Group size and predator surveillance in foraging house sparrows (Passer domesticus)

1983 ◽  
Vol 61 (1) ◽  
pp. 226-231 ◽  
Author(s):  
Michael Studd ◽  
Robert D. Montgomerie ◽  
Raleigh J. Robertson
Keyword(s):  
Group Size ◽  
Passer Domesticus ◽  
Flock Size ◽  
House Sparrows ◽  
Scanning Time ◽  
Time Scanning ◽  
Bird Feeder ◽  
Feeding Bout ◽  
High Level ◽  
Energy Advantage

Time budgets of house sparrows (Passer domesticus) foraging at a bird feeder revealed that the time an individual allocated to scanning for predators was negatively correlated with the size of the foraging group. The frequency of both aggressive and scanning bouts per individual did not vary significantly with group size. Reduced scanning time by individuals in larger groups was achieved by shortening scan bouts, rather than by decreasing scan rate as found in most other studies. For all group sizes, scan and interscan (mostly feeding) bout lengths were randomly distributed. We show analytically that even these birds scanning independently for random lengths of time were able to maintain a high level of predator surveillance while increasing the proportion of time spent foraging as flock size became larger. We also demonstrate a time–energy advantage to longer scanning bouts when ecological conditions allow birds to spend a relatively high proportion of their time scanning.

Individual vigilance profiles in flocks of House Sparrows (Passer domesticus)

2018 ◽  
Vol 96 (9) ◽  
pp. 1016-1023 ◽  
Author(s):  
Hakima Boujja-Miljour ◽  
Patrick A. Leighton ◽  
Guy Beauchamp
Keyword(s):  
Individual Differences ◽  
Group Size ◽  
Passer Domesticus ◽  
Population Level ◽  
Food Density ◽  
Flock Size ◽  
House Sparrows ◽  
Multiple Observations ◽  
State Dependent ◽  
Time Of Year

Individual vigilance against threats typically decreases with group size. However, group size often explains a small amount of variation in vigilance, suggesting that other factors such as individual differences might contribute. For instance, individuals could maintain different vigilance levels overall and also respond differently to variation in group size. We investigated individual variation in vigilance and its patterns of plasticity in flocks of House Sparrows (Passer domesticus (Linnaeus, 1758)). We carried out observations at one provisioned site and used multiple observations of the same individuals (n = 14) in flocks of different sizes over two consecutive months. The typical decline in vigilance with flock size occurred at the population level. Controlling for food density, flock size, time of year, and sex, we documented consistent individual differences in various measurements of vigilance. Plasticity of vigilance adjustments to variation in flock size occurred for the frequency of high vigilance postures. Male House Sparrows with larger bibs, which signal higher dominance status, tended to spend less time vigilant and obtained food at a higher rate, supporting a state-dependent explanation for the origin of individual vigilance profiles. Individual differences can contribute to explaining the large scatter in the relationship between vigilance and group size in many species.

THE EFFECT OF HANDLING TIME ON INTERFERENCE AMONG HOUSE SPARROWS FORAGING AT DIFFERENT SEED DENSITIES

Behaviour ◽  
2001 ◽  
Vol 138 (5) ◽  
pp. 597-614 ◽  
Author(s):  
Cheryl Johnson ◽  
James W.A. Grant ◽  
Luc-Alain Giraldeau
Keyword(s):  
Group Size ◽  
Ideal Free Distribution ◽  
Passer Domesticus ◽  
Handling Time ◽  
Foraging Success ◽  
House Sparrows ◽  
Interference Models ◽  
Foraging Time ◽  
Ideal Free ◽  
The Ideal

AbstractInterference models of the ideal free distribution (IFD) assume competition among foraging animals causes intake rates to decline with increasing competitor density and that the strength of the decline influences forager distributions among food patches. However, the resulting distributions of animals may depend on which components of foraging success contribute to interference. We examined the effect of group size (1-13 birds) on the prey encounter rates, handling times, and foraging rates of house sparrows, Passer domesticus, feeding at three seed densities in a suburban backyard. House sparrows did not experience interference during search. Interference arose primarily from foraging time lost handling seeds. Foraging rates decreased with increasing seed density as a consequence of increased handling times. Also, birds experiencing significant increases in handling time with group size suffered most from interference. Our results suggest that animals adjust handling time to avoid costly aggressive interactions, indicating that handling time may be an important component of interference in some foraging systems. Future studies estimating interference should try to identify which components of foraging contribute to interference, paying particular attention to handling times for species that monitor and avoid competitors.

Distance To Cover, Visual Obstructions, and Vigilance in House Sparrows

Behaviour ◽  
1987 ◽  
Vol 102 (3-4) ◽  
pp. 231-237 ◽  
Author(s):  
Steven L. Lima
Keyword(s):  
Group Size ◽  
Passer Domesticus ◽  
Exact Nature ◽  
House Sparrows ◽  
Factors Influencing ◽  
Risk Of Predation ◽  
Protective Cover

AbstractHouse sparrows (Passer domesticus) feeding away from protective cover decrease their level of vigilance as group size increases. In contrast to recent studies, however, their level of vigilance decreases when feeding farther from cover or in the presence of visual obstructions. These apparent discrepancies reflect the potential complexity in the response of vigilance to various aspects of the risk of predation; scanning need not necessarily increase with the risk of predation. Much work as to the exact nature of the factors influencing vigilance remains to be done before we can fully understand its response to various environmental manipulations.

Vigilance and Perception of Flock Size in Foraging House Sparrows (Passer Domesticus L.)

Behaviour ◽  
1984 ◽  
Vol 90 (4) ◽  
pp. 215-223 ◽  
Author(s):  
Melissa Posen ◽  
Paul J. Burren ◽  
Mark A. Elgar
Keyword(s):  
Passer Domesticus ◽  
Flock Size ◽  
House Sparrows

Factors Affecting Flock Size Mean and Variance in a Winter Population of House Sparrows (Passer Domesticus L.)

Behaviour ◽  
1980 ◽  
Vol 74 (1-2) ◽  
pp. 114-127 ◽  
Author(s):  
C.J. Barnard
Keyword(s):  
Ambient Temperature ◽  
Passer Domesticus ◽  
Time Of Day ◽  
Seed Density ◽  
Flock Size ◽  
House Sparrows ◽  
Feeding Site ◽  
Factors Affecting ◽  
Mean And Variance ◽  
Winter Population

Abstract1. In a field experiment with a winter population of house sparrows at a farm, flock size at a given feeding site appeared to be positively related to seed density. 2. The positive relationship between flock size and seed density resulted from individual birds spending longer in areas where seed density was high and from birds being recruited from elsewhere on the farm to experimental sites. 3. Mean flock size was positively related to and the variance of flock size negatively related to the time of day and both showed a tendency to be negatively correlated with the amount of human disturbance. Mean flock size was also positively related to ambient temperature and flock size variance negatively related to daylength. 4. The rate of fighting per bird increased with flock size and time of day but decreased with increasing ambient temperature. 5. The pattern of flock size distribution in house sparrows is compared to that in juncos and some differences between the two may be attributable to differences in the type of food supply and temperature range over winter.

Visuospatial Working Memory Deficits and Visual Pursuit Impairments are Not Directly Related in Schizophrenia

2009 ◽  
Vol 43 (8) ◽  
pp. 766-774 ◽  
Author(s):  
Luca Cocchi ◽  
Francesca Bosisio ◽  
Olivia Carter ◽  
Stephen J. Wood ◽  
André Berchtold ◽  
...  
Keyword(s):  
Working Memory ◽  
Task Performance ◽  
Memory Performance ◽  
Correct Choice ◽  
Head Movements ◽  
Visuospatial Working Memory ◽  
Visual Pursuit ◽  
Scanning Time ◽  
Time Scanning ◽  
Correct Path

Objective: Patients with schizophrenia show deficits in visuospatial working memory and visual pursuit processes. It is currently unclear, however, whether both impairments are related to a common neuropathological origin. The purpose of the present study was therefore to examine the possible relations between the encoding and the discrimination of dynamic visuospatial stimuli in schizophrenia. Method: Sixteen outpatients with schizophrenia and 16 control subjects were asked to encode complex disc displacements presented on a screen. After a delay, participants had to identify the previously presented disc trajectory from a choice of six static linear paths, among which were five incorrect paths. The precision of visual pursuit eye movements during the initial presentation of the dynamic stimulus was assessed. The fixations and scanning time in definite regions of the six paths presented during the discrimination phase were investigated. Results: In comparison with controls, patients showed poorer task performance, reduced pursuit accuracy during incorrect trials and less time scanning the correct stimulus or the incorrect paths approximating its global structure. Patients also spent less time scanning the leftmost portion of the correct path even when making a correct choice. The accuracy of visual pursuit and head movements, however, was not correlated with task performance. Conclusions: The present study provides direct support for the hypothesis that active integration of visuospatial information within working memory is deficient in schizophrenia. In contrast, a general impairment of oculomotor mechanisms involved in smooth pursuit did not appear to be directly related to lower visuospatial working memory performance in schizophrenia.

scholarly journals Non-breeding feather concentrations of testosterone, corticosterone and cortisol are associated with subsequent survival in wild house sparrows

2011 ◽  
Vol 279 (1733) ◽  
pp. 1560-1566 ◽  
Author(s):  
Lee Koren ◽  
Shinichi Nakagawa ◽  
Terry Burke ◽  
Kiran K. Soma ◽  
Katherine E. Wynne-Edwards ◽  
...  
Keyword(s):  
Stress Hormones ◽  
Passer Domesticus ◽  
House Sparrows ◽  
Long Term Study ◽  
Darwinian Fitness ◽  
Liquid Chromatography Tandem Mass ◽  
In The Wild ◽  
The Subject ◽  
As Stress

Potential mechanistic mediators of Darwinian fitness, such as stress hormones or sex hormones, have been the focus of many studies. An inverse relationship between fitness and stress or sex hormone concentrations has been widely assumed, although empirical evidence is scarce. Feathers gradually accumulate hormones during their growth and provide a novel way to measure hormone concentrations integrated over time. Using liquid chromatography–tandem mass spectrometry, we measured testosterone, corticosterone and cortisol in the feathers of house sparrows ( Passer domesticus ) in a wild population which is the subject of a long-term study. Although corticosterone is considered the dominant avian glucocorticoid, we unambiguously identified cortisol in feathers. In addition, we found that feathers grown during the post-nuptial moult in autumn contained testosterone, corticosterone and cortisol levels that were significantly higher in birds that subsequently died over the following winter than in birds that survived. Thus, feather steroids are candidate prospective biomarkers to predict the future survival of individuals in the wild.

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