Does Social Mating System Influence Nest Defence Behaviour in Great Reed Warbler (Acrocephalus arundinaceus) Males?

In birds with biparental care, males and females often conflict over how much care to provide to their offspring and it may be substantially influenced by increased level of polygamy. In accordance with sexual conflict theory, males of socially polygynous bird species provide much less care to their nestlings than do males of most socially monogamous species. Most of previous studies, however, have used feeding behaviour as an index for variations in male parental care only. However, this may be skewed if polygynous males compensate for lower feeding assistance through the provision of other parental care such as protection of nests from predators. In this paper, we examine nest defence behaviour in the facultatively polygynous great reed warbler with respect to sex and type of social mating system. We recorded latency to the first arrival, distance from the predator and defensive reaction of each parent towards a human intruder. Socially polygynous males with two simultaneously active nests defended primary females’ nests less vigorously than socially monogamous males, whereas no differences were found between monogamous and primary females. Generally, however, they took a bigger role in nest defence than males in all cases. Our results support an idea that sexual conflict is driven by polygamy and that type of social mating system can influence nest defence behaviour of facultatively polygynous birds. This finding should be taken into consideration when studying nest defence parental care in polygynous mating systems.     

Environmental Change and Extended Phenotypes: Does Eutrophication Influence Nest Building in Sticklebacks?

Many species use extended phenotypes, such as purpose‐built nests, to increase their reproductive success. These traits have to be adjusted to local environmental conditions to maximize fitness. An important question is whether species are able to adjust their extended phenotypes to human‐induced rapid environmental changes. We investigated whether populations of threespine stickleback, Gasterosteus aculeatus, exposed to different degrees of human‐induced eutrophication during the last decades, have differentiated phenotypically in their nest‐building behaviour. Stickleback males build nests that they use both in mate attraction and for offspring protection and whose characteristics vary with environmental conditions. We allowed males from parallel pairs of mildly and severely eutrophied habitats to build nests under standardized conditions in the laboratory. We recorded the time it took the males to build a nest, the size and neatness of the completed nest and the use of nest ornaments. We found eutrophication at the site of capture to influence nest‐building time – males from eutrophied habitats built faster. However, eutrophication did not alter nest structure or the use of nest ornaments. This is probably because the nests are concealed in vegetation or under stones and females cannot evaluate them before they have followed the male to the nest, and predators cannot detect them before close to the nest. Thus, reduced long‐range visibility does not influence the use of nests as mate choice cues or for offspring protection. This contrasts with a recorded effect of eutrophication on courtship behaviour, whose efficiency depends on long‐range visibility. This suggests that traits are adjusted to eutrophication depending on the influence of eutrophication on the function of the traits.     

Dynamic risk assessment: does a nearby breeding nest predator affect nest defence of its potential victim?

There is growing evidence that birds are able to discriminate different types of nest intruders and adjust their nest defence behaviour according to intruder dangerousness and distance from the nest (the dynamic risk assessment hypothesis). Here, we tested whether birds’ decisions about nest defence may additionally be affected by an increasing familiarity with a particular nest predator. We tested nest defence responses of great reed warblers Acrocephalus arundinaceus to a nest predator, the little bittern Ixobrychus minutus. Great reed warbler nests located close (≤7 m) to synchronously breeding little bitterns were “neighbour”, other nests were “solitary”. Great reed warbler specific aggression towards a little bittern dummy was much lower (~5-times) at neighbour than solitary nests. In contrast, generalised responses to a control innocuous intruder (the turtle dove, Streptopelia turtur) were statistically identical at neighbour and solitary nests. These patterns are in line with dynamic risk assessment hypothesis. We hypothesise that decreased great reed warbler aggression at neighbour nests also represents a specific behavioural adaptation to nesting in association with the little bittern. Little bitterns breeding closer to great reed warblers showed decreased risks of failure due to predation. However, further research is needed to experimentally test the causal links behind these patterns.     

Mate competition and resource competition are inter‐related in sexual selection

Sexual selection can be affected by the competition for limited breeding resources and/or the competition for limited mates. Although there is ample evidence for each type of competition by itself, little is known about their relative importance and interaction. To address these questions, we established 48 experimental breeding populations of the two‐spotted goby (Gobiusculus flavescens), a substrate‐breeding fish with paternal care. In three experimental treatments, males were limited in the access to either nest sites or mates or were provided with both nests and mates in excess. We quantified male competition behaviour (agonistic and courtship), the opportunity for selection and selection on male body size. Limited access to nests and mates produced similar opportunities for selection, but only limited access to mates increased male competitive behaviours and caused positive selection on male body size. Selection on body size in the mate‐limited treatment was due both to larger males being more likely to take up nests and to larger males being more likely to mate once they had a nest. These findings demonstrate that resource and mate limitation can differ in their effects on sexual selection. The results also reveal that resource and mating competition can be highly inter‐related and not always separated in time, implying that methods to disentangle the two processes must be chosen with care. Future research should consider experimental and analytical approaches similar to those of the present study in attempts to elucidate the interaction of resource and mating competition in animals.     

Eviction behaviour of the common cuckoo Cuculus canorus chicks

We studied the eviction behaviour of common cuckoo Cuculus canorus chicks by video recording at nests of great reed warblers Acrocephalus arundinaceus and reed warblers Acrocephalus scirpaceus . There were no significant differences in hatching mass and age at first eviction between cuckoos reared by either host. However, mass at eviction had a significant effect on the timing of first eviction event. No significant difference in time required to evict was found between serial intranest eviction events for cuckoos raised by either host. However, "great reed warbler" cuckoos evicted significantly quicker than "reed warbler" cuckoos during particular eviction events. A majority (70%) of "reed warbler" cuckoos evicted during the day, while most "great reed warbler" cuckoos evicted nocturnally (63%). We did not find any effect of the temperature inside or outside the nest on eviction behaviour. Both "great reed warbler" and "reed warbler" cuckoos evicted regardless the fact whether a parent was absent or present at the nest. Interestingly, individual cuckoos were consistent in their eviction behaviour relative to host presence or absence; particular cuckoo chick evicted only when the parents were present or absent from the nest.     

Polygynous great reed warblers Acrocephalus arundinaceus suffer more cuckoo Cuculus canorus parasitism than monogamous pairs

There is increasing evidence that hosts within a population may not be parasitized by common cuckoos Cuculus canorus with equal probability. Such non‐randomness has been documented, for example, for host nest sites and host quality. In this study we demonstrate association between successful cuckoo parasitism and host social mating system. We found that nests of socially polygynous great reed warblers Acrocephalus arundinaceus were more often successfully parasitized than the nests of their monogamous counterparts. We hypothesize that lack of parental assistance provided by polygynous males to their mates during egg laying period and higher nest activity in their territories could contribute to this discrepancy. These data imply that social mating system should be taken into account in future studies of brood parasitism.     

Mate Choice and Spawning Success in the Fighting Fish Betta splendens: the Importance of Body Size, Display Behavior and Nest Size

Courtship displays should be exaggerated enough to attract mates and yet tempered so as not to deter them. We tested this hypothesis in the fighting fish Betta splendens by studying courtship displays and body size and their relationships with male parental quality and female fecundity, as well as the effects of display behavior and body size on mate choice decisions and spawning success. Because of their high degree of parental investment, males are expected to be discriminating in their choice of mates. Males who displayed more frequently built larger nests, a measure of parental quality, but larger males did not. When females were paired with males with high display rates, however, the pair had fewer eggs in their nest, even when accounting for female body mass. In a mate choice test using computer‐generated male stimuli that differed only in display behavior, females showed no preferences for displaying males vs. non‐displaying males, or for males with higher display rates vs. lower display rates. In similar tests in which the computer‐generated males differed only in size, females preferred larger males, but also preferred males that differed with respect to body size (negative assortative mating). Males preferred computer‐generated females that performed courtship displays over non‐displaying females, but showed no preferences for female body size. Neither a female's body size nor her display behavior was a significant predictor of her fecundity as estimated by the number of eggs released during spawning. Thus, our results suggest that female B. splendens must balance male parental quality (nest size) with the risk of potentially disruptive or dangerous behavior during spawning, and that females may minimize these risks through negative size‐assortative mating. Female display behavior, while unrelated to fecundity in our study, may attract males because it indicates reproductive readiness or serves a species‐recognition function.     

Successive nest building and polygyny of Fan-tailed Warblers Cisticola juncidis

The polygynous mating system of the Fan-tailed Warbler Cisticola juqcidis was investigated between 1978 and 1981. The male warbler builds many nests unaided; however, he has no more than one active vacant nest for courting at any time. Nest building lasted from April until August. After completing the outer fabric of a nest, the male advertised it and led a female to the nest site by a unique invitation flight. On average a male built 6.5 nests during one breeding season and three of them were accepted by females. The most successful male completed 18 nests, and mated with 11 females. Out of a total of 111 males which established a territory, 30 had no mate, 14 were monogamous, and the rest were polygynous. About 50 to 70% males were polygynous over the four years. The sex ratio varied from 1.41:1 to 2.17:1 (females: male) in the breeding population. It was partly caused by the presence of 'floating males'. After the completion of the outer fabric of the nest, the male warbler did not take any further role in nesting and caring for young.
The polygynous mating system of the Fan-tailed Warbler is characterized by successive nest building. Its extreme development results from the long breeding period and the male having no role in parental care.     

Elaborate Nests in a Weaverbird: A Role for Female Choice?

Studies on sexual selection have focused on behaviour and morphology, but several groups of animals build elaborate structures associated with acquiring a mate. I investigated female choice for nests built by male baya weavers (Ploceus philippinus). Nest choice by females should be strong, as nests are obvious direct benefits provided by males. I used a field experiment supplemented with correlational information to ask whether females appear to base mate choice decisions on male behaviour, nest architecture, and nest location. When the nests of highly visited males were exchanged with those of poorly visited males, female visits remained highest at the original male and location. I found no relationship between female choice and male display or other behaviour. Correlational analyses show that nest location was a better predictor of female choice than was nest architecture. These data suggest that current female choice is driven more by access to safe nesting sites rather than to well‐built nests, possibly because all males are able to build nests of adequate quality. However, nest architecture is unlikely to be irrelevant to females, and its role deserves further investigation.     

An ecological analysis of mating biology of Xylocopa virginica in southern Ontario

1. Xylocopa virginica virginica Linnaeus is a wide‐ranging species with plastic nesting behaviour that appears to represent an intermediary between solitary and social nesting species. Over 3 years, a natural population was studied with the objective of quantifying the relationship among population dynamics, climate, female nest provisioning behaviour, and male mating strategy. 2. Males in the population congregated around female‐occupied nesting sites before the beginning of nest provisioning by females; both resident and satellite male mating strategies were observed. Overall, the present results are consistent with female defence polygyny. 3. Male mating strategies were consistent across the three breeding seasons of our study, in spite of annual variation in population size, sex ratio, and weather. Male mating behaviour was also consistent with that seen in other populations with longer breeding seasons. 4. Adult non‐breeding females that never leave nests are observed in nests throughout the breeding season and we hypothesise that males continue to defend territories after breeding females have mated because of a small probability they can mate with one of these non‐breeding females. 5. These results are important to our understanding of the relationship between mating systems and the evolution of sociality, contributing data on the role of ecological factors to male mating behaviour. Collection of such data for a variety of species that differ in sociality is necessary for the comparative analysis that is required to fully elucidate coevolution of mating systems and sociality.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.     

Competition and opportunity shape the reproductive tactics of males in the ant Cardiocondyla obscurior

Context-dependent adjustment of mating tactics can drastically increase the mating success of behaviourally flexible animals. We used the ant Cardiocondyla obscurior as a model system to study adaptive adjustment of male mating tactics. This species shows a male diphenism of wingless fighter males and peaceful winged males. Whereas the wingless males stay and exclusively mate in the maternal colony, the mating behaviour of winged males is plastic. They copulate with female sexuals in their natal nests early in life but later disperse in search for sexuals outside. In this study, we observed the nest-leaving behaviour of winged males under different conditions and found that they adaptively adjust the timing of their dispersal to the availability of mating partners, as well as the presence, and even the type of competitors in their natal nests. In colonies with virgin female queens winged males stayed longest when they were the only male in the nest. They left earlier when mating partners were not available or when other males were present. In the presence of wingless, locally mating fighter males, winged males dispersed earlier than in the presence of docile, winged competitors. This suggests that C. obscurior males are capable of estimating their local breeding chances and adaptively adjust their dispersal behaviour in both an opportunistic and a risk-sensitive way, thus showing hitherto unknown behavioural plasticity in social insect males.     

The Conflict between Nest Guarding and Mate Guarding in Penduline Tits (Remiz pendulinus)

In penduline tits (Remiz pendulinus), polygynous males build several very elaborate nests successively during one breeding season to attract females. The time and effort invested in nest building is positively related to their mating success. Intraspecific competition for nest material resulting in nest material theft, delays males' nest building progress which in turn decreases their mating success. Therefore, a nest guarding strategy was predicted. In many bird species, males develop some kind of paternity strategy during the female fertile phase. However, as nest building and the female fertile phase frequently coincide, one would expect a trade-off between these strategies. In this study we determined in particular how nest guarding in males conflicts with their mate guarding behaviour in penduline tits. Our results show that nest building is costly in terms of a male's time budget. Thieves benefit by increasing their rate of acquiring nest material which reduces the effort invested in nest building. Nest guarding is an efficient strategy to avoid thieves, as indicated by the negative relation between the presence of the male near the nest and the frequency of nest material theft. Nest guarding is required for the whole building period but males, however, increased their mate guarding effort during the peak fertile phase to ensure their paternity. The data suggest that, for the trade-off “mate guarding versus nest guarding”, paternity insurance seems to be more important.     

Tactic changes in dusky frillgoby Bathygobius fuscus sneaker males: effects of body size and nest availability

Field and laboratory studies were conducted to examine the effects of nest availability and body size on changes in male mating tactics from sneaking to nest‐holding in the dusky frillgoby Bathygobius fuscus. In the field, the body size of nest‐holding males decreased from early to mid‐breeding season, suggesting the possibility of a change in the tactics of sneaker males to nest‐holding. Many sneaker males did not use vacant spawning nests even when size‐matched nests were available, but they continued to reproduce as sneakers. Similarly, in aquarium experiments with available vacant nests, some sneaker males became nest‐holders irrespective of their body size, but some did not. These results showed that nest availability is not a limiting factor for changes in tactics by sneaker males in this species. Because tactic‐unchanged sneaker males were co‐housed with larger nest‐holding males in the tanks, the body size of nearby nest‐holding males may have affected the decision to change tactics for sneaker males. Moreover, smaller individuals among tactic‐changed males tended to spend more time until spawning, probably because they had relatively larger costs and smaller benefits of reproduction as nest‐holding males compared to larger males.     

Does competition for nests affect genetic monogamy in Cory's shearwater Calonectris diomedea?

Most bird species are socially monogamous. However, extra‐pair copulations (EPCs), resulting in extra‐pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow‐nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7‐year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within‐pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.     

Have your cake and eat it too: male sand gobies show more parental care in the presence of female partners

Traditionally, male parental effort and mate attraction effortare expected to be in conflict as they compete for the sameresource budget. However, the quality of care provided by themale may be of a direct benefit to females and may provide animportant mate choice cue. In a laboratory experiment, we examinedhow males modified their parental behavior with respect to matingopportunity by allowing male sand gobies to mate with a singlefemale either in a big or small nest (a constraint on futuremating potential). We then exposed half of these males to thevisual stimulus from additional females and recorded male eggfanning and nest building (two components of care), courtshipbehavior, and reproductive success through out the brood cycle.We found that males fanned longer and more frequently and didmore nest construction in the presence of females and in bignests. Males guarding large nests courted females more thandid males guarding small nests. All males consumed eggs duringthe brood cycle, but complete clutch cannibalism was most frequentwhen males were guarding small nests in the absence of females.The pattern of filial cannibalism that we observed suggeststhat males prematurely terminated care when their reproductivepotential was low, that is, when there was little nest spacefor additional mating and no mates present. We found no supportfor a trade-off between mate attraction and parental care. Indeed,taken together our results suggest that males may use parentalcare as a courtship strategy and that males who invest in mateattraction also have higher parental effort.     

Untersuchungen an Drossel- und Teichrohrs?nger(Acrocephalus arundinaceus, A. scirpaceus): Bestandsentwicklung, Brutbiologie, ?kologie

Zusammenfassung Von 1973–1978 wurden systematische Beringungen und regelmäßige Nestkontrollen einer Drs-Population im Fränkischen Weihergebiet (Nordbayern) durchgeführt (Auswertung von 487 Nestkarten). Die vorhandene Trs-Population wurde nicht systematisch erfaßt (645 Nestkarten).Der Bestand der einzelnen Teilpopulationen des Drs schwankte im Untersuchungszeitraum; die gesamte Population blieb annähernd konstant.Die Nestabstände benachbarter Drs-Bruten innerhalb eines günstigen Schilfstreifens lagen zwischen 7 m und ca. 300 m. Das kolonieartige Brüten der Trs wird mit Beispielen belegt.Medianer Legebeginn des Drs war der 29. Mai, der des Trs der 13. Juni. Der nach Erreichen des Maximums im Legemuster folgende Abfall war beim Drs deutlich steiler als beim Trs. Die mittlere Gelegegröße des Drs betrug 4,73, die des Trs 3,85 Eier. Bei beiden Arten fand eine Gelegegrößenreduktion mit fortschreitender Brutzeit statt.Das Schlüpfen der Jungen erfolgte beim Drs überwiegend am 12. bis 14. Tag nach Ablage des letzten Eies, beim Trs am 11. bis 13. Die Brutdauer betrug meist 14 (Drs) bzw. 13 (Trs) Tage.Beim Drs waren 59,7 % der Nester erfolgreich. Der Ausfliegeerfolg, bezogen auf erfolgreiche Nester, betrug 73,2 %, der Gesamtbruterfolg demnach 43,7 %. Beim Trs ergaben sich entsprechend die Werte 66,6 %, 82,9 % und 55,2 %. Auch die durchschnittliche Anzahl flügger Jungvögel pro Brutnest lag beim Drs mit 2,00 etwas niedriger als beim Trs mit 2,15. Als Reproduktions-rate des Drs wurde ein Wert von 2,24 flüggen Jungen pro errechnet. Für den Trs wird die Reproduktionsrate wesentlich höher geschätzt.Die Verluste wurden nach Ursachen aufgeschlüsselt, wobei besonders verglichen mit gleichaltrigen Trs die vielfach größere Empfindlichkeit nestjunger Drs gegen Regen und Kälte auffiel.In zwei Fällen konnten für Drs- Zweitbruten mittels Beringung nachgewiesen werden. Beobachtungen an Trs gaben zu Vermutungen von Zweitbruten bei dieser Art Anlaß.Bigamie wurde beim Drs mehrfach mittels Farbberingung nachgewiesen. Aus den Nestabständen konnte im Untersuchungsgebiet nicht auf monogames oder polygames Verhalten der Drs geschlossen werden. Es werden Angaben über Alter und Verhalten polygamer in verschiedenen Jahren gemacht. Paarzusammenhalt am Vorjahresbrutplatz wurde beim Drs mittels Beringung einmal nachgewiesen.Die meisten überlebenden der als Brutvögel beringten Drs kehrten ins Untersuchungsgebiet zurück, von den überlebenden nestjung beringten dagegen etwa ein Drittel. 3 nestjung beringte Trs wurden nach 1 bzw. 2 Jahren im Untersuchungsgebiet zur Brutzeit kontrolliert.Ein Drittel der Drs-Population stammte aus dem Untersuchungsgebiet. 2 nestjung beringte aus 78 km und 500 km Entfernung wurden als Brutvögel kontrolliert. Alter der Brutvögel 1–9 Jahre.An Beispielen wird die räumliche und zeitliche Einnischung beider Arten beschrieben.

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Studies onAcrocephalus arundinaceus andscirpaceus: Population trends, breeding biology, and ecology

Summary Results of 6 years (1973–1978) of systematic ringing and regular nest controls of a great reed warbler population in Northern Bavaria are given (data of 487 nests) as well as results on a population of the reed warbler (data of 645 nests).Numbers of great reed warblers fluctuated in different parts of the study area. The whole population, however, remained fairly constant.Data on the arrival of males in the breeding area are given.Distances between neighbouring nests of great reed warblers varied from 7 to about 300 m. Differences in nest densities in the reed warbler could be found.The mean first egg laying dates in the great reed warbler and the reed warbler were May 29 and June 13 respectively. The great reed warbler showed a distinct steeper decrease in its egg laying pattern than the smaller species. Average clutch size in the great reed warble was 4.73 eggs and 3.85 eggs in the reed warbler. In both species clutch size decreased during the season.Great reed warbler nestlings hatched on the 12th to 14th day after the last egg had been laid, reed warbler nestlings on the 11th to 13th day. The incubation period was mainly 14 days in the great reed warbler and 13 days in the reed warbler.In the great reed warbler 59.7 % of the nests were successful. The fledging success of successful nests was 73.2 %, accordingly the total nest success was 43.7 %. The corresponding data in reed warbler were 66.6 %, 82.9 % and 55.2 %. On average great reed warblers produced 2.00 fledglings per clutch, reed warblers 2.15. In the great reed warbler a reproduction rate of 2.24 fledglings per female was calculated. The reproduction rate in reed warbler was estimated substantially higher.Great reed warbler nestlings were much more sensitive to rain and cold weather than reed warbler nestlings of the same age.Two great reed warbler males were proved to make a second brood. The same is supposed for the other species but could not be proved so far.Polygyny was proved several times in the great reed warbler. Age and behaviour of polygynous males in different years are reported. Two great reed warblers were found breeding with their former mates at last year's breeding place.Most of the great reed warblers ringed as breeding birds returned into the study area. Nearly one third of the great reed warbler nestlings returned for breeding. Three reed warblers ringed as nestlings could be controlled in the study area during breeding period after 1 year and 2 years respectively.Distances of returned great reed warblers in relation to their birth places and their former breeding places are specified.One third of the great reed warbler population originates from the study area. Two females breeding in the study area were ringed as nestlings 78 km and 500 km apart.One-year-old to nine-year-old great reed warblers were found breeding. Data on the age composition of breeding birds are given.Plant species supporting the nests of great reed warbler and reed warbler were investigated. Differences in the spatial and temporal habitat selection of both species are described.

     

Infanticide in great reed warblers: secondary females destroy eggs of primary females

In 1994–1995 artificial nests with attached model eggs were put into territories that were known to have been occupied by male great reed warblers,Acrocephalus arundinaceusin previous years. Because the eggs were made of soft plasticine, predators left peckmarks in them and this enabled us to identify predators by comparing peckmarks with reference marks made by various species. Previous field data had suggested that infanticidal behaviour existed in our study population, as nests of primary females suffered a three times higher rate of nest loss during the egg-laying period than nests of secondary and monogamous females. The presence of infanticide was supported by the experiment. Small peckmarks resembling those of a great reed warbler occurred almost exclusively in territories occupied by great reed warblers, in particular when a new female settled in the territory. The newly settled females built nests closer to depredated than non-depredated nests. That small peckmarks occurred when new females settled strongly suggests that it is secondary female great reed warblers that commit infanticide on eggs of primary females. Females of low harem rank are expected to gain from infanticidal behaviour because a low ranked female gets a higher proportion of male parental investment when the nest of the primary female fails.     

Environmental change mediates mate choice for an extended phenotype,but not for mate quality

Sexual cues, including extended phenotypes, are expected to be reliable indicators of male genetic quality and/or provide information on parental quality. However, the reliability of these cues may be dependent on stability of the environment, with heterogeneity affecting how selection acts on such traits. Here, we test how environmental change mediates mate choice for multiple sexual traits, including an extended phenotype–‐the structure of male‐built nests – in stickleback fish. First, we manipulated the dissolved oxygen (DO) content of water to create high or low DO environments in which male fish built nests. Then we recorded the mate choice of females encountering these males (and their nests), under either the same or reversed DO conditions. Males in high DO environments built more compact nests than those in low DO conditions and males adjusted their nest structure in response to changing conditions. Female mate choice for extended phenotype (male nests) was environmentally dependent (females chose more compact nests in high DO conditions), while female choice for male phenotype was not (females chose large, vigorous males regardless of DO level). Examining mate choice in this dynamic context suggests that females evaluate the reliability of multiple sexual cues, taking into account environmental heterogeneity.     

Sex-related parental care strategies in the lesser spotted woodpecker Picoides minor: of flexible mothers and dependable fathers

We investigated sex-specific parental care behaviour of lesser spotted woodpeckers Picoides minor in the low mountain range Taunus, Germany. Observed parental care included incubation, nest sanitation as well as brooding and feeding of nestlings. Contributions of the two sexes to parental care changed in progress of the breeding period. During incubation and the first half of the nestling period, parental care was divided equally between partners. However, in the late nestling stage, we found males to feed their nestlings irrespective of brood size while females considerably decreased feeding rate with the number of nestlings. This behaviour culminated in desertion of small broods by females shortly before fledging. The fact that even deserted nests were successful indicates that males were able to compensate for the females' absence. Interestingly, the mating of one female with two males with separate nests could be found in the population, which confirms earlier findings of polyandry in the lesser spotted woodpecker. We conclude that biparental care is not essential in the later stage and one partner can reduce effort and thus costs of parental care, at least in small broods where the mate is able to compensate for that behaviour. Reduced care and desertion appears only in females, which might be caused by a combination of two traits: First, females might suffer higher costs of investment in terms of mortality and secondly, male-biased sex ratio in the population generally leads to higher mating probabilities for females in the following breeding season. The occurrence of polyandry seems to be a result of these conditions.