Waterfowl Nesting in Fall-Seeded and Spring-Seeded Cropland in Saskatchewan

Abstract: Waterfowl nesting in annual croplands has remained a little-known aspect of waterfowl nesting ecology because of the inability of many studies to systematically search this habitat through the nesting season. Where searches have been conducted, they are generally restricted to the period prior to seeding, and many nests found are destroyed by the seeding operation. Consequently, fall-seeded crops have been promoted as an alternative cropping practice that could increase nest survival of waterfowl nesting in croplands. During 1996–1999, we conducted 3–4 complete nest searches on 4,274 ha of cropland, including spring-seeded wheat and barley, winter wheat, and fall rye in southern Saskatchewan, Canada. Using suites of predictive models, we tested hypotheses regarding relative nest abundance and nest survival among crop types and tested the influence of several landscape-scale covariates on these metrics. Apparent nest densities were higher in fall-seeded crops (winter wheat: 0.39 nests/ha, fall rye: 0.25 nests/ha) than in spring-seeded crops (0.03 nests/ha), and nest density in spring-seeded croplands increased with percent cropland and percent wetland habitat in the surrounding landscape. Nest survival was higher in winter wheat (38%) than in either fall rye (18%) or spring-seeded crops (12%), and nest survival in spring-seeded crops increased with relative nest initiation date. Nest survival was unaffected by surrounding landscape characteristics but tended to be higher in years of average wetness. Based on our findings, winter wheat and fall rye have the potential to provide productive nesting habitat for ≥7 species of upland nesting ducks and fall-seeded crops are a conservation tool well suited to highly cropped landscapes.     

Elasticity of Phloem Tissues1

Linear displacement transducers and a pressure transducer wereused to simultaneously monitor pressure reduction and shrinkageassociated with phloem exudation following incision of the barkof Fraxinus americana L. The shrinkage associated with the pressurereduction indicated that the sieve tubes had elastic walls.Mathematical models of a mass flow system of phloem transporthave assumed rigid walls for the sieve tubes, but results demonstratedthat the dimensional changes associated with pressure potentialchanges would produce significant differences in volume flowrates if the pressure gradient were maintained at a constantvalue, and thus indicate a requirement for modification of themodels to accommodate elastic cell walls.     

Adjusting count period strategies to improve the accuracy of forest bird abundance estimates from point transect distance sampling surveys

Although point transect distance sampling methods have become widely used in surveys of forest birds, there has been no attempt to tailor field methods to maximize the accuracy of abundance estimates by minimizing the effects of violations of the method's critical assumptions, which are: (1) birds at distance 0 m are detected with certainty, (2) birds are detected at their initial location and (3) distances to objects are measured accurately. We investigate the effects on abundance estimates for Philippine forest birds of varying the count period from 2 to 10 min, and of including and excluding a pre‐count settling down period. Encounter rates were highly sensitive to count period length but density estimates from 10‐min count periods were, on average, only 13% higher than those from 2‐min periods, and in several cases were actually lower than those from periods of 6–8 min. This was because birds tended to be recorded at greater distances from the recorder as the count period went on, thus ‘stretching out’ detection functions while having little effect on detection rates close to the recorder. For some bird groups, including canopy frugivores and upperstorey gleaning insectivores, density estimates were more than twice as high without than with a settling down period. We suggest that movement away from the recorder is more common than attraction to the recorder, and that unless pilot studies show otherwise, similar studies should not use a settling down period for surveying many species. Count periods that maximized probability of bird detection close to the central point while minimizing the unwanted effects of bird movement during the count period were: 4 min for omnivores, 6 min for nectarivores and upperstorey gleaning insectivores, 8 min for understorey insectivores and canopy frugivores, and a full 10 min for sallying insectivores, ground‐dwellers, carnivores and coucals/koels. We use the results to suggest ‘group‐specific’ count period regimes that could help maximize the accuracy of density estimates from similar studies of tropical forest birds.     

Effects of artificial ultraviolet-B radiation on growth and fatty acid composition of duckweed (Lemna minor)

1. Duckweed (Lemna minor), collected either in summer or early fall was exposed under laboratory conditions to control (photosynthetically active and UV‐A radiation) or experimental (control plus UV‐B radiation) conditions. 2. Growth and survival were determined by counting the number of green, and brown/white fronds following 1–5 or 11 days of irradiation. Growth of duckweed was impaired by exposure to UV‐B radiation in the fall experiment but not in the summer. 3. Fatty acid compositions were analysed following 5 or 11 days of irradiation and a recovery period of 0, 5, 29 or 40 h. Concentrations of the major fatty acids, palmitic, linoleic (LA) and α‐linolenic (ALA) acids were similar in the summer and fall duckweed collections, but the summer samples had higher concentrations of the desaturation products of LA and ALA. 4. UV‐B exposure had small, but significant, and contrasting effects on duckweed fatty acid concentrations. In the summer experiment, duckweed exposed to UV‐B had slightly lower concentrations of major fatty acids than control duckweed, while the reverse was true in the fall experiments. 5. These minor effects of UV‐B on concentrations of LA and ALA would be unlikely to have a major impact on the supply of these essential fatty acids from duckweed to freshwater food webs.     

Isolation and characterization of polymorphic microsatellite markers of Anopheles sinensis,a malaria vector mosquito in the East Asia region

Eleven polymorphic dinucleotide (GA and CA) microsatellites were isolated and characterized in the mosquito Anopheles sinensis; this species is distributed over the East Asia region and is a primary vector of malaria, particularly in Korea. The number of alleles per locus ranged from 4 to 13. The observed heterozygosity (H_O) and expected heterozygosity (H_E) varied from 0.30 to 0.89 and from 0.59 to 0.90, respectively. These microsatellites could be useful in studying the evolution of the widely distributed A. sinensis in diverse environments.     

Modulation of the Adrenocortical Responses to Acute Stress in Arctic Birds: A Possible Ecological Basis

There is considerable evidence that the increases in circulatingcorticosterone levels following acute stress, such as suddenstorms, can trigger facultative behavioral patterns designedto maximize survival. During the breeding season, adrenocorticalresponses to aseasonal storms may trigger facultative behavioralpatterns resulting in temporary disruption of nesting. A renestingcycle often follows when conditions become favorable again.However, in arctic ecosystems the brief breeding season limitsthe capacity of most avian populations to renest, and yet springweather may be extreme. This led to the hypothesis that arcticbirds may down-regulate their sensitivity to acute stress (suchas severe storms) so that breeding can begin and be completedbefore the first storms of autumn (only 6–8 weeks later).To test this we have used the "stress-series protocol" thattakes advantage of the fact that capture, handling and restraintconstitutes a more-or-less equal stress among all vertebratespecies, and that corticosterone concentrations in small bloodsamples collected during the first hour post-capture indicatesensitivity of the hypothalamo-adenohypophysial- adrenal axisto acute stresses in general. Comparisons of the increases inplasma levels of corticosterone following capture in severaltaxa of arctic birds indicated that suppression of the adrenocorticalresponse to acute stress was not ubiquitous. Although some speciesdid show low amplitude responses of the circulating corticosteroneincrease during the stress series protocol, others did not,and some (especially males) showed an increase in sensitivityto acute stress. Additional hypotheses were suggested as follows:1) species with greater body mass have larger relative energyreserves and would be more able to resist acute stresses thansmaller energy reserves and would be more able to resist acutestresses than smaller species; 2) short-lived birds with anexpectancy of one or two breeding seasons should be more resistantto acute stress than long-lived birds that may have many attemptsat successful breeding; 3) resistance of the adrenocorticalresponse to stress is a function of the degree of parental careprovided by the individual (also takes into account sex differencesin parental investment). Correlations of the maximum corticosteronelevel and the ratio of maximum to minimum corticosterone levelsgenerated during the stress series protocol with body mass andlongevity were not significant. However, maximum corticosteronelevel was significantly lower in birds providing most parentalcare and almost significant for the ratio of maximum to minimumcorticosterone levels. These comparative data from free-livingarctic birds suggest an ecological basis for modulation of theadrenocortical responses to stress. In at least one species,up-regulation of the response appears to involve a change insensitivity to glucocorticosteroid feedback. Further investigationswill explore neuroendocrine mechanisms further in the lightof these ecological bases.