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Distress calls are produced by a wide variety of small prey species when they are captured by a predator and may serve as signals to warn group members of danger, to attract others that might aid the captured individual, and to confuse the predator. Tufted titmice (Baeolophus bicolor) produce distress calls when captured by a predator or a human. Here, we tested several hypotheses to explain the distress calling in this species. Individual titmice were captured in walk-in treadle traps. We recorded captured individuals in an ordered sequence that modeled approaching threat, capture, and finally escape. Titmice produced more total notes as the level of threat increased (as the observer moved closer to the trap restraining them) and as they were captured and held. Captured titmice produced distress calls comprising many high-frequency components but also many low-frequency broadband components and did so whether other titmice were present or absent. Playbacks of distress calls indicate that the notes of these calls transmit over long distances (>60 m) and do not readily attract larger avian predators to the area. Variation in production of lower frequency and broadband notes by captured titmice was not associated with variation in aggressive behavior. Taken together, our results lend support both to the “protean defense” hypothesis and to a dual “mobbing/alarm” hypothesis. Distress calls in titmice may therefore function either to confuse the predator or to warn conspecifics and facilitate their mobbing behavior. [ABSTRACT FROM PUBLISHER]

Use of socially derived information from other species is common in many types of decision making, but particularly in predation avoidance. In communities with diverse prey that share generalist predators, public information concerning predator location, type, or activity is often used by heterospecifics. Given that exploration and exploitation of the environment is constrained by predator avoidance, exactly how information about predators affects subsequent prey behavior is of increasing interest. In this study, we tested how social information (predation threat encoded in antipredator vocalizations of the tufted titmouse, Baeolophus bicolor) influences the exploratory behavior (movement, vigilance, and space use) of Northern cardinals (Cardinalis cardinalis). Cardinals, placed inside a small flight cage equipped with an array of perches, experienced randomly assigned playback treatments of titmouse antipredator vocalizations that varied in threat level. Exploratory behavior was videotaped during 3 periods—Before (B), During (D), and After (A) playbacks of titmouse calls. When titmouse vocalizations encoding more dangerous and immediate predation threats were played, cardinals significantly reduced active movements but increased visual scanning relative to subjects hearing calls that encoded low threat levels. Furthermore, they were also slower to return to prethreat behavior. Thus, we conclude that cardinals interpreted the antipredator signals correctly and responded accordingly, adjusting their activities to potentially reduce risk (decreasing movement and increasing vigilance). Our work demonstrates specifically how the trade-off between exploration (comprised of both movement and sensory scanning) and predator avoidance is actuated via spatial decision making in the cardinal. [ABSTRACT FROM PUBLISHER]

The prolonged brood care model rests on the assumption that retaining an offspring through the winter months in the face of a limited food supply should have a cost for parents. We tested this idea with a New World permanent-resident bird, the tufted titmouse (Baeolophus bicolor). Using DNA fingerprinting, we assessed the degree of relatedness between adult and juvenile birds in 17 winter groups, finding that in 8 of the groups no young bird was the offspring of the territorial pair. We compared the nutritional condition of territorial adult birds in small forest fragments from which their own offspring and other young had been removed with the nutritional condition of control birds from unmanipulated fragments. Contrary to the model's assumption, the nutritional condition of adults in treatment groups (young removed) appeared to be worse, not better, than in groups where a related juvenile was present. These results suggest that the prolonged brood care model may not be universal in its application and that under some ecological conditions, retaining offspring through the winter can result in a net benefit for territorial adults despite the necessity of sharing resources. [ABSTRACT FROM AUTHOR]

In the temperate zone, permanent-resident birds and mammals that do not hibernate must survive harsh winter conditions of low ambient temperature, long nights, and reduced food levels. To understand the energy management strategy of food-hoarding birds, it has been hypothesized that such birds respond to increased starvation risk by increasing the number of their hoards rather than by increasing their fat reserves and that they cache early in the day and retrieve their caches later to achieve fat reserves necessary to survive the night. We tested these hypotheses by observing the responses in captivity of a caching bird, the tufted titmouse (Parris bicolor), to the combined influences of reduced predictability of food and naturally occurring ambient temperature and photoperiod. When the food supply was unpredictable, birds significantly increased both internal fat reserves at dusk and external food caches. Initially leaner birds tended to increase their fat reserves to a greater extent and initially fatter birds tendedto cache more food and to fly significantly less. Half the birds also increased their dawn and mean daily body mass. All birds tended to forage, gain body mass, and cache food at significantly lower rates in the morning and at significantly higher rates in the evening. Cacheretrieval showed the opposite trend, with birds retrieving most of their caches in the morning. Our results do not support the hypothesisthat caching birds increase caching rate but not body mass under an unpredictable food regime. Instead fat reserves and food caches are both important complementary sources of energy in food-hoarding birds.Energy management by wintering birds occurs in response to a number of biotic and abiotic factors acting simultaneously; thus future models must incorporate independent variables in addition to the state ofthe food supply and time of day. [ABSTRACT FROM AUTHOR]