Jaroslav Picman

Experimental study of predation on eggs of ground-nesting birds: effects of habitat and nest distribution

Predation pressure on nests of ground-nesting birds was examined experimentally by offering predators artificial nests with small, white chicken eggs in three adjacent habitats: marsh, wet meadow, and upland thicket. In each habitat, 40 nests with eggs were distributed in three 80x 80-m quadrats according to random, uniform, and clumped distribution patterns and nests were examined for predation on days 5 and 10. In three sets of experiments during which each quadrat in each habitat received all nest distribution treatments, predation rates were highest in the upland thicket, intermediate in the wet meadow, and generally low in the marsh. The pattern ofnest distribution consistently affected predation rates in the upland thicket only, where the uniform distribution resulted in lower predation. In the upland thicket many predators were responsible for high predation and unpredictable predation patterns which presumably favor spacing out (uniform nest distribution) in this habitat. In contrast, low predation in the marsh, resulting from exclusion of many predators, appears to be unimportant in determining spatial distribution of marshnesting birds.

Autotoxicity in Parthenium hysterophorus and its possible role in control of germination

Abstract The autotoxic effect of water soluble secondary plant metabolites, sesquiterpene lactones and phenolic acids present in the aggressive weed Parthenium hystrophorus were examined. It was found that the germinaion rates of achenes of P. hysterophorus increased with increasing distance between them (decreasing achene density) and increasing washing period preceding the germination trials. The inhibition of germination processes by water soluble autotoxins is temporary and its duration is determined by the concentration of autotoxins in the environment. Sesquiterpene lactones, parthenin and coronopilin, which are present in large amounts in P. hysterophorus, are autotoxic to seedlings and older plants at a concentration of 0.1%. It is suggested that in P. hysterophorus, the water soluble plant metabolites play an important role not only in allelopathy and defense against herbivorous predators and diseases but also as autotoxins in population regulation and the timing of the germination processes.

Antipredation role of clumped nesting by marsh-nesting red-winged blackbirds

SummaryRed-winged blackbirds, Agelaius phoeniceus, breed in marshes in high densities and their nests are frequently clumped. Because predation is consistently the most important cause of redwing nesting mortality, high densities of breeding individuals could be an anti-predation adaptation. In our study site predation by marsh wrens, Cistothorus palustris, was the main cause of redwing nesting losses. In situations when marsh wrens were near, predation rates on redwing nests decreased with increasing female density. Group life could reduce predation because of improved nest defense, selfish herd effects, or predator dilution effects. We differentiated between these possibilities by introducing experimental colonies consisting of 3, 6, and 9 artificial nests near and away from active redwing nests. The experimental colonies near active nests suffered less predation, but predation rates were not correlated with colony size or a nests location within the colony. Therefore, the advantage of group life in this population is probably mutual nest protection.

Effect of brown-headed cowbirds on the evolution of yellow warbler anti-parasite strategies

Abstract The brown-headed cowbird, Molothrus ater, has recently expanded its breeding range into eastern North America. In the newly inhabited regions, brood parasitism by this generalist should present a strong selective force favouring the evolution of various anti-parasite strategies. The purpose of this study was to: (1) establish the impact of cowbird parasitism on reproductive success of yellow warblers, Dendroica petechia, and estimate its importance relative to nest predation; and (2) determine if yellow warblers in eastern Ontario have already evolved specific anti-parasite adaptations. The results suggest that parasitism accounted for 41% of all egg losses and was at least as important as nest predation. Yellow warblers tended to reject cowbird eggs if they were parasitized in the early egg-laying stages and if they had enough time left for re-nesting. Finally, results of aggression trials were consistent with predictions from the reproductive value-stimulus value model (i.e. warblers were most aggressive to a female cowbird at stages when they are most vulnerable to cowbird parasitism). These findings suggest that warblers recognize cowbirds as a specific threat to their nests. Strong selection pressures due to cowbird parasitism have already yielded several specific anti-parasite behavioural traits in eastern North American yellow warbler populations.

Antimicrobial activity of the Anseriform outer eggshell and cuticle

The avian eggshell is a complex, multifunctional biomineral composed of a calcium carbonate mineral phase and an organic phase of lipids and proteins. The outermost layer of the eggshell, the eggshell cuticle, is an organic layer of variable thickness composed of polysaccharides, hydroxyapatite crystals, lipids and glycoprotein. In addition to regulating gas exchanges, the eggshell cuticle may contain antimicrobial elements. In this study, we investigated the antimicrobial activity of eggshell cuticle and outer eggshell protein extracts from four Anseriform species: wood duck (Aix sponsa), hooded merganser (Lophodytes cucullatus), Canada goose (Branta canadensis) and mute swan (Cygnus olor). Cuticle and outer eggshell protein was extracted by urea or HCl treatment of eggs. C-type lysozyme, ovotransferrin and an ovocalyxin-32-like protein were detected in all extracts. Cuticle and outer eggshell protein extracts inhibited the growth of Staphylococcus aureus, Escherichia coli D31, Pseudomonas aeruginosa and Bacillus subtilis. The presence of active antimicrobial proteins within the avian cuticle and outer eggshell suggests a role in antimicrobial defense. Protein extracts from the cavity nesting hooded merganser were especially potent. The unique environmental pressures exerted on cavity-nesting species may have led to the evolution of potent antimicrobial defenses.

Avian antimicrobial proteins: structure, distribution and activity

Antimicrobial proteins are active against protozoans, fungi, viruses as well as gram-positive and gram-negative bacteria. In many cases, antimicrobial proteins are present as components of innate immunity and are capable of evading bacterial resistance mechanisms. Due to these characteristics, these proteins represent an appealing alternative to conventional antibiotic drugs. Considerable research has been conducted on antimicrobial proteins from invertebrate and mammalian sources. Within the last decade, over 20 novel antimicrobial proteins have been isolated from avian systems. The majority of these proteins has been isolated from the domestic chicken and therefore represents a minuscule fraction of the avian antimicrobial proteins that are potentially awaiting discovery. In this review, we elaborate on these discoveries and on the future of avian antimicrobial protein research.

Effect of flavonoids on mycelial growth of Verticillium albo-atrum☆

Twenty-five flavonoids were examined for their effect on the mycelial growth of a crop pathogen, Verticillium albo-atrum. The minimum inhibitory concentrations (MIC) for the two most active compounds, flavone and flavanone, were 1 and 5 ppm, respectively. Other flavonoids inhibited hyphal growth at concentrations above 5 ppm and some compounds were ineffective at 200 ppm, the highest concentration used. Active compounds did not share a common pattern of substitutions. The unsubstituted flavonoids were stronger growth inhibitors and, in most cases, increasing the number of substitutions (hydroxylation, methoxylation, and glycosylation) resulted in the loss of antifungal activity.

ANTIPREDATION VALUE OF COLONIAL NESTING IN YELLOW-HEADED BLACKBIRDS

Abstract Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) in Manitoba breed in dense colonies in cattail marshes. Their reproductive success is affected mainly by predation. The most important predator on blackbird nests is the Marsh Wren (Cistothorus palustris), which breaks blackbird eggs and kills small nestlings. We examined whether colonial nesting in Yellow-headed Blackbirds may represent an adaptation to reduce Marsh Wren predation. Marsh Wren predation may be reduced by (1) mutual nest defense by adult blackbirds, (2) predator satiation or dilution, or (3) selfish-herd effects. We tested these hypotheses using experimental nests and found that their safety increased with decreasing distance to the nearest blackbird nest and with increasing density of simultaneously active blackbird nests located nearby. Safety also was higher for nests placed inside a blackbird colony rather than outside. These findings support the nest-defense hypothesis. We also found that Marsh Wrens are capable of destroying a whole blackbird colony in a few days, and that colony size is not correlated with nest safety. These results suggest that the satiation or dilution benefits are negligible. Finally, we found that central nests are safer than peripheral nests in a blackbird colony, but not in an artificial colony, providing weak support for the selfish-herd hypothesis. We conclude that nest predation is reduced mainly by mutual nest defense of adult birds and may represent an important selective force favoring colonial nesting in this species.

EFFECT OF NEST-SITE LOCATION ON REPRODUCTIVE SUCCESS OF RED-THROATED LOONS (GAVIA STELLATA)

The Red-throated Loon (Gavia stellata) nests on the shores of freshwater ponds of the Arctic tundra and forages in nearby marine waters. We examined the effects of distance of the nest from foraging waters and of microclimate at the nest site on the loons reproductive success. As distance from the ocean increased, both density and nesting success decreased. Although hatching success did not vary with distance, success in rearing both chicks was significantly lower at distances greater than 9 km from the ocean. Loons with nests further from the ocean fed chicks less often and spent more time on foraging flights than did loons nesting within 9 km of the ocean. Brood reduction in nests far from the ocean presumably resulted from nestling starvation, and possibly also from higher predation due to less effective nest defense. We suggest that the higher density of breeding loons in areas near the ocean reflects preference of these birds for nesting grounds that are closer to their foraging areas. Microclimatic conditions also influenced reproductive success. In areas available for nesting earlier in the year, the loons initiated nesting earlier, but the probability of their reproductive failure due to predation was higher. However, successful pairs in these areas raised larger broods (two chicks) more often than those in areas where birds started breeding later. Received 2 December 1991, accepted 31 August 1992. REPRODUCTIVE SUCCESS of birds is usually de- termined by the availability of food and the intensity of predation (Kruuk 1964, Horn 1968, Ricklefs 1969, Hunt 1972). These factors, in turn, play a dominant role in shaping reproductive strategies such as those involved in habitat se- lection, nest-site selection, and mate choice. An adequate amount of food is a prerequisite for successful reproduction. If food is abundant and predictable in time and space, birds generally establish all-purpose territories. However, if food is unpredictable and is not economically defendable, colonial nesting optimizes forag- ing efficiency of birds (i.e. Horn 1968). The type and intensity of predation, however, also plays an important role in shaping reproductive strat- egies. Predation could favor two types of ad- aptations: (1) it might select for tactics improv- ing nest defense; and (2) it might select for predator-avoidance tactics, such as selection of a safe nesting site, and camouflage of nest and nesting activities. Some avian species forage in habitats where there are no opportunities for nesting. When

Is greater eggshell density an alternative mechanism by which parasitic cuckoos increase the strength of their eggs

Brood parasites lay unusually strong eggs, presumably to prevent puncture ejection of the eggs by hosts. However, it has been suggested that eggs of some parasitic cuckoos have normal strength. This suggestion was based on the eggshell thickness and shape of these eggs. Here, we propose that there may be other structural adaptations (such as increased eggshell density) that make the cuckoo eggs unusually strong. In this study, we compared the eggshell density of parasitic cuckoos to the eggshell density of two control groups, non-parasitic cuckoos and a sample of non-passerine species. The comparisons to both control groups demonstrated that the parasitic cuckoos have eggshells of significantly higher density than would be expected for their size. Our results support the hypothesis that the higher eggshell density is an alternative mechanism by which some cuckoos increase the strength of their eggs.