No abstract

Seed dispersal of white spruce (Picea glauca) (Moench) Voss) from stands bordering a large clearcut and a strip cut was studied. Seedfall fell sharply with distance from the clearcut edge to 100 m, but even at 300 m the average dispersed seed density exceeded 740 000 seedslha or 3% of that recorded within the stand. Dispersed seed density in the middle of the 200-metre-wide strip cut exceeded 1300000 seedslha or 20% of that recorded within the bordering stands. About one-third of the seeds was disseminated by the end of September. ResumeL'auteur etudia la dispersion des graines d'Epinette blanche (Picea glauca) (Moench) Voss) depuis des peuplements limitrophes d'une grande coupe ti blanc et d'une coupe par bandes. Le nombre de graines qui atteignirent le sol dBclina fortement a mesure que la distance de la limite du peuplement debout augmentait jusqu'g 100 m dans le terrain coupe a blanc, mais mdme i?~ 300 m, la densite exc6-dait 740 000 graineslha ou 3% de celle notee dans le peuplernent debout. Au milieu de la bande (coupee) large de 200 m, la densite des graines tombees au sol depassait 1300000 graineslha ou 20% de celle notee dans les peuplements debout adjacents. Vers la fin de septembre, environ 7/3 des graines avaient ete liberees des cdnes.

Summary1. Cross-fostering experiments have shown that egg mass per se positively aects post-hatching growth and development in passerine birds. In most studies, however, the initial in¯uence of egg mass was not sustained, leading to questions about the importance of egg mass relative to the cumulative eects of environmental factors during the period of post-hatching care. 2. In house wrens, Troglodytes aedon Vieillot, evidence from cross-fostering experiments suggests that food availability mitigates the in¯uence of egg mass on posthatching growth: early in the season, when food was putatively abundant, the initial eect of egg mass was lost as nestlings aged; however, later, when food was putatively scarcer, the eect of egg mass persisted until nestlings left the nest. 3. We tested the hypothesis that abundant food for provisioning nestlings can decouple the relationship between ®tness-related traits of nestlings and the mass of the eggs from which they hatch (`egg-mass override hypothesis') by providing daily mealworm supplements to broods of house wrens. 4. The food supplements did not increase ®nal nestling mass, ®nal nestling tarsus length, growth rate, or survival until nest-leaving in late-season broods, when the hypothesis of food limitation predicts that there should be such an eect. Instead, the food supplements signi®cantly, but only slightly, increased ®nal nestling mass in early-season broods, when food is putatively abundant. 5. The eect of the food supplements on ®nal nestling mass was independent of egg mass. Nestling survival in early-season broods, and ®nal nestling mass and tarsus length in both early and late-season broods signi®cantly increased with increasing egg mass in both experimental and control broods. 6. We propose that food was not limiting during the course of the experiments and that ®nal nestling mass and tarsus length remained positively related to egg mass because nestling growth and development in house wrens is`predetermined' by some component or property of eggs that covaries with egg mass.

Diurnal circumferential fluctuations were measured during late summer at different locations on the stems of several Douglas-fir trees.In one study, devices were installed to record periodically circumferential changes at five levels on the stems of study trees. The results indicated that the amplitude of diurnal fluctuation is considerably greater in a zone adjacent to midcrown than at levels above or below. Within this zone, shrinkage and subsequent dimensional recovery begin sooner and proceed at the greatest rates. The more dynamic fluctuation within this zone may relate to transpirational patterns in the crown and to factors determining "stem elasticity".In a related study, a tree was girdled. Results indicated that circumferential fluctuations are primarily seated in peripheral tissues removed in the process of girdling. Possible explanations and implications of the reported patterns are discussed.

This paper contributes to the growing body of literature on the reproductive biology of South American birds by providing 823 records of reproduction for 197 species breeding within the Tumbesian biome of Peru and Ecuador. Where applicable, we include notes on adult behaviour, nest architecture, eggs, nestlings, and fledglings. In general, our observations support previous reports of the seasonal nature of avian reproduction in the region.