Seasonal changes in the migratory behaviour of the toad Bufo bufo: direction and magnitude of movements

Summary The migratory behaviour of the toad Bufo bufo was studied from February 1985 to April 1986 in the submontane region of Bavaria, West Germany. Toads were fitted with a mechanical tracking device to record individual paths of migration. Three aspects of migratory behaviour were quantified: orientation in relation to the breeding site, straightness of path, and locomotory activity. The annual activity period began with migration from the hibernation sites to the breeding pond in April. The paths went straight towards the breeding pond independent of the distance (70–420 m). During the period of oviposition the preference for the breeding site direction vanished and toads moved away from the breeding pond, but in less straight paths than before. In summer migratory activity decreased considerably and was restricted to small areas, the home ranges, at distances of 55–1600 m from the natal breeding pond. The straightness of path was rather low, because toads often returned to their starting points. During rainy nights toads occasionally left their home ranges for extensive excursions. In autumn most toads again migrated towards the breeding pond, but paths were significantly less straight and direct than in spring. However, toads stopped before reaching the breeding pond and hibernated in holes or under the leaf layer. The mortality rate of tracked toads was about 45%. The relative influence of 17 environmental variables on locomotory activity was evaluated by principal component analysis and stepwise multiple regression. Temperature at night and rainfall variables accounted for significant amounts of variance, whereas temperature by day, air humidity, and atmospheric pressure showed no correlation. Activity decreased if temperature approached 0° C or after long periods without rainfall. Within a certain range of tolerance, however, the locomotory activity of the toads was widely independent of environmental factors, indicating that endogeneous factors are more important sources of variation in the migratory behaviour of these toads than commonly assumed.     

The effects of density,rainfall and environmental temperature on body condition and fecundity in the common toad,Bufo bufo

The body length and body weight of all adult common toads (Bufo bufo) breeding at a pond in south Dorset were measured between 1983 and 1993. Each toad was placed into one of four categories depending on its sex and whether it was either a first time breeder or an animal that had previously bred. The body condition of each male and female toad for each year was compared with the average body condition of all the male and female toads captured over the 11 years of the study so that between-year differences in condition could be detected. Changes in body condition were compared with changes in body condition were compared with changes in toad density, rainfall and climatic temperature during the previous summer (March–September), during hibernation (October–February) and during the month preceding the start of spawning. During the study there was a decline in the body condition of all toad categories and these changes were significantly correlated with changes in toad density and climatic temperature. Toads were also more likely to enter hibernation in poor condition following a hot dry summer than after either cool wet or hot wet summers. Body condition explained 41% of the size-specific variation in fecundity.     

The straight and narrow path: the evolution of straight-line dispersal at a cane toad invasion front

At the edge of a biological invasion, evolutionary processes (spatial sorting, natural selection) often drive increases in dispersal. Although numerous traits influence an individual''s displacement (e.g. speed, stamina), one of the most important is path straightness. A straight (i.e. highly correlated) path strongly enhances overall dispersal rate relative to time and energetic cost. Thus, we predict that, if path straightness has a genetic basis, organisms in the invasion vanguard will exhibit straighter paths than those following behind. Our studies on invasive cane toads (Rhinella marina) in tropical Australia clearly support this prediction. Radio-tracking of field-collected toads at a single site showed that path straightness steadily decreased over the first 10 years post-invasion. Consistent with an evolved (genetic) basis to that behavioural shift, path straightness of toads reared under common garden conditions varied according to the location of their parents'' origin. Offspring produced by toads from the invasion vanguard followed straighter paths than did those produced by parents from long-established populations. At the individual level, offspring exhibited similar path straightness to their parents. The dramatic acceleration of the cane toad invasion through tropical Australia has been driven, in part, by the evolution of a behavioural tendency towards dispersing in a straight line.     

Mapping the Relative Probability of Common Toad Occurrence in Terrestrial Lowland Farm Habitat in the United Kingdom

Introduction

The common toad (Bufo bufo) is of increasing conservation concern in the United Kingdom (UK) due to dramatic population declines occurring in the past century. Many of these population declines coincided with reductions in both terrestrial and aquatic habitat availability and quality and have been primarily attributed to the effect of agricultural land conversion (of natural and semi-natural habitats to arable and pasture fields) and pond drainage. However, there is little evidence available to link habitat availability with common toad population declines, especially when examined at a broad landscape scale. Assessing such patterns of population declines at the landscape scale, for instance, require an understanding of how this species uses terrestrial habitat.

Methods

We intensively studied the terrestrial resource selection of a large population of common toads in Oxfordshire, England, UK. Adult common toads were fitted with passive integrated transponder (PIT) tags to allow detection in the terrestrial environment using a portable PIT antenna once toads left the pond and before going into hibernation (April/May-October 2012 and 2013). We developed a population-level resource selection function (RSF) to assess the relative probability of toad occurrence in the terrestrial environment by collecting location data for 90 recaptured toads.

Results

The predicted relative probability of toad occurrence for this population was greatest in wooded habitat near to water bodies; relative probability of occurrence declined dramatically > 50 m from these habitats. Toads also tended to select habitat near to their breeding pond and toad occurrence was negatively related to urban environments.     

The effect of winter temperatures on the timing of breeding activity in the common toad Bufo bufo

A 19-year study of a common toad population in south Dorset, UK, was carried out between 1980 and 1998. The daily arrival of sexually mature male and female toads at a breeding pond was recorded each year. The timing of the main arrival of toads at the breeding pond was highly correlated with the mean daily temperatures over the 40 days immediately preceding the main arrival. When the temperatures were higher than average, breeding occurred significantly earlier in the year than if they were either average or lower than average. During the study, the toad breeding seasons were early (2–13 February) in 5 years (1989, 1990, 1993, 1995, 1998), late (16–23 March) in 2 years (1986, 1996) and average (25 February–8 March) during the remaining 12 years. Evidence was found suggesting that common toads have a daylength threshold of about 9 h, below which the migration to the breeding pond does not occur. Evidence was also found indicating that common toads in southern England have a threshold temperature for activity of about 6°C and that the onset of breeding activity is highly correlated with the number of days during the 40 days prior to the main arrival at the breeding pond that were at or above this temperature. Predicting the start of the main breeding migration to a pond in any year may be possible by comparing the pattern of the 40-day running mean daily temperatures from 21 December the preceding year with those from previous years when the start of breeding activity is known. Although all five of the earliest recorded toad breeding years occurred during the last 10 years, and were associated with the occurrence of particularly mild winters, a significant trend towards earlier breeding in recent years compared with previous years was not found. Received: 16 July 1998 / Accepted: 14 September 1998     

Husbandry and breeding of the Puerto Rican toad (Peltophryne lemur) with comments on its natural history

The methods used in the breeding and rearing of Peltophryne lemur along with comments on reintroduction efforts are described. Breeding was induced by injections of leutinizing releasing hormone, and fertile eggs were produced. Eggs hatched in approximately 24 h. Newly hatched tadpoles were small (5.0 mm) and delicate. Metamorphosis occurred in 20–30 days, and newly metamorphosed toads grew evenly and quickly to maturity in about 1 yr. Seventy-five 20-mm young were returned to Puerto Rico in May 1983. These toads were released at a pond where adult and young P lemur were seen. The successful maintenance and breeding of this species indicate it can survive in captivity. Future work on P lemur should concentrate on its status and survival in the wild.     

Competitive mate searching in male common toads, Bufo bufo

The reproductive behaviour of a population of individually marked toads Bufo bufo was studied at a pond where males outnumbered females by between four and five to one. There was intense competition between the males for mates and only 20·5 % of them bred successfully. Of the successful males, 38·5 % got mates by fighting and displacing other males from the backs of females (takeovers). Larger males enjoyed greater reproductive success because they were stronger and better able to achieve takeovers. When competing for females, some males searched at the spawn site while others searched away from spawn. The numbers searching in the two areas can be predicted by a model which assumes that unpaired males distribute themselves so that there is a spatial ESS, where individuals have equal expectations of finding a female both at and away from the spawning ground.     

Non-random mating by size in American toads, Bufo americanus

Male American toads, Bufo americanus, captured in amplexus at least once during the season were significantly longer than males captured only singly in the same breeding population in all three cases studied. Absence of any correlation between the body lengths of the members of amplexing pairs argues against selection for optimal relative size. Males successful at breeding were those that (1) were larger, (2) were at the pond more nights, and (3) spent more time calling than unsuccessful males. Residency, per se, did not enhance breeding success, however, as on any given day successful males were equally likely to come from recaptured males previously present at the pond and unmarked males presumed new to the pond. Amount of movement about the pond did not vary with breeding success; all males tended to remain in one area on any given night and to change areas between nights. A very low displacement rate (about 7%) of males in amplexus argues against primacy of this form of male-male competition in producing differential mating by size. Rather it appears that some combination of other forms of intrasexual competition and female choice caused the mating pattern seen.     

Celestial orientation in the marbled newt (Triturus marmoratus)

Orientation toward breeding ponds plays an important role in the seasonal movements of amphibians. In this study, adult marbled newts were tested in a circular arena to determine sensory cues used to locate breeding ponds. Animals were collected from a temporary pond situated in northern Spain, taken to the experimental site 340 m distant, and tested for orientation under a variety of conditions (i.e., orientation under a clear night sky, orientation under an overcast night sky, and orientation under a clear night sky in the presence of an altered geomagnetic field). These investigations have demonstrated that the marbled newt is able to orient using celestial cues. Animals chose a compass course in the direction of their breeding pond only when celestial cues were available. Conversely, the ambient geomagnetic field does not seem to be relevant to orientation of marbled newts since they were unable to orient themselves using the ambient geomagnetic field in the absence of celestial cues. Electronic Publication     

Female polyandry and size‐assortative mating in isolated local populations of the Japanese common toad Bufo japonicus

In anurans, female polyandry under male harassment is distributed across taxa because of external aquatic fertilization. According to the sexual selection theory, male–male competition for access to females is affected by the operational sex ratio (OSR) and population density. The Japanese common toad, Bufo japonicus, is widespread in mainland Japan, and like the European common toad, B. bufo, it engages in explosive breeding. In this study, we observed the breeding behaviour of B. japonicus in isolated local populations for over four years in two breeding ponds with different population sizes and densities: large‐low (L‐pond) and small‐high (S‐pond). We analysed the relative polyandry ratio in egg clutches laid by females and estimated the size‐assortative mating pattern to be an indicator of male–male competition in the two ponds. Both ponds tended to exhibit a size‐assortative mating pattern; however, the frequency of polyandry was different in the two ponds (L‐pond = 20% and S‐pond = 90%). Our results showed that polyandry could occur without multiple amplexus with a high population density, i.e. eggs were often fertilized by free‐swimming sperm in the small shallow pond. We propose that high female polyandry ratios without continuous male harassment are generated because of a male‐biased OSR and a high population density in the small pond. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 236–242.     

Use of a Magnetic Compass for Nocturnal Homing Orientation in the Palmate Newt, Lissotriton helveticus

Previous studies have shown that migrating palmate newts (Lissotriton helveticus) can rely on acoustic cues for orientation to breeding ponds. Nonetheless, although acoustic cues are reliable over relatively short distances, they are unlikely to account for the long‐distance homing demonstrated in several other species of newts. Most individuals of L. helveticus migrate only a few hundred meters (Diego‐Rasilla, F. J. & Luengo, R. M. 2007: Acoustic orientation in the palmate newt, Lissotriton helveticus. Behav. Ecol. Sociobiol. 61, 1329—1335), raising the possibility that this species may only utilize short‐distance cues (Joly, P. & Miaud, C. 1993: How does a newt find its pond? The role of chemical cues in migrating newts (Triturus alpestris). Ethol. Ecol. Evol. 5, 447—455; Russell, A. P., Bauer, A. M. & Johnson, M. K. 2005: Migration of amphibians and reptiles: an overview of patterns and orientation mechanisms in relation to life history strategies. In: Migration of Organisms (Elewa, M. T., ed). Springer‐Verlag, Berlin Heidelberg, pp. 151—203; Sinsch, U. 2006: Orientation and navigation in Amphibia. Mar. Freshw. Behav. Phy. 39, 65—71). Therefore, experiments were carried out to investigate the use of the geomagnetic field in the nocturnal homing orientation of L. helveticus. Tests were carried out at night in an outdoor circular arena, under total overcast sky that prevented access to celestial compass cues. Individual newts were tested in one of four symmetrical alignments of an earth‐strength magnetic field. We studied the orientation behaviour of newts from two breeding ponds located 9.05 km west‐southwest and 19 km east‐northeast of the testing site. The distribution of magnetic bearings from both groups of newts exhibited significant orientation in the homeward direction. These findings indicate that palmate newts are capable of long‐distance homing and are able to orient in the homeward direction at night using the magnetic compass as the sole source of directional (i.e., compass) information.     

The toad fly Lucilia bufonivora: its evolutionary status and molecular identification

The blow fly genus Lucilia is composed largely of saprophages and facultative myasis agents, including the economically important species Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) and Lucilia sericata (Meigen). Only one species is generally recognized as an obligate agent of myiasis, Lucilia bufonivora Moniez, and this is an obligate parasite of toads. Lucilia silvarum (Meigen), a sister species, behaves mainly as a carrion breeder; however, it has also been reported as a facultative parasite of amphibians. Morphologically, these species are almost identical, and historically this has led to misidentification, taxonomic ambiguity and a paucity of studies of L. bufonivora. In this study, dipterous larvae were analysed from toad myiasis cases from the U.K., The Netherlands and Switzerland, together with adult specimens of fly species implicated in amphibian parasitism: L. bufonivora, L. silvarum and Lucilia elongata Shannon (from North America). Partial sequences of two genes, cox1 and ef1α, were amplified. Seven additional blow fly species were analysed as outgroups. Bayesian inference trees of cox1, ef1α and a combined‐gene dataset were constructed. All larvae isolated from toads were identified as L. bufonivora and no specimens of L. silvarum were implicated in amphibian myiasis. This study confirms L. silvarum and L. bufonivora as distinct sister species and provides unambiguous molecular identification of L. bufonivora.     

Non‐Selective and Time‐Dependent Behavioural Responses of Common Toads (Bufo bufo) to Predator Acoustic Cues

Acoustic predator recognition has rarely been studied in anurans, in spite of the fact that hearing is widespread in these animals and that it has been demonstrated to play an important role in both arthropods and other vertebrates. Using field playback experiments, we tested the hypothesis that adult common toads (Bufo bufo) are capable of recognizing natural vocalizations of a common predator, the Eurasian otter (Lutra lutra), and show antipredator responses. We found that toads exposed to both natural (two types of otter sounds) and synthetic stimuli [white noise (WN) and otter sound‐based amplitude modulated WN] increased time allocated to locomotion and escape behaviour. These responses were correlated with time elapsed from sunset to the onset of testing and were independent from the type of acoustic signal, toad features and other environmental factors monitored. We conclude that B. bufo has not developed a selective recognition of predator vocalizations, suggesting that low‐frequency or seismic sounds associated with predator movements may provide anurans with better cues about an approaching risk. We propose that the time‐dependent response to acoustic stimuli of common toads represents a case of threat‐sensitivity and demonstrates that it can occur even when the response to the threat is not predator specific.     

Negative effects of Rhabdias bufonis (Nematoda) on the growth and survival of toads (Bufo bufo)

Summary The growth and survival of juvenile toads, Bufo bufo, infected with a common lung nematode, Rhabdias bufonis, were studied. Toads were raised from tadpoles in the laboratory and infected 2 months after metamorphosis. Individual toads were exposed to doses of 10, 40, 80 or 160 larvae, which enabled examination of the hypothesis that parasite-induced mortality is affected by worm numbers. Growth of infected toads began to diverge from that of uninfected controls at 6 weeks post infection (WPI) and by 12 WPI the most heavily infected toads were approximately half the mass of controls. No controls died throughout the experiment; however, mortality of infected toads was strongly affected by parasite density. A mechanism for mortality is suggested by the significant negative relationship between parasite density and dietary intake. This parasite-induced anorexia was detected at 3 WPI and persisted up to 9 WPI. Patterns of reduced host growth, survival and dietary intake provide experimental evidence of the negative consequences of parasitic infection in a natural parasite-host system which may also be present under natural conditions.     

Interspecific spawning between Common frogs (Rana temporaria) and Common toads (Bufo bufo)

The interaction between Common frogs (Rana temporaria) and Common toads (Bufo bufo) during the breeding season was studied at a small pond on Portland, Dorset. Although the frogs started and finished spawning earlier than the toads there was a period during which interspecific spawning between female toads and male frogs took place. This appears to have resulted from reduced male toad activity caused by the cold breeding season given that spatial, temporal and behavioural species separation did not occur.     

The Light and Magnetic Compass of the Weaver Ant,Oecophylla smaragdina (Hymenoptera: Formicidae)

Some of the foraging of the arboreal Australian weaver ant Oecophylla smaragdina takes place on the ground. Odor trails and compass orientation are used to return to the trunk of their nesting tree. Field experiments established directional responses to light and the natural magnetic field. The precision of the light compass orientation is much greater than that of the magnetic compass orientation: the respective average wrapped-around standard deviations (WSD) of directional choices towards home are WSD = ± 48° and WSD = ± 105°.     

Size-structured effects of common carp on reproduction of pond-breeding amphibians

The role of fish in driving amphibian communities has been widely recognized. However, little is known about size-structured interactions between amphibian and fish populations. This study compared the taxonomic occurrence and densities of larval amphibians between unstocked ponds and ponds stocked with different age cohorts of common carp Cyprinus carpio differing in average body size. The average total densities of early and late breeding anurans known to be vulnerable to fish were by 1–2 orders of magnitude greater in the presence of young-of-the-year carp than that of older cohorts. The probabilities of occurrence of the most common taxa did not differ between ponds stocked with young-of-the-year fish and ponds free of carp, but were significantly larger in those ponds than in ponds stocked with large-size cohorts. No significant differences between pond categories were found for densities of unpalatable Bufo bufo larvae. In aquatic systems harbouring size-structured fish populations, a fish age/size gradient may explain differential habitat suitability for breeding amphibians better than the fish presence/absence dichotomy. When dominated by young cohorts incapable of predation or of adverse habitat alteration, fish-abundant waters are suitable for amphibian reproduction. Conversely, even a ‘non-predatory’ fish, after attaining large body size, may exert a detrimental impact on amphibian breeding success. These findings may be particularly important for amphibian conservation at pond fisheries characterized by spatial separation of age/size distributed stocks.     

Impacts of climate and density on the duration of the tadpole stage of the common toad Bufo bufo

In an ongoing long-term study of a breeding population of common toads Bufo bufo at a pond in southern England, the dates of first spawning have been recorded since 1980, the dates of toadlet emergence since 1984, and the numbers of emergent toadlets estimated since 1988. The dates when spawn was first laid varied considerably between years from the earliest on 2 February 1993 (day 33) to the latest on 19 March 1996 (day 79). The duration of the tadpole stage was negatively correlated with the date of appearance of first spawn and was up to 30 days longer in early spawning years than in late ones. Despite this, toadlets still emerged from the natal pond up to 36 days earlier in early spawning years than in late ones. Significant positive correlations were found between the duration of the tadpole stage and both the proportion of days during the tadpole stage when the minimum ground temperature was at or below 0°C and the proportion of days when 10 mm or more rain fell. Tadpole mortality was positively correlated with the proportion of days during the tadpole stage when the minimum ground temperature was at or below 1.5°C. Evidence was also found to suggest that tadpole mortality was density-dependent, being proportionately higher when initial tadpole numbers were high than when they were low. Received: 7 May 1999 / Accepted: 19 July 1999     

Population differentiation of migratory directions in birds: comparison between ringing results and orientation behaviour of hand-raised migrants

Summary Blackcaps (Sylvia atricapilla) from five areas in Central Europe were hand-raised. Their autumn migratory orientation was tested in funnel-shaped cages. Their directional choices were compared to recoveries of conspecifics ringed during the breeding season in the same areas, which are situated on a transect across a migratory divide between southeastward and southwestward migrating populations. Results from ringing and orientation tests were in good agreement with respect to mean direction and dispersion of flight directions. An exception is the area around Linz (NW Austria), right on the migratory divide, where ringing yielded a strong scatter, but hand-raised birds chose westerly directions. The recent establishment of a novel migration route toward the British Isles was reflected in both data sets: in southern Germany the percentage of northwestward migrants is 6.8% according to orientation tests and 11.8% according to ringing recoveries. Testing the orientation of young passerines in captivity can yield valuable information about population differentiation of migratory behaviour. It is more efficient than ringing in this respect, because it circumvents the low recovery rates and is free of biases affecting ringing data. In the blackcap, geographic differentiation of migratory directions occurs on a finer scale than previously recognized and can change significantly within 2–3 decades.     

The successful elimination of Cane toads, <Emphasis Type="Italic">Bufo marinus</Emphasis>, from an island with breeding habitat off Bermuda

The 6.5 Ha Nonsuch island nature reserve in Castle harbour, Bermuda, under restoration as a “Living museum” of Bermuda’s pre-colonial terrestrial flora and fauna since 1962, was unexpectedly compromised by the colonization of a manmade freshwater pond by the invasive Cane toad Bufo marinus, which managed to cross a 175 m seawater barrier isolating the island. The toad was considered to pose a threat to the endemic Skink, for which Nonsuch is a key sanctuary, and to the burrow nesting Bermuda petrel or Cahow, which was about to be translocated to that larger island in order to establish a colony safe from the global warming threat of sealevel rise. A non-lethal method of removing the toads was devised through installation of a toad barrier around the freshwater pond, constructed of robust high density polyethylene (HDPE). Toads outside the barrier were no longer able to breed and were captured and removed by night searches over a five year period as they piled up against it. Removal of the breeding population inside the barrier was only possible by capturing all individuals resulting from each spawning before they could reach breeding age. This also took 5 years despite the small size (0.06 Ha) of the pond. A total of 1,244 toads were removed to Bermuda’s mainland. As breeding age is attained in 2 years the collection total for the first 2 years provided an approximation of the population density on the island before removal began (~80 per Ha). Although the immigration rate to Nonsuch is estimated to be less than one per year, this still requires maintaining the barrier as a permanent fixture. As future immigrants can be fairly quickly intercepted, the toad is now essentially extaxic on Nonsuch. This is the first published report of a successful eradication of the species from an island with breeding habitat.