Flock size and formation in black-billed gulls

1982 ◽  
Vol 60 (8) ◽  
pp. 1806-1811 ◽  
Author(s):  
Roger M. Evans
Keyword(s):  
Size Distribution ◽  
Causal Model ◽  
Causal Explanation ◽  
Flock Size ◽  
Group Foraging ◽  
Foraging Site ◽  
Site Tenacity

Black-billed gulls (Larus bulleri) depart form breeding colonies and foraging sites in nonrandom, clumped formations (flocks). Flocks leaving colonies were significantly smaller than those leaving foraging sites, in part owing to more "upflights" at foraging sites. When more birds left a colony per unit time, flocks were both larger and more frequent.A causal model was developed based on the assumptions that flock departures from a colony or foraging site result from the effects of social attractions superimposed on otherwise random departure intervals. This model successfully predicted the size distribution of flocks departing from four colonies and foraging sites. In conjunction with the concepts of site tenacity and habituation, the model also permits a causal explanation of differences in the size of flocks departing colonies compared with foraging sites, and of size differences in flocks arising from "upflights" as opposed to the more common "straggling" columnar formations. The model and results are consistent with the hypothesis that colonies function as assembly points that facilitate group foraging.

Flock formation in white pelicans

1982 ◽  
Vol 60 (5) ◽  
pp. 1024-1031 ◽  
Author(s):  
J. Brian E. O'Malley ◽  
Roger M. Evans
Keyword(s):  
Alternative Interpretation ◽  
Flock Size ◽  
Functional Information ◽  
Local Enhancement ◽  
Group Foraging ◽  
Gliding Flight ◽  
Effective Use

White pelicans travel between breeding colonies and distant foraging sites in flocks. We described the process of flock formation during departures from colonies at East Shoal Lake, Manitoba. Interdeparture intervals in 1978 and 1979 were significantly clumped, which suggests individual white pelicans follow one another when initiating foraging trips.Flocks increased in size and made increasing use of air thermals as they travelled toward foraging areas. Flocks were most common and most variable in size between 1145 and 1345. Flock size was stable over the season, while the number commuting each day increased geometrically to a maximum by the end of the nestling period.Flocks observed near the colonies were characterized by low, horizontal, flap-gliding flight. Further enroute they flew higher and showed greater frequencies of gliding and ascending flight associated with increasing use of thermals.Our results provide no support for the view that colonies and flocks represent manifestations of functional information centers. The results are in agreement with the alternative interpretation that colonies and flocks facilitate group foraging and permit effective use of local enhancement as a means of locating thermals.

scholarly journals A Sideways Look at Faithfulness for Quantum Correlations

2021 ◽  
Vol 118 (1) ◽  
pp. 28-42
Author(s):  
Peter W. Evans ◽  
Keyword(s):  
Quantum System ◽  
Causal Model ◽  
Single Photon ◽  
Causal Explanation ◽  
Quantum Correlations ◽  
Quantum Systems ◽  
Causal Modeling ◽  
Fine Tuning ◽  
Symmetry Relation ◽  
Modeling Techniques

Despite attempts to apply causal modeling techniques to quantum systems, Wood and Spekkens argue that any causal model purporting to explain quantum correlations must be fine tuned; it must violate the assumption of faithfulness. This paper is an attempt to undermine the reasonableness of the assumption of faithfulness in the quantum context. Employing a symmetry relation between an entangled quantum system and a “sideways” quantum system consisting of a single photon passing sequentially through two polarizers, I argue that Wood and Spekkens’s analysis applies equally to this sideways system also. As a result, we must either reject a causal explanation in this single photon system, or the sideways system must be fine tuned. If the latter, a violation of faithfulness in the ordinary entangled system may be more tolerable than first thought. Thus, extending the classical “no fine-tuning” principle of parsimony to the quantum realm may be too hasty.

Where and When To Feed: Sex and Experience Affect Access To Food in Wintering Snow Buntings

Behaviour ◽  
1997 ◽  
Vol 134 (1-2) ◽  
pp. 143-160 ◽  
Author(s):  
Richard D. Smith ◽  
Neil B. Metcalfe
Keyword(s):  
Flock Size ◽  
Foraging Success ◽  
Group Foraging ◽  
Feeding Station ◽  
Plectrophenax Nivalis ◽  
Access To Food ◽  
Winter Flocks ◽  
Differential Access

AbstractIn group-foraging species an individual's ability to feed in the most beneficial situations could influence its overall foraging success more than its ability to find and handle food. Here we examined whether sex, age or site experience of individual snow buntings Plectrophenax nivalis in winter flocks could help explain how frequently they were found in advantageous foraging situations. We found that inexperienced females were scarcer than expected in large flocks, that females fed less often in the early parts of flock feeding bouts, and that older and more experienced birds were more likely to feed in central flock positions. In addition, the likelihood of moving around the feeding station increased more with flock-size in females, while older birds were better at retaining access to the feeding patch. Previously reported differences in peck-rate between sex and age/experience categories of this species are therefore likely to be magnified by differential access to sources of food. We suggest that experience may help individuals to integrate within the feeding flock, but aggression from larger males may cause females to delay feeding or to feed in smaller flocks.

The extinction time of a general birth and death process with catastrophes

1986 ◽  
Vol 23 (04) ◽  
pp. 851-858 ◽  
Author(s):  
P. J. Brockwell
Keyword(s):  
Laplace Transform ◽  
Size Distribution ◽  
Sufficient Conditions ◽  
Necessary And Sufficient Conditions ◽  
Death Process ◽  
Extinction Time ◽  
Birth And Death Process ◽  
Different Types ◽  
The Laplace Transform ◽  
Necessary And Sufficient

The Laplace transform of the extinction time is determined for a general birth and death process with arbitrary catastrophe rate and catastrophe size distribution. It is assumed only that the birth rates satisfyλ0= 0,λj> 0 for eachj> 0, and. Necessary and sufficient conditions for certain extinction of the population are derived. The results are applied to the linear birth and death process (λj=jλ, µj=jμ) with catastrophes of several different types.

Macrostructure and microphysics of Saturn's E-ring

1984 ◽  
Vol 75 ◽  
pp. 607-613 ◽  
Author(s):  
Kevin D. Pang ◽  
Charles C. Voge ◽  
Jack W. Rhoads
Keyword(s):  
Size Distribution ◽  
Spherical Shape ◽  
Mie Scattering ◽  
Narrow Size Distribution ◽  
Electrostatic Levitation ◽  
Volcanic Origin ◽  
Micron Diameter

Abstract.All observed optical and infrared properties of Saturn's E-ring can be explained in terms of Mie scattering by a narrow size distribution of ice spheres of 2 - 2.5 micron diameter. The spherical shape of the ring particles and their narrow size distribution imply a molten (possibly volcanic) origin on Enceladus. The E-ring consists of many layers, possibly stratified by electrostatic levitation.

Grain Refinement in Titanium-Erbium Alloys

1974 ◽  
Vol 32 ◽  
pp. 522-523
Author(s):  
B. B. Rath ◽  
J. E. O'Neal ◽  
R. J. Lederich
Keyword(s):  
Electron Microscopy ◽  
Size Distribution ◽  
Grain Refinement ◽  
Grain Growth ◽  
Volume Fraction ◽  
Pure Titanium ◽  
Systematic Investigation ◽  
Second Phase ◽  
Titanium Matrix ◽  
Average Size

Addition of small amounts of erbium has a profound effect on recrystallization and grain growth in titanium. Erbium, because of its negligible solubility in titanium, precipitates in the titanium matrix as a finely dispersed second phase. The presence of this phase, depending on its average size, distribution, and volume fraction in titanium, strongly inhibits the migration of grain boundaries during recrystallization and grain growth, and thus produces ultimate grains of sub-micrometer dimensions. A systematic investigation has been conducted to study the isothermal grain growth in electrolytically pure titanium and titanium-erbium alloys (Er concentration ranging from 0-0.3 at.%) over the temperature range of 450 to 850°C by electron microscopy.

Formation and Structure of Casein Micelles in Lactating Mammary Tissue

1970 ◽  
Vol 28 ◽  
pp. 150-151
Author(s):  
Robert J. Carroll ◽  
Marvin P. Thompson ◽  
Harold M. Farrell
Keyword(s):  
Size Distribution ◽  
G Protein ◽  
Milk Proteins ◽  
Mammary Tissue ◽  
Colloidal System ◽  
Casein Micelles ◽  
The Stability

Milk is an unusually stable colloidal system; the stability of this system is due primarily to the formation of micelles by the major milk proteins, the caseins. Numerous models for the structure of casein micelles have been proposed; these models have been formulated on the basis of in vitro studies. Synthetic casein micelles (i.e., those formed by mixing the purified αsl- and k-caseins with Ca2+ in appropriate ratios) are dissimilar to those from freshly-drawn milks in (i) size distribution, (ii) ratio of Ca/P, and (iii) solvation (g. water/g. protein). Evidently, in vivo organization of the caseins into the micellar form occurs in-a manner which is not identical to the in vitro mode of formation.

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