摘要:

The winter feeding habits of the short-eared owl (Asio flammeusPontoppidan) were studied during the period of 1936 to 1942 in the vicinity of Toronto, Ont. The owls used restricted roosts in several groups of Douglas fir (Pseudotsuga taxifolia) on a golf course. By means of frequent owl population censuses and collection of pellets, food requirements and correlations were calculated.The winter incursions of the owls were found to be cyclic and to coincide with the local meadow vole (Microtus pennsylvanicus) cycle and to be independent of meteorological factors. Roosting behaviour was found to vary with snow cover.From an analysis of 3000 pellets it was found that the meadow vole formed 82% of the food taken. The next animal most commonly preyed upon was the deer mouse (Peromyscus leucopus), which comprised 17% of the food, while birds formed 1%. No significant seasonal change in diet was noted over a period of five months.It was calculated that a short-eared owl eats between 700 and 1600 mice per year. The average figure is thought to be nearer the minimum estimate. Translated to weight of mice this is equivalent to between 55.5 and 127 lb.It was demonstrated that the amount of snow on the ground affected the relative availability of meadow voles and deer mice. This fact was reflected in changes in pressure on the populations of the two mice species due to owl predation.The data presented pointed to the possibility that concentrations of avian predators could have an appreciable effect on local meadow vole populations. In the case under study it was estimated that winter short-eared owl predation might account for 10% of the vole population.The data also suggested that during periods of deep snow, because of decreased availability of meadow voles, less food is taken and during open periods increased availability of these mice is reflected by increased food consumption.

ISSN:1923-4287    

DOI:10.1139/cjr47d-003

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

Fully grownCephus cinctuslarvae go into an obligatory diapause, the ending of which involves the elimination of two separate factors. The first, orxfactor, is eliminated only at subdevelopmental temperatures and has a positive temperature coefficient in a temperature range from the undercooling point up to the developmental threshold. The second, oryfactor, is eliminated at either low or moderate temperatures, having a positive coefficient in a temperature range from the undercooling point up to about 30 °C. When thexfactor reaction is complete, diapause may be said to be 'broken', but it is not 'eliminated' until theyfactor reaction is complete.When thexfactor reaction is complete but theyfactor is still present, the insect can be returned to diapause by either high temperatures or a lack of adequate moisture or a combination of these. This sometimes occurs in nature, resulting in a two-year life cycle. Once theyfactor has been eliminated the insect starts postdiapause development and can no longer return to a state of diapause.Postdiapause development under constant favourable conditions is rather uniform after it has once started, but the time of its initiation is variable, dependent on theyfactor. Evidence is presented that indicates that theyfactor is eliminated faster in large larvae than in smaller ones, accounting for the rather wide variability in development in samples uniformly treated but not selected as to size.At 10 °C. roughly 40 to 110 days were required to break diapause, each larva requiring a definite conditioning period. Thus the process ends abruptly in individuals, gradually in a group. Under natural conditions diapause was broken as early as Oct. 19, 1945, in a few cases, and was broken in all cases by the end of January 1946.

ISSN:1923-4287    

DOI:10.1139/cjr47d-004

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

The structure of the proventriculus of the larva ofMacronema zebratumHagen is described. The form of the organ is similar to that of some other larvae of the Hydropsychidae. It probably functions as a masticator or compressor of food.

ISSN:1923-4287    

DOI:10.1139/cjr47d-005

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

The rates of opercular beat of 16 specimens ofFundulus diaphanus diaphanuswere recorded over a temperature range from 4.3° to 17.5 °C. in order to determine how this respiratory movement varied with temperature and some of the sources of variation in rate. While the rate of beat varies directly as the temperature, over a period of several hours at any constant temperature continuous recordings of the rate show recurring cycles of rise and fall in beat frequency that are chiefly responsible for the scatter of the observations. Both the duration of a cycle and the limits of rise and fall for each cycle are definitely set by the temperature. The possible dependence of these phenomena upon central nervous activity is discussed.

ISSN:1923-4287    

DOI:10.1139/cjr47d-006

出版商:NRC Research Press    

年代:1947

数据来源: NRC