COMMUNAL ROOSTING BEHAVIOUR OF THE AUSTRALASIAN HARRIER CIRCUS APPROXIMANS IN NEW ZEALAND

The Australasian Harrier Circus upproximans habitually roosts communally in New Zealand but not in Australia. As many as 100 birds can occupy a roost in a small area of swamp. They start to assemble about one hour before dark and communal aerial displays in the vicinity of the roost are an integral part of the roosting behaviour. Roosts may be occupied all the year round, non-breeding birds continuing to roost communally throughout the summer. In New Zealand the habit is neither connected with migration nor is it an anti-predator device. It is considered that the abundance of food caused by the spread of introduced mammals and the large increase of habitat created by European settlement has built the harrier population up to such a size that the number required to elicit the response of communal roosting occurs at all times of year in most districts. Numbers within individual roosts fluctuate throughout the year and it is suggested that communal displays before roosting may provide the necessary feed-back for the initiation of population adjustments.     

Predation risk and resource availability explain roost locations of Whimbrel Numenius phaeopus in a tropical mangrove delta

Roosts are important sites for shorebirds in non‐breeding areas at night and during high tides. How the spatial configuration of food and risk of predation and disturbance influence roost site use in tropical locations remains poorly known. We analysed the locations of nocturnal roosts of Whimbrel Numenius phaeopus in mangroves of Sanquianga National Park, Colombia, with respect to variation in spatial variables related to food resources and risk of predation and disturbance. We contrasted characteristics of all 13 known nocturnal roost locations with those of all other mangrove islands (n = 209) within the limits of the park. We estimated the distance from roosts and other mangrove islands to foraging sites, and sources of predators and human disturbance. Larger areas of feeding habitat surrounded nocturnal roosts than other mangrove islands, and the average distance to individual feeding patches was shorter. Roosts were also more isolated than other islands, but proximity to sources of human disturbance did not differ. We conclude that Whimbrel roost site use in Sanquianga was best explained by a combination of access to feeding territories and isolation from potential sources of mainland predators, but not by avoidance of human disturbance. Beyond identifying factors influencing roost site selection, the large aggregations of individuals in single locations may suggest that presence of conspecifics itself also plays a role in the formation of Whimbrel roosts. We highlight the interaction of food and risk landscapes with intraspecific attraction on the roost site selection by Whimbrels and the importance of mangroves as roosting sites in tropical regions.     

Mixed roosts in the Montagu’s harrier Circus pygargus during courtship

Mixed communal roosting of Montagu’s harrier Circus pygargus in the pre-laying period was observed on Calcareous Marshes in Eastern Poland from 1992 to 1995. To my knowledge, this behaviour was described in literature for the first time. The communal roosting in Montagu’s harrier during courtship can help in estimation of mate attraction and finally in mate choice. Harriers from communal roosts start egg laying earlier when compared to the outside roosts. Communal roosting as anti-predator behaviour can help with predator detection and provides benefits to all members of the group. The pair formation process has led to disintegration of communal roosting. Males were more common in the roosting places than females. The time of roosting was correlated with the photoperiod. The weather and predators impact delayed the formation of mixed roosting places.     

The benefit of being a social butterfly: communal roosting deters predation

Aposematic passion-vine butterflies from the genus Heliconius form communal roosts on a nightly basis. This behaviour has been hypothesized to be beneficial in terms of information sharing and/or anti-predator defence. To better understand the adaptive value of communal roosting, we tested these two hypotheses in field studies. The information-sharing hypothesis was addressed by examining following behaviour of butterflies departing from natural roosts. We found no evidence of roost mates following one another to resources, thus providing no support for this hypothesis. The anti-predator defence hypothesis was tested using avian-indiscriminable Heliconius erato models placed singly and in aggregations at field sites. A significantly higher number of predation attempts were observed on solitary models versus aggregations of models. This relationship between aggregation size and attack rate suggests that communally roosting butterflies enjoy the benefits of both overall decreased attack frequency as well as a prey dilution effect. Communal roosts probably deter predators through collective aposematism in which aggregations of conspicuous, unpalatable prey communicate a more effective repel signal to predators. On the basis of our results, we propose that predation by birds is a key selective pressure maintaining Heliconius communal roosting behaviour.     

Experimental test of the mechanism underlying sexual segregation at communal roosts of harvestmen (Prionostemma spp.)

Closely related, ecologically similar species often roost in distinctly different habitats, and roosting patterns also vary within species in relation to sex, age and season. The causes of such variation are not well understood at either a proximate or ultimate level. We studied communal roosting in two congeneric species of Prionostemma harvestmen at a rainforest site in Nicaragua. Previous research showed that Prionostemma sp. 1 forms male‐biased communal roosts in tree‐root cavities, while Prionostemma sp. 2 forms communal roosts of variable but temporally stable sex ratios on spiny palms. Here, we investigate potential mechanisms underlying variation in roosting site choice between and within these syntopic species. First, we present the results of a field experiment designed to probe the mechanism underlying skewed roost sex ratios in Prionostemma sp. 2. Previous studies have suggested that these harvestmen use conspecific scent to locate communal roosts and that new roosts can be established via group translocation. Therefore, to test the hypothesis that skewed roost sex ratios in this species arise from sex differences in scent marks, we translocated single‐sex groups of ca. 30 individuals to each of 20 previously unoccupied spiny palms. Female release sites attracted new recruits of both sexes, while male release sites attracted almost exclusively males. We infer that Prionostemma sp. 2 females preferentially roost in sites scent‐marked by females and that this mechanism is sufficient to explain the skewed roost ratios. Further adding to knowledge of Prionostemma roosting behavior, we show that Prionostemma sp. 1 forms female‐biased communal roosts on spiny palms, that some roosts contain both species, and that the species composition is stable on a time scale of at least 2 weeks. To the best of our knowledge, this study is the first experimental test of mechanisms underlying sexual segregation at communal roosts in any taxon.     

High warning colour polymorphism in Heliconius hybrid zone roosts

1. Communal roosting behaviour has been documented among a wide range of taxa, particularly among groups of butterflies that display warning colourations. These aggregations of conspecifics and/or other species that share mimetic warning colour patterns can have a large impact on predator learning, and thus the survival of an aposematic form. Yet there has been limited investigation of communal roosting within areas where new and diverse warning colour forms are generated, such as hybrid zones. 2. Here, roosting behaviour was examined in a Heliconius erato hybrid zone in French Guiana between races with divergent warning colourations on their wings. In this hybrid zone, native individuals with nine distinct warning colourations, as well as individuals with altered forms that are not native in the French Guiana population, were marked and observed to determine if divergently coloured individuals participated in communal roosting, and if the proportions of colour pattern forms at roosts differed from the proportions that are found in the population. 3. The results demonstrated that divergently coloured individuals of the same species, including altered, non‐native forms, will readily and repeatedly participate in nocturnal communal roosting, often with extreme fidelity to specific perch locations. 4. These findings suggest that roosts composed of polymorphic warning patterns may be common in phenotypic transition zones, which could have major implications on predator training and selection dynamics in hybrid zones.     

Common Myna Roosts Are Not Recruitment Centres

We studied communal roosting in the Common Myna (Acridotheres tristis) in the light of the recruitment centre hypothesis and predation at the roost. The number and sizes of flocks departing from and arriving at focal roosts were recorded over a two year period. We also recorded the sizes and behaviour of foraging flocks. We found that flock sizes of birds departing from roosts at sunrise were larger than those at the feeding site, suggesting that there was no recruitment from the roosts. Flocks entering the roosts during sunset were larger on average than those leaving the following sunrise, suggesting no consolidation of flocks in the morning. Flocks entering the roosts at sunset were also larger on average than those that had left that sunrise, although there was no recruitment at the feeding site. There was no effect of group size on the proportion of time spent feeding. Contrary to expectation, single birds showed lower apparent vigilance than birds that foraged in pairs or groups, possibly due to scrounging tactics being used in the presence of feeding companions. Thus, the recruitment centre hypothesis did not hold in our study population of mynas. Predation at dawn and dusk were also not important to communal roosting: predators near the roosts did not result in larger flocks, and resulted in larger durations of arrival/departure contrary to expectation. Since flock sizes were smallest at the feeding site and larger in the evening than in the morning, but did not coincide with predator activity, information transfer unrelated to food (such as breeding opportunities) may possibly give rise to the evening aggregations.     

Cliffs Used as Communal Roosts by Andean Condors Protect the Birds from Weather and Predators

The quality and availability of resources influence the geographical distribution of species. Social species need safe places to rest, meet, exchange information and obtain thermoregulatory benefits, but those places may also serve other important functions that have been overlooked in research. We use a large soaring bird that roosts communally in cliffs, the Andean condor (Vultur gryphus), as a model species to elucidate whether roost locations serve as a refuge from adverse weather conditions (climatic refuge hypothesis, CRH), and/or from predators or anthropogenic disturbances (threats refuge hypothesis, TRH). The CRH predicts that communal roosts will face in the opposite direction from where storms originate, and will be located in climatically stable, low precipitation areas. The TRH predicts that communal roosts will be large, poorly accessible cliffs, located far from human-made constructions. We surveyed cliffs used as communal roosts by condors in northwestern Patagonia, and compared them with alternative non-roosting cliffs to test these predictions at local and regional scales. We conclude that communal roosting places provide refuge against climate and disturbances such as, for instance, the threats of predators (including humans). Thus, it is not only the benefits gained from being aggregated per se, but the characteristics of the place selected for roosting that may both be essential for the survival of the species. This should be considered in management and conservation plans given the current scenario of global climate change and the increase in environmental disturbances.     

Roost use by long-tailed bats in South Canterbury: examining predictions of roost-site selection in a highly fragmented landscape

We studied the roosting ecology of the long-tailed bat (Chalinolobus tuberculatus) during the springautumn months from 1998–2002 at Hanging Rock in the highly fragmented landscape of South Canterbury, South Island, New Zealand. We compared the structural characteristics and microclimates of roost sites used by communally and solitary roosting bats with those of randomly available sites, and roosts of C. tuberculatus occupying unmodified Nothofagus forest in the Eglinton Valley, Fiordland. Roosting group sizes and roost residency times were also compared. We followed forty radio-tagged bats to 94 roosts (20% in limestone crevices, 80% in trees) at Hanging Rock. Roosts were occupied for an average of 1 day and 86% were only used once during the study period. Colony size averaged 9.8 ± 1.1 bats (range 2–38) and colonies were dominated by breeding females and young. Indigenous forest, shrubland remnants and riparian zones were preferred roosting habitats. Communally roosting bats selected roosts in split trunks of some of the largest trees available. Selection of the largest available trees as roost sites is similar to behaviour of bat species occupying unmodified forested habitats. Temperatures inside 12 maternity roosts measured during the lactation period were variable. Five roosts were well insulated from ambient conditions and internal temperatures were stable, whereas the temperatures inside seven roosts fluctuated in parallel with ambient temperature. Tree cavities used by bats at Hanging Rock were significantly nearer ground level, had larger entrance dimensions, were less well insulated, and were occupied by fewer bats than roosts in the Eglinton Valley. These characteristics appear to expose their occupants to unstable microclimates and to a higher risk of threats such as predation. We suggest that roosts at Hanging Rock are of a lower quality than those in the Eglinton Valley, and that roost quality may be one of the contributory factors in the differential reproductive fitness observed in the two bat populations. The value of introduced willows (especially Salix fragilis) as bat roosts should be acknowledged. We recommend six conservation measures to mitigate negative effects of deterioration of roosting habitat: protection and enhancement of the quality of existing roosts, replanting within roosting habitat, provision of high quality artificial roosts, predator control, and education of landowners and statutory bodies.     

Genetic similarity in long-eared owl communal winter roosts: a DNA fingerprinting study

The long-eared owl is a nocturnal predator which winters communally and breeds in the same areas in loose colonies during the spring. We tested the hypothesis that roosts, particularly stable roosts, are formed by close relatives, a condition under which group-related behaviours such as information sharing or helping at nest are more likely to be developed. DNA fingerprinting analysis was used to examine genetic similarity within and between two long-eared owl populations, one wintering in a traditional roost and the other in an unstable roost, and both breeding around their roosting sites. Although genetic similarity within roosts was higher than that between roosts, the difference was not significant. Observed genetic similarity within roosts was smaller than that reported in the bird species whose roosts work as information centres. On the other hand, the presence of some closely related individuals in the roost and behavioural observations suggest that co-operation between kin might have occurred, at least in one of the two study sites.     

Roost selection by the north Queensland long-eared bat Nyctophilus bifax in littoral rainforest in the Iluka World Heritage Area,New South Wales

Abstract The aim of this study was to describe the roosts of Nyctophilus bifax in littoral rainforest in Iluka Nature Reserve on the north coast of New South Wales. Radio-telemetry was used to track 17 bats in November 1988 (lactation season) and 11 in May 1989 (mating season) to 87 roosts in 49 trees within the littoral rainforest. The bats frequently changed roosts, which were clustered within a small area. During November, lactating females moved twins between diurnal roosts and some carried twins while foraging. Twins represented a load of up to 95% of their mother's bodyweight. Bats roosted communally in foliage and tree hollows, beneath peeling bark, among epiphytes, and between strangler figs and host trees. Hollows were used more frequently when bats were lactating, while the use of foliage roosts was greater during the mating season. Roosts were concentrated in four tree species, although a wide range of other tree species was used. Roost trees used in November were taller (17m) than those used in May (8. 2 m), and reflect selection of Syzygium leuhmannii and Acmena hemilampra, both trees of the forest interior. The converse applied for selection of Cupaniopsis anacardioides, a small tree of the littoral zone, in May. These results identify the need for conserving a diversity of roosts for this species of bat.     

Emergence time in forest bats: the influence of canopy closure

The role of the forest canopy in protecting bats roosting in forest from predators is poorly known. We analysed the effect of canopy closure on emergence time in Barbastella barbastellus in a mountainous area of central Italy. We used radio-tracking to locate roosts and filmed evening emergence. Comparisons were made between roosts in open areas and those in dense forest. Median emergence time and illuminance were correlated. Moreover, from pregnancy to late lactation bats emerged progressively earlier, probably because of the exceptionally high wing loading affecting pregnant bats and the high energy demand of lactation. A significant influence of canopy closure on median emergence time was revealed after adjusting for the effects of light and reproductive state. Bats in open habitat emerged later than those roosting beneath closed canopy. In cluttered habitats, predators relying on vision may find it more difficult to detect and catch bats at light levels which would offer more chances of success when attacking prey in open habitats. Bats in dense forest are less vulnerable to predators and may take advantage of an earlier emergence by prolonging foraging. Although more vulnerable, lactating females roosting at open sites may benefit from warmer roosting conditions. Roosts in dense forest may be preferred under intense predation pressure. Forest management should favour canopy heterogeneity to provide bats with a range of roosting conditions. Our work emphasises the role of a fine-grained spatial scale in the roosting ecology of forest bats.     

Roosting behavior and group stability of the big fruit-eating bat Artibeus lituratus (Chiroptera: Phyllostomidae)

The roosting behavior of the big fruit-eating bat, Artibeus lituratus (Phyllostomidae, Stenodermatinae) in an Andean region of Venezuela is described. Sixty-four video recordings made at three separate foliage roosts during 1 year showed that group size varied between two and 14 individuals. One male was regularly observed roosting with more females than others, and this male was associated with the highest quality roost, defined here as the highest, most structurally stable, and least disturbed. Males invariably occupied exclusive roosts during the study, whereas females frequently moved among adjacent roosts. The high roost fidelity of males appears to be related to the defense of the highest quality roosts. Because females were observed roosting with each of the three males present at the study site, female groups were considered unstable. We suggest that shuttling movements of individuals may reflect a commonly observed adaptation of foliage roosting bats related to the avoidance of predators and/or parasites. The type of male–female association observed in A. lituratus is consistent with a resource defense polygyny hypothesis.     

Hunting Activity Effects on Roost Selection by Male Wild Turkeys

Roosting is an important component of wild turkey (Meleagris gallopavo; turkey) ecology as roosts provide security from predators and inclement weather. Males call (gobble) from roosts during the reproductive season, and roost locations are important for maximizing access to females and transmission of calls across the landscape, while also minimizing predation risk. Spring hunting of male turkeys occurs during the reproductive season, and hunting activity influences male behaviors and calling. Because roost sites are important for wild turkey ecology, we evaluated roost site selection and fidelity of male turkeys relative to land cover types, vegetative characteristics, and the presence of hunting activity during 2017–2018 in Georgia, USA. Prior to onset of hunting, males selected roosts nearest to hardwood and pine (Pinus spp.) forests. Roost site fidelity was low and distances between roosts were large. After onset of hunting, males selected pine forests less and exhibited greater plasticity in roost selection while fidelity remained minimal, suggesting that males may have altered selection to mitigate risk from hunting while maintaining the strategy of moving about their ranges and roosting at different sites on consecutive nights. Future research should examine potential effects of hunting-induced shifts in resource selection on other aspects of male turkey behavior and ecology. © 2019 The Wildlife Society.     

Aerial hunting behaviour and predation success by peregrine falcons Falco peregrinus on starling flocks Sturnus vulgaris

Predators use diverse hunting strategies to maximize hunting success, while preys adopt anti‐predator strategies to maximize escape chances, among which flocking, communal roosting, and the related collective responses are a common pattern in gregarious species. Prey‐predator interactions involving a single predator and flocks, a common situation in birds, have received little attention. We studied predation behaviour and success of peregrine falcons Falco peregrinus on starlings Sturnus vulgaris, a highly gregarious species, in proximity of two winter roosts. A total of 328 hunting sequences, with an overall success of 23.1% were recorded. They usually consisted of several attacks, predation success being higher when hunting sequences lasted less than 1.5 min, included less than 3 attacks and no other falcons were hunting simultaneously. Predation success was higher when hunts were directed on singletons than on flocks. However, most hunting sequences were directed towards flocks. Nine hunting strategies on flocks were identified. The most frequent was the ‘surprise attack’, which was also the most successful. We suggest that this strategy minimizes the amount of anti‐predator display elicited by flocks and economizes energy spent in hunting. The constant predation pressure did not seem to affect the use of roosts by starlings, consistent with the ‘dilution’ hypothesis, while falcons captured at least one prey item every evening. Communal roosting may benefit predator and prey, as both sides could have reached a mutual local equilibrium.     

THE POPULATION,ECOLOGY AND CONSERVATION OF THE BLACK OYSTERCATCHER HAEMATOPUS MOQUINI

Summers, R. W. & Cooper, J. 1977. The population, ecology and conservation of the Black Oystercatcher Haematopus moquini. Ostrich 48:28-40.

The population of Black Oystercatchers Haematopus moquini in the southwestern Cape, South Africa, was estimated to be 2 942 birds. Birds occurred most abundantly on coastal islands and were also abundant on mixed (sandy and rocky) shores of the mainland. Sandy shores and coastal wetlands supported few birds. Black Oystercatchers bred mainly from December to February with the number of clutches present reaching a peak in the first half of January. The most frequent clutch size was two eggs, the mean clutch size was 1,81. No significant differences were found in either linear dimensions or mass between the first and second eggs. The mean proportion of juveniles in groups of birds in July was 3,6 % suggesting a low recruitment to the adult population. The breeding population at Marcus Island is apparently sedentary throughout the year. The primary moult season for adults extends from March to October (eight months). Introduced mammalian predators should be controlled on islands and important mainland breeding sites should be protected by the creation of nature reserves and restricting human access during the breeding season.     

Social and Thermal Cues Influence Nest‐site Selection in a Nocturnal Gecko,Oedura lesueurii

In oviparous species lacking parental care, successful reproduction depends on females selecting nest sites that facilitate embryonic development. Such sites may be limited in the environment, which can lead to multiple females using the same nest site simultaneously. However, there are several alternative explanations for communal nesting, including natal homing, predator satiation, and adaptive benefits to offspring. We used laboratory experiments to evaluate three hypotheses about nest‐site selection in velvet geckos (Oedura lesueurii), which often nest communally. We investigated whether the trend to nest communally is influenced by the following: (1) evidence of previous nesting (hatched eggshells); (2) body size; and/or (3) thermal regimes. When given the choice, females laid their eggs in shelters containing hatched eggshells rather than in empty shelters, and this was not influenced by body size. Females selected nest sites that were cooler than their own mean selected body temperatures, suggesting that thermal requirements of their developing embryos could outweigh their own thermoregulatory preferences. Field observations of natal homing and high predation rates on gravid females suggest that imprinting on nest sites and/or predator swamping also play roles in communal nesting. Collectively, our results suggest that female velvet geckos use multiple cues to select appropriate nest sites, and hence that multiple mechanisms result in communal nesting behavior in this species.     

Temporal variation in habitat selection breaks the catch‐22 of spatially contrasting predation risk from multiple predators

Predator avoidance depends on prey being able to discern how risk varies in space and time, but this is made considerably more complicated if risk is simultaneously present from multiple predators. This is the situation for an increasing number of mammalian prey species, as large carnivores recover or are reintroduced in ecosystems on several continents. Roe deer Capreolus capreolus in southern Norway illustrate a case in which prey face two predators with contrasting patterns of predation risk. They face a catch‐22 situation: spatially avoiding the risk from one predator (lynx Lynx lynx in dense habitat) implies exposure to the other (hunters in open habitat). Using GPS‐data from 29 roe deer, we tested for daily and seasonal variation in roe deer selection for habitat with respect to the habitats’ year‐round average risk level. Generally, roe deer altered their habitat selection between night and day in a pattern consistent with being able to avoid predicted risk from the nocturnal lynx during night and predicted risk from human hunters during day. However, seasonal variation in habitat selection only partially corresponded with the predicted seasonal variation in risk. Whereas roe deer avoided areas with high risk from hunters more strongly during the hunting season than in other seasons, there was a lack of selection towards areas and time periods lowering the risk of lynx predation during winter. It seems likely that the risk of starvation and thermal stress constrain roe deer habitat selection during this energetically challenging season with cold temperatures, snow cover and limited natural forage. The habitat selection pattern of roe deer fits thus only partly with the two contrasting risk gradients they face. Adjusting risk‐avoidance behavior temporally can be an adaptive response in the case of several predators whose predation patterns differ in space and time.     

Roosting Behavior of Colonial and Solitary Flying Foxes in American Samoa (Chiroptera: Pteropodidae)1

We examined characteristics of roosting sites utilized by two flying fox species (Pteropus tonganus and P. samoensis) in American Samoa. The colonial roosting sites of P. tonganus were observed over a ten‐year period, including two years when severe hurricanes devastated bat populations and destroyed roost trees. Prior to the hurricanes, roosts were located on cliff faces above the ocean or steep mountainsides, locations that were either inaccessible to people or in protected areas where hunting was not allowed. In the years immediately following the hurricanes, P. tonganus colonies split into smaller groups that moved frequently to different locations. Four years after the second hurricane, colonies had coalesced and returned to many of the traditional roosting sites used before the hurricanes. Common tree species in upland and coastal forest were selected as roosts. The isolated locations selected for P. tonganus roosts were apparently the result of hunting pressure on the colonies. The solitary roosts of P. samoensis were observed during 29 months. Roosting bats were well concealed and hard to detect within the forest; even bats on exposed branches were cryptic. Mature primary forest was favored as roosting habitat. Individual bats used specific branches or trees as roosts and returned to them for up to 29 months. Unlike P. tonganus, people did not alarm roosting P. samoensis easily and some roosts were located near houses and along roads.     

Predator Avoidance of Transgenic Channel Catfish Containing Salmonid Growth Hormone Genes

Transgenic channel catfish (Ictalurus punctatus) containing salmonid growth hormone genes can grow 33% faster than normal channel catfish under aquaculture conditions. However, before transgenic catfish are released and utilized by the private sector, their genetic impact on the natural environment must be examined. Predator avoidance is one of the major fitness traits determining potential environmental risk. To determine the predator avoidance ability and growth performance of transgenic catfish in a natural habitat, various densities of transgenic and nontransgenic channel catfish were communally stocked in 0.04-ha earthen ponds without supplemental feeding. Largemouth bass (Micropterus salmoides) and green sunfish (Lepomis cyanellus) were stocked as predators. Nontransgenic fry had better predator avoidance than transgenic channel catfish when data were pooled (p < .01). When data were not pooled, nontransgenic catfish had better predator avoidance in six trials and transgenic individuals had better predator avoidance in four trials. There was no difference in predator avoidance in three trials. Overall predator avoidance was also better for nontransgenic individuals (p < .01) when the fish were evaluated as 3.5-g fingerlings, more clearly than as fry, as transgenic individuals were more vulnerable in 3 of 4 trials at this life stage. There was no significant difference in growth performance between transgenic and nontransgenic channel catfish in ponds without supplemental feeding. These findings indicate that transgenic channel catfish could be used for commercial aquaculture without affecting the natural environment. Although transgenic channel catfish may be released to nature by accident, any ecological effect would be unlikely because the increased susceptibility of transgenic channel catfish to predators would most likely decrease or eliminate the transgenic genotype. Received March 8, 1999; accepted June 3, 1999.