Spawning timing of the cleaner wrasse, Labroides dimidiatus, on a warm temperate rocky shore

We observed spawning behaviors of the haremic cleaner wrasse Labroides dimidiatus at a rocky reef in southern Japan. Females released pelagic eggs daily from June to September after a spawning ascent by pairs. When the high tide occurred between noon and evening (quarter moon to new or full moon), they spawned around the time of the tide providing fast offshore currents. For the rest of the lunar cycle, spawnings occurred during late afternoon independent of the state of the tide at the time of day. This spawning pattern is quite different from that of conspecifics on coral reefs that always spawn around the high tide at all lunar stages to avoid potential egg predators. The wrasse ascended high in the water column, probably because of its predator-immune characters as a cleaner. The steep slope of the study site seemed to contribute to releasing gametes far above aggregating planktivores. Thus, gametes were not subject to heavy predation. Current direction might not always affect survival of spawned pelagic eggs on the temperate reefs so crucially as it does on coral reefs. We conclude that spawning during unfavorable tidal conditions during the daytime may be better than spawning during the best tidal condition in the crepuscular period when predation pressure on adults will be high. Intraspecific variation in the timing and location of spawning of the wrasse may result from different conditions for larval survival. Received: February 6, 2000 / Revised: June 16, 2000 / Accepted: July 17, 2000     

Bumblebees (Bombus terrestris) use social information as an indicator of safety in dangerous environments

Avoiding predation is one of the most important challenges that an animal faces. Several anti-predation behaviours can be employed, yet simply using the presence of conspecifics can be a good signal of safety in an environment with potential predation hazards. Here, we show, for the first time, that past experience of predation causes bumblebees (Bombus terrestris) to aggregate with conspecifics, facilitating the identification of safe foraging patches. Bees were trained to differentiate between flowers that harboured predators and flowers that were predator free. When test subjects were subsequently presented solely with the previously predator-infested flower species, there was a significant preference to only land on flowers occupied by other feeding conspecifics. Yet, when safe flowers were made available to subjects previously entrained to discriminate safe from predator-occupied flowers, subjects ignored other bees and the social information potentially provided by them, demonstrating that attraction towards conspecifics is confined to dangerous situations. Our findings demonstrate a previously unknown social interaction in pollinators which may have important implications for plant–pollinator interactions.     

Aspects of the spawning of labrid and scarid fishes (Pisces: Labroidei) at Enewetak Atoll,Marshall Islands with notes on other families

Synopsis Spawning of 32 species of Labridae and 13 species of Scaridae was seen at Enewetak Atoll, Marshall Islands. Most spawned on a reef bisecting the main ocean-lagoon passage which had strong tidal currents. Others spawned on lagoon reefs and in Halimeda beds. Polygynous haremic, lek-like and promiscuous mating systems were found which were species specific. Data on reproductive patterns, sexual dichromatism, sexual dimorphism, seasonality and spawning behavior were determined. Many spawned during the day in a time-phase dependent pattern from near sunrise to sunset. Scarid spawning began at slack high water or after when currents were starting to move out of the lagoon. Labrid spawning usually started about 30 min later with some continuing up to 2 h after high tide. With high tide before sunrise, scarid spawning began 30–50 min after sunrise as the current started flowing over the reef. With high tide near sunset, spawning occurred with an incoming current. Most labroids spawned on all phases of the moon. Acanthuridae (6 spp), Caesionidae (1 sp.) and Zanclidae (1 sp.) spawned after high tide at the same time as labroids. Pomacanthidae (5 spp.) spawned only shortly before sunset without reference to tidal currents. Fishes producing pelagic eggs at the lagoon-ocean channel spawned (1) at or slightly after high tide (44spp.), (2) in late afternoon without reference to tide (6 spp.) or (3) after slack low water (1 sp. ). Spawning style can vary within a single species in different environments. Despite the presence of many piscivores, no successful predation on spawning adults was seen. Predation on newly released eggs was uncommon. Labrichthys unilineata and Anampses twistii attempted to defend their eggs for a few sec after release. Attacks by piscivores on spawning adults on tropical reefs occur once per 100–1000 spawnings. Most are wary when preparing to spawn and prespawning behavior is easily interrupted. The risk from piscivores goes down and spawning ascent speed decreases with increasing size of spawners. Egg predation by zooplanktivores is less for pair spawners than group spawners possibly due to less conspicuous gamete clouds and times of spawning. Increasing height of egg release, speed and length of the spawning ascent, and trajectory alteration of ascending adults are believed to make it more difficult for zooplanktivores to locate eggs after release. For labrids, permanent full sexual dichromatism was found among haremic, lek-like and promiscuous mating systems. Species with temporary full dichromatism, permanent and temporary partial dichromatism and monochromatism were haremic. Smaller scarids were believed to have lek-like, and larger species haremic, mating systems. Smaller scarids had male looping behavior and post spawning displays, plus faster spawning ascents and different locations for egg release than larger ones. Eggs of 21 labrids were spherical or nearly spherical, ranging from 0.55–0.80 mm in diameter, and most had one oil globule. Among 7 is scarids, 6 had spindle-shaped eggs ranging from 1.25 ×0.50 mm 2.14× 0.48 mm while one had a nearly spherical egg. One scarid egg lacked an oil globule.     

Paternal defence,cannibalism and polygamy: factors influencing the reproductive success of painted greenling (Pisces,Hexagrammidae)

The relative costs and benefits of paternal egg-guarding behaviour were identified for painted greenling, Oxylebius pictus, a small fish inhabiting temperate rock reefs. Because males must guard embryos against conspecifics of both sexes and against other fishes, their movements were curtailed, and an energy cost resulted. The males' somatic condition declined in proportion to the time spent guarding. Paternal males partially compensated by cannibalizing a small fraction of their progeny. Male O. pictus thus parasitize females by consuming their spawn. Polygamous matings were nonetheless advantageous for individual females as well as for males. The reproductive success of males and females increased for male broods with greater numbers of clutches, because there was a general dilution of predation loss in larger broods. The success of females, moreover, varied depending on the rank (chronological) order of spawning; success was greater for those that contributed earliest to the male's brood. The results support the hypothesis that the breeding cycles typical of paternal teleosts have evolved partly because of energy costs imposed by site-dependent care. For multiple-clutch species with protracted breeding seasons like O. pictus, the long-term benefits of polygamous spawnings perhaps outweight short-term losses sufficiently for filial cannibalism to evolve and be maintained. Alternatively (or in addition), the foraging milieu may exert a stronger average environmental influence than kin selection does.     

Reproductive behavior,egg trading,and correlates of male mating success in the simultaneous hermaphrodite,Serranus tabacarius

Synopsis Serranus tabacarius (Serranidae), the tobaccofish, is a simultaneous hermaphrodite which belongs to a group of seabasses that exhibit a wide variety of social and mating systems. The reproductive behavior of tobaccofish is similar to other hermaphroditic seabasses, with individuals assuming sex-specific spawning behaviors that allow for the assignment of male and female roles in a mating sequence. Virtually all matings involved pairs of individuals, although streaking, an alternative male mating tactic, was observed once. Pairs engage in egg trading, where individuals divide their daily clutch into a series of sequentially released parcels and take turns releasing eggs for their partner to fertilize. Individuals mate over a late afternoon spawning period with a number of partners sequentially. Larger individuals have both more total matings and more spawning partners. Egg trading is not symmetrical, the number of male and female matings for an individual in a spawning sequence is often unequal. Overall, the ratio of male to female matings increases with individual size. Large individuals are socially dominant, chase conspecifics during the reproductive period, and are more likely to end a spawning bout with a partner immediately after mating in the male role. In addition, larger individuals are less likely to reciprocate female matings by a partner, either by only mating once (as a male) in a spawning bout or by mating consecutively as a male within a series of matings. Although larger individuals show this relative specialization in the male role, they maintain their simultaneous hermaphroditism and obtain a substantial percentage of their mating success through female function. Egg trading appears to reduce the opportunity for large individuals to specialize as pure males, and thus interacts with the environmental potential for polygamy in shaping the mating system and sex allocation pattern in this species.     

An indirect cue of predation risk counteracts female preference for conspecifics in a naturally hybridizing fish Xiphophorus birchmanni

Mate choice is context dependent, but the importance of current context to interspecific mating and hybridization is largely unexplored. An important influence on mate choice is predation risk. We investigated how variation in an indirect cue of predation risk, distance to shelter, influences mate choice in the swordtail Xiphophorus birchmanni, a species which sometimes hybridizes with X. malinche in the wild. We conducted mate choice experiments to determine whether females attend to the distance to shelter and whether this cue of predation risk can counteract female preference for conspecifics. Females were sensitive to shelter distance independent of male presence. When conspecific and heterospecific X. malinche males were in equally risky habitats (i.e., equally distant from shelter), females associated primarily with conspecifics, suggesting an innate preference for conspecifics. However, when heterospecific males were in less risky habitat (i.e., closer to shelter) than conspecific males, females no longer exhibited a preference, suggesting that females calibrate their mate choices in response to predation risk. Our findings illustrate the potential for hybridization to arise, not necessarily through reproductive "mistakes", but as one of many potential outcomes of a context-dependent mate choice strategy.     

The reproductive behaviour ofAequidens vittatus (Pisces,Cichlidae) in Surinam,South America

Synopsis The behaviour of free-living pairs ofAequidens vittatus was observed in Surinam, South America. An ethogram of breeding behaviour is presented, based on those observations and on aquarium-held fish. This is a biparental, substrate-guarding species that spawns on a movable platform. Sexual differentiation of parental roles was more pronounced when the young were in the embryonic interval than when they were mobile juveniles. Females spent more time near their brood, attacked juvenile conspecifics more often, and fanned and mouthed embryos more than males did. Males were more involved than females in territorial spacing of pairs. The movable spawning leaf provides support for eggs on detritus substrate and may also provide protection against predators and rapid water level changes.     

Trade-off between mating and predation risk in the marine snail, Littorina plena

Abstract. We investigated the hypothesis that predation risk affects mating decisions in the intertidal snail Littorina plena in Bamfield Inlet, Northeast Pacific. First, we conducted a field tethering experiment to test the assumption that mating pairs of snails are more susceptible to predation than solitary individuals, and then performed a laboratory experiment to quantify the effect of predation threat on the propensity of snails to form mating pairs. Our results support the hypothesis, in that "mating pairs" were more frequently killed than single snails in the field, and snails were less likely to form mating pairs in the laboratory when simulated predation risk was high (chemical cues from crushed conspecifics were added to the water) than when it was low (no risk cues were added to the water). In contrast to several earlier studies, we found no effect of individual size on snail susceptibility to predation, perhaps because our two size classes were contiguous and snails within them were not dissimilar enough. The results of the behavioral experiment were consistent with this lack of individual size effect on snail vulnerability; both size classes of snails showed a significant and similar tendency to decrease mating when predation risk was high. Taken together, the results of this and recent studies indicate that predators can considerably affect the behavior of littorinid snails, including their movement patterns, feeding, and reproduction. We argue that greater consideration should be given to how marine invertebrates trade off predation risk and activities related to reproduction.     

Aspects of the spawning of western Atlantic butterflyfishes (Pisces: Chaetodontidae)

Synopsis The status of knowledge of spawning among the five shallow waterChaetodon species in the western Atlantic is reviewed. Spawning has been observed for three species in Puerto Rico, St. Croix and the Bahamas, with possible courtship in a fourth.Chaetodon aculeatus spawned near the time of sunset over objects on the reef as single female/male pairs or as two females and one male, with pair spawning in rapid succession. Spawning occurred during much of the lunar month from February to April and it is uncertain whether any lunar periodicity to spawning exists. Male-male aggression was noted. Spawning sites (coral heads) were alternated daily and it is likely that females spawn only once every two days. A single female produced as many as 2090 eggs in a single spawning.Chaetodon capistratus spawned during much of the lunar month from February to April. It spawned about 5 min afterC. aculeatus, occasionally using the same sites, and alternated sites daily. A female produced as many as 3710 eggs in one spawning.Chaetodon striatus spawned from February to April but it is unknown if it has any lunar spawning cycle. No predation attempts by piscivores on spawning adults were seen. Predation byMelichthys niger on eggs ofC. striatus occurred. No egg predation was observed forC. aculeatus andC. capistratus. With an assumed four month reproductive season, alternate day spawning and observed egg production values,C. aculeatus andC. capistratus produce respectively about 100 000 and 200 000 eggs per large female per year. The reproductive strategy of smaller species may be to produce moderate numbers of eggs per day over a spawning season of at least a few months while larger species may produce more eggs per day for a shorter period.     

Conspecifics and Their Posture Influence Site Choice and Oviposition in the Damselfly Argia moesta

Finding a suitable oviposition site can be costly because of energy and time requirements, and ovipositioning can be dangerous because of the risk of predation and harassment by males. The damselfly Argia moesta oviposits, contact-guarded by her mate, on vegetation in streams. Oviposition aggregations are commonly observed in this species, despite their territorial nature during other behaviors. We conducted experiments in the field to test the hypothesis that aggregations are the result of conspecific attraction. In the first experiment, two oviposition sites (sycamore leaves) were provided, one with models of ovipositing pairs, and one without. In the second experiment, one leaf again had ovipositing models, while the other had models of uncoupled males and females in a resting posture. In both experiments, damselfly pairs preferred the site with ovipositing models. In general, they visited the ovipositing models first more often than expected by chance, stayed longer there, were more likely to oviposit there, and laid a greater total number of eggs there. These results support the hypothesis that conspecific attraction is responsible for ovipositing aggregations in A. moesta and that posture is an important cue for attraction. Using conspecific cues could be a beneficial strategy to save in search costs while taking advantage of the presence of ovipositing conspecifics to dilute the effects of harassment and predation.     

Effects of habitat features on size-biased predation on salmon by bears

Predators can drive trait divergence among populations of prey by imposing differential selection on prey traits. Habitat characteristics can mediate predator selectivity by providing refuge for prey. We quantified the effects of stream characteristics on biases in the sizes of spawning salmon caught by bears (Ursus arctos and U. americanus) on the central coast of British Columbia, Canada by measuring size-biased predation on spawning chum (Oncorhynchus keta) and pink (O. gorbuscha) salmon in 12 streams with varying habitat characteristics. We tested the hypotheses that bears would catch larger than average salmon (size-biased predation) and that this bias toward larger fish would be higher in streams that provide less protection to spawning salmon from predation (e.g., less pools, wood, undercut banks). We then we tested for how such size biases in turn translate into differences among populations in the sizes of the fish. Bears caught larger-than-average salmon as the spawning season progressed and as predicted, this was most pronounced in streams with fewer refugia for the fish (i.e., wood and undercut banks). Salmon were marginally smaller in streams with more pronounced size-biased predation but this predictor was less reliable than physical characteristics of streams, with larger fish in wider, deeper streams. These results support the hypothesis that selective forces imposed by predators can be mediated by habitat characteristics, with potential consequences for physical traits of prey.     

Pelagic spawning of the hawkfish Oxycirrhites typus (Cirrhitidae)

Synopsis Pelagic spawning of the deep slope coral-dwelling cirrhitid Oxycirrhites typus was observed for two social groups at Papua New Guinea. This species was previously reported to be a demersal spawner in an aquarium. Courtship in social groups consisting of a single male and one or two females commenced just prior to or after sunset among the branches of gorgonian or antipatharian corals. Males and females occupied separate corals; males either visited females at their corals or met them at an adjacent coral just prior to courtship. Courtship was sequential and consisted of two or more bouts with each female that culminated in a rapid ascent into the water column and the release of floating eggs. Fertilized eggs, taken from a third social group, were spherical and averaged 0.69 mm in diameter. Spawning pairs sought refuge in their resident corals or in the coral where courtship occurred immediately after spawning was completed.     

Nest-site partitioning in a strandveld shrubland bird community

Nest-site selection may vary adaptively among co-existing species as a result of competitive interactions among the species or in response to density-dependent nest predation. We examined nest-site characteristics and degree of partitioning among 14 co-existing bird species breeding in dwarf strandveld shrubland at Koeberg Nature Reserve, South Africa. Habitat characteristics of nest sites differed significantly among species, indicating strong nest-site partitioning. The principal variables distinguishing nest-site characteristics among species (substrate height, cover at 1m, cover at 2m) were features that distinguish tall-shrub species which are strongly associated with patches of Dune Thicket from shorter-shrub species which are strongly associated with more open Sand Plain Fynbos. Two groups of species which differ primarily in their selection of habitat patch type within the patchy nesting landscape were identified. One group nested predominantly in low shrubs associated with open Sand Plain Fynbos. A second group nested at a variety of heights within tall-shrub species associated with Dune Thicket. Species within each of these groups differed from each other in their relative nest height (ratio of nest height to substrate height), distance of nest from foliage edge, nest concealment and choice of particular substrate plant species. On average, stepwise discriminant function analysis classified 52.6% of the nest sites correctly as belonging to one of the 14 species, considerably better than the expected random classification of 11.8%. Individual species' classifications were 2–12 times better than a random classification. We suggest that high levels of nest predation may have selected for strong nest-site partitioning in this community.     

Evaluation of a conservation strategy: a spawning aggregation closure for red hind, Epinephelus guttatus, in the U.S. Virgin Islands

Many tropical reef fishes spawn in large aggregations, which are readily targeted by fishers. By the 1980s, at least two grouper spawning aggregations were eliminated by intensive fishing off the island of St. Thomas, U.S. Virgin Islands, and another aggregating species, red hind, was intensively targeted. By 1988, the average length of red hind had greatly decreased to 295 mm, and the sex ratio was extremely skewed to 15 females per male, suggesting a heavily fished stock. Since this species is a protogynous hermaphrodite, the loss of large individuals (primarily males) could potentially result in sperm limitation in spawning aggregations. In 1990, a spawning aggregation closure was implemented. By 1997, average size of red hind had increased to 395 mm and sex ratio had shifted to 4 females per male. Fish were observed aggregating only in structurally complex habitat along the insular shelf edge. This habitat type is apparently not common along most of the shelf edge off St. Thomas and may provide shelter while reducing risk of predation during aggregation periods. These data suggest that protection of spawning aggregations is a sound management strategy with considerable potential for aiding the sustainable use of reef fish resources.     

Ecological Risk Aversion and Foraging Behaviors of Juvenile Squirrel Monkeys (Saimiri sciureus)

The ‘ecological risk aversion hypothesis’ [C.H. Janson and C.P. van Schaik, Juvenile Primates, Oxford Univ. Press, New York (1993), pp. 57–74] proposes that the pattern of slow growth characteristic of juvenile primates is a response to ecological risks (predation and starvation) experienced by juveniles. Juveniles are thought to avoid predation risk by positioning themselves near conspecifics, therefore experiencing high levels of feeding competition with older individuals, reduced access to resources and, consequently, high starvation risks during periods of food scarcity. The present study compared the foraging behaviors of juvenile and adult squirrel monkeys, a small neotropical primate characterized by a long juvenile period, to determine how predation and starvation risks affected juvenile behaviors. The study was conducted in Eastern Amazonia, in a seasonal environment. Due to their slow development, small body size and large group sizes, it was expected that juveniles in this species would behave in a manner consistent with the risk aversion hypothesis. However, age differences in foraging efficiency and foraging success were smaller than predicted. There was also no evidence that juveniles sacrificed access to food for predator protection. Adults did not have preferential access to fruit patches and direct competition was rare. Feeding competition for prey, the most common resource in the troop's diet, was negligible. Therefore, the slow growth and long juvenile period of squirrel monkeys do not correspond with evidence of predation or starvation risk, as predicted by the risk aversion hypothesis.     

Facultative nest patch shifts in response to nest predation risk in the Brewer’s sparrow: a “win-stay, lose-switch” strategy?

Facultative shifts in nesting habitat selection in response to perceived predation risk may allow animals to increase the survival probability of sessile offspring. Previous studies on this behavioral strategy have primarily focused on single attributes, such as the distance moved or changes in nesting substrate. However, nest site choice often encompasses multiple habitat elements at both the nest site and nest patch scales. We studied the within-season re-nesting strategy of a multi-brooded songbird, the Brewer’s sparrow (Spizella breweri), to determine whether pairs utilized a “win-stay, lose-switch” decision rule with respect to inter-nest distance, nest substrate and/or nest patch characteristics in response to previous nest fate. Pairs moved sequential nest sites slightly farther following nest predation versus success. When inter-nest distance was controlled, however, pairs changed nest patch attributes (shrub height, potential nest shrub density) associated with probability of nest predation to a greater extent following nest predation than success. The strategy appeared to be adaptive; daily nest survival probability for previously depredated pairs increased with greater Euclidian habitat distances between attempts, whereas previously successful pairs were more likely to fledge second attempts when nest sites were similar to those of previous attempts. Our results suggest that nesting birds can use prior information and within-season plasticity in response to nest predation to increase re-nesting success, which may be a critical behavioral strategy within complex nest predator environments. Re-nesting site selection strategies also appeared to integrate multiple habitat components and inter-nest distances. The consideration of such proximate, facultative responses to predation risk may clarify often unexplained variation in habitat preferences and requirements.     

Overdispersion of ant colonies: a test of hypotheses

Summary The nest locations of two ant species in the Colorado Desert are intraspecifically overdispersed. Intraspecific overdispersion has been thought to represent strong intraspecific competition. Here we consider this hypothesis along with three competing hypotheses: microhabitat selection by foundress queens, predation on foundress queens, and predation on established colonies. To test these hypotheses five types of data were collected: (1) the forager population sizes of Veromessor pergandei and Pogonomyrmex californicus, (2) the response of the territory use of V. pergandei to varying levels of food, (3) the encounter rates of conspecifics and other ant species to foundress queens artificially placed near and far from conspecific colonies, (4) predation on colonies as a function of colony spacing, and (5) the relationship between the plant microhabitat at the nest and colony spacing. The results show that established colonies have no apparent selectivity for a particular type of plant microhabitat nor do foundress queens show avoidance or attraction toward conspecifics. V. pergandei workers show only a slight ability to find V. pergandei queens that are artificially placed near their entrances. Certain spiders are the most common ant predators on our study area. Direct observations on spiders indicate that colonies with closer neighbors are not prone to a higher risk of predation. In addition, the estimates of the death rate of workers from a mark-recapture technique indicate that colonies with closer neighbors lose similar numbers of workers as compared to colonies with further neighbors. In favor of the competition hypothesis, the summed size of intraspecific nearest neighbor pairs are larger for colonies that are spaced further apart than those colonies that are spaced closer together. We also develop an index of foraging directionality for the column foraging species V. pergandei. Using this measure, we find that nearest neighbors tend to avoid foraging toward each other. The response of territory use to food levels was tested with experiments involving patches of cracked wheat. These experiments showed that patches away from nearest neighbors were found significantly sooner than patches toward nearest neighbors. The above five sets of data together suggest that resource competition and perhaps queen predation by established colonies account for the intraspecific spatial patterns of these species.     

Testing the differential predation hypothesis for the invasion of rusty crayfish in a stream community: laboratory and field experiments

1. We tested the hypothesis that the non‐native rusty crayfish (Orconectes rusticus) is less vulnerable to predators than two native species (O. propinquus and O. obscurus) it is replacing in streams of the upper Susquehanna River catchment (New York, U.S.A.). 2. We used laboratory experiments to compare species‐specific predation rates by smallmouth bass (Micropterus dolomieu) on crayfish of equal size and field tethering experiments to compare relative predation rates between native O. propinquus and non‐native O. rusticus by the suite of crayfish predators in our system. We predicted that crayfish size would affect predation rate but that predation rates would be equal among species when size was controlled. 3. We also tested for two potential artefacts of tethering. We tethered crayfish in cages to test whether the ability to escape from tethers is size specific, and we tested whether tethering alters differential predation among crayfish species by the smallmouth bass. 4. In the laboratory, smallmouth bass predation on rusty crayfish was lower than on either of the native species. In the field, predation risk for tethered crayfish was inversely related to size but did not differ among species when size was taken into account. Because rusty crayfish in the field experiment were slightly larger than the native species, as in nature, mortality was overall lower for the rusty crayfish. 5. In cages, smaller crayfish were more probably to escape from tethers than larger ones, an artefact that may partially confound results from our tethering experiments. Unexpectedly, tethering nearly eliminated predation by smallmouth bass. This artefact prevented us from testing for an interaction of tethering with differential predation and means that the results of field tethering experiments do not include any contribution from smallmouth bass predation. 6. Our experiments highlight the importance of explicitly considering potential artefacts that could confound results. 7. Our results indicate that differential predation contributes to the rusty crayfish's invasion of a stream community. In our study system, predation rates on rusty crayfish are lower than for native species mostly because of selection by predators for smaller crayfish; species‐specific characteristics such as behaviour that further reduce predation may also contribute, especially where smallmouth bass predation is important.     

Experimental test on public information use in the colonial Lesser Kestrel

The formation of colonies and the evolution of coloniality have been suggested to be a by-product of the use of public information to select breeding habitats. In this study we performed an experimental test to investigate whether the Lesser Kestrel (Falco naumanni) uses breeding success of conspecifics as a source of public information to select a breeding colony. We considered four potential cues based on reproductive performance of conspecifics in each colony: mean and variance of breeding success measured in both all pairs (TRS, total reproductive success), and only successful pairs (PRS, partial reproductive success). Both mean PRS and mean TRS could be predictive cues of the future reproductive output at a given site, because they varied among colonies and were autocorrelated from one year to the next. To dissociate any relationship between habitat quality and reproductive success we manipulated the mean brood sizes by transferring chicks among ten colonies. In five colonies, all the broods with at least two nestlings were reduced in one chick and in other five colonies all broods were enlarged by one chick. In the following year, we found that the number of adult immigrant kestrels settled at a colony was only explained by mean PRS in the previous year. We also examined the settlement of yearlings, which lack of information on breeding success in previous years. Unlike adult immigrant kestrels, yearlings tended to settle more frequently in those colonies with low mean PRS in the previous year, probably because of the lower pressure for occupation in those colonies. A multiple regression analysis showed that the growth of colonies was positively dependent on the mean PRS in the experimental year, and negatively on the number of predated nests. This study provides a solid support to the hypothesis that colonial species can use mean breeding success of successful pairs as a source of public information to make settlement decisions.     

Does attraction to conspecifics explain the patch‐size effect? An experimental test

Recent theory suggests that attraction to conspecifics during habitat selection can be one potential, yet untested, mechanism for animal sensitivity to habitat fragmentation. The least flycatcher Empidonax minimus , a highly territorial migratory bird, has previously been shown to be attracted to conspecifics and sensitive to patch size by avoiding small patches of riparian forest in Montana, USA. I used a large-scale field experiment in this region to test the conspecific attraction hypothesis for explaining sensitivity to patch size, and I supplemented this experiment by estimating whether vegetation structure, nest predation, or nest parasitism rates could better explain patterns of sensitivity to patch size. Vegetation structure did not vary consistently with patch size, based on a random sample of patches across 150  km of the Madison and Missouri Rivers, Montana. Nest predation and parasitism rates by brown-headed cowbirds Molothrus ater also did not vary with patch size during the experiment. However, when conspecific cues were simulated across a gradient of patch sizes, flycatchers settled in all patches – and their sensitivity to patch size vanished – providing strong support for the conspecific attraction hypothesis. These results provide the first experimental evidence that attraction to conspecifics can indeed help explain area sensitivity in nature and highlight how understanding the role of animal behavior in heterogeneous landscapes can aid in interpreting pressing conservation issues.