Nonlocal male mountain white-crowned sparrows have lower paternity and higher parasite loads than males singing local dialect

Bird song often varies geographically, and when this geographicvariation has distinct boundaries, the shared song types arereferred to as song dialects. We investigated the role of songdialect in male mating success in a wild breeding populationof mountain white-crowned sparrows (Zonotrichia leucophrysoriantha). In 2 of 3 years, males singing unusual songs ("nonlocal"males) had lower total fertilization success (measured by microsatellitepaternity analysis) than did males singing the local dialect ("local" males). Similarly, females produced disproportionately more young with local than with nonlocal males. However, dialectwas not a significant predictor of male mating success whencontrolling for other factors that might affect paternity.Instead, the low mating success of nonlocal males was apparentlydue to an interaction between song dialect and parasite load.Nonlocal males were more severely infected by bloodborne Haemoproteusthan were local males, although they did not differ in anyother measured aspect of quality. Immigrant birds may be immunologically disadvantaged, possibly due to a lack of previous experiencewith the local parasite fauna, resulting in low mating success.     

Under adverse conditions,older small tree finch males (Camarhynchus parvulus) produce more offspring than younger males

Females of many bird species prefer mating with older males, presumably because they provide superior parental care and possibly superior genes. A previous study found that female small tree finches (Camarhynchus parvulus) preferred pairing with old males and had a higher breeding success when paired with old males because their nests were more concealed, higher up in the canopy and therefore less likely to be depredated. However, causes for brood loss have changed over the last decade: predation of small tree finch nests has decreased, whereas brood losses due to parasitism by the invasive parasitic fly Philornis downsi have increased. In the present study, we investigated (a) how the change in predation and parasitism by P. downsi influenced the breeding success of small tree finches, (b) whether there were still differences in breeding success between young and old males, (c) whether P. downsi infestation had a differential effect on nests of young and old males and (d) whether young and old males differed in foraging success. During 2012–2016, we found an overall low influence of predation and a high influence of P. downsi, but neither differed between nests of young and old males. Nests of old males had more fledglings than those of young males. However, the difference in breeding success disappeared when P. downsi numbers were experimentally reduced by injecting an insecticide into nests. This indicates that older males were able to compensate for the detrimental effects of parasitism.     

Patterns of dawn singing by Buff-breasted Flycatchers

ABSTRACT.   Many passerine species exhibit a "dawn chorus"—a bout of intense singing activity before or at dawn, but our understanding of this phenomenon is poor. Tyrant flycatchers (Tyrannidae) exhibit pronounced daily bouts of dawn singing. I documented this behavior in several populations of Buff-breasted Flycatchers ( Empidonax fulvifrons ) in Arizona, tape recording >30,000 songs of 23 individuals during dawn singing. Individual males sang a dawn bout each morning, even during breeding phases when daytime song was almost completely absent. Dawn bouts began 5–10 min before local civil twilight and continued for 25–30 min. Each male possessed two song types delivered at high rates during dawn singing (four times the rate during sustained daytime singing). Song rate varied significantly over the course of dawn bouts, increasing to 55 songs / min at mid-bout, then declining to the end of the bout. Type 2 songs comprised about 30% of songs during dawn singing, and decreased significantly in proportion during the final 10 min of the bout. Songs of the two types were delivered in a nonrandom fashion. Males sang at locations near territory boundaries and pairs of neighbors engaged in counter-singing from the same locations each morning. A number of dawn singing bouts ended with attempted or successful copulations. These observations are consistent with the social dynamics hypothesis for the functional significance of dawn singing in this species.     

Risk taking during parental care: a test of the harm-to-offspring hypothesis

Amount of risk taking during parental care is often explainedin relation to the reproductive value of the offspring. The"harm-to-offspring hypothesis" focuses on the relative harma period of no parental care can do to the offspring. Accordingto this hypothesis, parents should take greater risks for offspringin poor condition than for offspring in good condition. We manipulatedoffspring condition in the pied flycatcher (Ficedula hypoleuca)and tested the harm-to-offspring hypothesis by exposing parentsto a predator model (a sparrowhawk, Accipiter nisus). Time elapseduntil a parent first entered the nest-box was used as a risk-takingmeasure. Parents spent significantly shorter time until first nestvisit for offspring in poor condition than for offspring ingood condition. Hence, the harm-to-offspring hypothesis wassupported.     

The impact of learning foster species' song on the evolution of specialist avian brood parasitism

Obligate interspecific avian brood parasites do not build nestsof their own but lay their eggs in the nests of other species.It has been proposed that a flexible song learning mechanism(copying the heterospecific songs of the foster species) facilitatesthe evolution of brood-parasitic behavior. Some sort of songcopying is common to all songbirds; hence, to better understandthe evolution of brood parasitism it is important to study therole of song learning. The proposed hypothesis does not takeinto account that flexible song learning might make mate acquisitionmore difficult because males that are preferred by brood-parasiticfemales would be initially rare. We examine this by means oftwo population dynamic models. By using a recurrence equationmodel of brood parasites competing with their nestbuilding ancestors,we show that flexible song learning is indeed an obstacle tothe evolution of brood parasitism. Results from a more realistic,individual-based model, in which the brood-parasitic trait canevolve more gradually, confirm this finding. However, we alsoshow that the obstacle of flexible song learning can be overcomequite easily when males also are carriers of the brood-parasitictrait. This is probably because brood parasitism is a neutraltrait in males, which increases the number of mutants carryinggenes for brood parasitism, and thus makes the female task offinding suitable partners easier.     

Perch selection by singing chaffinches: a better view of surroundings and the risk of predation

Predation risk varies among perches, and the vulnerability ofsinging chaffinches (Fringilla coelebs) might differ dependingon where they perch in a tree. To find out how singing of thechaffinch is associated with antipredatory behavior, I studiedperch selection in mature pine forest and in pine saplings,two habitats differing in the amount of cover for protection from predators. My results show that male chaffinches preferto sing below the canopy of mature pines and in the uppermostparts of sapling pines. Although these are the canopy partsmost exposed to sparrowhawk (Accipiter nisus) attacks, stayingin open sites may be a beneficial strategy for singing chaffinchesbecause it makes it possible to improve antipredatory vigilance.This assumption was supported by the hawk experiments. Afterbeing exposed to the sparrowhawk model, all of the singingbirds selected the conspicuous perch below the canopy of maturepines. The males that perched higher in the canopy before theexperiment moved to the lower canopy, whereas those males thatsang below the canopy did not change their singing perch.     

Nest defence by Magpies(Pica pica) and the brood parasitic Great Spotted Cuckoos(Clamator glandarius) in parasitized and unparasitized nests

Summary Nest defence is a frequent and widespread parental behaviour which enhances brood survival. We have found that in a Spanish Magpie population which is heavily parasitized by the brood parasitic Great Spotted Cuckoo, Magpies defend (1) unparasitized more frequently than parasitized nests, and (2) at the end of the nestling period more frequently than in other stages of the breeding cycle. Great Spotted Cuckoos are brood parasites, which means that their eggs are incubated and their nestlings are raised by members of a host species. Brood parasites are not thought to take care of their own offspring. However, we have found that Great Spotted Cuckoos sometimes scolded us on our regular visits to parasitized magpie nests (but never on those to unparasitized nests). Frequency of nest defence by cuckoos differed significantly among years, being significantly higher at the beginning of the study. Although sporadic observations of adult brood parasites feeding juveniles have been recorded, nest defence has not previously been suggested for any brood parasite.

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Nestverteidigung von durch den Häherkuckuck(Clamator glandarius) parasitierten und unparasitierten Nestern bei Elstern(Pica pica)

Zusammenfassung Nestverteidigung ist ein häufiges und weit verbreitetes elterliches Verhalten zur Erhöhung des Bruterfolges. In einer spanischen Elsterpopulation, die sehr intensiv vom Häherkuckuck parasitiert ist, wurden unparasitierte Nester häufiger verteidigt als parasitierte, und zum Ende der Nestlingsperiode wurden Nestern häufiger verteidigt als zu früheren Phasen des Brutzyklus. Häherkuckucke sind Brutparasiten, deren Eier von den Wirtseltern bebrütet und die Nestlinge von ihnen aufgezogen werden. Solche Brutparasiten kümmern sich im allgemeinen nicht selbst um ihre Nachkommen. Manchmal jedoch haßten Häherkuckuck auf uns, wenn wir parasitierte Nester der Elster kontrollierten, während an unparasitierten Nestern ein solches Hassen niemals erfolgte. Die Häufigkeit dieser Nestverteidugung der Kuckucke variierte zwischen Jahren und war signifikant häufiger zu Beginn unserer Untersuchung. Zwar wurde gelegentlich schon Füttern der Jungvögel durch elterliche Brutparasiten beobachtet, die hier festgestellte Nestverteidung ist bisher aber von keinem Brutparasiten beschrieben.

     

Overlapping signals in banded wrens: long-term effects of prior experience on males and females

We tested the signal value of song overlapping in banded wrens(Thryothorus pleurostictus), using interactive playback to eitheroverlap or alternate with their songs. Males shortened songduration and decreased variability in song length when theirsongs were overlapped by playback, suggesting that they wereattempting to avoid being overlapped and perhaps being lessaggressive. A novel finding was an effect of long-term priorexperience: song lengths remained relatively short in alternatingtrials that followed two or more days after overlapping trials.Approach responses to the two treatments did not differ overall,but there was a parallel effect of prior experience: males tendedto stay further from the speaker during alternating treatmentsif they had previously been overlapped by playback. Some femalespaired to the male subjects sang in response to playback andwere also influenced by prior experience, singing more duringalternating trials that had not been preceded by an overlappingtrial. Male overlappers may signal dominance over a rival toother male or female receivers in a communication network, butit is currently unclear whether overlapping indicates motivationto escalate an aggressive interaction or whether this singingstrategy is related to male quality. Banded wrens are long livedand maintain year-round territories, so modifying responsesto rivals based on prior experience is likely to be importantfor success.     

Death comes suddenly to the unprepared: singing crickets, call fragmentation, and parasitoid flies

Male field crickets are subject to a delicate dilemma becausetheir songs simultaneously attract mates and acoustic predators.It has been suggested that in response, crickets have modifiedvarious temporal song parameters to become less attractiveto acoustic predators. We investigated whether crickets withchirping (versus trilling) song structures are less likely toattract acoustically orienting parasitoid flies. Experimentally,we evaluated the phonotactic quest of the parasitoid fly Ormiaochracea in response to broadcast cricket calls, presentedboth simultaneously (choice paradigm) and sequentially (no-choiceparadigm). Flight trajectories were recorded in darkness usingthree-dimensional active infrared video tracking. The flies showed remarkable phonotactic accuracy by landing directly onthe loudspeaker. The introduction of acoustic fragmentationthat resembles calls of many chirping crickets altered theflies' phonotactic accuracy only slightly. Our results documentdifferential attraction between trilling and chirping cricket songs and quantitatively demonstrate that chirping songs, ifpresented alone, do not impair the efficiency (temporal investmentand landing accuracy) of the flies' phonotactic quest. Thisstudy shows that song fragmentation is no safeguard againstacoustic parasitism. We conclude that, in general, a cricket may reduce predation only if its neighbors are acousticallymore conspicuous, chiefly by amplitude.     

田间转Bt基因水稻上稻飞虱卵量、孵化率及天敌作用

为了评估转基因水稻释放后对非靶标害虫及其天敌的影响, 本研究在浙江大学实验农场和中国水稻研究所实验农场2008和2009年连续两年监测了转Bt基因水稻对田间稻飞虱着卵量、卵孵化率、卵被捕食率、卵被寄生率和卵死亡率的影响。结果表明: 两年2个调查地点3个水稻品系（克螟稻1、克螟稻2和秀水11）上的稻飞虱平均每分蘖着卵量、卵孵化率、卵被捕食率和卵被寄生率的趋势基本一致, 而且田间3个水稻品系上稻飞虱卵量的高峰期均持续2周左右; 但是两年2个调查地点3个水稻品系上稻飞虱卵死亡率则没有一致的趋势。此外, 总体上3个水稻品系上稻飞虱平均每分蘖着卵量、卵孵化率、卵被捕食率、卵被寄生率和卵死亡率差异均不显著（P>0.05）。因此, 稻田中转Bt基因水稻对稻飞虱卵没有显著的影响。     

Public information and conspecific nest parasitism in goldeneyes: targeting safe nests by parasites

Conspecific nest parasitism (CNP) is a widespread alternativereproductive tactic in birds. Several hypotheses have been putforward to explain the evolution and occurrence of CNP, butno generally applicable hypothesis exists. Recent experimentalresults from the common goldeneye (Bucephala clangula), a cavity-nestingduck, have revealed that parasitic females preferentially layeggs in safe nest-sites, implying that nest predation risk isan important ecological determinant of CNP. The present studyfocuses on the mechanisms by which parasites identify safe nest-sites.Predation risk of a given nest-site was predictable betweensuccessive breeding seasons. At the end of the nesting season,females prospected active nest-sites more frequently than nest-sitesthat did not have a nest in the current season. Nest-sites thathad been prospected more frequently by females in year t hada higher probability to be parasitized in year t + 1. The resultssuggest that the use of public information, derived throughnest-site prospecting, enabled parasites to target safe nests.These findings provide a new and potentially generally applicableperspective to understand the evolution and occurrence of CNP.     

The development of coordinated singing in cooperatively displaying long-tailed manakins

Long-tailed manakins (Chiroxiphia linearis) have a puzzlingsocial system in which teams of two males display cooperativelyin dispersed lek arenas, but only the alpha partner mates withvisiting females. One benefit of performing as a nonmatingpartner might be to gain experience as an "apprentice" to improvethe performance of the complex duet song and joint dance. Weexamined the relationship between the age of singers and twomeasures of singing performance: song variability and soundfrequency matching. Singing performance improved with age;variability in four song characteristics of males less than3 years old was greater than that in their older partners,and frequency matching increased with the age of the younger partner. Randomization tests of song samples from seven well-establishedteams showed that males did not track the song-to-song variationin their partners' singing. Another randomization test showedthat frequency matching by these teams was higher than thatof randomly paired partners. We considered three alternativehypotheses for the congruent songs: (1) short-term accommodation to the partner's song; (2) active choice of partners with similarintrinsic frequencies; and (3) long-term development of congruentsong through either practice or song copying. Our results andevidence from long-term monitoring of banded birds best supportthe hypothesis that frequency matching develops over severalyears during the complex and protracted process of partner formation. Nonmating males may benefit from increasing theircompetence at display, eventually enjoying increased matingsuccess when they inherit display sites from older males.     

No terminal investment in pipefish males: only young males exhibit risk-prone courtship behavior

Animals are expected to trade-off current and future reproductionin order to maximize lifetime reproductive success. Old individualsmay accept higher risks during courtship and mate choice astheir residual reproductive value (RRV) diminishes (the terminalinvestment hypothesis). Alternatively, young individuals maybe forced to take higher risks during courtship to compensatefor their lower competitiveness and/or attractiveness (the compensationhypothesis). In this study, we used the sex-role reversed pipefishSyngnathus typhle to test how mate choice and courtship behaviorof males with different RRV were affected by an increase inpredation risk. Males of different ages were given the opportunityto court and choose between 2 partners. In half of the trials,a predator was present in a separate aquarium. We found no supportfor the terminal investment hypothesis: no difference in responseto the increased predation risk by males of different ages wasevident. In agreement with the compensation hypothesis, youngmales invested more in courtship behavior compared with oldermales. In addition, in the absence of a predator, we found thata high female activity was important for male mate choice decisions.During increased predation risk, this relationship was, however,reversed and males preferred less active, and thus less conspicuous,partners. This suggests that both female activity and size areimportant factors for male mating decisions in this speciesand that these decisions mainly are affected by predation riskand advantages in mate acquisition.     

Song discrimination suggests premating isolation among sympatric indigobird species and host races

Indigobirds (Vidua spp.) are host-specific brood parasites thathave diversified in a recent radiation apparently driven byhost colonization. Behavioral imprinting of both male and femaleindigobirds on host song is thought to promote rapid speciationbecause it results in assortative mating between indigobirdsassociated with a particular host. We conducted a song playbackexperiment to test whether male indigobirds discriminate amongpotential competitors based on song. Of particular interestwas the behavior of two sympatric host races of the Cameroonindigobird Vidua camerunensis that differ only in host songmimicry and other components of their vocal repertoires. Territorialmales of the two V. camerunensis host races and Vidua raricola,a morphologically distinct indigobird species, were tested withplaybacks of each other's songs. Males of all three groups respondedmost aggressively to songs of their own species and/or hostrace, as evidenced by strong and highly significant differencesin a variety of response variables. This differential territorialdefense suggests that an intruding male with different songsdoes not represent a competitive threat and is expected if femalesmate assortatively with respect to song. Thus, our results provideevidence of premating reproductive isolation among recentlyevolved indigobird species and host races.     

Nest use by territorial males in a shell-brooding cichlid: the effect of reproductive parasitism

Male Telmatochromis vittatus, a substrate-brooding Tanganyikan cichlid, exhibit two parasitic reproductive tactics: takeover of spawning by larger males (pirates) and sneaking by smaller males (sneakers). Medium-sized males are territorial and pair-spawn within nests of clumped shells that harbor several resident females that are potential mates of the territory owner. To study nest use by territorial males, we analyzed the relationship between the body size of territorial males and nest quality, the number of females per nest, the distance between nests, and the frequency and intensity of reproductive parasitism. The size of males was not correlated with nest quality, the number of females, or the number of sneakers, but was negatively correlated with the frequency of intrusion by pirates and was positively correlated with the distance between nests. Territorial males effectively defended nests against sneakers but failed to defend against pirates. These results suggest that larger territorial males selected nests that have a lower risk of usurpation of spawning. We hypothesize that the risk of intrusion by pirate males affects the selection of nests by territorial males in this species.     

Social context affects risk taking by a satellite species in a mixed-species foraging group

Mixed-species flocks of birds form during winter in the easterndeciduous forests of North America. These flocks consist oftwo flock-leading nuclear species, tufted titmouse (Baeolophusbicolor) and Carolina chickadee (Poecile carolinensis), andseveral follower, or satellite, species, including downy woodpecker(Picoides pubescens) and white-breasted nuthatch (Sitta carolinensis).Hypotheses explaining the adaptiveness of participation in suchmixed-species foraging groups have focused on increased foragingsuccess and/or decreased predation risk. We tested the predictionthat if nuthatches join nuclear species to reduce predationrisk, they should be more reluctant to visit an exposed feederin the absence of titmice than in their presence. When the feederwas positioned 16 m from forest cover, latency to visit thefeeder was greater for both male and female nuthatches whentitmice were absent. Removal of titmice had no effect on latencyat 8 m. In the absence of titmice, nuthatches visited the feederless frequently at both distances. These results indicate thatreduced predation risk is a benefit that satellite species gainby flocking with nuclear species.     

Relationship Between Nest Predation Suffered by Hosts and Brown-Headed Cowbird Parasitism: A Comparative Study

There are at least four main hypotheses that may explain how the evolution of host selection by avian brood parasites could be linked to nest predation among their potential hosts. First, selection may have favoured parasite phenotypes discriminating among hosts on the basis of expected nest failure. Second, parasitized nests may be more easily detected by predators and extra costs of parasitism may accelerate the evolution of host defences. Third, selection may have favoured predator phenotypes avoiding parasitized nests because parasitism enhances nest defence. Fourth, female brood parasites may directly or indirectly induce host nesting failures in order to enhance future laying opportunities. We collected data on brood parasitism and nest failure due to predation to test these hypotheses in a comparative approach using North American passerines and their brood parasite, the brown-headed cowbird Molothrus ater. Under the hypotheses 1 or 3 we predicted brood parasitism to be negatively associated with nest predation across species, whereas this relation is expected to be positive if hypotheses 2 or 4 are true. We demonstrate that independent of host suitability, nest location, habitat type, length of the nestling period, body mass and similarity among species due to common ancestry, species experiencing relatively high levels of nest predation suffered lower levels of cowbird parasitism. Our results suggest a previously ignored role for nest predation suffered by hosts on the dynamics of the coevolutionary relationships between hosts and avian brood parasites. Co-ordinating editor: Dr. F. Stuefer     

Predators, reproductive parasites, and the persistence of poor males on leks

Lekking males are thought to face strong directional selectionon secondary sexual traits. How variation in male traits canpersist under these conditions remains problematic (the lekparadox). Here, we present several game-theoretic models thatshow that avoidance of costly and mobile predators, sneakers,or brood parasites (enemies) leads to variation in female choice.This can result in maintenance of variation in male quality."Enemies" will congregate around higher quality males. Femalesmust then trade-off the benefits of mating with high-qualitymales against the increased risk of enemies. At equilibrium,the models predict a positive correlation between the qualityof a male and the proportions of both enemies and females visitinghim. In the first model, we use this framework to predict thelowest quality male on the lek that will receive any matings.In the second model, we examine the influence of this female-enemygame on the maintenance of variation in male quality. Low-qualitymales are likely to persist when enemies are costly to femalesor occur at high density, and when there is some spatial structureon the lek, so that neighboring males are typically of similarquality. If enemies are more costly to males than to females,high-quality males may benefit from receiving fewer female visits.In the third model, we consider the special case when enemiesare male reproductive parasites. These models illustrate theimportance of considering the simultaneous decisions of multipleplayers in mate choice games.