Examination of the effects of disturbance on birds with reference to its importance in ecological assessments

National, European and International legislation regarding the conservation of species and habitats requires professional statements to be made in respect of land use change, as, for example, illustrated by developments. Some developments may cause disturbance to wildlife. Knowledge of the way in which species respond to disturbance has been fragmented, yet is an important consideration in environmental impact assessments. This paper reviews what is known about disturbance factors on the best studied group, birds. A set of extensive appendices summarize the literature on disturbance effects on breeding, breeding success, nest-site choice, population density, community structure, distribution and habitat use. The paper considers human-induced disturbance, public access, water-based recreation, shooting and industrial developments. Mitigation measures are discussed.Human-induced disturbance can have a significant negative effect on breeding success by causing nest abandonment and increased predation. Outside the breeding season, recreation (particularly power boating, sailing and coarse fishing on wetlands) reduces the use of sites by birds. Compensatory feeding at night by some species can probably recoup some of the energy losses caused by disturbance. Public and vehicular access to open landscapes has been shown negatively to affect grazing geese in winter and lowland and upland waders during breeding. Shooting disturbance has been shown to be most important for herbivore feeders which need to spend long periods of the day feeding in order to maintain their energy balance, e.g. wigeon. The provision of refuges devoid of shooting has been fundamental in attracting wildfowl away from non-refuge sites. The response of birds to scaring devices and other control measures is discussed.Effects from industrial developments include direct loss of habitat, disturbance through the presence of humans during the construction process and the presence of artificial light used to illuminate construction sites. On estuaries, engineering operations should avoid the proximity to established roost sites of wading birds. A number of studies showed increased vigilance (and hence reduced feeding time) in flock members feeding near structures which impede their vision of the approach of potential predators.A number of principal management techniques used to reduce disturbance on a site, or to attempt to compensate for habitat loss, are given. For wetland sites, these include excavating new shallow lagoons and grading bank sides, flooding of low-lying pasture, reducing salinity levels in coastal lagoons thereby making them more attractive to the birds' food invertebrates, manipulating water levels to expose mud regularly and creating feeding areas for geese and wigeon, using manipulative livestock grazing. Also used are increasing nesting cover, planting macrophytes, providing islands, spits and promontories, purchasing more land to make a refuge bigger, concealing observers with banks and screens, zoning activities and prohibiting access and avoiding the obstruction of flyways between feeding and roosting areas.     

Opportunity costs of implementing forest plans

Intellectual concern with the National Forest Management Act of 1976 has followed a course emphasizing the planning aspects of the legislation associated with the development of forest plans. Once approved, however, forest plans must be implemented. Due to the complex nature of the ecological systems of interest, and the multiple and often conflicting desires of user clientele groups, the feasibility and costs of implementing forest plans require immediate investigation. For one timber sale on the Coconino National Forest in Arizona, forest plan constraints were applied and resulting resource outputs predicted using the terrestrial ecosystem analysis and modeling system (TEAMS), a computer-based decision support system developed at the School of Forestry, Northern Arizona University, With forest plan constraints for wildlife habitat, visual diversity, riparian area protection, and soil and slope harvesting restrictions, the maximum timber harvest obtainable was reduced 58% from the maximum obtainable without plan constraints.Former Graduate Student at Northern Arizona University.     

Necromass production: studies in undisturbed and logged Amazon forests.

Necromass stocks account for up to 20% of carbon stored in tropical forests and have been estimated to be 14-19% of the annual aboveground carbon flux. Both stocks and fluxes of necromass are infrequently measured. In this study, we directly measured the production of fallen coarse necromass (> or = 2 cm diameter) during 4.5 years using repeated surveys in undisturbed forest areas and in forests subjected to reduced-impact logging at the Tapajos National Forest, Belterra, Brazil (3.08 degrees S, 54.94 degrees W). We also measured fallen coarse necromass and standing dead stocks at two times during our study. The mean (SE) annual flux into the fallen coarse necromass pool in undisturbed forest of 6.7 (0.8) Mg x ha(-1) x yr(-1) was not significantly different from the flux under a reduced-impact logging of 8.5 (1.3) Mg x ha(-1) x yr(-1) With the assumption of steady state, the instantaneous decomposition constants for fallen necromass in undisturbed forests were 0.12 yr(-1) for large, 0.33 yr(-1) for medium, and 0.47 yr(-1) for small size classes. The mass weighted decomposition constant was 0.15 yr(-1) for all fallen coarse necromass. Standing dead wood had a residence time of 4.2 years, and approximately 0.9 Mg x ha(-1) x yr(-1) of this pool was respired annually to the atmosphere through decomposition. Coarse necromass decomposition at our study site accounted for 12% of total carbon remineralization, and total aboveground coarse necromass was 14% of the aboveground biomass. Use of mortality rates to calculate production of coarse necromass leads to an underestimation of coarse necromass production by 45%, suggesting that nonlethal disturbance such as branch fall contributes significantly to this flux. Coarse necromass production is an important component of the tropical forest carbon cycle that has been neglected in most previous studies or erroneously estimated.     

Resource supplements cause a change in colony sex-ratio specialization in the mound-building ant, Formica exsecta

We examine the role of food resources on split sex ratios in Formica exsecta. Models of resource-based sex allocation predict that greater resources will cause an increase in the production of reproductive females (gynes) and an increase in overall size of offspring. We experimentally increased food resources for a subset of colonies in a polygynous population with a very male-biased sex ratio. This increase in food availability caused colonies that were male specialists the prior year to switch to female production. Overall, a significantly greater proportion of food-supplemented colonies produced gynes, compared to control colonies. Moreover, food-supplemented colonies produced significantly larger workers and males (but not gynes), compared to those produced by control colonies. There was, however, no significant difference in the numerical productivity of food-supplemented and control colonies. We also measured the natural association between colony sex specialization and proximity to conifers, which typically harbor honeydew-bearing aphids (an important natural food source). In line with the view that resources play an important role for determining sex ratios in social insects, we found that female-producing colonies were significantly closer to conifers than were male-producing colonies.     

Male reproductive success: paternity contribution to queens and workers in Formica ants

The relative number of workers and female sexuals fathered by two males mated with a queen were directly assessed using microsatellite and allozyme markers in field colonies of the ants Formica exsecta and F. truncorum. In both species one of the two males consistently fathered more offspring than the other. There was, however, no evidence that one male might be particularly successful in fathering a disproportionally high proportion of female sexuals relative to the proportion of workers. Moreover, in F. exsecta, the proportions of worker pupae and worker adults fathered by each male did not differ significantly between cohorts. The most likely explanation for this pattern is that females store different amounts of sperm from the two males they mated with. Received: 10 January 1997 / Accepted after revision: 22 March 1997     

Experimental conversion of colony social organization by manipulation of worker genotype composition in fire ants (<Emphasis Type="Italic">Solenopsis invicta</Emphasis>)

Previous studies have shown that colony social organization in Solenopsis invicta is under strong genetic control. Colonies containing some proportion of workers with the Bb or bb genotypes at the gene Gp-9 display polygyne social organization (multiple reproductive queens per colony), whereas colonies with only BB workers express monogyne organization (single reproductive queen per colony). The hypothesis that the presence of workers bearing the b allele confers the polygyne social phenotype on a colony leads to the prediction that social organization can be manipulated by experimentally altering frequencies of adult workers bearing this allele. We did this by replacing queens in colonies of each social form with single queens of the alternate form, which differ in Gp-9 genotype. As worker Gp-9 genotype compositions changed, experimental colonies switched to the alternate social organization. These switches occurred when frequencies of workers with the b allele passed an identifiable threshold, such that colonies with fewer than 5% such workers behaved like monogyne colonies and those with more than 10% behaved like polygyne colonies. Our data thus confirm the prediction that colony social organization in this ant can be altered by manipulating adult worker genotype compositions, and thereby support the hypothesis that the expression of polygyny requires the presence of adult workers bearing the b allele at Gp-9.