned sparrows, Zonotrichia leucophrys nuttalli, can learn tape-recorded song only until they are about 50 days of age. However, they can learn either conspecific or allospecific song after they are 50 days of age when a live tutor is used. Because the live-tutored birds had not been exposed to song during the first 50 days of life, a question regarding the reasonableness of applying these results to the natural, field situation can be raised. In the experiments reported here, hand-raised nestling white-crowned sparrows between 10 and 50 days of age were tutored in the laboratory with one song, and were then placed with a live tutor singing a different dialect when they were over 50 days of age. Eight of 13 males, and none of 10 females, adopted the song of the second tutor. Birds were also captured in the field as fledglings, and were placed with a live tutor singing a song different from that of the natal area: three of seven males, and one of five females, adopted the song of the live tutor. Four birds that had been group-isolated (two males and two females) were exposed to a live tutor when they were 100 days old, and none acquired normal song; all sang isolate song. The results of these studies indicate that there is considerable plasticity in the song learning of whitecrowned sparrows, and that, for many individuals, song can be modified quite readily. The implications of these findings for the nature of the sensitive phase and for mechanisms of song learning are discussed.     

Intraspecific acoustical interference in the white-throated sparrow (Zonotrichia albicollis)

Intraspecific acoustical interference was studied in the white-throated sparrow (Zonolrichia albicollis). It was found that individuals avoid singing during a song of a conspecific. The effect is significantly greater with neighbours that are closer to them. The evolutionary implications of this phenomenon for the properties of song in Z. albicollis are discussed.     

Semen characteristics of the swamp buffalo (Bubalus bubalis)

The semen characteristics were studied in 182 ejaculates collected with a bovine artificial vagina from five swamp buffalo (Bubalus bubalis) bulls. The mean values were: volume, 2.9 ml; general motility, 70.7%; live (unstained) sperm, 86.5%; abnormal sperm, 10.3%; intact acrosomes, 82.4%; sperm concentration, 1.06 × 10⁹cells/ml and total sperm/ejaculate, 3.18 × 10⁹cells/ml. Among the sperm abnormalities noted were “knobbed” acrosome, abaxial implantation, the “Dag” defect and the corkscrew midpiece. There were no significant (P > 0.05) monthly variations for any of the semen characteristics studied.     

Finite state grammars for dialects of the advertising song of the savannah sparrow (PasserculusSandwichensis)

Right-linear finite state grammars were extracted for song sequences of Savannah Sparrows (Passerculus sandwichensis) from Ontario and Nova Scotia. The Nova Scotia grammar was found to be longer than the Ontario grammar (possess more rewrite statements) and allow for the production of sequences containing consecutive trills. These differences are discussed with respect to genetic and environmental factors shaping song behaviour in the two regions. Limitations of a nonstochastic finite state grammar procedure are also addressed.     

Foraging and territory utilization of blackbirds (Turdus merula) and song thrushes (Turdus philomelos)

Territory utilization of blackbirds and song thrushes is examined in relation to spatial and temporal changes in the distribution of prey. Pairs within a territory showed similar preferences for particular areas. There was considerable diurnal variation in foraging localities and overall the two species tended to concentrate their search effort in areas of high prey density. Rates of feeding attempts and feeding techniques also varied with time of day. Changes were similar in the two species. At high rates of feeding during the middle of the day the foraging range was more restricted than at other times. Over short time periods individuals searched non-randomly by avoiding recently exploited areas.     

Female response song in the ephippigerines Steropleurus stali and Platystolus obvius (Orthoptera,Tettigoniidae)

Stridulation by females of Steropleurus stali and Platystolus obvius in response to the calling song of the males was observed and recorded. The response has only been stimulated by the appropriate male song, either directly or from a recording. The structure of the files and the form of stridulation in both sexes is described. The male song of S. stali is remarkable in that only a few teeth on the file are struck in each wing movement. It is also notable that both opening and closing wing strokes contribute more or less equally to the syllable. The female song is similar but distinct. The song of P. obvius male is a single chirp involving nearly all the teeth on the file and with the main emphasis on the closing syllable. The response song of the female is a very brief chirp. These species are only sporadic singers, but when the female responds they are stimulated into greater activity. They thus contrast with reiterative singers like Ephippiger in which there is no female response. The implications of these contrasting behavioural patterns is discussed.     

Integration of environmental stimuli in the migratory orientation of the savannah sparrow (Passerculus sandwichensis)

Two ‘cue-conflict’ experiments were designed to evaluate the role of (1) solar cues at sunset and stars, and (2) solar cues at sunset and geomagnetic stimuli, in the migratory orientation of the savannah sparrow (Passerculus sandwichensis). A sunset and stars experiment exposed birds in the experimental group to a mirror-reflected sunset followed by an unmanipulated view of stars. Experimental birds shifted their migratory activity in accordance with the setting sun despite exposure to a normal night sky. The sunset and geomagnetism experiment exposed birds in the experimental group to a simultaneous shift in both the position of sunset and the earth's magnetic field. Again experimentals shifted their activity in accordance with the setting sun rather than the artificially shifted magnetic field. Savannah sparrows probaly use stars as celestial landmarks to maintain a preferred direction and do not reorient their activity when exposed to an alternative cue once a direction is established. Moreover, savannah sparrows with experience of migration do not require geomagnetic information in order to use the solar cues available at sunset to select a migratory direction.     

Geographic analysis of nucleotide diversity and song sparrow (Aves: Emberizidae) population history

Mitochondrial DNA (mtDNA) control-region (CR) sequences were analysed to address three questions regarding the evolution of geographical variation in song sparrows. (i) Are mtDNA sequences more informative about phylogenetic relationships and population history than previously published restriction fragment (RFLP) data? (ii) Are song sparrow CR sequences evolving in a selectively neutral manner? (iii) What do the haplotype cladogram and geographical pattern of nucleotide diversity (π) suggest about the recent evolutionary history of song sparrow populations? Results from phylogenetic analyses of CR sequences corroborate RFLP results and reveal instances in which haplotypes do not group by locality. Neutrality tests ( 51 ) suggest that song sparrow mtDNA is evolving in a selectively neutral manner, although exceptions are noted. A novel geographical pattern of π suggests a model of song sparrow population history involving multiple Pleistocene refugia and colonization of some formerly glaciated regions from multiple sources. Moreover, application of coalescence theory to the haplotype cladogram suggests that two different haplotypes (48NF and 151HA) may have predominated in different parts of the song sparrow's range. This model provides insight into the current distribution of song sparrow mtDNA haplotypes and may explain the discordance between evolutionary history inferred from mtDNA and morphology in this species.     

The role of the pineal gland in the photoperiodic control of bird song frequency and repertoire in the house sparrow, Passer domesticus

Temperate zone birds are highly seasonal in many aspects of their physiology. In mammals, but not in birds, the pineal gland is an important component regulating seasonal patterns of primary gonadal functions. Pineal melatonin in birds instead affects seasonal changes in brain song control structures, suggesting the pineal gland regulates seasonal song behavior. The present study tests the hypothesis that the pineal gland transduces photoperiodic information to the control of seasonal song behavior to synchronize this important behavior to the appropriate phenology. House sparrows, Passer domesticus, expressed a rich array of vocalizations ranging from calls to multisyllabic songs and motifs of songs that varied under a regimen of different photoperiodic conditions that were simulated at different times of year. Control (SHAM) birds exhibited increases in song behavior when they were experimentally transferred from short days, simulating winter, to equinoctial and long days, simulating summer, and decreased vocalization when they were transferred back to short days. When maintained in long days for longer periods, the birds became reproductively photorefractory as measured by the yellowing of the birds' bills; however, song behavior persisted in the SHAM birds, suggesting a dissociation of reproduction from the song functions. Pinealectomized (PINX) birds expressed larger, more rapid increases in daily vocal rate and song repertoire size than did the SHAM birds during the long summer days. These increases gradually declined upon the extension of the long days and did not respond to the transfer to short days as was observed in the SHAM birds, suggesting that the pineal gland conveys photoperiodic information to the vocal control system, which in turn regulates song behavior.