Tetranucleotide microsatellite loci from eastern bluebirds Sialia sialis

We describe primers and polymerase chain reaction (PCR) conditions to amplify 18 tetranucleotide microsatellite DNA loci in eastern bluebirds (Sialia sialis). The primers were tested using individuals from two study sites in Georgia and South Carolina. Among individuals from the Georgia population (n = 23), the primer pairs developed in this study yielded an average of 6.6 alleles per locus (range 2–12), an average observed heterozygosity of 0.56 (range 0.24–0.96) and an average polymorphic information content of 0.65 (range 0.3–0.86). Among individuals from the South Carolina population (n = 19), the primer pairs yielded an average of 5.8 alleles per locus (range 2–9), an average observed heterozygosity of 0.56 (range 0.05–0.86) and an average polymorphic information content of 0.63 (range 0.29–0.83).     

Repeatable nest defense behavior in a wild population of Eastern bluebirds (Sialia sialis) as evidence of personality

Consistent individual differences in behavior, or personality, have been demonstrated in a variety of species other than humans, including mammals, birds, and invertebrates. Behavioral consistency has been shown to affect dispersal, foraging, exploration, and antipredator responses, which may have an impact on parental and offspring survival. Despite increasing research in behavioral consistency, the repeatability of nest defense behavior has rarely been assessed in wild bird populations. Furthermore, previous studies investigating nest defense behavior have utilized laboratory studies or mounted predators to elicit defensive behavior. It is important to assess personality in wild populations to fully understand the fitness consequences of behavioral consistency across natural contexts and to utilize live predators or competitors for accurate assessment of defensive behavior. We used an ecologically relevant, live, invasive, nest site competitor, the house sparrow (Passer domesticus), to elicit nest defense behavior in a wild population of Eastern bluebirds (Sialia sialis) to determine if nest defense behavior is repeatable within and between years for males and females (males: 2009, N?=?17; 2010, N?=?18; both years, N?=?9. Females: 2009, N?=?22; 2010, N?=?15; both years, N?=?11). We also determined if individual behavior changes as a function of season, parental age, brood size, or the number of house sparrows around the nest site. We found that females demonstrated repeatable behavior both within and between years. Male nest defense behavior was only repeatable in 1 year and was influenced by season in the other year. Parental age, brood size, and the number of house sparrows around the nest site did not affect nest defense behavior. We conclude that Eastern bluebirds demonstrate consistent nest defense behavior, or personality, although males are more plastic than females.     

Structural coloration signals condition, parental investment, and circulating hormone levels in Eastern bluebirds (Sialia sialis)

Many of the brilliant plumage coloration displays of birds function as signals to conspecifics. One species in which the function of plumage ornaments has been assessed is the Eastern bluebird (Sialia sialis). Studies of a population breeding in Alabama (USA) have established that plumage ornaments signal quality, parental investment, and competitive ability in both sexes. Here we tested the additional hypotheses that (1) Eastern bluebird plumage ornamentation signals nest defense behavior in heterospecific competitive interactions and (2) individual variation in plumage ornamentation reflects underlying differences in circulating hormone levels. We also tested the potential for plumage ornaments to signal individual quality and parental investment in a population breeding in Oklahoma (USA). We found that Eastern bluebirds with more ornamented plumage are in better condition, initiate breeding earlier in the season, produce larger clutches, have higher circulating levels of the stress hormone corticosterone, and more ornamented males have lower circulating androgen levels. Plumage coloration was not related to nest defense behavior. Thus, plumage ornamentation may be used by both sexes to assess the physiological condition and parental investment of prospective mates. Experimental manipulations of circulating hormone levels during molt are needed to define the role of hormones in plumage ornamentation.     

Wall lizards combine chemical and visual cues of ambush snake predators to avoid overestimating risk inside refuges

The threat sensitivity hypothesis assumes that multiple cues from a predator should contribute in an additive way to determine the degree of risk-sensitive behaviour. The ability to use multiple cues in assessing the current level of predation risk should be especially important to prey exposed to multiple predators. Wall lizards, Podarcis muralis, respond to predatory attacks from birds or mammals by hiding inside rock crevices, where they may encounter another predator, the smooth snake, Coronella austriaca. We investigated in the laboratory whether chemical cues may be important to wall lizards for detection of snakes. The greater tongue-flick rate and shorter latency to first tongue-flick in response to predator scents indicated that lizards were able to detect the snakes' chemical cues. We also investigated the use of different predatory cues by lizards when detecting the presence of snakes within refuges. We simulated successive predator attacks and compared the propensity of lizards to enter the refuge and time spent within it for predator-free refuges, refuges containing either only visual or chemical cues of a snake, or a combination of these. The antipredatory response of lizards was greater when they were exposed to both visual and chemical cues than when only one cue was presented, supporting the threat sensitivity hypothesis. This ability may improve the accuracy of assessments of the current level of predation risk inside the refuge. It could be especially important in allowing lizards to cope with threats posed by two types of predators requiring conflicting prey defences.     

Artificial surveillance cues do not increase generosity: two meta-analyses

Many studies have seemingly demonstrated that anonymous individuals who are shown artificial cues of being watched behave as if they are being watched by real people. However, several studies have failed to replicate this surveillance cue effect. In light of these mixed results, we conducted two meta-analyses investigating the effect of artificial observation cues on generosity. Overall, our meta-analyses found no evidence to support the claim that artificial surveillance cues increase generosity, either by increasing how generous individuals are, or by increasing the probability that individuals will show any generosity at all. Therefore, surveillance cue effects should be interpreted cautiously.     

Why do Corsican Blue Tits Cyanistes caeruleus ogliastrae not use nest boxes for roosting?

We compared winter roosting behaviour of Blue Tits Cyanistes caeruleus in the mainland of southern France and on the island of Corsica in small-holed nest boxes. While in southern France Blue Tits use nest boxes for roosting, Corsican Blue Tits do not. We suggest that this behaviour is innate because Corsican wild-caught as well as F1 and F2 birds born in captivity do not use nest boxes in aviaries even when kept adjacent to mainland tits that sleep in boxes. We suggest that the cost/benefit balance differs between mainland France and Corsica: in Corsica, the costs of roosting in the canopy are less than in mainland France because (1) predators, e.g. owls, are rare in Corsica while abundant on the mainland, (2) the permanent evergreen foliage of the dominant tree in Corsica, the holm oak, could be preferred to nest boxes which are not risk-free, and (3) the costs of using cavities for roosting could be higher in Corsica because of increased mammal predator pressure and higher ectoparasite load than on the mainland.     

Nature versus nurture: Structural equation modeling indicates that parental care does not mitigate consequences of poor environmental conditions in Eastern Bluebirds (Sialia sialis)

How organisms respond to variation in environmental conditions and whether behavioral responses can mitigate negative consequences on growth, condition, and other fitness measures are critical to our ability to conserve populations in changing environments. Offspring development is affected by environmental conditions and parental care behavior. When adverse environmental conditions are present, parents may alter behaviors to mitigate the impacts of poor environmental conditions on offspring. We determined whether parental behavior (provisioning rates, attentiveness, and nest temperature) varied in relation to environmental conditions (e.g., food availability and ectoparasites) and whether parental behavior mitigated negative consequences of the environment on their offspring in Eastern Bluebirds (Sialia sialis). We found that offspring on territories with lower food availability had higher hematocrit, and when bird blow flies (Protocalliphora spp.) were present, growth rates were reduced. Parents increased provisioning and nest attendance in response to increased food availability but did not alter behavior in response to parasitism by blow flies. While parents altered behavior in response to resource availability, parents were unable to override the direct effects of negative environmental conditions on offspring growth and hematocrit. Our work highlights the importance of the environment on offspring development and suggests that parents may not be able to sufficiently alter behavior to ameliorate challenging environmental conditions.     

Insular tammar wallabies (Macropus eugenii) respond to visual but not acoustic cues from predators

We studied the way in which a population of tammar wallabies(Macropus eugenii), which have been isolated from mammalianpredators since the last ice age, responded to the sight andsound of historical and ontogenetically and evolutionarilynovel predators. Tammars were shown a range of visual stimuli,including taxidermic mounts of two evolutionarily novel predators,a red fox (Vulpes vulpes) and a cat (Felis catus), and a modelof an extinct predator, the thylacine (Thylacinus cynocephalus).Controls were a conspecific, the cart on which all mounts werepresented, and blank trials in which spontaneous change in behaviorwas measured. We played back recorded sounds to characterizeresponses to acoustic cues from predators and to a putativeconspecific antipredator signal. Treatments included the howlsof dingoes (Canis lupus dingo), an evolutionarily novel predator;calls of a wedge-tailed eagle (Aquila audax), a historicaland current predator; and wallaby foot thumps. Controls werethe song of an Australian magpie (Gymnorhina tibicen) and ablank trial. After seeing a fox, wallabies thumped their hindfeet in alarm, suppressed foraging, and increased looking.The sight of a cat similarly suppressed foraging and increasedlooking. The sounds of predators did not influence responsiveness,but wallabies foraged less and looked more after thump playbacks.Our results suggest that tammars respond to the sight, butnot the sounds, of predators. In contrast, the response to footthumps demonstrates that this particular sound functions asan antipredator signal. We suggest that responsiveness to visualcues has been preserved under relaxed selection because predatormorphology is convergent, but vocalizations are not.     

Juvenile western toads, Bufo boreas, avoid chemical cues of snakes fed juvenile, but not larval, conspecifics

Previous investigations have demonstrated the importance of predator diet in chemically mediated antipredator behaviour. However, there are few data on responses to life-stage-specific predator diets, which could be important for animals like amphibians that undergo metamorphosis and must respond to different suites of predators at different life-history stages. In laboratory choice tests, we investigated the chemically mediated avoidance response of juvenile western toads, Bufo boreas, to four different chemical stimuli: (1) live conspecific juveniles; (2) live earthworms; (3) snakes fed juvenile conspecifics; and (4) snakes fed larval conspecifics (tadpoles). Juvenile toads avoided chemical cues from snakes that had eaten juvenile conspecifics, but did not respond to the other three stimuli, including chemical cues from snakes fed larval conspecifics. In addition, the response to cues from snakes fed juveniles differed significantly from that of snakes fed larvae. To our knowledge, this is the first study to demonstrate the importance of diet in predator avoidance of juvenile anurans and the ability of juvenile toads to distinguish between chemical cues from predators that have consumed larval versus juvenile conspecifics. Copyright 2000 The Association for the Study of Animal Behaviour.     

Timing an ontogenetic niche shift: responses of emerging salmon alevins to chemical cues from predators and competitors

Ontogenetic niche shifts are ubiquitous in nature. However, in most species little is known about phenotypic plasticity in the timing of shifts and in the associated characters. Following a period of endogenous feeding on yolk, salmonid alevins emerge from their gravel nests into the open water and start feeding exogenously. We studied, by using replicated artificial nests, whether the responses of emerging Atlantic salmon ( Salmo salar ) alevins to chemical cues from two piscivorous fish predators and conspecific competitors are plastic. We hypothesised that the alevins should delay emergence in response to predator cues, whereas cues from competitors should induce earlier emergence. We found that chemical cues from predatory burbot ( Lota lota ) delayed emergence, whereas cues from brown trout ( S. trutta ) tended to induce earlier emergence. The earlier emergence in response to trout cues was associated with a smaller body size and more yolk resources remaining at emergence, but burbot cues did not alter these traits. Predator cues also influenced the daily pattern of emergence: more alevins emerged during the morning in the burbot treatment, and fewer alevins emerged during the afternoon in the trout treatment. Chemical cues from conspecific competitors had no effect on emergence patterns. The results indicate that salmon alevins exhibit flexible ontogenetic niche shifts in the timing of emergence in response to predator cues, and that the responses are predator-specific. As timing of emergence is a major determinant of territory acquisition, these responses are likely to have an impact on later fitness of the fry.     

Blackcap Sylvia atricapilla nestlings do not produce begging calls until they are able to escape from predators

Nest predation is a major source of reproductive failure in birds and thus it can exert selection on both parental and offspring strategies. Begging calls are known to be a powerful component of parent–offspring communication but these calls can also increase predation risk. Here we demonstrate a sophisticated strategy for the development of begging vocalization in a species under high nest predation. Blackcap Sylvia atricapilla nestlings spend most of their nesting period silent, and develop begging calls just before they are able to fledge. The onset of begging vocalization matches the onset of endothermy, which enables Blackcap chicks to leave the nest. We demonstrate experimentally that begging calls function as a signal of the increased needs of homeothermic nestlings. Playback of begging calls conducted in nests with silent nestlings resulted in a significant increase in feeding rates and a decrease in brooding. Development of begging calls only at the age of endothermy allows species under high nest predation to keep the risky period of begging vocalizations and frequent feeding to a minimum. This strategy may constitute an evolutionary solution to high predation pressure in some open nesting passerines. This is the first study to demonstrate the existence of silent begging in a passerine.     

Tadpoles of three common anuran species from Thailand do not prey on mosquito larvae

Tadpoles are often considered to be predators of mosquito larvae and are therefore beneficial for the control of certain disease vectors. Nevertheless, only a few species have actually been recorded to prey on mosquito larvae. The mosquito larvae predation rates of tadpoles of three common Thai anuran species (Bufo melanostictus, Kaloula pulchra and Hylarana raniceps) were experimentally tested. Tadpoles in varying developmental stages were used to assess a size/age effect on the predation rate. In addition, different instars of Culex quinquefasciatus were used in order to assess a prey size effect on the predation rates. All three species failed to show any evidence of mosquito larvae predation. Neither small nor large tadpoles fed on mosquito larvae. Prey size also did not affect predation. Although tadpoles do not feed on mosquito larvae, there may be other direct or indirect inter‐specific interactions that adversely impact the development of larvae in shared habitats with tadpoles.     

The widespread declines of songbirds in rural Britain do not correlate with the spread of their avian predators

During the last 30 years, there have been marked declines in the populations of many British songbirds breeding on farmland, while two of their main predators, sparrowhawk (Accipiter nisus) and magpie (Pica pica), have spread back into areas from which they had disappeared. The causes of the songbird declines remain unclear but given the coincidence in timing, it might appear that increased predation could be responsible. Although many studies have failed to find links between changes in the populations of breeding songbirds and mortality from avian predators, previous work has, with few exceptions, involved only short-term studies on small spatial scales. Here we use large-scale, long-term data from a national bird census scheme to examine whether magpies and sparrowhawks could have depressed the rates of year-to-year population change in 23 songbird species. Our results indicate that magpies and sparrowhawks are unlikely to have caused the songbird declines because patterns of year-to-year population change did not differ between sites with and without these predators.     

Male tree weta are attracted to cuticular scent cues but do not discriminate according to sex or among two closely related species

Recognition of conspecifics is an essential precursor of successful mating. Where related species coexist, species discrimination might be important, but because related species are similar, species signal recognition may actually be low. Chemical cues such as cuticular hydrocarbons (CHCs) are frequently used by insects to identify suitable sexual partners. We predicted that New Zealand tree weta (Hemideina spp.), a genus of nocturnal ensiferan Orthoptera that live both allopatrically and sympatrically, use chemical signals from either frass or CHCs to find mates. In a series of six laboratory trials using both H. thoracica and H. crassidens, we found that male tree weta, but not female tree weta, occupied cavities primed with female cuticular cues more often than cavities without. However, males did not discriminate between chemical cues of male and female conspecifics, or between conspecifics and heterospecifics. In field trials, tree weta did not occupy artificial cavities primed with either female frass or female cuticular cues more often than unscented cavities. However, in both trials weta preferentially returned to cavities that had already been occupied earlier in the trials. A final field trial confirmed the presence of mixed species harems during the mating season in one region of sympatry. Our results suggest that selection on sex and species specific chemical cues that could be used to find conspecific mates is weak. Mixed species aggregations suggest that identification of conspecific mating cues has not evolved to be species specific. We infer that for male tree weta, the cost of mating with heterospecifics is likely less than not mating at all.     

Crows and common ravens do not reciprocally exchange tokens with a conspecific to gain food rewards

Human economic transactions are based on complex forms of reciprocity, which involve the capacities to share and to keep track of what was given and received over time. Animals too engage in reciprocal interactions, but mechanisms such as calculated reciprocity have only been shown experimentally in few species. Various forms of cooperation, for example food and information sharing, are frequently observed in corvids, and they can engage in exchange interactions with human experimenters and accept delayed rewards. Here, we tested whether crows and common ravens would reciprocally exchange tokens with a conspecific in an exchange task. Birds received a set of three different types of tokens, some valuable for themselves, that is, they could exchange them for a food reward with a human experimenter, some valuable for their partner and some without value. The valuable tokens differed between the birds, which means that each bird could obtain more self-value tokens from their partner's compartment. We did not observe any active transfers, that is one individual giving a token to the experimental partner by placing it in its beak. We only observed 6 indirect transfers, that is one individual transferring a token into the compartment of the partner (3 no-value, 1 partner-value and 2 self-value tokens) and 67 “passive” transfers, that is one subject taking the token lying in reach in the compartment of the partner. Individuals took significantly more self-value tokens compared with no-value and partner-value tokens. This indicates a preference for tokens valuable to focal individuals. Significantly more no-value tokens compared with partner-value tokens were taken, likely to be caused by experimental partners exchanging self-value tokens with the human experimenter, and therefore, more no-value tokens being available in the compartment. Our results presently do not provide empirical support for reciprocity in crows and ravens, most likely caused by them not understanding the potential roles of receiver and donor. We therefore suggest further empirical tests of calculated reciprocity to be necessary in corvids.