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.     

Gap detection in the starling (Sturnus vulgaris)

Summary Gap-detection thresholds of single units were determined from auditory forebrain neurons of the awake starling. Nine different response types were statistically defined from the discharge pattern to a 400 ms broadband noise stimulus. The gap stimuli consisted of two broadband noise bursts which were separated by a gap ranging from 0.4 to 204.8 ms duration. The median minimumdetectable gap for 121 out of 145 units that had a significant threshold 204.8ms was 12.8 ms; 20% of the neurons showed thresholds between 0.4 and 3.2 ms. The neurons of the nine response types differed significantly in their minimum-detectable gaps; neurons with phasic-tonic and phasic excitation exhibited the best (i.e. shortest) minimum-detectable gaps. The neurons of the three different recording areas (field L, NCM and HV) were significantly different in their minimumdetectable gaps; field L neurons showed the best temporal resolution for gaps in broadband noise. Gap-detection thresholds are compared with psychophysical thresholds determined with the same stimuli and the relevance of forebrain units for temporal resolution is discussed.Abbreviations CS control stimulus - HV hyperstriatum ventrale - HVc hyperstriatum ventrale pars caudalis - NB noise burst - NCM neostriatum caudale pars medialis - NS noise stimulus - SGS standard gap series - TW time window     

Sleep pattern in the starling (Sturnus vulgaris)

Electrographic and behavioural observations were conducted on two male and two female captive starlings (Sturnus vulgaris) under natural illumination conditions during autumn. Polygraphically sleep and wakefulness of starling were similar to those of other birds. Starling's total sleep (TS) and slow wave sleep (SWS) lasted 39.0 +/- 1.4% and 38.3 +/- 1.7% of the 24-h period respectively. Paradoxical sleep (PS) was 1.8 +/- 0.2% of the total sleep time. The mean durations individual of TS, SWS and PS episodes were 6.8 +/- 0.2 min, 5.0 +/- 1.0 min and 18 +/- 3 s respectively. The daily percentage of SWS was correlated with the mean episode duration while that of PS was correlated with the number of episodes rather than with the mean episode duration. Starling females spent in sleep a greater percentage of the 24-h period than males.     

Gap detection in the European starling (Sturnus vulgaris)

Summary Gap-detection thresholds were determined for single units in the cochlear ganglion and in auditory nerve fibres of the starling from responses to two broad-band noise bursts separated by a temporal gap of between 0.4 and 204.8 ms. All 35 units showed a threshold within the range of gap sizes tested. The median minimum-detectable gap was 12.8 ms with the minimum being 1.6 ms. A multiple regression analysis revealed that the size of the minimum-detectable gap was not significantly correlated with the neuron's CF, with its sharpness of tuning as given by its bandwidth 10 dB above threshold, or with its Q_10dB value. Only the level of stimulation above the neuron's threshold showed a significant negative correlation with the size of the minimum-detectable gap. These results are discussed with respect to theoretical considerations of limits posed on temporal resolution by the characteristics of peripheral filters. These findings are also discussed in the context of the coding of gaps at different levels of the starling's auditory system and in relation to psychoacoustic results in the starling on gap detection and time resolution described by temporal modulation transfer functions.     

Azimuthal sound localization in the European starling (Sturnus vulgaris)

Summary The physical measurements reported here test whether the European starling (Sturnus vulgaris) evaluates the azimuth direction of a sound source with a peripheral auditory system composed of two acoustically coupled pressure-difference receivers (1) or of two decoupled pressure receivers (2).A directional pattern of sound intensity in the freefield was measured at the entrance of the auditory meatus using a probe microphone, and at the tympanum using laser vibrometry. The maximum differences in the soundpressure level measured with the microphone between various speaker positions and the frontal speaker position were 2.4 dB at 1 and 2 kHz, 7.3 dB at 4 kHz, 9.2 dB at 6 kHz, and 10.9 dB at 8 kHz. The directional amplitude pattern measured by laser vibrometry did not differ from that measured with the microphone. Neither did the directional pattern of travel times to the ear. Measurements of the amplitude and phase transfer function of the starling's interaural pathway using a closed sound system were in accord with the results of the free-field measurements.In conclusion, although some sound transmission via the interaural canal occurred, the present experiments support the hypothesis 2 above that the starling's peripheral auditory system is best described as consisting of two functionally decoupled pressure receivers.Abbreviations CM cochlear microphonics - ITD interaural time difference - IID interaural intensity difference - MRA minimum resolvable angle - dB SPL sound-pressure level (re 0.00002 Pa)     

Metabolic costs of egg production in the European starling (Sturnus vulgaris)

The energy cost of egg production in passerine birds has typically been estimated to be 45%-60% of basal metabolic rate (BMR), but this is based on theoretical models using data on energy content of eggs and reproductive tissue; there are still very few empirical data on egg production costs. In this study, we directly measured resting metabolic rate (RMR) in egg-laying female European starlings (Sturnus vulgaris) over 3 yr. We compared these data with RMR of nonbreeding and chick-rearing birds and with estimated energy expenditure generated from a typical energy content model by using empirically derived data from body composition analysis for this species. We found marked variation in RMR between years and between reproductive stages, which complicates comparisons among breeding stages for the assessment of relative egg production costs. On the basis of this method, RMR during egg laying varied from +74% to -13% of nonbreeding RMR and from +20% to -7% of chick-rearing RMR. We therefore used an alternate approach: measuring changes in RMR through the complete cycle of follicle development and ovulation. The increase in RMR from the beginning of prelaying to the six-follicle stage (before first ovulation) when birds have a complete developing follicle hierarchy was 22.4%. This value is still much lower than that estimated from our energy content model. We discuss conceptual problems associated with the theoretical energy content approach but also suggest, on the basis of earlier work done in our lab, that the measured increase in RMR might still underestimate the actual cost of egg production if birds reallocate energy between different physiological systems.     

Foraging rate versus sociality in the starling Sturnus vulgaris

It is well established that social conditions often modify foraging behaviour, but the theoretical interpretation of the changes produced is not straightforward. Changes may be due to alterations of the foraging currency (the mathematical expression that behaviour maximizes) and/or of the available resources. An example of the latter is when both solitary and social foragers maximize rates of gain over time, but competition alters the behaviour required to achieve this, as assumed by ideal free distribution models. Here we examine this problem using captive starlings Sturnus vulgaris. Subjects had access to two depleting patches that replenished whenever the alternative patch was visited. The theoretical rate-maximizing policy was the same across all treatments, and consisted of alternating between patches following a pattern that could be predicted using the marginal value theorem (MVT). There were three treatments that differed in the contents of an aviary adjacent to one of the two patches (called the 'social' patch). In the control treatment, the aviary was empty, in the social condition it contained a group of starlings, and in a non-specific stimulus control it contained a group of zebra finches. In the control condition both patches were used equally and behaviour was well predicted by the MVT. In the social condition, starlings foraged more slowly in the social than in the solitary patch. Further, foraging in the solitary patch was faster and in the social patch slower in the social condition than in the control condition. Although these changes are incompatible with overall rate maximization (gain rate decreased by about 24% by self-imposed changes), if the self-generated gain functions were used the MVT was a good predictor of patch exploitation under all conditions. We discuss the complexities of nesting optimal foraging models in more comprehensive theoretical accounts of behaviour integrating functional and mechanistic perspectives.     

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     

A dynamic model of food allocation to starling (Sturnus vulgaris) nestlings

We present a dynamic model of food allocation to starling nestlings.Based on the premise that current reproductive activities mayhave detrimental effects on future breeding episodes, the modelis elaborated around the concept of a state variable. In thisimplementation, the state variable represents body mass. A numberof activities can be followed during the breeding season, andwe measured the value of these actions in terms of the contributionof the action to the fitness of the animal at the end of thenestling period. Using the final states reached by parents andyoung, we determined fitness by summing current breeding productionand future reproductive potential. We used backward inductionto find for each combination of states and nestling age thebehavioral options that maximize fitness. Subsequently, forwardsimulations were used to find average trajectories across timeof the following variables: parental and offspring states, foragingtime, and allocation of energy. We also investigated the effectsof brood size and harvest. Physiological parameters, necessaryto translate foraging decisions into body mass changes, aretaken from studies on starlings (Sturnus vulgaris). The resultsappear to closely fit available evidence for this species. Thediscussion relates basic findings of the model to previous resultsof static and deterministic approaches. Limits to the usefulnessof the model are discussed. [Behav Ecol 1991; 2: 21-37]     

The breeding biology of the starling Sturnus vulgaris in northern Finland

The breeding biology of the starling Sturnus vulgaris was studied in three populations in northern Finland, with additional reference localities in nearby areas. Results from a total of 329 nests are presented from years 1962-1976.
The onset of laying in the Oulu area took place on 5 May, the median date being 10 May, about one week later than in southern Finland and 2–3 weeks later than in central Europe. The clutch-size was 5.29 ± 0.05 in the first nests and 5.06 ± 0.26 in later ones. Incubation time was 12.1 ± 0.6 d. An average of 3.31 ± 0.10 fledglings was produced per pair, 3.69 ± 0.08 in succesful clutches, which is significantly less than usually reported from central Europe. Most of the losses were due to starvation of the young.
No second broods were observed in the Oulu area, and repeated nesting was not common, probably because of the general late start of laying.
The reasons for the recent decline in several Finnish starling populations do not lie in the production capacity but must be sought for elsewhere.     

Developmental stress, social rank and song complexity in the European starling (Sturnus vulgaris)

Bird song is a sexually selected trait and females have been shown to prefer males that sing more complex songs. However, for repertoire size to be an honest signal of male quality it must be associated with some form of cost. This experiment investigates the effects of food restriction and social status during development on song complexity in the European starling (Sturnus vulgaris). Birds that experienced an unpredictable food supply early in life produced a significantly smaller repertoire of song phrases than those with a constant food supply. Social status during development was also significantly correlated with repertoire size, with dominant birds producing more phrase types. This study therefore provides novel evidence that social as well as nutritional history may be important in shaping the song signal in this species.     

Female presence affects male behavior and testosterone levels in the European starling (Sturnus vulgaris)

In this study, we confronted individually housed male European starlings (Sturnus vulgaris) with a female conspecific for 60 min to study the consequences on behavior and plasma testosterone (T) concentrations. Control males experienced a similar procedure, the only difference being that they were tested in the absence of a female. Female presence significantly affected both behavior and plasma T levels of male starlings. Experimental males spent significantly more time singing in the nest box and flew significantly more into the nest box with green nesting material during female presentations than during control periods. Control males never showed these mate attraction behaviors. In total 5 of the 16 experimental males did not respond behaviorally to the female stimulus bird (NR males). In contrast to T levels of control males, plasma T concentrations of both experimental males that did respond to the female (R males) and of NR males (which only perceived the female stimulus) were positively influenced by female presentation. The time spent singing in the nest box by experimental males (R and NR males combined) during female presence tended to be positively correlated with changes in plasma T levels. Finally, before introduction of a female, plasma T levels of R males were significantly higher than those of NR males indicating that individually housed males respond to the presence of a female conspecific by increasing their mate attraction behaviors only when a threshold plasma T concentration has been reached.     

Azimuthal sound localization in the European starling (Sturnus vulgaris): II. Psychophysical results

Small songbirds have a difficult analysis problem: their head is small compared to the wavelengths of sounds used for communication providing only small interaural time and level differences. Klump and Larsen (1992) measured the physical binaural cues in the European starling (Sturnus vulgaris) that allow the comparison of acoustical cues and perception. We determined the starling’s minimum audible angle (MAA) in an operant Go/NoGo procedure for different spectral and temporal stimulus conditions. The MAA for broadband noise with closed-loop localization reached 17°, while the starling’s MAA for open-loop localization of broadband noise reached 29°. No substantial difference between open-loop and closed-loop localization was found in 2 kHz pure tones. The closed-loop MAA improved from 26° to 19° with an increase in pure tone frequency from 1 to 4 kHz. This finding is in line with the physical cues available. While the starlings can only make use of interaural time difference cues at lower frequencies (e.g., 1 and 2 kHz), additional interaural level difference cues become available at higher frequencies (e.g., 4 kHz or higher, Klump and Larsen 1992). An improvement of the starling’s MAA with an increasing number of standard stimulus presentations prior to the test stimulus has important implications for determining relative (MAA) localization thresholds.     

Dynamics of Campylobacter colonization of a natural host, Sturnus vulgaris (European starling)

Wild European Starlings ( Sturnus vulgaris ) shed Campylobacter at high rates, suggesting that they may be a source of human and farm animal infection. A survey of Campylobacter shedding of 957 wild starlings was undertaken by culture of faecal specimens and genetic analysis of the campylobacters isolated: shedding rates were 30.6% for Campylobacter jejuni , 0.6% for C. coli and 6.3% for C. lari. Genotyping by multilocus sequence typing (MLST) and antigen sequence typing established that these bacteria were distinct from poultry or human disease isolates with the ST-177 and ST-682 clonal complexes possibly representing starling-adapted genotypes. There was seasonal variation in both shedding rate and genotypic diversity, both exhibiting a maximum during the late spring/early summer. Host age also affected Campylobacter shedding, which was higher in younger birds, and turnover was rapid with no evidence of cross-immunity among Campylobacter species or genotypes. In nestlings, C. jejuni shedding was evident from 9 days of age but siblings were not readily co-infected. The dynamics of Campylobacter infection of starlings differed from that observed in commercial poultry and consequently there was no evidence that wild starlings represent a major source of Campylobacter infections of food animals or humans.     

Song as an honest signal of past developmental stress in the European starling (Sturnus vulgaris)

Bird song is a sexually selected male trait where females select males on the basis of song quality. It has recently been suggested that the quality of the adult male song may be determined by nutritional stress during early development. Here, we test the 'nutritional-stress hypothesis' using the complex song of the European starling. Fledgling starlings were kept under experimental treatment (unpredictable short-term food deprivations) or control conditions (ad libitum food supply), for three months immediately after independence. We measured their physiological and immune responses during the treatment and recorded song production during the following spring. Birds in the experimental group showed increased mass during the treatment and also a significantly suppressed humoral response compared with birds in the control group. There was no difference between the groups in the cell-mediated response. Next spring, males in the experimental group spent less time singing, sang fewer song bouts, took longer to start singing and also sang significantly shorter song bouts. These data support the hypothesis that both the quality and quantity of song produced by individual birds reflect past developmental stress. The results also suggest the 'nutritional-stress hypothesis' is best considered as a more general 'developmental-stress hypothesis'.     

Lesions to the medial preoptic area affect singing in the male European starling (Sturnus vulgaris)

The aromatization of testosterone (T) in the medial preoptic nucleus (POM) is known to regulate male courtship and sexual behaviors expressed prior to, and in anticipation of, copulation. Singing in male European starlings is used to attract mates prior to physical sexual contact, suggesting that the POM might be involved. The present study was performed to examine the effects of lesions targeting the POM on singing and courtship behavior in reproductively active male starlings. A significant decrease in song output and the gathering of green nest materials was observed in males with lesions to the POM compared to males with damage to brain areas outside of the POM. Lesions did not affect a male's tendency to remain near a female or to occupy a nestbox, suggesting that the effects of POM lesions were specific to courtship behaviors. Behavioral differences were not related to testis mass or volume, and GnRH immunoreactivity was observed within the hypothalamus and median eminence for each male, suggesting that the effects of POM lesions were related specifically to POM involvement in song expression rather than to a disruption of the GnRH axis. These results suggest a general role for the POM in the expression of behaviors related to sexual arousal or anticipation, including song.     

Allozyme polymorphism and interspecific relationships in the Common starling (Sturnus vulgaris) and Spotless starling (S. unicolor) (Aves: Sturnidae)

This paper reports a genetic study of Sturnus vulgaris and S. unicolor (Sturnidae), two similar bird species which have recently become sympatric in north-eastern Spain. Seven enzyme systems (alcohol dehydrogenase, esterase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase, leucin aminopeptidase, L-lactate dehydrogenase and superoxide dismutase) were analyzed, resolving 22 presumed genetic loci with 28 alleles; 27 of them were found in both species. Gene flow was estimated to be number of migrants per generation (Nm) = 6, and genetic identities among populations were high, ranging from I = 0.96 to I = 0.99. On the whole, the results demonstrate that these Sturnus populations share a gene pool, showing slight genetic differences between the two starling speices.     

Genetic differentiation of starling (Sturnus vulgaris: Aves) populations in New Zealand and Great Britain

Several hundred starlings (Sturnus vulgaris) were introduced to New Zealand from Great Britain during1860–1880. Allozymic variation at 24 loci was analysed in winter populations sampled at six localities in each country. New Zealand samples had fewer alleles per locus but the same mean heterozygosity (3% per locus) and proportion of polymorphic loci as did British samples. Winter populations in Britain contain European migrants and were genetically homogeneous. Paradoxically, genetic distances among derived New Zealand populations, and between New Zealand and Great Britain were much greater, similar in magnitude to those observed among allopatric populations in other avian species. The geographical pattern of genetic variation in New Zealand suggests that reproductive isolation of populations and random drift have contributed to the development of population differentiation.     

Intraspecific nest parasitism in the grey starling (Sturnus cineraceus)

We studied intraspecific nest parasitism in the grey starling (Sturnus cineraceus) in 1992 and 1993. We used three criteria to detect nest parasitism: (i) the appearance of more than one egg per day while the host was laying; (ii) the appearance of extra eggs after the host completed its clutch; and (iii) the appearance of eggs which were of a different shape, size and color to other eggs in the clutch. There were 290 nests (157 nests in 1992; 133 nests in 1993) in which the clutch was completed early (clutches initiated before May 10). Twenty-nine (1992) and 32 (1993) nests contained at least one parasitic egg. Parasitic eggs hatched if they were laid during the laying period and early in the incubation period of their host, and a few of them fledged. Fledging success of parasitic eggs was not different from that of eggs in non-parasitized nests if parasitic eggs were laid during the host's laying period. However, fledging success of all parasitic eggs was fewer than that of eggs in non-parasitized nests. By comparison, fledging success of parasitized nests was not a great as that of non-parasitized nests.     

Follicular development and plasma yolk precursor dynamics through the laying cycle in the European starling (Sturnus vulgaris)

We investigated the quantitative matching of plasma yolk precursor supply (the plasma pool) to follicle demand during yolk formation in European starlings (Sturnus vulgaris). Plasma concentrations of the two yolk precursors, vitellogenin (VTG) and very low density lipoprotein (VLDL), were only elevated coincident with rapid yolk development (RYD) and matched variation in total yolky follicle mass. VTG and VLDL were low (<0.4 microg/mL and <4.2 mg/mL, respectively) in nonbreeders and prebreeders with no yolky follicles, and at clutch completion. They increased to 4.02 microg/mL and 19.4 mg/mL in birds with a full follicle hierarchy (F1-F4), and concentrations then remained high and actually increased up to the point where only a single, yolky (F1) follicle remained. However, there was some evidence for mismatching of supply and demand: (a) precursor concentrations increased throughout the laying cycle even though the number of developing follicles decreased. We suggest that this is because of a requirement to maintain a large precursor pool to maintain high uptake rates; and (b) in birds with a full follicle hierarchy, precursor concentrations were negatively correlated with total follicle mass. This suggests that high uptake rates in large follicles can actually deplete circulating precursor concentrations. Plasma concentrations of both yolk precursors increased rapidly in the early morning with (predicted) time after ovulation, consistent with a lack of fine control of precursor concentrations. However, mean plasma VTG concentrations did not differ between morning or evening samples. In contrast, plasma VLDL concentrations were lower in the morning (16.8 mg/mL) than in the evening (22.9 mg/mL). Although there is marked individual variation in plasma VTG and VLDL (four- to eightfold), both precursors were repeatable in the short term (24 h), and plasma VTG was repeatable over a 14-d interval between successive breeding attempts.