Intraspecific nest parasitism in Starlings Sturnus vulgaris: effects of disturbance on laying females

Female Starlings Sturnus vulgaris that laid distinctive eggs at Worplesdon, Surrey, in 1988 and 1989 were made to desert their partially completed first clutches by removing their eggs part way through the laying sequence. Most of these Starlings continued to lay, but in other Starlings' nests, and most of them subsequently laid a replacement clutch that they reared themselves. Using estimates of the success of nests in the colony over 14 breeding seasons, it is concluded that intraspecific nest parasitism offers a means of maximizing annual chick production in the event of disturbance causing the loss of first-clutch eggs.     

Effects of dietary quality on basal metabolic rate and internal morphology of European starlings (Sturnus vulgaris)

European starlings (Sturnus vulgaris) were fed either a low- or high-quality diet to test the effects of dietary quality on basal metabolic rate (BMR) and internal morphology. Basal metabolic rate did not differ significantly between the two dietary groups, but internal morphology differed greatly. Starlings fed the low-quality diet had heavier gastrointestinal tracts, gizzards, and livers. Starlings fed the high-quality diet had heavier breast muscles. Starlings on the low-quality diet maintained mass, while starlings on the high-quality diet gained mass. Dry matter digestibility and energy digestibility were lower for starlings fed the low-quality diet, and their food and water intake were greater than starlings on the high-quality diet. The lack of dietary effect on BMR may be the result of increased energy expenditure of digestive organs paralleling a reduction of energy expenditure of organs and tissues not related to digestion (i.e., skeletal muscle). This trade-off in energy allocation among organs suggests a mechanism by which organisms may alter BMR in response to a change in seasonal variation in food availability.     

The relationship between introduced European Starlings and the reproductive activities of Mountain Bluebirds and Tree Swallows in British Columbia,Canada

The European Starling Sturnus vulgaris is an introduced species in North America and is an aggressive competitor for tree cavity nest‐sites. Starlings are commonly considered to influence nest‐site selection and reproductive success of native cavity‐nesting species negatively. We examined the relationship between Starling nest density and the fecundity of two native secondary cavity‐using passerines, Mountain Bluebird Sialia currucoides and Tree Swallow Tachycineta bicolor. We monitored a total of 622 nests (approximately equal numbers for each of the three species) in woodpecker‐excavated and naturally occurring cavities in 29 small forest groves in central British Columbia, Canada, between 2000 and 2009. The dimensions of cavities used and the timing of nest initiation overlapped for all species, although Starlings initiated clutches earliest. Mixed‐effects models were used to assess whether nest abundance, clutch size or nest success were affected directly by Starling nest abundance, or indirectly via a shift in cavity selection or timing of breeding. Starlings and Mountain Bluebirds showed inverse trends in nest abundance. Mountain Bluebird clutch sizes were smaller if they were initiated later in the breeding season. There was weak evidence that Tree Swallow clutch size decreased with cavity depth when Starling nests were abundant, and increased with cavity depth where there were few Starling nests. We conclude that despite the aggressive nature of this exotic cavity‐nester, the influence of Starlings on native secondary cavity‐nesting passerines is modest where cavities are abundant.     

European starlings recognize the location of robotic conspecific attention

Looking where others are allocating attention can facilitate social interactions by providing information about objects or locations of interest. We asked whether European starlings follow the orientation behaviour of conspecifics owing to their highly gregarious behaviour. Starlings reoriented their attention to follow that of a robot around a barrier more often than when the robot''s attention was directed elsewhere. This is the first empirical evidence of reorienting in response to conspecific attention in a songbird. Starlings may use this behaviour to obtain fine-tuned spatial information from conspecifics (e.g. direction of predator approach, spatial location of food patches), enhancing group cohesion.     

The effect of sward height and drainage on Common Starlings Sturnus vulgaris and Northern Lapwings Vanellus vanellus foraging in grassland habitats

Agricultural change is often cited as a causal factor in the decline of the UK's farmland birds because bird declines have mirrored changes in agricultural practices. Although much is known about the mechanisms driving population declines on arable systems, mechanisms in grassland systems are relatively poorly studied, despite receiving a similar degree of intensification. Agricultural intensification may affect bird declines by reducing food abundance or accessibility, forager mobility or predation risk. Here we examine experimentally the effects of sward height on the foraging behaviour of adult Common Starlings Sturnus vulgaris , and the effects of sward height and drainage on the behaviour of Northern Lapwing Vanellus vanellus chicks. Both species are declining across the UK and both forage in farmed grassland habitats, but they differ in their foraging methods because Starlings probe for soil invertebrates whereas Lapwing chicks glean prey from surfaces. Overall, after controlling for prey abundance, short swards were found to be more productive for both species. Prey capture rate within foraging bouts did not differ with sward height for Starlings, but Starlings spent more time foraging on short swards and captured 33.2% more prey. Starlings walked more steps on short swards. Lapwing chick foraging rates declined as sward height increased. Soil moisture was not found to be a predictor of Lapwing chick foraging rates within the observed range. Our results suggest that short swards are a more profitable foraging habitat for soil and surface invertebrate feeders. Short swards may facilitate surface prey detection, improve forager mobility and increase foraging time by altering vigilance patterns. Provision of short swards in areas where these are lacking could be simple method of improving foraging habitats for grassland birds.     

The effect of a period of food restriction on gonad size and moult of male and female Starlings Sturnus vulgaris under constant photoperiod

The effects of food availability on the reproductive cycle and on the timing and duration of moult were investigated in first-year male and female Starlings Sturnus vulgaris under a constant photoperiod of 12 hours. A 20% lower body mass during the first 9 weeks of restricted feeding had a slight negative effect on testicular growth during the first 3 weeks of the experiment and delayed the onset of moult for 12 days after the return to ad libitum feeding conditions. No effects were found on changes of beak colour and moult duration of males. Females exposed to the shorter feeding time similarly showed a reduced body mass (21%) but compared with controls, did not differ in beak colour, in follicle growth, or in the onset and duration of moult. In contrast to males, body mass of the experimental females after the food restriction period remained lower for more than 6 weeks, compared to control birds. Females had a longer reproductive cycle and started moult later than males. The later an individual started to moult, the faster it moulted. Two females started to moult extremely late and did not moult their first primaries.
These results indicate that in male Starlings food restriction slightly affected the rate of photoinduced gonadal growth and the onset of postnuptial moult. These effects were not observed in females subjected to the same experimental conditions.     

Comparison of germination rates and fruit traits of indigenous Solanum giganteum and invasive Solanum mauritianum in South Africa

There is a global threat of invasive alien plants to biodiversity and ecosystem services. Of these, fleshy-fruited species are credited as some of the worst invaders and this is largely due to their mutualisms with local dispersers. Comparative studies between invasive and indigenous species can shed new insights into the traits which promote invasive plants success over their indigenous counterparts. This study compared the germination success of indigenous Solanum giganteum and invasive Solanum mauritianum, following ingestion by Red-winged Starlings (Onychognathus morio, Sturnidae) and Speckled Mousebirds (Colius striatus, Coliidae) and compared these with de-pulped seed and whole fruit controls. Nutritive and morphological fruit traits were also considered. Seed retention times were only obtained for Red-winged Starlings on both diets, and these did not differ. For both plant species, ingested and de-pulped seeds had similar germination success and mean daily germination, irrespective of frugivore type. However, pulp removal was important for S. giganteum. The type of avian frugivore affected the onset of germination, with the comparatively larger Red-winged Starlings promoting earlier germination of both S. mauritianum and S. giganteum seeds when compared to their controls, except for de-pulped S. mauritianum. These germinated at the same time as ingested S. mauritianum, but significantly earlier than de-pulped S. giganteum. Speckled Mousebirds consumed more S. mauritianum than S. giganteum, while Red-winged Starlings showed the opposite. While S. mauritianum had larger yellow fruits, their seeds were smaller, lighter and more numerous than those in the red fruits of S. giganteum. Furthermore, S. mauritianum fruits contained considerably more sugar content than S. giganteum fruits. In summary, offering greater nutritional rewards and generating greater reproductive outputs than indigenous species, can explain why fleshy-fruited exotics become highly invasive.     

Diet of Starling Sturnus vulgaris nestlings on farmland: the importance of Tipulidae larvae

Capsule?Tipulidae larvae are a key resource for adult Starlings provisioning their young on lowland farmland.

Aims?(i) To describe Starling nestling diet on lowland farmland. (ii) To examine the effects of brood size variation and nestling age on Starling parental food provisioning.

Methods?Over 4 years, we observed parental food provisioning at 42 nests across 4 sites on lowland farmland in Oxfordshire, UK using nestbox video recorders.

Results?Tipulidae larvae were the most frequent prey item recorded in provisioning loads (52%), the next most frequent were winged insects (11%), then Coleoptera larvae (6%), Lepidoptera larvae (5%) and Lumbricidae (5%), with 21% of prey unidentified. Estimates of prey lengths, dry mass and total energy content also confirmed that Tipulidae larvae were the key prey source. Generalized linear mixed-effects models showed that larger broods received fewer Tipulidae larvae per nestling per day and that the proportion of Tipulidae larvae in the diet did not vary with brood size or nestling age.

Conclusion?Our results support the idea that Tipulidae larvae are the primary dietary item for nestling Starlings on lowland farmland.     

THE AFRICAN SKIMMER RHYNCHOPS FLAVIROSTRIS: POPULATION COUNTS AND BREEDING IN THE NSEFU GAME RESERVE

Craig, A. J. F. K., Hulley, P. E. &; Walter, G. H. 1989. Nesting of sympatric Redwinged and Pale-winged Starlings. Ostrich 60:69-74.

Observations were made over four breeding seasons at Cradock, South Africa, where Redwinged Starlings Onychognathus morio and Palewinged Starlings O. nabouroup nest on the same cliffs. Nests were not accessible, and the stage of breeding was determined by the behaviour of the birds. Both species reuse the same nest sites, and only the females incubate, but both sexes feed the young. The timing of breedingMaybe more variable in the Palewinged Starling. A review of the available data on nest site selection and nest construction shows apparent species-specific differences: Redwinged Starlings usually nest on ledges, often on buildings, and use mud in the nest base; Palewinged Starlings favour vertical crevices, and do not use mud.     

A general framework for understanding the effects of variability and interruptions on foraging behaviour

A general framework for analysing the effects of variability and the effects of interruptions on foraging is presented. The animal is characterised by its level of energetic reserves, x. We consider behaviour over a period of time [0,T]. A terminal reward function R(x) determines the expected future reproductive success of an animal with reserves x at time T. For any state x at a time in the period, we give the animal a choice between various options and then constrain it to follow a background strategy. The best option is the one that maximizes expected future reproductive success. Using this framework, we show that sensitivity to variability in amount of energy gained is logically distinct from sensitivity to variability in the time at which food is obtained. We also show that incorporating interruptions results in both a preference for variability in time and a preference for a reward followed by a delay as opposed to the same delay before the reward.     

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.     

Subtle cues of predation risk: starlings respond to a predator's direction of eye-gaze

For prey animals to negotiate successfully the fundamental trade-off between predation and starvation, a realistic assessment of predation risk is vital. Prey responses to conspicuous indicators of risk (such as looming predators or fleeing conspecifics) are well documented, but there should also be strong selection for the detection of more subtle cues. A predator's head orientation and eye-gaze direction are good candidates for subtle but useful indicators of risk, since many predators orient their head and eyes towards their prey as they attack. We describe the first explicit demonstration of a bird responding to a live predator's eye-gaze direction. We present wild-caught European starlings (Sturnus vulgaris) with human 'predators' whose frontal appearance and gaze direction are manipulated independently, and show that starlings are sensitive to the predator's orientation, the presence of eyes and the direction of eye-gaze. Starlings respond in a functionally significant manner: when the predator's gaze was averted, starlings resumed feeding earlier, at a higher rate and consumed more food overall. By correctly assessing lower risk and returning to feeding activity earlier (as in this study), the animal gains a competitive advantage over conspecifics that do not respond to the subtle predator cue in this way.     

栗喉蜂虎捕食差异

2010年4～5月和2011年4～6月,用焦点动物取样法对云南省保山市潞江镇怒江河谷栗喉蜂虎捕食差异进行了观察。对栗喉蜂虎雌性成年鸟、雄性成年鸟、青年鸟捕食种类、数量、成功率、食物组成、食物资源量、处理食物成功率及处理时间进行了统计。结果表明,栗喉蜂虎捕食种类包括7类昆虫,以膜翅目Hymenoptera、蜻蜓目Odonate、鳞翅目Lepidoptera昆虫为主;成年雄鸟捕食频次高于成年雌鸟和青年鸟;成年鸟与青年鸟处理食物成功率无显著差异,但二者捕食成功率和处理食物时间差异显著。     

Is the distribution of Starlings Sturnus vulgaris within roosts determined by competition?

Observations were made in five aviaries to determine the role of competition in roost site selection by captive Starlings Sturnus vulgaris. Their behaviour in selecting perches in a simple roost "tree" indicated that (1) a dominance hierarchy exists in birds selecting roosting locations, (2) the roost positions occupied are determined through competition, (3) higher and inner roost positions are preferred over others and (4) dominant Starlings tend to occupy these most preferred positions.     

An evolutionarily stable strategy for aggressiveness in feeding groups

Animals searching for food in groups display highly variabledegrees of aggressiveness. In this paper I present an individual-basedgame theoretical model of how gregarious animals should adjusttheir level of aggressiveness to their environmental conditions.In accordance with behavioral observations, the predicted levelof aggressiveness increases progressively with decreasing foodavailability and increasing animal density. The proposed modelalso predicts a positive influence of food energy value andhandling time on the level of aggressiveness within the group.In addition, the model provides information about the influenceof aggressive behavior on individual foraging success, interference,and population dynamics. Adaptive behavioral rules for aggressivenessin consumers are predicted to respond to both competitors and food density in a way that contributes to stabilization of thedynamics of population systems.     

Habitat affects escape behaviour and alarm calling in Common Starlings Sturnus vulgaris

Animals should adapt their escape behaviour to both physical and social surroundings in order to maximize their probability of survival. Cover can be both obstructive, reducing the visibility of the surroundings and hindering escape, and protective, providing refuge. We investigated how the provision of cover (long grass) affected (1) the escape behaviour and (2) the alarm call behaviour of Common Starlings Sturnus vulgaris responding to a model hawk during a simulated attack. Starlings always retreated away from the predator and sometimes alarm-called. Their escape trajectory was close to the ground when escaping in long grass, which could be explained by either tall swards hindering take-off or such swards being used as protective cover. On short grass their escape trajectory was much steeper (> 45°). We also investigated the use of alarm calls in Starlings according to predictions arising from the costs and benefits to callers and receivers. Callers could benefit from using alarm calls through dilution or confusion if their use initiates flock departures, thus reducing their probability of being targeted. If there is no cost to the producer of alarm calls we predicted that detectors should call at all times to gain these benefits (i.e. irrespective of grass length), but if their use is costly we predicted that they would be used only when the benefits outstrip the costs. In this case we would predict that alarm calls would be given when other (visual) signals were impaired on long grass but not when they were effective on short grass. Starlings used alarm calls on long grass when visibility was reduced more frequently than on short grass, suggesting that calling has a cost to the producer. The contrasting escape strategies of Starlings in relation to a relatively small (10 cm) change in grass height demonstrates the potential importance of habitat structure in determining predation risk.     

Seasonal effects on metabolism and thermoregulation abilities of the Red-winged Starling (Onychognathus morio)

Basal metabolic rate (BMR) of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, and in particular changes in ambient temperatures (T_a). Southern Africa is characterized by an unpredictable environment with daily and seasonal variation. This study sought to evaluate the effects of seasonal changes in T_a on mass-specific resting metabolic rate (RMR), BMR and body temperature (T_b) of Red-winged Starlings (Onychognathus morio). They have a broad distribution, from Ethiopia to the Cape in South Africa and are medium-sized frugivorous birds. Metabolic rate (VO₂) and T_b were measured in wild caught Red-winged Starlings after a period of summer and winter acclimatization in outdoor aviaries. RMR and BMR were significantly higher in winter than summer. Body mass of Starlings was significantly higher in winter compared with summer. The increased RMR and BMR in winter indicate improved ability to cope with cold and maintenance of a high T_b. These results show that the metabolism of Red-winged Starlings are not constant, but exhibit a pronounced seasonal phenotypic flexibility with maintenance of a high T_b.     

铜和镉胁迫对海洋青鳉摄食行为的影响

以海洋青鳉(Oryzias melastigma)为试验动物, 分析了铜和镉两种重金属离子胁迫对海洋青鳉摄食行为特征的影响, 包括摄食响应时间、摄食量、摄食成功率和摄食效率等参数。结果显示, 随着Cu2+浓度的升高, 开始时, 海洋青鳉的摄食量有所升高, 当Cu2+浓度达到0.087 mg/L时有最大的摄食量和最短的摄食响应时间。随后, 摄食量出现下降, 在0.174 mg/L时达到最低。低浓度的Cu2+还能提高海洋青鳉的摄食成功率和摄食效率, 而Cu2+的高浓度和长时间暴露则降低海洋青鳉的摄食成功率和摄食效率。Cd2+对海洋青鳉的摄食行为具有明显的抑制效应, Cd2+抑制海洋青鳉摄食的最低可见效应浓度为 0.65 mg/L, 摄食量、摄食成功率和摄食效率均随着Cd2+浓度的升高而降低。此外, 在Cu2+和Cd2+胁迫下, 对食物的响应时间有性别差异, 雌性显著短于雄性, 还存在群体显著短于个体等现象。     

Distribution and dispersal in populations capable of resource depletion

Summary A simulation model has been used to investigate the influence of animal (insect) distribution and dispersal among exhaustable resource units (food plants). Population size and stability were used as measures of success. The results showed that population size and stability are highest when egg batch size is as large as can be supported by the average food plant or slightly larger if larval dispersal occurs. Clumping of egg batches of food plants increases population stability when egg batches are small by insuring that some food plants will not be overcrowded. Increasing the proportion of larval dispersers or the success of dispersers can increase or decrease population size and stability depending on the original egg batch distribution, but individuals which produce offspring some of which disperse, generally have a selective advantage. Density dependent larval dispersal decreases population stability. Finally, individuals with lower reproductive capacities can have a selective advantage over those with higher reproductive capacities under certain conditions of egg batch size and larval dispersal.     

Usefulness of multiple chalk‐based food colorings for inducing better gene silencing by feeding RNA interference in planarians

Planarians have become widely recognized as one of the major animal models for regeneration studies in invertebrates. To induce RNA interference (RNAi) by feeding in planarians, the widely accepted protocol is one in which animals undergo two or three feedings of food containing double‐stranded RNA (dsRNA) plus visible food coloring (e.g., blood) for confirmation of feeding by individual animals. However, one possible problem is that incorporated food coloring is often retained within the gut for several days, which makes it difficult to confirm the success of each round of dsRNA feeding based on the difference of the color density within the gut before and after feeding. As a consequence, the difference of appetite levels among individuals undergoing dsRNA feeding leads to phenotypic variability among them due to insufficient knockdown. In our attempts to overcome this problem, we have developed a novel method for achieving robust confirmation of the success of dsRNA feeding in individuals fed multiple times by means of including a combination of three different colored chalks (pink, yellow and blue) as food coloring. Notably, we found that this method is superior to the conventional method for positively marking individuals that actively consumed the dsRNA‐containing food during four times of once‐daily feeding. Using these selected animals, we obtained stable and sufficiently strong RNAi‐induced phenotypes. We termed this improved multi‐colored chalk‐spiked method of feeding RNAi “Candi” and propose its benefits for gene function analysis in planarians.