Chick-a-dee call syntax,social context,and season affect vocal responses of Carolina chickadees (<Emphasis Type="Italic">Poecile carolinensis</Emphasis>)

Chick-a-dee calls in many chickadee (Poecile) species are common vocal signals used in a diversity of social contacts. The calls consist of four notes, A, B, C, and D, which follow simple rules of syntax (note ordering and composition) to generate many unique call types. We used field playbacks with Carolina chickadees, P. carolinensis, to ask whether violations of a syntactical rule affected their vocal responses. We show that chickadee responses to typical calls (e.g. AAAACCCC and CCCCDDDD) differ from responses to atypical calls (e.g. CACACACA and DCDCDCDC) depending on playback note composition, season, and social context (presence of heterospecifics). In the fall/winter, playbacks of typical calls with A and C notes elicited the greatest number of A and B notes in chick-a-dee call responses and typical calls with D notes elicited the greatest number of C notes, when in the presence of heterospecifics. In contrast, the corresponding atypical calls did not elicit similar responses. This suggests communicative significance is lost in calls that violate a rule of syntax in the fall/winter. In the spring, neither chickadee feebeefeebay song rate nor chick-a-dee calls responses differed by playback type. We suggest that call syntax is less salient for mated pairs in the spring than it is for fall/winter flocks that rely more on conspecific communication for foraging success and flock cohesion. This study represents the first experimental evidence that chickadees attend to both note composition and ordering in chick-a-dee calls.Communicated by W.A. Searcy     

Female encounter rate and the calling behavior and mating propensity of male Requena verticalis (Orthoptera: Tettigoniidae)

Mating effort, the energy exerted in finding and persuading a member of the opposite sex to mate, may be influenced by how frequently potential mates are encountered. Specifically, males that frequently encounter females may reduce calling effort and be less eager to mate than males that infrequently encounter females. An experiment was set up to test this hypothesis, using the tettigoniid Requena verticalis. We examined the song structure, calling activity and mating propensity of individual males exposed to one of five different encounter rates with virgin females. Song structure and calling effort were significantly altered by an encounter with a female. After an encounter, males significantly increased chirp rate and decreased variability in interchirp interval. Encounters also stimulated a male to call and to continue to call for up to two hours. The elapsed time since mating affected mating propensity but not calling activity. Mating propensity asymptotically increased to reach a maximum by day 17 since last mating. However, neither the frequency of encounters, nor the number of previous encounters experienced by a male, influenced calling activity or the propensity of a male to mate. The significance of changes in song structure and calling activity following an encounter, and of increasing male mating propensity over time, are discussed. Correspondence to: G.R. Allen     

Schooling behavior of Antarctic krill (Euphausia superba) in laboratory aquaria: Reactions to chemical and visual stimuli

Antarctic krill,Euphausia superba, often exhibit abnormal behavior in laboratory aquaria, usually hovering in a stationary position, unresponsive to most external stimuli. In the austral summer of 1985–1986 at Palmer Station on Anvers Island, Antarctica, we provided laboratory conditions which inducedE. superba to school in large aquaria. Captive krill swam horizontally and exhibited the full spectrum of behaviors normally displayed while schooling at sea. Schooling krill avoided visually contrasting stimuli, with avoidance distances correlated with stimulus size. Schools responded in qualitatively different ways to presentations of food, chemical compounds, and abrupt increases in light intensity. We describe the conditions necessary for aquarium schooling and discuss the importance of an appropriate social environment for displays of escape, avoidance, and feeding behaviors and of positional preference within the school.     

Simultaneous behavior of skipjack (Katsuwonus pelamis), bigeye (Thunnus obsesus), and yellowfin (T. albacares) tunas, within large multi-species aggregations associated with drifting fish aggregating devices (FADs) in the equatorial eastern Pacific Ocean

Ten separate experiments monitoring the simultaneous behaviors of 26 skipjack (Katsuwonus pelamis), 26 bigeye (Thunnus obesus), and 33 yellowfin (T. albacares) tunas within large multi-species aggregations associated with drifting fish aggregating devices (FADs) were investigated using ultrasonic telemetry in the equatorial eastern Pacific Ocean. Experiments were conducted during a research cruise aboard a chartered purse seine vessel. Purse seine sets were made on the tuna aggregations associated with FADs at the termination of six of the ten experiments. Seventeen of the 44 tagged tunas were not recaptured indicating the transient nature of the associative behavior of tunas with FADs. Although there was considerable overlap in the depths of the three species, by day and night, there were some species-specific differences and diel differences within species. While we documented spatial and temporal differences in the schooling behavior of the three tuna species, the differences do not appear sufficient such that modifications in purse seine fishing practices could effectively avoid the capture of small bigeye and yellowfin tunas, while optimizing the capture of skipjack tuna in purse seine sets on FADs.     

Predator recognition and evasive behavior by sweat bees, <Emphasis Type="Italic"> Lasioglossum umbripenne </Emphasis>(Hymenoptera: Halictidae), in response to predation by ants, <Emphasis Type="Italic"> Ectatomma ruidum </Emphasis>(Hymenoptera: Formicidae)

Ectatomma ruidum is an abundant soil-nesting Neotropical ant, which displays extensive behavioral flexibility during foraging activities. We studied here one unusual element of their behavioral repertoire: ambush predation. A worker of E. ruidum waits near a nest of a social sweat bee, Lasioglossum umbripenne, lunging at incoming bees, or less frequently, at departing bees. However, bees detected ambushing ants and modified their behavior. Dead ants placed at bees' nest entrances significantly decreased bee activity, indicating that bees recognized dead ants as potential predators. Neither simple black models (square and rectangle) nor olfactory cues had any effect on overall bee activity. A returning bee usually approached her entrance and immediately entered, but if an ant was waiting at the nest, a bee was significantly more likely to abort the first approach flight and then to re-approach the nest on the side opposite the ant's position. As models became increasingly ant-like, returning bees more frequently aborted their first approach flight, expressing other behaviors before entering nests. These behaviors included withdrawal followed by an approach from a different direction; zigzagging flights, either from a distance or close to the entrance or even a close inspection; landing a short distance from the nest, then approaching on foot or waiting for several seconds before entering. Ants responded with effective counter-behaviors. Behavioral flexibility in nest entering/exiting by L. umbripenne and in hunting strategy by E. ruidum shows the complexity of this predator-prey relationship, and illustrates the importance of information processing by both species involved in determining the outcome of the interspecific interaction.