Evolution of polyandry in a communal breeding system

The evolution of polyandry requires an asymmetrical factor thatfavors more matings per breeding female than per breeding male,thus reversing Bateman's principle. Here a model is presentedfor the evolution of avian cooperative polyandry. The modelshows that polyandry can evolve if communal breeding is initiallyadvantageous and if increasing clutch size beyond an optimumis detrimental. The advantage of communal breeding favors theaddition of more breeders (either males or females) and thusselects against breeding as single pairs (monogamy). The optimaldutch size creates the asymmetry that favors adding male breeders(polyandry) over adding female breeders (polygyny). Adding femalesis detrimental because females must lay eggs to reproduce andcan therefore increase the clutch size of the group. On theother hand, males can reproduce by sharing paternity withoutincreasing dutch size. It is shown that cooperative polyandryevolves either because it maximizes both male and female fitnessor because polygyny and monogamy are behaviorally unstable.Data from acorn woodpeckers support the assumptions of the modeland suggest that cooperative polyandry evolved because it isbehaviorally more stable. The persistence of monogamy and polygynyin acorn woodpeckers (at a lower incidence than polyandry) isalso examined. Polygyny in these birds represents a case ofthe Prisoner's Dilemma     

Kin clustering in barnacle geese: familiarity or phenotype matching?

We investigated the settling pattern of barnacle geese Branta leucopsis that returned to breed in their natal colony. Femalesnested close to their parents and sisters, but settling ofmales conformed to a random pattern. The apparent preferencefor breeding close to kin in females could be a by-productof extreme philopatry to the natal nest site. However, sistersalso nested close to each other when settling on a differentisland than the one where their parents bred, pointing at agenuine preference for breeding close to kin. Females onlynested close to sisters born in the same year (i.e., sistersthat they had been in close contact with). This suggests thatthe clustering of female kin in barnacle geese does not resultfrom phenotype matching. We did not detect any direct benefitsof settling close to birth site or kin, but the analyses lackedpower to detect small benefits of proximity to kin given themany other factors that may influence breeding success. Coloniallybreeding birds share characteristics that are generally believedto promote the evolution of cooperation, yet kin clusteringand kin selection have been little studied in this group. Futureresearch should be directed to studying the possible rolesof kin clustering and kin selection in the evolution of coloniality.     

Can information sharing explain recruitment to food from communal roosts?

The debate over whether communal nests and roosts function primarilyas information centers (they facilitate the sharing of foraginginformation) remains unresolved. Here I use evolutionary gametheory to investigate the relative importance of this influentialhypothesis and an alternative: that roosts, in particular,function as recruitment centers (they facilitate aggregationat food patches). Basing my model on juvenile common raven (Corvus corax) behavior, I assume there is no net cost to beingat food patches in groups, and foragers roost communally. Moreover,one strategic outcome is the observed raven behavior: individualssearch independently and recruit from the roost once a patchis found (they play Search-and-Recruit, or SR). I investigatethe stability of this in two scenarios that differ in the magnitudeof the lost opportunity costs to mutants playing SR in populations of other strategies. When these costs only involve a chanceof not being in a group at a located carcass, SR is the onlyevolutionarily stable strategy under all conditions. However,when these costs also include missing opportunities to be sociallydominant, SR no longer enjoys exclusive dominance in the strategyset. Nevertheless, in both cases, there are conditions where group foraging benefits have no effect on the evolutionary stabilityof SR. Thus, contrary to assertions in the literature, theopportunity to share foraging information can be sufficientto drive the evolution and maintenance of recruitment to foodfrom communal roosts. However, I conclude that both informationand grouping benefits are likely to underlie communal roostingbehavior in my focal system.     

On the evolution of delayed recruitment to food bonanzas

Whereas food sharing by immediate recruitment to food bonanzasis relatively common, especially among birds, delayed recruitmentfrom overnight roosts is comparatively rare, although it hasbeen studied extensively in the common raven (Corvus corax).Two hypotheses have been advanced to explain the evolution ofdelayed recruitment. Under the status-enhancement hypothesis,delayed recruiting is favored because the recruiter's social statusincreases with the number of followers it leads to a food source.The posse hypothesis also focuses on the number of individualsrecruited to a site, but in this case aggregation is favoredbecause larger groups are more likely to usurp a carcass defendedby a pair of territorial adult ravens. We used a game-theoreticmodel to explore the logic of immediate versus delayed recruitmentin the light of these hypotheses. In particular, we identified threecritical values of the probability of immediate recruitment:that below which delayed recruitment is a cooperative strategy,that below which delayed recruitment is an evolutionarily stablestrategy, and that below which a mutant strategy of delayedrecruitment will invade a population of immediate recruitersto reach fixation. The model demonstrates that either status enhancementor the posse effect may alone suffice for the evolution of delayed recruitmentto food bonanzas via mutualistic information sharing at communal roosts.     

Influence of helping and breeding experience on reproductive performance in the Seychelles warbler: a translocation experiment

Reproductive success of the cooperative breeding Seychelleswarbler (Acrocephalus sechellensis) increases with age. Thisage effect is not due to differential survival or increasedreproductive effort, but to accumulated helping and breedingexperience. In their first year of breeding, reproductive performanceof inexperienced warblers with neither helping nor breedingexperience was significandy lower than that of warblers of thesame age with either previous helping or breeding experience.Reproductive performance was the same for primiparae with helpingexperience and for birds with breeding experience. Female primiparaewith helping experience or breeding experience built betternests and spent more time incubating than inexperienced females,which led to increased hatching success. Male primiparae withhelping experience or males with breeding experience guardedthe clutch better than inexperienced males, which led to reducedegg predation. Even-aged warblers with different previous experienceswere transferred to unoccupied islands, where birds startedbreeding immediately in high-quality territories. The experimentshowed that birds with helping experience produced their firstfledgling as fast as experienced breeders, and significandyfaster than inexperienced birds. Breeding performance did notimprove further with experience after the first successful breedingattempt. Only birds with previous breeding experience who pairedwith inexperienced birds, were likely to change mate. The otherpair combinations remained stable. Thus, primiparous birds withhelping experience have greater lifetime reproductive successthan inexperienced primiparae of the same age. This experimentshows that helping behavior has not only been selected for inthe context of promoting an individual's indirect fitness, butalso in the context of gaining helping experience which translatesinto improved reproductive success when a helper becomes a breeder.[Behav Ecol 7: 326-333 (1996)]     

Evolutionary drivers of seasonal plumage colours: colour change by moult correlates with sexual selection,predation risk and seasonality across passerines

Some birds undergo seasonal colour change by moulting twice each year, typically alternating between a cryptic, non‐breeding plumage and a conspicuous, breeding plumage (‘seasonal plumage colours’). We test for potential drivers of the evolution of seasonal plumage colours in all passerines (N = 5901 species, c. 60% of all birds). Seasonal plumage colours are uncommon, having appeared on multiple occasions but more frequently lost during evolution. The trait is more common in small, ground‐foraging species with polygynous mating systems, no paternal care and strong sexual dichromatism, suggesting it evolved under strong sexual selection and high predation risk. Seasonal plumage colours are also more common in species predicted to have seasonal breeding schedules, such as migratory birds and those living in seasonal climates. We propose that seasonal plumage colours have evolved to resolve a trade‐off between the effects of natural and sexual selection on colouration, especially in seasonal environments.     

Evolution of breeding plumages in birds: A multiple‐step pathway to seasonal dichromatism in New World warblers (Aves: Parulidae)

Many species of birds show distinctive seasonal breeding and nonbreeding plumages. A number of hypotheses have been proposed for the evolution of this seasonal dichromatism, specifically related to the idea that birds may experience variable levels of sexual selection relative to natural selection throughout the year. However, these hypotheses have not addressed the selective forces that have shaped molt, the underlying mechanism of plumage change. Here, we examined relationships between life‐history variation, the evolution of a seasonal molt, and seasonal plumage dichromatism in the New World warblers (Aves: Parulidae), a family with a remarkable diversity of plumage, molt, and life‐history strategies. We used phylogenetic comparative methods and path analysis to understand how and why distinctive breeding and nonbreeding plumages evolve in this family. We found that color change alone poorly explains the evolution of patterns of biannual molt evolution in warblers. Instead, molt evolution is better explained by a combination of other life‐history factors, especially migration distance and foraging stratum. We found that the evolution of biannual molt and seasonal dichromatism is decoupled, with a biannual molt appearing earlier on the tree, more dispersed across taxa and body regions, and correlating with separate life‐history factors than seasonal dichromatism. This result helps explain the apparent paradox of birds that molt biannually but show breeding plumages that are identical to the nonbreeding plumage. We find support for a two‐step process for the evolution of distinctive breeding and nonbreeding plumages: That prealternate molt evolves primarily under selection for feather renewal, with seasonal color change sometimes following later. These results reveal how life‐history strategies and a birds' environment act upon multiple and separate feather functions to drive the evolution of feather replacement patterns and bird coloration.     

Reproductive success of solitarily and communally nesting white-footed mice and deer mice

To determine the fitness consequences of communal nesting inwhite-footed mice, Peromyscus leucopus, and deer mice, P. maniculalus,I compared the reproductive success of field populations offemales nesting solitarily, in communal groups of more thanone female, in extended families of successive litters, andin communal groups with extended families. Mean first littersize of weanlings and juveniles 6 weeks old did not differ significantlyfor pups raised under the four nesting situations. Similarly,for pups born into extended families, litter sizes of pups fromsecond litters did not differ significantly from those of firstlitters or from pups born to solitarily nesting females. Delayeddispersal of juvenile females did not result in resource competitionor inhibition of reproduction. Thus, reproductive success offemales was not significantly affected by additional membersin the nest. At least 26 of 28 communally nesting females wereclose relatives. Solitary nesting is the common breeding patternin Peromyscus, and extended families and communal nesting arealternative reproductive tactics in response to limited space,delayed dispersal, and local grouping among related females.     

Space and habitat use by Red Kites Milvus milvus during winter in the Guadalquivir marshes: a comparison between resident and wintering populations

Differences in habitat selection, diet and behaviour of resident and wintering Red Kites Milvus milvus were studied in Donana National Park, southwest Spain. Adult resident Red Kites roosted at their nests, while immature residents and wintering birds gathered at communal roosts. Individuals remained on average for two consecutive nights (range 1–8) at the same communal roost. Wintering kites spent significantly more time foraging gregariously than residents. The use of the marsh was greater by wintering kites while residents more often used the forest. Wintering birds consumed more goose carrion than the residents. Wintering kites had larger core areas, moved farther from their roost sites to feed and changed foraging areas more frequently than residents. Among residents, adult females had the smallest home ranges (core area, distances travelled and time spent flying). We suggest that Red Kites wintering in Donana occupy the marsh because it provides high food availability, and is vacated by Black Kites M. migrans which exploit this profitable habitat during the breeding season.     

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 BURROW-EXCAVATION PHASE IN THE BREEDING CYCLE OF THE SAND MARTIN RIPARIA RIPARIA

Observations were carried out at a Sand Martin colony in a working sand-pit, where fresh burrows have to be dug each year. Sand Martins arrive at the breeding pit from migration unpaired, and their social organization is then at its lowest. Burrow excavation occurs only as the climax to a form of group display. Digging is communal in character, and the number of holes dug is roughly equal to the number of individual birds present. The mounting excitement and mutual stimulation of the display period induces a climax at which the birds begin to build nests and lay. This period of display produces close synchronization which seems to be a necessary condition for the communal behaviour of the birds during the rest of the breeding cycle.     

The Avian Shoulder: An Experimental Approach

SYNOPSIS. This essay is in two parts. The first describes functionalstudies of the shoulder in modern vertebrates that led to theformulation of the hypotheses that motor patterns of homologousmuscles have been maintained during the evolution of the tetrapodshoulder, and that a primitive organization of the neural controlcomponents has persisted in derived groups. The second part of this essay focuses upon a longstanding questionin vertebrate evolution: what neuromuscular and musculoskeletalchanges in the tetrapod shoulder accompanied the evolution offlight in birds? The lack of empirical data on shoulder functionin extant birds limited our insight into this question, andprompted our initiation of experimental studies. Preliminarykinematics of the furcula and humerus of European starlings(Sturnus vulgaris) flying in a wind tunnel, as revealed by highspeed cineradiography, are presented. The two halves of thefurcula, which contact the coracoids dorsally, are bent laterallyduring downstroke and medially during upstroke by as much as60% of the intrafurcular resting distance. High speed film andelectromyographic studies of freeflying pigeons (Columba livia)reveal that the supracoracoideus muscle is strongly activatedduring wing elevation and, as predicted from studies of Varanusand Didelphis, an additional activation burst occurs at mid-downstrokein 48% of the recordings.     

Effects of Aging and Mate Retention on Reproductive Success of Captive Female Peregrine Falcons

SYNOPSIS. Separating ecological (extrinsic) factors affectingreproduction from physiological and experiential (intrinsic)factors can be problematic in free-ranging animals. This studyexamined age-related changes in six measures of reproductivesuccess (clutch size, fertility, hatchability, brood size athatching, survivorship of nestlings, and brood size at fledging)for captive female peregrine falcons (Falco peregrinus) whereecological factors (i.e., access to mates, nesting sites, andfood) were not limiting and were similar across years and betweenindividuals. Mean nestling survivorship increased throughoutthe lifespan of the female while all other measures of reproductionpeaked at about seven years of age and decreased thereafter.Birds with prior breeding experience had higher productivitythan inexperienced birds of the same age. Productivity increasedwith increasing experience of the pair. Productivity droppedby an average of 53% when females experienced a change of mate,and then subsequently increased over a period of several years.Productivity was not affected when birds were moved to differentbreeding sites. There was no evidence that early improvementsin reproduction were related to chronological aging in the absenceof experiential differences. Birds that began breeding earlierproduced more fledglings during their lifetimes as a resultof higher annual productivity. Lifetime reproduction was notcorrelated with longevity because birds with higher maximalegg production had shorter breeding lifespans. Birds retainingmates produced more fledglings during their lifetime than birdsthat changed mates, but birds that changed mates more than oncedid not have lower lifetime reproduction than birds that hadonly one mate change. These results suggest that 1) age-relatedchanges in reproduction are not necessarily resource-mediated,2) in the absence of resource limitation, experience of thepair is a primary factor determining annual reproductive success,3) benefits of increasing experience may be offset by the onsetof senescence, 4) the cost of present egg production on futurereproductive potential supports a "pleiotropic" theory of aging,and 5) costs associated with mate changes may encourage selectionfor low "divorce" rates (i.e., lifetime monogamy) in this species.     

Strong evidence for selection for larger brood size in a great tit population

We measured the selection pressure on brood size in a recentlyestablished population of great tits (Parus major L.) in thenorthern Netherlands by manipulating brood size in three years(1995: n = 51, 1997: n = 66, 1998: n = 51), and we estimatedfitness consequences in terms of local survival of both offspringand parents. Enlarged broods had highest fitness; the offspringfitness component was positively affected by manipulation andthe parental fitness component was unaffected. Parental survivaland the probability that parents produced a second clutch werenot affected by the treatment. However, parents that had raisedenlarged broods produced their second clutch later in the season.Clutch size, brood size, and laying date of birds recapturedin the next breeding season were largely independent of thetreatment. We conclude that there is strong evidence for selectionfor larger brood size and reject the individual optimizationhypothesis for this population because the number of young inthe nest predicts fitness independently of the manipulationhistory.     

OBSERVATIONS ON THE COMMUNAL ROOSTING OF AFRICAN BLACK OYSTERCATCHERS

Hockey P. A. R. 1985. Observations on the communal roosting of African Black Oystercatchers. Ostrich 56: 52–57.

There are currently three main hypotheses for the adaptive significance of avian communal roosts: physiological advantages, predator avoidance and information centres. The African Black Oystercatcher Haematopus moquini is territorial throughout the year and forms communal roosts during the nonbreeding season, but does not breed communally. Roosts generally are small, and site fidelity is high. Roosts are normally sited on a rocky promontory with adjacent offshore rocks (west coast), or in flat areas with extensive all-round visibility. The main predators of African Black Oystercatchers are nocturnal terrestrial mammals and nocturnal communal roosts are larger and more tightly packed than daytime roosts. Breeding birds do not roost communally during the breeding season and at this time of year mortality due to mammal predators at a study site in Saldanha Bay was greatest (X² = 9.46; p<0.01). It appears therefore that predator avoidance is an important adaptive feature of communal roosting in this species.     

Cladistic analysis of cassiduloid echinoids: trying to see the phylogeny for the trees

Using DNA fingerprinting we estimated the reproductive success of 49 adult birds belonging to 16 breeding groups of the sexually monomorphic brown skua (Calharacta lonnbergi) from the Chatham Islands (New Zealand). This population has a variable mating system, breeding in both monogamous and polyandrous groups. The parentage of 45 chicks produced over three breeding seasons was unequivocally determined using the multilocus probes 33.15 and 33.6. We found no evidence of either extra-pair or extra-group fertilization and there was no evidence to suggest egg dumping by females in any breeding group. Consequently, in the case of pairs, parentage of all chicks was assigned to the resident adult birds. In addition, band sharing analysis indicated that members of communal groups were not close relatives. In the 10 communally breeding groups examined, multiple paternity within a clutch was recorded on two of the 12 occasions in which two chicks were reared. Analysis of the parentage of offspring belonging to different groups, from different years, demonstrated that the number of chicks produced by some adult males varied considerably between seasons. In contrast, the reproductive success of other individuals was constant; for example, one male produced two chicks in each of the three seasons it was studied, while other males in communal groups did not produce any chicks during the course of this study. Fitness is a lifetime parameter, and any assessment of it requires studies over at least the average lifetime of an individual. The findings presented in this study suggest that, for brown skuas, there are significant differences in the reproductive success of some adult males in different breeding seasons. These results indicate that estimates of reproductive fitness based on only a single breeding season's data can be seriously inaccurate. Should temporal changes in paternity (and/or maternity) be shown to be common phenomena in other species, then such results would have major implications for the interpretation of parentage studies.     

Bird-pollinated flowers in an evolutionary and molecular context

Evolutionary shifts to bird pollination (ornithophily) haveoccurred independently in many lineages of flowering plants.This shift affects many floral features, particularly thoseresponsible for the attraction of birds, deterrence of illegitimateflower visitors (particularly bees), protection from vigorousforaging by birds, and accurate placement of pollen on bird'sbodies. Red coloration appears to play a major role in bothbee-deterrence and bird-attraction. Other mechanisms of bird-attractioninclude the production of abundant dilute nectar and the provisionof secondary perches (for non-hovering birds). As a result ofselection for similar phenotypic traits in unrelated bird-pollinatedspecies, a floral syndrome of ornithophily can be recognized,and this review surveys the component floral traits. The strongconvergent evolution evident in bird-pollinated flowers raisesa question about the nature of the genetic mechanisms underlyingsuch transitions and whether the same gene systems are involvedin most cases. As yet there is too little information to answerthis question. However, some promising model systems have beendeveloped that include closely related bee and bird-pollinatedflowers, such as Ipomoea, Mimulus, and Lotus. Recent studiesof floral developmental genetics have identified numerous genesimportant in the development of the floral phenotype, whichare also potential candidates for involvement in shifts betweenbee-pollination and bird pollination. As more whole-genome informationbecomes available, progress should be rapid. Key words: Anthocyanin pigmentation, bird-pollination, candidate gene, developmental genetics, honey-eaters, hummingbirds, nectar, ornithophily, pollination syndrome, sunbirds Received 2 November 2007; Revised 21 December 2007 Accepted 7 January 2008     

The social organization and behaviour of the Hoatzin Opisthocomus hoazin in central Venezuela

The social organization and behaviour of the Hoatzin Opisthocomus hoazin , a cooperatively-breeding folivorous bird, was studied in the central plains (llanos) of Venezuela. In this area Hoatzins nested in communal social units of two to eight individuals. Units were usually composed of a breeding pair and up to six helpers at the nest. Helpers, usually offspring retained from the previous years' nesting, aided in all breeding activities of their social unit except egg production. On the study site, Hoatzin units defended extremely small, all-purpose territories along watercourses during the rainy (breeding) season, but migrated up to 2 km to areas with permanent water during the dry season. Nesting extended from early May to October. Nest and egg measurements and growth rates of young are provided. Nesting success was low (27%), primarily due to predation by Cebus olivaceus and several other species. Annual survival of adults and young was high. Young did not breed during their first year; 90% of yearlings remained on their natal territories as helpers. Females appear to be the dispersing sex. The results are discussed in relation to previous work on the Hoatzin. The demography of the study population fits the criteria for several recent theories regarding the evolution of cooperative breeding in birds.     

Mechanisms and fitness effects of interspecific information use between migrant and resident birds

Interactions with potential competitors are an important componentof habitat quality. Due to the costs of coexistence with competitors,a breeding habitat selection strategy that avoids competitorsis expected to be favored. However, many migratory birds appearto gain benefits from an attraction to the presence of residentbirds, even though residents are assumed to be competitivelydominant. Thus far the mechanisms of this habitat selectionprocess, heterospecific attraction, are unknown, and the consequencesfor resident birds of migrant attraction remain untested. Throughheterospecific attraction, migrants may gain benefits if thedensity or territory location of residents positively reflectshabitat quality, and/or they gain benefits through increasedfrequency of social interactions with residents in foragingor predator detection. In this experiment, we examined the reciprocaleffects of spatial proximity on fitness-related traits in migrantpied flycatcher (Ficedula hypoleuca) and resident great tit(Parus major) by experimentally forcing them to breed eitheralone or in close proximity to each other. Surprisingly, greattits bore all the costs of coexistence while flycatchers wereunaffected, even gaining slight benefits. In concert with anearlier study, these results suggest that flycatchers use titsas information about good-quality nest-site locations whilebenefits from social interactions with tits are possible butless important. We suggest that utilizing interspecific socialinformation may be a common phenomenon between species sharingsimilar resource needs. Our results imply that the effects ofinterspecific information use can be asymmetric and may thereforehave implications for the patterns and consequences of speciescoexistence.     

青海北部高寒草甸雀形目鸟类繁殖生态学的研究进展

从鸟巢特征、巢址选择、窝卵数、育幼行为、雏鸟生长发育、繁殖生产力以及繁殖对策等方面,对青藏高原高寒草甸雀形目鸟类繁殖生态学进行了综合分析与评述。高寒草甸雀形目鸟类受适合繁殖季节长度、食物资源和捕食压力的影响,或选择逐步投资对策,或选择一次投资对策;每个种群的常见窝卵数就是最适窝卵数;雏鸟的发育模式相对固定,不存在补偿性生长,但是生长期长度是可变化的。①研究亲-子通讯行为的进化和稳定性,提出适应高寒草甸雀形目鸟类的亲-子间的通讯行为假设;②建立在巢环境特征变化梯度(开放到封闭)上的生命表,找出决定适合度的生命表参数(繁殖率和存活率)的因果关系;③测定在巢环境特征变化梯度上的生态领域变化将是未来研究的3个方向。