Passerine morphology: external measurements of approximately one-quarter of passerine bird species

Autumn and winter time-energy budgets were constructed for brown thornbills, Acanthiza pusilla, and eastern yellow robins, Eopsaltria australis, inhabiting a temperate wet forest in south-eastern Australia. Birds spent 84-88% of daylight hours foraging in both seasons, but decreased the metabolic cost of other activity in winter by spending more time on energetically inexpensive behaviours. Estimated daily energy expenditures were either seasonally constant or increased (thornbill) or decreased (robin) in winter by no nore than l0%, depending on the assumed degree of substitution for the thermoregulatory requirement. Thornbills increased foraging efficiency in winter to compensate for the reduction in absolute foraging time. Less dramatic changes in behavioural strategies were required to achieve energy balance than have been recorded for many small north temperate birds. Brown thornbills used an energetically expensive, active search foraging technique to capture small, cryptic prey at a fast rate. Yellow robins employed an inexpensive, 'sit-and-wait' strategy to capture larger, more conspicuous prey at a slower rate. Both species had similar time investments in foraging, but allocated greatly differing proportions of energy to active foraging and resting alert. These contrasting strategies offer the potential for performing several activities simultaneously in the yellow robin and for reducing foraging and vigilance investments through exploiting gregariousness in the brown thornbill.

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Anti-predator behavior along elevational and latitudinal gradients in dark-eyed juncos

Current Zoology ◽

10.1093/cz/zoz046 ◽

2019 ◽

Vol 66 (3) ◽

pp. 239-245 ◽

Cited By ~ 2

Author(s):

Madelin Andrade ◽

Daniel T Blumstein

Keyword(s):

Human Impacts ◽

Bird Species ◽

Passerine Bird ◽

Latitudinal Gradients ◽

Junco Hyemalis ◽

Predator Density ◽

Elevational Gradients ◽

Main Driver ◽

Flight Initiation ◽

Predator Behavior

Abstract Flight-initiation distance (FID), the distance between an individual and experimenter when it begins to flee, can be used to quantify risk-assessment. Among other factors, prior studies have shown that latitude explains significant variation in avian FID: at lower latitudes, individuals and species have longer FIDs than those living at higher latitudes. No prior studies have focused on the effect of elevation on FID. Given the similar patterns of seasonality, climate, and potentially predator density, that covary between latitude and elevation, birds at higher elevations might tolerate closer approaches. We asked whether elevation or latitude would explain more variation in the FID of a common passerine bird species, dark-eyed juncos (Junco hyemalis). Juncos live in a variety of habitats along both latitudinal and elevational gradients. We found that statistical models containing elevation as a variable explained more of the variation in FID than did models containing latitude. We also found, unexpectedly, that birds at higher elevation fled at greater distances. While more predators were sighted per hour at higher elevations than at lower elevations, the frequency of predator sightings did not explain a significant amount of variation in FID. This result questions whether predator density is the main driver of risk perception along elevational gradients. Nonetheless, because elevation explains more variation in FID than latitude in at least one species, these findings have direct implications on how human impacts on birds are managed. Specifically, those designing set-back zones to reduce human impact on birds may consider modifying them based on both latitude and elevation.

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