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Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds

ABSTRACT: A survey of 166 hummingbird species reveals novel associations of bill-length sexual dimorphism (BLSD) with plumage and breeding behaviours. Across all species, female bills become proportionately longer than male bills (higher female-to-male BLSD ratio) as sexual dichromatism increases. However, male bills are proportionately longer (lower female-to-male BLSD ratio) in both lekkers (traditional group display) and clustered breeders (female harems or colonial nests) compared with dispersed breeders. The overall positive association of plumage with BLSD suggests that social status determines priority of access to nectar-providing flowers. Furthermore, the distinctive BLSD associated with breeding aggregations may arise from behaviours that impose constraints on the usual male priority at flowers: female dominance over males around nest colonies and male residence on lek-mating territories. These various factors appear to alter plumage and bill characters of both sexes to produce the range of dimorphisms within the various dispersed and aggregated breeding system categories. Feedback loops caused by ecological consequences of breeding behaviour may alter the evolutionary dynamics of breeding systems, bird-plant interactions, and competing pollinators, as well as help explain the lek paradox.

SUBMITTER: Bleiweiss R

PROVIDER: S-EPMC1690480 | biostudies-literature | 1999 Dec

REPOSITORIES: biostudies-literature

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Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds

Bleiweiss R

Proceedings. Biological sciences 19991201 1437

A survey of 166 hummingbird species reveals novel associations of bill-length sexual dimorphism (BLSD) with plumage and breeding behaviours. Across all species, female bills become proportionately longer than male bills (higher female-to-male BLSD ratio) as sexual dichromatism increases. However, male bills are proportionately longer (lower female-to-male BLSD ratio) in both lekkers (traditional group display) and clustered breeders (female harems or colonial nests) compared with dispersed breed ...[more]

PMID: 10693820

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Project description:Animals living in and interacting with natural environments must monitor and respond to changing conditions and unpredictable situations. Using information from multiple sensory systems allows them to modify their behavior in response to their dynamic environment but also creates the challenge of integrating different, and potentially contradictory, sources of information for behavior control. Understanding how multiple information streams are integrated to produce flexible and reliable behavior is key to understanding how behavior is controlled in natural settings. Natural settings are rarely still, which challenges animals that require precise body position control, like hummingbirds, which hover while feeding from flowers. Tactile feedback, available only once the hummingbird is docked at the flower, could provide additional information to help maintain its position at the flower. To investigate the role of tactile information for hovering control during feeding, we first asked whether hummingbirds physically interact with a feeder once docked. We quantified physical interactions between docked hummingbirds and a feeder placed in front of a stationary background pattern. Force sensors on the feeder measured a complex time course of loading that reflects the wingbeat frequency and bill movement of feeding hummingbirds, and suggests that they sometimes push against the feeder with their bill. Next, we asked whether the measured tactile interactions were used by feeding hummingbirds to maintain position relative to the feeder. We created two experimental scenarios-one in which the feeder was stationary and the visual background moved and the other where the feeder moved laterally in front of a white background. When the visual background pattern moved, docked hummingbirds pushed significantly harder in the direction of horizontal visual motion. When the feeder moved, and the background was stationary, hummingbirds generated aerodynamic force in the opposite direction of the feeder motion. These results suggest that docked hummingbirds are using visual information about the environment to maintain body position and orientation, and not actively tracking the motion of the feeder. The absence of flower tracking behavior in hummingbirds contrasts with the behavior of hawkmoths, and provides evidence that they rely primarily on the visual background rather than flower-based cues while feeding.

Project description:Occupational enrichment emerges as a promising strategy for improving the welfare of farmed animals. This form of enrichment aims to stimulate cognitive abilities of animals by providing them with more opportunities to interact with and control their environment. Predictability of salient daily events, and in particular predictability of feeding, is currently one of the most studied occupational enrichment strategies and can take several forms. In fish, while temporal predictability of feeding has been widely investigated, signalled predictability (based on a signal, such as light or sound) has received little attention. Depending on the type of predictability used and the ecology of the species, the effects on fish welfare often differ. The present study aimed to determine which feeding predictability would be most appropriate for rainbow trout, the main continental farmed fish in Europe, and what the consequences might be for their welfare. We tested four feeding predictability conditions: temporal (based on time of day), signalled (based on bubble diffusion), temporal + signalled (based on time and bubble diffusion), and unpredictable (random feeding times). Behavioural and zootechnical outcomes recorded were swimming activity, aggressive behaviours, burst of accelerations, and jumps, emotional reactivity, and growth. Our results showed that rainbow trout can predict daily feedings relying on time and/or bubbles as predictors as early as two weeks of conditioning, as evidenced by their increased swimming activity before feeding or during feed omission tests, which allowed to reinforce their conditioned response. Temporal predictability alone resulted in an increase in pre-feeding aggressive behaviours, burst of accelerations, and jumps, suggesting that the use of time as the sole predictor of feedings in husbandry practices may be detrimental to fish welfare. Signalled predictability with bubbles alone resulted in fewer pre-feeding agonistic behaviours, burst of accelerations, and jumps than in the temporal predictability condition. The combination of temporal and signalled predictability elicited the highest conditioned response and the level of pre-feeding aggression behaviours, burst of accelerations and jumps tended to be lower than for temporal predictability alone. Interestingly, fish swimming activity during bubble diffusion also revealed that bubbles were highly attractive regardless of the condition. Rainbow trout growth and emotional reactivity were not affected by the predictability condition. We conclude, therefore, that the use of bubbles as a feeding predictor could represent an interesting approach to improve rainbow trout welfare in farms, by acting as both an occupational and physical enrichment.

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Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds

Publications

Joint effects of feeding and breeding behaviour on trophic dimorphism in hummingbirds

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