Offspring retention in the Siberian jay {Perisoreus infaustus): the prolonged brood care hypothesis

We examined aggressive behavior in Siberian jay groups containingboth retained offspring and immigrant juveniles during winterfeeding and during breeding. Selective tolerance of retainedoffspring by parental birds in winter suggests that cooperationevolved through kin selection. Parents exhibited a self-restraintin aggression towards retained offspring at food in winter.Comparatively, nonkin immigrants were aggressively preventedfrom sharing food by the local pair. Parental tolerance in wintercould bring inclusive fitness gains through the direct kin componentif retained offspring experience relaxed competition and enhancedsurvival. Parental tolerance would then favor the evolutionof delayed dispersal. There is no evidence that delayed dispersalamong Siberian jays should have evolved because of indirectfitness benefits to retained offspring from helping to raiseyounger siblings. Offspring retained by parents did not participatein incubation, feeding or nest defense.     

Premating Behavior in the Subgenus Limia (Pisces: Poeciliidae): Sexual Selection and the Evolution of Courtship

A three-year field-study of Richardson's ground squirrels was conducted to assess whether alarm calling functions to warn close relatives (“kin selection” hypothesis) or manipulate conspecifics (a “selfish” hypothesis). S. richardsonii had distinct calls for terrestrial and aerial predators, and the responses of squirrels varied appropriately according to the context of calls, implying that calling conveyed correct information concerning the nature of the danger. Alarm calling elicited by naturally occurring encounters with potential predators during 454 h of observation, and by a thrown frisbee in 70 experimental trials, was not equally probable for all age/sex classes. Squirrels were most likely to call when they had offspring or siblings nearby, which is supportive of the hypothesis that alarm calling is maintained by kin selection. Adult males, residing in the vicinity of either their probable progeny or their nonlittermate half-siblings, were the most likely age/sex class to call during the lactation period when young were below ground and were most vulnerable. I conclude that alarm calling by Richardson's ground squirrels is nepotistic rather than manipulative.     

Parental nepotism enhances survival of retained offspring in the Siberian jay

The evolutionary payoff accruing to parents from breeding offspringcould be an incentive for prolonged investments in the offspring.Enhanced survival for offspring as a result of such a prolongedparental investment would increase the value of remaining inthe natal territory for the offspring. Here we show that first-yearsurvival in Siberian jays is higher in the company of theirparents. Two observations point to that the enhanced survivalof retained offspring is due to nepotistic parents rather thanto the quality of a shared habitat. First, winter survivalis higher only for those retained offspring whose parents havesurvived too ; this precludes the possibility that the linkbetween timing of dispersal and survival should reflect a higher phenotypic quality of retained offspring in general. Second,there is no support for the more parsimonious explanation thatthis link between the survival of parents and retained offspringreflects habitat quality of a shared territory. We could, withhigh statistical power, reject the possibility of a correlationbetween the survival of parental birds and unrelated immigrantsto the territory. Such a correlation would have been expectedif survival reflected habitat quality and not kinship. Our data instead suggest a direct fitness gain to retained offspringin enhanced survival through parental nepotism (parental facilitation).The behavior of parents in allowing retained offspring accessto food that is denied to immigrants is one proximate mechanismmediating a benefit of delayed dispersal.     

Distress Calls of Birds in a Neotropical Cloud Forest1

Distress calls are loud, harsh calls given by some species of birds when they are captured by a predator or handled by humans. We recorded the frequency of distress calls and struggling behavior in 40 species of birds captured in mist nets during the dry season in a Costa Rica cloud forest. We tested the following hypotheses proposed to explain the function of distress calls: (1) calling for help from kin or reciprocal altruists; (2) warning kin; (3) eliciting mobbing behavior; (4) startling the predator; and (5) distracting the predator through attraction of additional predators. Our results did not support the calling‐for‐help, warning kin, or mobbing hypotheses. Indeed, genera that regularly occurred with kin or in flocks were not more likely to call than non‐flocking genera. There was no relationship between calling frequency and struggling behavior as predicted by the predator startle hypothesis. Genera of larger birds tended to call more than smaller birds, providing some support for both the predator distraction hypothesis and predator startle hypotheses. Calls of higher amplitude may be more effective in startling the predator. Distress calls of larger birds may also travel greater distances than those of smaller birds, supporting the predator manipulation hypothesis, but this requires further testing.     

Vocal and Escape Responses of Columbian Ground Squirrels to Simulated Terrestrial and Aerial Predator Attacks

Most ground-dwelling sciurids emit nonrepetitive and repetitive calls in response to predators. In this study, I simulated terrestrial (badger Taxidea taxus) and aerial (flying disc) predator attacks to elicit escape and vocal responses in Columbian ground squirrels (Spermophilus columbianus). In response to the badger, ground squirrels often ran, but rarely to a burrow, and were most likely to give nonrepetitive calls before running or without running; rarely did they enter burrows. Ground squirrels in direct line of the flying disc (i.e., “target” squirrels under “attack”), ran to, and into, the nearest escape burrow and rarely gave a nonrepetitive call. Squirrels distant from the flying disc often called, usually while running or after assuming an upright posture at the nearest burrow. These results suggest that ground squirrels incur little cost when calling in response to aerial predators. Nonrepetitive and repetitive calling in response to the badger and flying disc did not differ significantly among age-sex classes; however, parous females were more likely than nonparous females to give both types of calls in response to the badger. Nonparous females either with or without close nondescendant kin rarely called in response to the badger. Thus, there was no indication that females exposed to the badger behaved nepotistically toward close kin other than their juvenile offspring. Nonrepetitive calling in response to the badger apparently functions primarily to warn vulnerable offspring and, hence, is a component of maternal investment. Although the occurrence of antipredator calling in response to the flying disc did not vary significantly among parity-kin classes, there was evidence that adult and yearling females were more likely to emit repetitive, and to a lesser extent, nonrepetitive calls, if close nondescendant kin were in the colony. I conclude that indirect fitness benefits, that is, kin selection, probably contributes to the maintenance of antipredator calling in response to aerial predators.     

The evolution of vocal alarm communication in rodents

On encountering a predator, many species emit potentially riskyvocalizations known as alarm calls. We evaluated the relativeimportance of two adaptive hypotheses on the evolution of calling:(1) communicating to predators, which may function by deterringpursuit and hence increasing individual survival, and (2) analternative nepotistic hypothesis for alarm calling wherebycallers obtain direct and indirect fitness by warning relatives.Focusing on 209 species of rodents, we found significant associationsbetween diurnality and alarm calling, living socially and alarmcalling, and diurnality and sociality. Diurnality, however,accounted for nearly three times as much variation in whetheror not a species alarm called than did sociality. Phylogenetictests revealed that the evolution of diurnality preceded theevolution of alarm calling, and that the evolutions of diurnalityand sociality were unrelated. Our results are consistent withthe hypothesis that alarm communication evolved to communicateto predators. If so, then nepotistic benefits, although importantfor the maintenance of alarm calling in some rodents, may berelatively less important in its evolution.     

Alarm calls of the Southern House Wren Troglodytes musculus: variation with nesting stage and predator model

Alarm calls given by parents when risk is detected during nesting may be considered a form of parental defense. We analyzed variations in callings of breeding pairs of the Southern House Wren Troglodytes musculus during the nesting cycle and when faced with different predator models. Nesting birds were exposed to stuffed models at different nesting stages (early and late during incubation, and nests with younger and older nestlings). Nests were also exposed to different predator models where the calling response of breeding adults and acoustic structure variations of the calls were analyzed. The presence of a predator model increased the parents’ alarm calls along the nesting stage. This result supports the hypothesis that the higher the nest reproductive value, the higher the nest defense performed by the Southern House Wren. However, it also supports the notion that alarm calls could be used by parents to silence nestlings and reduce their detectability. Alarm calls also varied according to the predator model presented. We suggest that alarm calls variations of Southern House Wrens could encode information about the kind of predator and the risk envisaged through variations of call rates.     

The consequences of crowned eagle central-place foraging on predation risk in monkeys

The African crowned eagle (Stepahnoaetus coronatus) is the primary predator for arboreal primates throughout sub-Saharan forests. Monkeys typically respond with alarm calls when they are aware of the presence of crowned eagles and such calls can be considered a corollary of predation risk within primate groups. Alarm calls from six species of monkeys were recorded across the home range of an eagle pair in Taï National Park, Côte d''Ivoire. Spatial and temporal variation in primate alarm calling was found to be related to eagle ranging behaviour according to the predictions of central-place foraging models. Radio-tracking data indicate that eagle activity is higher in the centre of their home range and monkey alarm-calling rates are correspondingly elevated near eagle nests as opposed to farther away. Alarm-calling rates are also temporally coupled with measures of eagle activity. There were considerable differences between the species in both rates and spatial patterns of alarm calling. The variation we measure in predation risk is expected to have consequences at the behavioural and population level.     

Why offspring delay dispersal: experimental evidence for a role of parental tolerance

Approximately 3% of all bird species live in families based on a prolonged parent-offspring association. Formation of family groups often appears to be associated with various constraints on the possibilities of independent reproduction for the offspring. However, delayed dispersal is not the only alternative for offspring that defer reproduction. To account for the formation of a family group it is also necessary to explain why non-dispersing offspring forego the alternative options to join other groups as 'extra birds' or to become 'floaters' and roam between territories. We removed fathers from Siberian jay Perisoreus infaustus family groups to test the proposal that nepotistic parental tolerance gives the natal territory a special value for the offspring, which they cannot find elsewhere and that makes them stay. In this species, parents are more tolerant of their retained offspring than towards immigrant extra birds. In response to the removal of fathers, retained offspring dispersed, whereas there was no similar response among the unrelated extra birds. Retained offspring, however, left only after despotic immigrant alpha-males replaced removed fathers, indicating that the presence of fathers is an essential motive for offspring to delay their dispersal. By blocking immigrant and unrelated males from becoming alpha-males and by being tolerant themselves, fathers provide a 'safe haven' in the natal territory where retained offspring can avail themselves of available resources without any, or only mild, competitive interference.     

Nepotistic vigilance behavior in Siberian jay parents

Many Siberian jay offspring (up to 50%) postpone independenceand stay with their parents for up to 3 years. Parents offersuch nondispersers a benefit in that they increase their vigilancewhile feeding together with retained offspring. In contrast,parents reduce their vigilance while in company of nonrelatedflock members according to the "many eyes" principle. The preferentialtreatment offered by the parents provides an incentive for offspringto forego dispersal. Given evidence for mortality via surpriseattacks by predators (goshawks), such nepotistic vigilance byparents could have a bearing on offspring survival and therebypromote delayed dispersal.     

Semantic communication in birds: evidence from field research over the past two decades

What do animal signals mean? This is a central question in studies on animal communication. Research into the semantics of animal signals began in 1980, with evidence that alarm calls of a non-human primate designated predators as external referents. These studies have challenged the historical assumption that such referential signaling is a unique feature of human language and produced a paradigm shift in animal communication research. Over the past two decades, an increasing number of field studies have revealed similar complexity in anti-predator communication of birds. The acoustic structures of avian alarm calls show a high degree of variation in pitch, duration, shape, and repetition rate. In addition to such distinct and graded variations, several birds combine discrete types of notes or calls into higher complex sequences. These variations in alarm calls are typically associated with the predator’s attributes, such as predator type and distance, and receivers respond to them with appropriate anti-predator behaviors. Although alarm calls of several bird species, as well as those of monkeys, appear to denote predator attributes, almost nothing is known about the cognitive processes that underlie the production and perception of these signals. In this review, I explore the existing evidence for referential signaling in birds and highlight the importance of the cognitive approach to animal communication research. I hope this review will promote further investigations of alarm-calling behavior in birds and will help enhance our understanding of the ecology and evolution of semantic communication.     

Effect of alarm calling by male Red‐winged Blackbirds on nestling begging and female provisioning behavior

ABSTRACT Nestling begging and parental provisioning can attract nest predators and reduce reproductive success, so parents and their offspring might be expected to respond adaptively by minimizing predator‐attracting cues when predators threaten nests. Male Red‐winged Blackbirds (Agelaius phoeniceus) are well known for their antipredator alarm calls that contain information about the approach of potential nest predators. We examined the begging behavior of nestlings and the provisioning behavior of females in response to antipredator alarm calls of males to test the adaptive response hypothesis. Playback experiments provided no evidence that alarm calls function to switch off vocal begging; nestlings were equally likely to beg vocally during playback and control periods. Video recordings showed that male alarm calling had no significant effect on inappropriate vocal begging (in the absence of an adult), but significantly reduced the incidence of spontaneous calling (in the absence of begging). Adult females responded to male antipredator alarm calls by delaying their provisioning visits. In addition, although having no significant effect on use of nest‐arriving calls by females, male alarm calling significantly reduced their use of nest‐leaving calls. We conclude that nestling and female Red‐winged Blackbirds respond to male alarm calls in ways that might reduce the risk of predation, but nestlings beg vocally when females arrive to feed them, regardless of male alarm calling, perhaps to avoid a competitive disadvantage with broodmates.     

Parental Alarm Calls of the White‐Crowned Sparrow Fail to Stimulate Corticosterone Production in Nest‐Bound Offspring

Alarm calling by parents is widespread among animals and has strong implications for parent and offspring fitness, yet it is virtually unknown whether parental alarm calls can initiate a corticosterone response in offspring. We investigated whether parental alarm calls of the white‐crowned sparrow, Zonotrichia leucophrys, activated the corticosterone response of their nest‐bound young, as such a response might prepare older nestlings for premature fledging and increase their survival when contacted by a predator at the nest. We conducted an experiment in which nestlings were either exposed to parent alarm calls (treatment) or experienced a period without parental alarm calls (control) immediately prior to blood sampling. We then sampled nestlings to measure corticosterone levels within 4 min of first contact (baseline corticosterone) and 60 min later (handling‐induced corticosterone). Young nestlings (i.e. 3–4 d post‐hatch) did not exhibit a corticosterone response to parental alarm calls or to handling, as mean corticosterone levels were similar in the control and treatment groups for both baseline and 60‐min post‐baseline samples. Against our predictions, there was no difference in mean levels of baseline corticosterone between control and treatment groups in older nestlings (i.e. 7?8 d post‐hatch) that were capable of surviving out of the nest. However, we did find a significant increase in mean levels of corticosterone after handling in both groups, which indicated that older nestlings were able to mount a functional corticosterone response when confronted with a potential predator. Why older nestlings did not initiate a corticosterone response after exposure to parental alarm calls is unclear but may have occurred because the costs of mounting such a response outweighed the benefits, perhaps because of growth or developmental costs.     

To call or not to call: parents assess the vulnerability of their young before warning them about predators

Communication about predators can reveal the effects of both conspecific and heterospecific audiences on signalling strategy, providing insight into signal function and animal cognition. In species that alarm call to their young, parents face a fundamental dilemma: calling can silence noisy offspring and so make them less likely to be overheard, but can also alert predators that young are nearby. Parents could resolve this dilemma by being sensitive to the current vulnerability of offspring, and calling only when young are most at risk. Testing whether offspring vulnerability affects parental strategy has proved difficult, however, because more vulnerable broods are often also more valuable. We tested experimentally whether parent white-browed scrubwren, Sericornis frontalis, assessed brood noisiness when alarm calling near nests. When a model predator was nearby, parents gave more alarm calls when playbacks simulated noisy broods, yet brood noisiness did not affect adult calling when only a control model was present. Parents were therefore sensitive to the tradeoff between silencing young and alerting predators to the presence of nests. Our study demonstrates that receiver vulnerability can affect signalling decisions in species other than primates.     

Kea Nestor notabilis mothers produce nest-specific calls with low amplitude and high entropy

Vocal behaviour of nesting altricial birds is subject to selection pressure from several sources. Offspring beg to attract parents’ attention, thus increasing the chances of being fed, but also increasing the chances of being detected by predators. Research on passerines has shown that parents may reduce the risk of nest predation by alarm calling to warn nestlings to be quiet, and by producing food calls which solicit begging when parents are present to defend the nestlings. Both nestlings and parents may reduce the risk of predator detection by producing calls of low amplitude and high entropy which are acoustically difficult to locate. Although extensive research has been undertaken on nesting passerine vocalizations, little is known about parrots in this regard, and studies are needed to determine whether parrots show similar adaptations. We investigated the calling behaviour of Kea Nestor notabilis mothers during the nesting period to determine whether maternal vocalizations were adapted in a way that could increase the chance of brood success. A microphone was installed inside the nest to record calls produced both inside the nest and in the direct vicinity. Our prediction was that calls outside the nest would be easy to locate and could function as alarm calls to alert conspecifics or distract the predator, whereas calls inside the nest would be difficult to locate and could serve to communicate with nestlings without alerting predators. Our results accorded with these predictions. Calls produced outside the nest were loud and tonal, and corresponded to previously described Kea alarm calls. Calls produced inside the nest, however, were high-entropy and low-amplitude calls, and formed a distinct structural category. We thus provide the first evidence that a parrot species has a vocal category for communication inside the nest, and that calls within this category are structured in a way that could reduce the risk of nest predation.     

Bird calls: just emotional displays or something more?

Two widely held assumptions about the sounds of birds and other animals are (1) they are impulsive and involuntary, and cannot be controlled, and (2) they are based only on emotion, apparently because the stimuli eliciting them are thought to be very generalized. The validity of these assumptions has been tested in studies of the alarm calling and food calling behavior of domestic chickens. Videotapes of aerial and ground predators–a hawk overhead and a raccoon on the ground–were effective in eliciting the two major classes of alarm calls. The frequency of aerial alarm calling was strongly affected by presence or absence of a companion, while other aspects of antipredator behavior were unchanged. This so-called "audience effect" on calling is not found with the ground predator call, apparently because this call is addressed to the predator as well as companions. The rules for audience effects are different again with food calling. Evidently calling is not completely impulsive, but can be controlled. By varying the attributes of digitized video images of predators we have shown that stimuli eliciting the aerial predator alarm call are quite specific, encoding different information than the ground predator call. Playback experiments demonstrate that another chicken can decode this information, and react adaptively. Although emotion is undoubtedly involved in bird calling, we conclude that simple emotion-based models of bird calls are inadequate as the sole basis for explaining the vocal behavior of birds.     

Bird calls: just emotional displays or something more?

Two widely held assumptions about the sounds of birds and other animals are (1) they are impulsive and involuntary, and cannot be controlled, and (2) they are based only on emotion, apparently because the stimuli eliciting them are thought to be very generalized. The validity of these assumptions has been tested in studies of the alarm calling and food calling behavior of domestic chickens. Videotapes of aerial and ground predators–a hawk overhead and a raccoon on the ground–were effective in eliciting the two major classes of alarm calls. The frequency of aerial alarm calling was strongly affected by presence or absence of a companion, while other aspects of antipredator behavior were unchanged. This so-called "audience effect" on calling is not found with the ground predator call, apparently because this call is addressed to the predator as well as companions. The rules for audience effects are different again with food calling. Evidently calling is not completely impulsive, but can be controlled. By varying the attributes of digitized video images of predators we have shown that stimuli eliciting the aerial predator alarm call are quite specific, encoding different information than the ground predator call. Playback experiments demonstrate that another chicken can decode this information, and react adaptively. Although emotion is undoubtedly involved in bird calling, we conclude that simple emotion-based models of bird calls are inadequate as the sole basis for explaining the vocal behavior of birds.     

Avoiding predators at night: antipredator strategies in red-tailed sportive lemurs (Lepilemur ruficaudatus)

Although about one-third of all primate species are nocturnal, their antipredator behavior has rarely been studied directly. Crypsis and a solitary lifestyle have traditionally been considered to be the main adaptive antipredator strategies of nocturnal primates. However, a number of recent studies have revealed that nocturnal primates are not as cryptic and solitary as previously suggested. Thus, the antipredator strategies available for diurnal primates that rely on early detection and warning of approaching predators may also be available to nocturnal species. In order to shed additional light on the antipredator strategies of nocturnal primates, I studied pair-living red-tailed sportive lemurs (Lepilemur ruficaudatus) in Western Madagascar. In an experimental field study I exposed adult sportive lemurs that lived in pairs and had offspring to playbacks of vocalizations of their main aerial and terrestrial predators, as well as to their own mobbing calls (barks) given in response to disturbances at their tree holes. I documented the subjects' immediate behavioral responses, including alarm calls, during the first minute following a playback. The sportive lemurs did not give alarm calls in response to predator call playbacks or to playbacks with barks. Other behavioral responses, such as gaze and escape directions, corresponded to the hunting strategies of the two classes of predators, suggesting that the corresponding vocalizations were correctly categorized. In response to barks, they scanned the ground and fled. Because barks do not indicate any specific threats, they are presumably general alarm calls. Thus, sportive lemurs do not rely on early warning of acoustically simulated predators; rather, they show adaptive escape strategies and use general alarm calls that are primarily directed toward the predator but may also serve to warn kin and pair-partners.     

Reduced mortality selects for family cohesion in a social species

Delayed dispersal is the key to family formation in most kin-societies. Previous explanations for the evolution of families have focused on dispersal constraints. Recently, an alternative explanation was proposed, emphasizing the benefits gained through philopatry. Empirical data have confirmed that parents provide their philopatric offspring with preferential treatment through enhanced access to food and predator protection. Yet it remains unclear to what extent such benefits translate into fitness benefits such as reduced mortality, which ultimately can select for the evolution of families. Here, we demonstrate that philopatric Siberian jay (Perisoreus infaustus) offspring have an odds ratio of being killed by predators 62% lower than offspring that dispersed promptly after independence to join groups of unrelated individuals (20.6% versus 33.3% winter mortality). Predation was the sole cause of mortality, killing 20 out of 73 juveniles fitted with radio tags. The higher survival rate among philopatric offspring was associated with parents providing nepotistic predator protection that was withheld from unrelated group members. Natal philopatry usually involves the suppression of personal reproduction. However, a lower mortality of philopatric offspring can overcome this cost and may thus select for the formation of families and set the scene for cooperative kin-societies.     

Predator‐Associated Vocalizations in North American Red Squirrels (Tamiasciurus hudsonicus): To Whom are Alarm Calls Addressed and How do They Function?

Alarm vocalizations produced by prey species encountering predators can serve a variety of functions. North American red squirrels are a small-bodied mammal popularly known for producing loud, conspicuous alarm calls, but functional accounts of calling in this species are few and contradictory. We conducted research over a 3-yr period on a sample of 47 marked red squirrels in the foothills of the Canadian Rockies. We recorded the production of alarm calls during encounters with natural predators and in a series of simulated predator experiments. We tested for variation in call production patterns consistent with three traditional hypotheses concerning the conspecific warning functions of alarm calling: namely that they serve as warnings to kin, to potential mates, or to territorial neighbors with which callers have an established relationship. Patterns of calling did not provide clear support for any of these hypothesized functions. We consider several possible qualifications to our results. We also consider the possibility that conspicuous calls given by red squirrels during encounters with predators are directed at the predators themselves and function to announce their detection and possibly deter them. This possibility is consistent with additional life-history features of red squirrels including that they are a relatively solitary and territorial, food-hoarding species that produces the same conspicuous vocalizations in response to other squirrels intruding on their territory to steal cones. An important corollary of this account is that red squirrel alarm calls probably do not entail referentially specific messages about different types of predator, as proposed previously.