Male nest building but not display behaviour directly influences mating success in the polygynous Red Bishop,Euplectes orix

Previous studies of the highly polygynous and strikingly sexually dimorphic Red Bishop, Euplectes orix (Ploceinae, weaverbirds), have suggested random female settlement patterns and no correlates of male reproductive success except the number of nest frames (‘cock's nests’) built by the male. Although this confirms the central role of the nest in weaverbird courtship it also contrasts with demonstrated sexual selection on male morphology and behaviour in several closely related Euplectes species. Two major aspects of male sexual advertising have not been included in previous studies; display behaviour and territory size. In this study we use multivariate selection analysis, with the number of active nests in a territory as the fitness measure, to identify direct and indirect sexual selection on male sexual behaviour, territory size and nest building. In accor–dance with previous findings, mating success was not strongly skewed among the territorial males, and females appeared to settle randomly with respect to available nests. The number of cock𠀧s nest built was the only determinant of male breeding success, even when controlling for male display activity and territory size. We argue that, despite their conspicuous sexual dimorphism, females settle independently of both male or territory quality, and that variance in male reproductive success is a consequence of male–male competition.     

Experimentally elevated testosterone levels enhance courtship behaviour and territoriality but depress acquired immune response in Red Bishops Euplectes orix

The immunocompetence handicap hypothesis (ICHH) posits that the hormone testosterone mediates a trade‐off between investment in reproduction and immunological condition. In this study, we tested the ICHH in the Red Bishop Euplectes orix, a polygynous weaverbird. Males of this strongly sexually dimorphic species show an elaborate courtship display to attract females and compete aggressively with other males for nesting sites in breeding colonies. We experimentally elevated testosterone levels in breeding male Red Bishops kept in an aviary with a subcutaneous implantation of testosterone‐releasing pellets. We then compared behaviour, development of territory size and immunological condition (as assessed through a white blood cell count) of the experimental group with a control group treated with placebos. In addition, we measured the primary and secondary response to phytohaemagglutinin (PHA) to investigate the effect of testosterone on both innate and acquired immunity. Males with elevated levels of testosterone enlarged their territories and conducted more courtship behaviour, while showing a decrease in health, expressed by an increased heterophil/lymphocyte ratio compared with the control group. Males of the control group showed an increase of the secondary response to PHA, as expected under the assumption that repeated exposure to an antigen enhanced the immune response due to acquired immunity. However, males with experimentally increased testosterone levels did not show such an enhanced immune response in the secondary PHA test (although sample size and power of the statistical tests were low), indicating that testosterone treatment might directly or indirectly suppress some component of the acquired immune response.     

Plumage Colouration,Age, Testosterone and Dominance in Male Red Bishops (Euplectes orix): A Laboratory Experiment

Visual signals such as plumage characteristics in birds often play a key role in the establishment of dominance in contests by acting as a badge of status that can be used to assess individual fighting ability. We studied the role of plumage colouration in males of the red bishop (Euplectes orix), a sexually dimorphic and polygynous weaverbird species occurring in sub‐Saharan Africa and breeding in dense colonies around water. Males are highly territorial and often engage in competition over limited resources such as breeding sites and potential mates. By experimentally staging male–male contests over a limited food source, we wanted to determine whether the orange–red breeding plumage in this species serves as a dominance signal between individuals, with males with redder plumage being dominant over those with duller plumage. In the first set of experiments, we staged contests between unfamiliar and unmanipulated males. The setup of the second set of experiments was identical to the first, with the exception that those males with the lowest chroma and hue values had their plumage experimentally reddened within the range of the natural variation. In addition to plumage colouration, we incorporated testosterone levels, body condition and age into the analysis of factors contributing to contest outcome. Our results show a consistent and strong age effect in both sets of experiments, which seems to be independent of plumage colouration, testosterone and body condition. This suggests that in the red bishop, the outcome of male–male competitions over limited resources is determined by age‐related acquired experience rather than by status signalling through plumage colouration.     

Nest and mate choice in the red bishop (Euplectes orix) : female settlement rules

We investigated female settlement in a colony of red bishops(Euplectes orix), a territorial and highly polygynous weaverbirdwidely distributed over sub-Saharan Africa. An earlier studyshowed that male reproductive success is mainly determinedby the number of nests a male builds in his territory, whichappeared to be a good indicator of male quality. Because malesprovide no parental care or food resources within the territory,females sharing a territory do not compete for material resourcesand might therefore be expected to settle preferentially interritories of males that build many nests to gain the possiblegenetic benefit of high-quality offspring. An analysis of femalesettlement, however, revealed that females did not show a preferencefor territories of males with many nests and that the distribution of female breeding attempts with regard to the number of vacantnests within a territory could be explained best by randomfemale settlement in 3 out of 4 years. Females settled moreoften than expected by chance (in 3 out of 4 years) in territoriesalready containing occupied nests, indicating that residentfemales did not discourage settlement of additional females.However, sharing a territory with other females might imposecosts in terms of an increased predation risk because nestsin territories that contained other nests with young sufferedfrom higher predation than nests in territories that did notcontain other nests with young. Females therefore might tradethe possible benefits of settling in territories of males withmany nests against the costs of sharing a territory with otherfemales. This might result in the mating pattern found withrandom female settlement and male reproductive success beingdirectly proportional to the number of nests built. We discuss possible implications of this mating pattern for sexual selectionon males.     

Colony size and nest density predict the likelihood of parasitism in the colonial Southern Red Bishop Euplectes orix– Diderick Cuckoo Chrysococcyx caprius system

Colonial nesters are potentially susceptible to brood parasitism because they present an aggregated source of accessible nests to brood parasites. However, colonial breeding may confer fitness advantages on potential host species that outweigh the costs of parasitism, particularly if colonies are large or dense enough for corporate vigilance to deter parasitism. In addition, some studies have suggested that the spatial habitat structure near host populations is a critical determinant of parasitism rate, with cuckoos targeting those colonies close to cover. We examined the determinants of the likelihood of parasitism by Diderick Cuckoos Chrysococcyx caprius on their main southern African host, the colonially breeding Southern Red Bishop Euplectes orix , from 24 colonies and 1141 nests over two seasons. The likelihood of parasitism by Diderick Cuckoos decreased significantly with increasing colony size and nest density, but not with distance to cover from a colony, providing no support for the spatial habitat structure hypothesis. We suggest that proximate constraints, such as visibility in the semi-closed nest, limit the ability of the host to recognize the Cuckoo egg, giving rise to low rates of rejection of Cuckoo eggs. However, the Cuckoo cannot exploit this apparent weakness when the host breeding population is in large colonies that are protected by corporate vigilance. Consequently, the Diderick Cuckoo – Southern Red Bishop system may represent an evolutionary equilibrium in host and parasite defences.     

The ecology of cooperative breeding behaviour

Ecology is a fundamental driving force for the evolutionary transition from solitary living to breeding cooperatively in groups. However, the fact that both benign and harsh, as well as stable and fluctuating, environments can favour the evolution of cooperative breeding behaviour constitutes a paradox of environmental quality and sociality. Here, we propose a new model – the dual benefits framework – for resolving this paradox. Our framework distinguishes between two categories of grouping benefits – resource defence benefits that derive from group‐defended critical resources and collective action benefits that result from social cooperation among group members – and uses insider–outsider conflict theory to simultaneously consider the interests of current group members (insiders) and potential joiners (outsiders) in determining optimal group size. We argue that the different grouping benefits realised from resource defence and collective action profoundly affect insider–outsider conflict resolution, resulting in predictable differences in the per capita productivity, stable group size, kin structure and stability of the social group. We also suggest that different types of environmental variation (spatial vs. temporal) select for societies that form because of the different grouping benefits, thus helping to resolve the paradox of why cooperative breeding evolves in such different types of environments.     

Stress-dependent trade-off Between Immunological Condition and Reproductive Performance in the Polygynous Red Bishop (<Emphasis Type="Italic">Euplectes orix</Emphasis>)

According to life-history theory, a condition-dependent trade-off between reproductive performance and immune function might be expected, with only superior individuals being able to allocate many resources into reproduction without having detrimental effects on their immune system. However, little attention has been paid to the possibility that annual variations in environmentally and socially induced stress levels modify this trade-off. We analysed haematological parameters and investigated the relationship between male immunological condition and reproductive performance as measured by reproductive effort and success in a colony of the highly polygynous red bishop (Euplectes orix) for five consecutive breeding seasons. Haematological parameters can be used to assess an individuals’ stress level, and especially the heterophile/lymphocyte ratio (H/L ratio) is known to increase in response to a wide variety of stressors. Relative basophile counts, heterophile counts, lymphocyte counts, absolute leukocyte counts and H/L ratios of territorial males varied significantly among seasons. Both relative heterophile counts and H/L ratios were significantly positive related to overall breeding activity within the colony as measured in terms of total number of nests accepted and total number of eggs laid in the study colony within a breeding season. The relationship between immunological condition (as assessed by relative lymphocyte and heterophil counts and the H/L ratio) and both male reproductive effort (as measured by the number of nests built by the territorial males) and reproductive success (as measured by the number of nests accepted) varied considerably among seasons, ranging from significant negative to significant positive correlations. Across seasons, we found a significant negative relationship between the within-season correlation coefficients of individual H/L ratios against reproductive performance and the average H/L ratio of all territorial males in that season. Thus, a positive association between the immunological condition of a male and his reproductive performance (indicated by a negative correlation between H/L ratio and reproductive performance) exists only in seasons with high average H/L ratios (i.e. high average stress levels). We conclude that the trade-off between immunological condition and male reproductive performance might be important only in seasons with an overall reduced level of male immunological condition due to environmentally and/or socially induced stress and immunosuppressive conditions.Co-ordinating editor: L.D. Hurst     

The breeding behaviour of Gammarus duebeni

The breeding behaviour of a population of Gammarus duebeni is investigated. The breeding system includes a precopulatory guarding phase by a male of a female and the length of this phase varies markedly over the season. Large size is not of as great advantage in reproductive competition between males as in a stream population of G. pulex. In the spring of 1981 oligochete worms, Nais elinguis, were found in the brood pouches of some females; eggs were seldom present with the worms but rather amorphous debris. The occurrence of the worms and the debris in the females' pouches coincided with the pattern of abundance of the worms previously reported.     

The effect of Azolla on mosquito breeding

Surface agents to smother mosquito breeding sites have been used extensively for mosquito larval control. Such agents range from oil films and chemical monolayers, to expanded polystyrene beads(1,2). Here, Lu Bao-lin discusses the use of Azolla - a floating fern - for a similar effect. The fern has the additional advantage of providing a useful source of green manure as a crop fertilizer.     

The effect of food availability on the foraging behaviour of breeding Great Skuas Catharacta skua and Arctic Skuas Stercorarius parasiticus

Seabirds' behavioural activity budgets have been proposed as an indicator of changes in marine food supplies. Reduced recruitment and a low biomass of sandeels Ammodytes spp. around Shetland in the late 1980s were associated with a dramatic increase in the foraging effort of breeding skuas. We present data on the territorial attendance patterns of breeding Great Skuas Catharacta skua and Arctic Skuas Stercorarius parasiticus in Shetland in 1987 and examine three aspects of the recorded increase in foraging effort.
Time budget studies indicate that recording territorial attendance by infrequent, daily spot observations provides an accurate measure of the time spent off-territory by both skua species. None of the pairs of Arctic Skua studied ever left their chicks unattended in 1987. The same was true of 10 out of 27 pairs of Great Skuas. Although the remaining pairs of Great Skuas frequently left their chicks unprotected, evidence of pair co-ordination to minimise this suggests that their foraging schedules were still constrained by the need to protect their offspring. During periods of high chick-demand, variation between pairs' foraging efforts largely reflected variation in those of the females. Thus, we suggest that increased chick neglect in years of food shortage arises as females abandon their role of guardian for that of provider. By the end of the breeding season in 1987, both male and female Great Skuas foraged from 65 to 89% of daylight hours. The lack of any further increase in the foraging effort of Great Skuas in subsequent years of poorer reproductive success was almost certainly because time and energy constraints prevented either sex from doing so. We suggest that the comparatively short amount of time spent foraging by Arctic Skuas in 1987 may reflect an advantage conferred by their role as specialist kleptoparasites.     

Observations on the breeding biology and behaviour of the Lesser Jacana,Microparra capensis

Two Lesser Jacana nests were found in Hwange National Park, Zimbabwe and were observed over a period of four months beginning in March 2000. Both sexes were involved in preparing the breeding platform, incubation, and caring for the chicks, which were not carried by the adults. Both nests had three eggs. The incubation period for one clutch of eggs was not less than 19 days. The chicks all hatched on the same day and remained in the vicinity ofthe nest for the first few days where they were brooded by an adult. Initially the adults brought food to the chicks but the chicks started feeding themselves when they moved away from the nest. Ten days after hatching the chicks had doubled in size and were walking confidently with the attending adult some distance from the nest. First flight was seen at 32 days old, and the chicks appeared to be independent 63 days after hatching.     

Status of breeding seabirds on the Northern Islands of the Red Sea,Saudi Arabia

We undertook breeding surveys between 2010 and 2011 to assess the status of breeding birds on 16 islands in the northern Saudi Arabia. Sixteen bird species were found breeding at three different seasons; i.e. winter (Osprey), spring (Caspian and Saunder’s Terns), and summer (Lesser Crested, White-cheeked, Bridled Terns). It is postulated that food availability is an important factor influencing the breeding of seabirds in the northern Saudi Arabian Red Sea. Several species laid eggs earlier in northern parts of the Red Sea than in southern parts. The predicted increases in temperatures (T_a) could have a negative effect on species survival in the future, especially on those whose nests that are in the open. Finally, disturbance, predation and egg collection were probably the main immediate threats affecting the breeding seabird species in the northern Red Sea.     

The cichlid fishes of Guyana, South America, with notes on their ecology and breeding behaviour

Field studies in Guyana, north-eastern South America, from 1957 to 1962 included observations on the ecology and behaviour of cichlids in natural waters. Collections made were examined at the British Museum (Natural History) together with other cichlid material from Guyana. This paper records these observations and gives keys for the field indentification of these cichlids. Fifteen genera comprising at least 35 species occur in Guyana, mostly species with a wide distribution in tropical South America. In the predatory Cichla ocellaris which grows larger than other South American cichlids, growth continues long after the fish matures. Males tend to be larger than associated females. The behaviour of Cichla ocellaris and Cichlasoma festivum when guarding their young suggests that the caudal ocellus has a vital role in the orientation of young to parent. Most of these cichlids in which breeding habits are known are substratum-spawners. An attachment gland, producing viscous threads, was found on the heads of recently hatched Geophagus jurupari young, although this species carries the young in the mouth.     

The effect of rainfall on tick challenge at Kyle Recreational Park,Zimbabwe

The effect of rainfall pattern on tick challenge was investigated at Kyle Recreational Park, Zimbabwe, from 1991 to 1992 using drag and removal plot methods to sample environmental tick density. The abundance of adults and nymphs of the brown ear-tick Rhipicephalus appendiculatus and larvae of the bont tick Amblyomma hebraeum was positively correlated with monthly rainfall, whereas no relationship with rainfall was revealed for larval R. appendiculatus, adults of the red-legged tick R. evertsi, or larvae of the blue tick Boophilus decoloratus. A comparison between 1991 (490 mm rainfall) and the drought year of 1992 (161 mm) revealed significant differences in the abundance of R. appendiculatus, A. hebraeum, and B. decoloratus. During the wet season, R. appendiculatus adults were 2–3 time more numerous in the environment during the higher rainfall year of 1991. A. hebraeum larval abundance exhibited a similar pattern to that of R. appendiculatus adults, but B. decoloratus larvae were more abundant in the drought year of 1992 during both the wet and dry seasons. Comparable tick abundance data collected at Kyle during the above-average rainfall years of 1975–1977 (mean = 1029 mm) were compared with tick challenge during the below-average rainfall years of 1991–1992 (mean = 326 mm). In grassland sand habitat and all habitats combined R. appendiculatus adults, nymphs, and larvae were much more abundant during the high rainfall years. In contrast, larvae of B. decoloratus were more numerous during the drier years. A. hebraeum larvae were also more abundant during the drier years. The strong positive correlation of adult R. appendiculatus abundance with rainfall and the coincidence of increased adult tick challenge with increased rainfall indicates that adult R. appendiculatus tick burden on hosts would be heaviest during the wet season and high rainfall years.     

The influence of pair-status on the breeding behaviour of the Kittiwake Rissa tridactyla before egg-laying

The breeding behaviour of individually marked Kittiwakes Rissa tridactyla that retained mates from the previous year (SAME) was compared, over the period from pair-formation to egg-laying, with those that changed mates (CHANGE). Position of nest-site in colony and breeding experience did not differ in the two groups studied. Hirds in CHANGE pairs attended the nest-site more frequently and as a result probably had less 'off-duty' time during which to forage. Rates of greeting were higher in CHANGE pairs. Differences between the two groups were usually greatest during the first two weeks after pair-formation an decreased toward egg-laying. CHANGE pairs copulated over a longer period before egg- laying, but stopped copulating sooner than SAME pairs. Copulation rates were higher in SAME pairs immediately before egg-laying. The causation of the behavioural differences between the two groups is discussed in terms of mate familiarity. It is suggested that the recorded differences explain the lower reproductive success in CHANGE pairs reported by other workers.