Nest‐site selection by Blue‐black Grassquits in a Neotropical savanna: do choices influence nest success?

ABSTRACT.   Nest-site choice affects individual fitness and possibly reflects natural selection of the capacity of individuals to select appropriate microhabitat features. From 2003 to 2005, we examined nest-site characteristics and nesting success of Blue-black Grassquits ( Volatinia jacarina ) in central Brazil. We compared the characteristics of nest sites and nonused sites, as well as the characteristics of successful and unsuccessful nests. Grassquit nest sites were structurally more complex than nonused sites. Shrub height and the interaction between vegetation height and percentage of ground coverage were the most important predictors of nest placement. Grassquits used only four (20%) of the 20 grass species in the study area, with Paspalum pectinatum used less than expected based on availability and Melinis minutiflora more than expected. The only variable that differed between unsuccessful and successful nests was the distance to nearest conspecific nest; the latter were about twice as far from neighboring nests as unsuccessful nests. The evaluation of microhabitat candidate models indicated that the daily survival probability of nests varied chiefly as a function of the interaction between their external height and inner depth. Greater survival occurred when the external height was minimized in combination with augmentation of internal depth of the nest cup. The link between nest success and the inverse association of external height and internal depth suggests that minimizing the visual cues of nest presence while maintaining a viable incubation chamber can positively affect nest success. Thus, we suggest that nest concealment is the most critical attribute associated with nest site choice for Blue-black Grassquits in the study area. Vegetation cover above the nest seems to be particularly important, perhaps as a strategy to deter visually oriented aerial predators.     

Are parental care trade‐offs in shorebirds driven by parental investment or sexual selection?

Sexual selection, mating systems and parental behaviour are closely linked, although the exact nature of their relationship is controversial. The parental investment hypothesis (PIH) states that parental care disparity drives sexual selection intensity, because the sex providing less care competes for the sex that provides more. In contrast, the sexual selection hypothesis (SSH) asserts that more intense sexual selection on males leads to reduced male parental investment. We tested these hypotheses using directional phylogenetic comparative methods in shorebirds, which have an unusually diverse array of breeding systems. Changes in parental care and sexual selection intensity were tightly correlated, and we carried out three sets of analyses focusing on changes in male behaviour, female behaviour and in either sex. The results from the analyses were consistent with both PIH and SSH, although the patterns in male transition were sensitive to model values. We propose two explanations for these results. First, phylogenetic transitions may be idiosyncratic so that they depend on the ecological circumstances of individual species. Second, transitions in social traits, such as breeding systems, may be rapid and take place in ecological time, so directional phylogenetic methods that work through longer time scales may not infer accurately the timing and direction of all changes.     

How do sucker‐footed bats hold on,and why do they roost head‐up?

Individuals of most bat species hang head‐down by their toenails from rough surfaces, but Madagascar's endemic sucker‐footed bat (Myzopoda aurita) clings head‐up to smooth leaves using specialized pads on its wrists and ankles. We investigated the adhesive performance of 28 individuals and found that attachment performance on brass was not affected by the presence or absence of a seal around the pad–surface interface. Furthermore, on smooth acrylic, the wrist pads were more than nine‐fold weaker when lifted perpendicular to the surface than when pulled parallel to it. The unimportance of a seal and the difference in strength in those directions on a smooth surface are characteristic of wet adhesion, but not of suction. Thus, despite its name, the sucker‐footed bat appears to adhere using wet adhesion. We observed that when wrist pads were pushed anteriorly, they unpeeled easily from the surface because of deformation of the pads. This most likely permits rapid detachment during crawling, but would also cause passive detachment if bats roosted head‐down. This provides an ecomorphological explanation to the head‐up roosting behaviour of these unique bats. The results obtained in the present study thus link morphology, behaviour, and roosting ecology for an enigmatic Malagasy endemic. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 233–240.     

Is selection of host plants by Plagiodera versicolora based on plant‐related performance?

Plant-related performance may be one of the most important factors in the selection of host plants by insect herbivores. We investigated the importance of plant-related performance in host selection by the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), on four willow species: Salix chaenomeloides Kimura, Salix eriocarpa Fr. et Sav., Salix   integra Thunb., and Salix serissaefolia Kimura (Salicaceae). Bagging experiments in the field revealed that the performance of P. versicolora adults and larvae differed significantly among willow species under enemy-free conditions and at constant densities. Egg clutch and larval abundance were positively related to adult abundance. Plagiodera versicolora adults did not discriminate strongly among willow species for feeding and oviposition. Larval performance did not differ among willow species in the presence of natural enemies, suggesting that interspecific differences in host quality were overridden by mortality from natural enemies. Adult and egg clutch abundance of P. versicolora changed seasonally despite the temporal stability of adult and larval performance under enemy-free field conditions. Thus, plant-related performance of P. versicolora adults and larvae may contribute little to population growth and temporal dynamics of host use in P. versicolora . Potential factors that reduce discrimination of P. versicolora among host willow species are discussed.     

Host selection in parasitic birds: are open‐cup nesting insectivorous passerines always suitable cuckoo hosts?

How do potential hosts escape detrimental interactions with brood parasites? Current consensus is that hole‐nesting and granivorous birds avoid brood parasites, like common cuckoos Cuculus canorus, by their inaccessible nest‐sites and food unsuitable for parasites, respectively. Any open‐nesting insectivorous hosts are believed to remain open to brood parasite exploitation which leads to the evolution of costly host defences like egg or chick discrimination. In contrast to this coevolutionary scenario, we show for the first time that a previously not studied but seemingly suitable host species escapes brood parasites. The Asian verditer flycatcher Eumyias thalassinus, feed newly hatched chicks entirely with beetles and grasshoppers. These are poor quality and hard to digest diet items that are rarely fed to own or cuckoo chicks by regular hosts. Indeed, chick cross‐fostering experiments showed that these food items remained undigested by either cuckoos or other sympatric passerines causing them to die quickly. Egg discrimination experiments showed that the flycatcher accepts any foreign eggs. Although most but not all other potential explanations can be safely excluded at present, the most parsimonious historical explanation for these patterns is that the flycatcher exploits a trophic niche that no other sympatric bird can exploit, and that any cuckoo lineages that switch from their original hosts to the flycatcher have no possibilities for establishing viable populations. Thus, the current classification of host suitability based on diet composition may need revision, raising an important cautionary tale for comparative studies and the interpretation of apparent host rejection of parasitic chicks.     

Female ground tits prefer relatives as extra‐pair partners: driven by kin‐selection?

Socially monogamous female birds routinely mate with males outside the pair bond. Three alternative hypotheses consider genetic benefits as the major driver behind the female strategy. The inbreeding avoidance hypothesis predicts that females paired with closely related males should seek copulations with distantly related extra-pair partners to avoid fitness loss from inbreeding depression; the outbreeding avoidance hypothesis predicts the opposite; the kin-selection hypothesis suggests that regardless of social mate relatedness, females should give related males extra-pair fertilization opportunities to gain inclusive fitness if the costs from inbreeding are minor. We test these hypotheses with a facultative cooperative breeder, the ground tit (Parus humilis). Social pairs of ground tits formed randomly with respect to genetic relatedness. In both bi-parental and cooperative groups, a female's engaging in extra-pair mating was independent of relatedness to her social mate; however, females preferred extra-pair sires to which they were more related than to their social mates. Moreover, females had higher relatedness with either their extra-group extra-pair sires in both bi-parental and cooperative groups, or within-group helper sires in cooperative groups, than expected by chance. When more than one potential extra-pair partner was available around a female's nest, she tended to select a relative. There was no indication of fitness reduction from extra-pair mating, which occurred at an intermediate level of inbreeding. These data support the kin-selection hypothesis, although there might be alternative nongenetic reasons associated with the extra-pair mating preference. Our finding offers a new explanation for why female birds pursue extra-pair mating. It also may broaden our understanding of the role of kin-selection in the evolution of cooperative society.     

Do Birds Alter Levels of Parental Investment Based on Nest‐Site Habitat Features?

Many habitats have undergone rapid changes over the past century as a result of anthropogenic activities. Organisms can respond to changes in their environment in many ways, including how much they invest in a given reproductive bout. Optimality theory and life history theory together have provided a framework for understanding how individuals make decisions about the risks and rewards of investing high levels of resources into their offspring within the context of current vs. future reproduction. Shrubland birds in the United States often breed in habitat that has been impacted by humans to varying degrees and provide an ideal system for examining whether organisms alter their levels of parental investment based on the habitat around the nest site. In this study, we assessed levels of nest‐defense behavior during a simulated nest predation event in four shrubland birds: American robins (Turdus migratorius), gray catbirds (Dumetella carolinensis), brown thrashers (Toxostoma rufum), and northern cardinals (Cardinalis cardinalis). We found that thrashers and catbirds exhibited significantly higher levels of nest defense compared to robins and cardinals and that birds with larger broods acted more aggressively in defending them. We also found that thrashers acted less aggressively as the proportion of shrubland around the nest increased and as the proportion of developed land around the nest decreased and that cardinals acted less aggressively as the proportion of developed land around the nest increased. These patterns suggest that nest‐defense behavior can covary with features of the landscape surrounding the nest, but that the factors shaping that behavior can differ by species.     

Does anti‐parasitoid defense explain host‐plant selection by a polyphagous caterpillar?

While studies of tri-trophic interactions have uncovered a variety of mechanisms influencing the dietary specialization of insect herbivores, such studies have neglected host-plant selection by generalists. Here, we report an initial investigation on how host-plant quality and a tachinid parasitoid interact to affect the survival and host-plant selection by a polyphagous herbivore. This herbivore, Grammia geneura (Strecker) (Lepidoptera: Arctiidae), is a food-mixing caterpillar that feeds preferentially on forbs. A previous study suggested that G. geneura might eat certain host species for reasons other than benefits of physiological utilization. We hypothesized that host-plant mediated defenses could act against parasitoids, the major mortality agents of late instar G. geneura . Field observations indicated that caterpillars sometimes survived an attack by the parasitoid Exorista mella Walker (Diptera: Tachinidae) in nature. Laboratory experiments showed that the survival of parasitized caterpillars increased on acceptable but nutritionally inferior host-plant species, indicating that anti-parasitoid defense may explain host-plant selection in this dietary generalist. We found no indication that host-plant selection changed according to the parasitism status of individual caterpillars.     

Do cavity‐nesting primates reduce scent marking before retirement to avoid attracting predators to sleeping sites?

The largest population of endangered golden lion tamarins (Leontopithecus rosalia, GLTs) decreased from approximately 330 to 220 individuals between 1995 and 2000 due to a dramatic increase in predation at sleeping sites. We used behavioral data from eight social groups in this population to test two hypotheses: First, if GLTs attempt to mitigate the risk of predation at sleeping sites, they should reduce their rates of scent marking just prior to retirement. Second, if the benefits of scent marking prior to entering the sleeping site merit an increase in the rate of marking, then tamarins should increase their rate of pre-retirement scent marking during the breeding season, when such behavior would have its greatest impact on reproductive fitness. We used a generalized linear model (GLM) repeated-measures analysis to compare rates of daytime scent marking with rates of marking just prior to retirement for males and females. In addition, we compared scent marking prior to retiring in the nonbreeding season to marking rates before retirement in the breeding season for males and both sexes considered concurrently. Contrary to our expectations, GLTs significantly increased their rates of scent marking during the 30 min prior to entering their sleeping site-an observation driven by an increase in male (but not female) rates of marking. Rates of marking before entering the sleeping site were greater in the nonbreeding season compared to the breeding season, when both sexes were considered concomitantly and when males were evaluated alone. We conclude that GLTs do not attempt to minimize predation risk by decreasing scent marking in the period before they enter their sleeping site, and that tamarins do not scent mark at this time of day in order to transmit information about reproductive status or to control reproduction of subordinates. We speculate that scent marking in the 30 min prior to entering sleeping sites may serve to reduce predation risk by enabling tamarin groups to return quickly to favored sleeping sites in the evening when crepuscular predators are active.     

Ground‐nesting by the chimpanzees of the Nimba Mountains,Guinea: environmentally or socially determined?

The chimpanzees (Pan troglodytes verus) of the Nimba Mountains, Guinea, West Africa, commonly make both elaborate ("night") and simple ("day") nests on the ground. In this study we investigated which factors might influence ground-nesting in this population, and tested two ecological hypotheses: 1) climatic conditions, such as high wind speeds at high altitudes, may deter chimpanzees from nesting in trees; and 2) a lack of appropriate arboreal nesting opportunities may drive the chimpanzees to nest on the ground. In addition to testing these two hypotheses, we explored whether ground-nesting is a sex-linked behavior. Data were collected monthly between August 2003 and May 2004 along transects and ad libitum. To identify the sex of ground-nesting individuals, we used DNA extracted from hair samples. The results showed that the occurrence and distribution of ground nests were not affected by climatic conditions or a lack of appropriate nest trees. Support was found for the notion that ground-nesting is a sex-linked behavior, as males were responsible for building all of the elaborate ground nests and most of the simple ground nests sampled. Elaborate ground nests occurred mostly in nest groups associated with tree nests, whereas simple ground nests usually occurred without tree nests in their vicinity. These results suggest that ground-nesting may be socially, rather than ecologically, determined.     

Production and costs of nesting attempts in Snow Buntings Plectrophenax nivalis: why do they attempt second broods?

During 1988–1993, pairs of Snow Buntings Plectrophenax nivalis on our study sites in northeast Scotland reared an average of 1.2 broods. Clutch sizes of first and second broods were similar, but partial losses were greater in second broods, leading to a difference of at least 40% in overall nest productivity between successful first and second broods. Over and above this, total nest failure was four times higher in the second broods, and autumn sightings of ringed nestlings from second broods were only a third of those of first-brood nestlings. As a result, second broods produced a mere 10% of future recruits to the breeding population. However, there was also little evidence of costs associated with producing, or attempting to produce, second broods. Young from first broods were not less likely to reach independence if a second brood was attempted, between-year return rates of double-brooded adults were similar to those of single-brooded birds and double-brooded adults did not appear to be less fecund in the following summer. Therefore low costs to the adults of attempting second broods may allow the continuation of a strategy which appears to have only a marginal influence on overall reproductive success in the area studied.     

Effects of water level on sleeping-site selection and inter-group association in proboscis monkeys: why do they sleep alone inland on flooded days?

A one-male group (BE-Group) of proboscis monkeys was studied along the Menanggul River, a tributary of the Kinabatangan River, Sabah, Malaysia, from May 2005 to 2006. It has generally been assumed that proboscis monkeys only set up their sleeping sites along the riverbank; however, when more than 1 m of water covered the forest floor for more than 700 m inland from the riverbank during the seasonal flood, the BE-Group slept inside the forest. It seems that the sleeping-site selection of the BE-Group was not influenced by food availability during the flooded months because the food availability by the vegetational survey did not vary much between flooded and non-flooded months. In addition, feeding behaviors of the focal monkey in the BE-Group also did not vary much between flooded and non-flooded days. On the other hand, the water level statistically influenced the sleeping-site selection. The proboscis monkeys remained in inland forest during the flooded days because of the reduced predation threat, as terrestrial predators such as clouded leopards are prevented from foraging by deep water covering the forest floor. On non-flooded days when the BE-Group slept at the riverbank, they frequently slept close to other one-male groups on the riverside trees. Contrastingly, when the group slept inside the forest on flooded days when the water level was high, they slept away from other groups. This difference in the need for one-male groups to sleep close to each other might be attributed to the decreased predation threat during high water level in the flooded days.     

Amphibious fish: why do they leave water?

Summary Amphibious behaviour in fish has evolved separately many times since the first amphibious fishes, the rhipidistian crossopterygians, ventured onto land about 350 million years ago. This behaviour has resulted in the colonization and eventual domination by vertebrates of the terrestrial habitat. It is generally proposed that aquatic hypoxia, owing to metabolic oxygen consumption and organic decay, was the most important selective force in the evolution of air-breathing vertebrates (e.g. Randall et al., 1981). Modern amphibious fish species give an insight into the reasons for leaving and eventually abandoning the aquatic habitat. Amphibious fishes today leave the water for a variety of reasons associated with degradation of their aquatic habitat, or biotic factors within it.The possible causal factors which may elicit an emergence response are summarized in Fig. 1(a) and (b). Amphibious fish inhabiting closed systems, as typified by freshwater or intertidal pools, may leave water for any of the reasons detailed in Fig. 1(a). The relative importance of any one stimulus is likely to vary between different species. However, it is possible that in closed systems, adverse fluctuations in physico-chemical parameters will have a more important effect in eliciting amphibious behaviour than will biotic factors. In open systems, such as coastal waters or large freshwater bodies, effectively two routes of escape from adverse aquatic conditions are available to amphibious fish. They may move onto land, or alternatively they may move underwater to find better conditions. In such a system, where physico-chemical parameters remain relatively constant, abiotic factors are unlikely to have a significant influence on amphibious behaviour. The dominant stimulus in open systems is possibly the three-way interaction between predation, competition, and short-or long-term food availability (Fig. 1(b)).It is unlikely that any one of the factors discussed in this review will act alone in causing amphibious behaviour, and in this respect the available literature on fish leaving water is lacking. Much of it is fragmentary and partly anecdotal, and the limited amount of experimental work tends to concentrate on individual causal factors. There is evidently scope for detailed examination of emersion in a number of amphibious fishes, testing a matrix of environmental and biotic stimuli, in an attempt to determine in more detail the reasons for such behaviour.     

Cold‐water coral habitats on seamounts: do they have a specialist fauna?

Aim The large biogenic structures formed by colonial cold‐water scleractinian corals provide valuable habitat for marine invertebrates on seamounts and the continental slope of all world oceans. These patchily distributed long‐lived structures are easily damaged by several human activities, particularly bottom trawling for fish, and are potentially vulnerable to ocean acidification caused by climate change. Consequently, an important conservation question is whether these structures support a specialized invertebrate fauna restricted to these habitats. Here we investigate the relationship between structures formed by the coral Solenosmilia variabilis and its associated ophiuroid (brittlestar) fauna, one of the dominant components of deep‐sea ecosystems. Location Seafloor habitat around Southern Australia, New Zealand, and the Macquarie Ridge from 35 to 53° S and 117° E–176° W, 500–1500 m depth. Methods Data were derived from samples collected by numerous scientific expeditions to the study region. Because these samples were collected using a variety of gear and effort, a two‐step approach was used. First, the largest consistently collected data set (73 ophiuroid species from 59 samples) was assembled for multivariate analysis. ANOSIM was used to test for differences in ophiuroid community composition between Solenosmilia and non‐Solenosmilia habitat on seamounts and the continental slope, and SIMPER was used to identify species that characterized Solenosmilia habitat. Second, these results were validated against all known data to ensure that these characteristic species had not been found in non‐Solenosmilia habitat elsewhere. Results The ophiuroid assemblages from Solenosmilia habitat were distinct from those found on other habitats on the continental slope and offshore seamounts across the study region. Although a suite of ophiuroid species characterized Solenosmilia habitat, most have also been collected from dead coral or other rubble, suggesting a physical rather than biological association between the coral matrix and its associated invertebrate fauna. Main conclusions Despite the lack of an exclusive ophiuroid–coral relationship, cold‐water scleractinian coral remains the principal habitat for a number of ophiuroid species across southern Australia and New Zealand. The slow growth rate of the coral and the low dispersal potential of some associated species suggest that recovery of damaged cold‐water coral assemblages will be a long‐term process.     

Climb and flight speeds of shorebirds embarking on an intercontinental flight; do they achieve the predicted optimal behaviour?

Most Arctic-breeding waders wintering in West Africa cover the first 4000 km of their northward journey in spring by a single flight to western Europe. We examined the extent to which waders economize their flight behaviour during departure by comparing climb rates and forward flight speeds with predictions based on flight mechanic theory and the relevant morphological measurements made of birds collected on the site. With an optical range finder, we followed 98 wader flocks on their departure from Banc d'Arguin in Mauritania. We also measured wind speed and direction at different altitudes by tracking helium-filled balloons and thus were able to deduce airspeeds from groundspeeds of the departing flocks. Of the nine species examined, six showed the predicted negative relationship between climb rate and airspeed, although only one was statistically significant. By normalizing the data, we found a statistically significant negative correlation across all species. Although 17% of the observed climb rates were greater than the predicted theoretical maximum, the average observed climb rate was lower than the predicted optimum and the average observed airspeed was higher. The absolute deviations of climb rates from theory may have been because of the existence of pockets of rising and sinking air at the boundary of desert and ocean. That the absolute deviations in average climb rate and airspeed followed the predicted negative relationship is in accordance with the current theory of flight mechanics.     

Old comb for nesting site recognition by <Emphasis Type="Italic">Apis dorsata?</Emphasis> Field experiments in China

The Asian giant honey bee, Apis dorsata, often conducts seasonal, long-distance migrations in southern China, between a preferred tree (having more than one nest) and alternate sites. Although worker bees cannot make a round-trip journey, colonies re-utilize preferred trees after an absence of several months. We performed comb experiments in which bases and all abandoned combs were entirely scraped off trees and their sites covered with plastic, or comb was moved to trees of the same species. Swarms of giant honey bees investigated trees where combs were removed and continued to nest on the same trees. In contrast, placing combs in nets on previously used trees, or on nearby trees of the same species, did not attract more swarms. The same number of colonies that left them returned to previously occupied trees. Our findings suggest that direct olfactory or sensory contact with old comb bases might regulate nest establishment, but individual trees, lacking normal visual or chemical cues of old nests, are relocated using behavioral devices that remain to be elucidated. Received 12 February 2007; revised 5 June 2007; accepted 13 September 2007.     

Sexual selection: do flies lie with asymmetric legs?

A newly described species of empidid or 'dance fly' shows a bizarre polymorphism in their forelegs, which presumably serve as a mating lure. This trait may have evolved by frequency-dependent deceptive male signalling.