Oh et al. showed that US consumers are willing to pay higher prices if the fruit were grown locally in a wild friendly farming way that conserve birds.Birds can also play a detrimental role in agroecosystems, specially species of blackbirds , cardinals , doves and parakeets . These species can take advantage of the concentration of food resources in agricultural fields causing reduction in yields .The degree of crop damage may be related to the type of crop grown and other habitat features. For example, in Argentina monk parakeets were found to prefer sunflower instead of corn . According to Fuller-Perrine and Tobin major grape damage in North American vineyards is caused by European starlings , American crows , House finches and Common grackles . Somers and Morris reported that grape damage in Canadian vineyards was related mainly to the presence of the exotic European starling that were found in flocks from 5-200 individuals/daily, although some other native birds were also found but in reduced numbers and just a few times during the season. The same study showed that American crows were also found in large numbers but they did not forage in vineyards. There is spatial localization of bird grape consumption, where upper vine tiers and vineyard edges exhibited more damage than lower tiers and grapes growing at the center of the vineyard . In California, bird damage was estimated to cause profit loss in nuts of 9.6%, in grapes of 9%,best grow pots in berries of 5.7%, and in fruit orchards of 5% . Different techniques have been employed in order to reduce the damage caused by birds to crops.
Berge et al. reported that one effective method was the utilization of electronic devices that emit alarm sounds and distress calls that drive off birds. Although netting the crops was the most effective method to avoid bird damage, it is expensive. The use of nets that cover grapes was proposed as an effective way to control bird grape consumption , but other studies did not find this method to be as effective . Baldwin et al. reported that the most common methods used to avoid bird damage in California were frightening devices, exclusionary devices, and shooting.Agriculture has transformed nearly 40% of the earth’s surface , causing direct effects on wildlife populations, among them birds. Intensive agriculture is considered one of the main threats to biodiversity . Agricultural intensification has been linked with wildlife decline . For example, Karp et al. found in tropical agroecosystems that beta diversity is reduced by 40% under intensive agriculture.Implications of land use change are related not only to habitat loss, fragmentation and lack of connectivity in the agricultural matrix, but direct impacts on species. Global vertebrate extinction has increased significantly since the rise of industrial society when compared to historic and prehistoric times . This process of “defaunation” corresponds not only to a loss of species but also to shifts in species composition, function and interactions that impact the provision of ecosystem services and human well-being . Land use change is one of an interacting group of drivers of extinction . A worldwide multi-taxon study reported strongly negatively impacts on composition and diversity of species by land conversion from primary vegetation to agricultural landscapes, forest plantations, and urban areas . In a global analysis of local diversity affected by increased human population and land use change scenarios from the Intergovernmental Panel on Climate Change. Newbold et al. showed that by the end of the century the within-the same land use of the most impacted habitats species richness will be reduced by 76.5% on average, total abundance by 39.5% and rarefied richness by 40.3% of 47 taxonomic terrestrial groups .
These impacts are more likely to disproportionally occur in countries with high biodiversity but economic poverty although this projection could change if there is sufficient social pressure to revert trends . For example, in Mexico the rate of crop expansion over native grasslands/shrubland in the Chihuahua desert, negatively impacted the overwintering habitat of 28 migratory species in North America . Pan-tropical bird occurrence and abundance decreases along a anthropogenic land use intensity gradient compared to undisturbed habitats . In Germany, models predict that conversion from agriculture to bio-fuel production in order to reduce carbon dioxide emissions will have negative effects on biodiversity. A loss of 10% of the present farmland bird population by 2050 is estimated with expansion of bio-fuel monocultures . In another case study of land use change and bio-energy crops, Everaas et al. modeled the impact on bird breeding of changes from current farms to bio-energy monoculture crops, and reported negative impacts for the majority of species analyzed, suggesting that biodiversity impacts of the spread of intensive monocultures in Germany cannot be mitigated only by conserving 10% of land surface set aside within farms, a current European agro-scheme practice.Under current global scenarios of land use change and scaling rates of per capita consumption, reconciling agricultural production and biodiversity conservation goals is a priority . Different approaches have been proposed in order to achieve these goals. One of the most debated questions is how can we best produce crops to enhance food security while conserving natural areas . Land sharing and land sparing strategies as well as a combination of both have been proposed . The land sharing approach proposes agroecology as a strategy to spatially, temporally, and biologically diversify farms and to increase the value of the agricultural matrix for wildlife habitat . This approach values the relationship of humans with nature and integrates traditional knowledge into management of agroecosystems .
The main contention of the land sharing approach is that low yields from non-intensive agriculture will promote agricultural expansion detrimental to natural areas . However, this yield gap argument has been contested by Ponisio et al. by meta-analysis showing that diversification of organic agriculture can reduce the yield gap between conventional and organic agriculture from ~19% to ~8%. Land sparing proponents have favored high agrochemical input levels aimed at enhancing crop yields and argue that with high production in target crop areas, natural areas land surface will be spared from conversion to crop production . However, current agrochemical use can impact non-target wildlife species. For example pesticide applications in arable farms decrease arthropods that are consumed by Yellowhammer in the reproductive season, negatively impacting their breeding performance . Use of highly toxic pesticides have a direct effect on bird population in US grasslands . Intensive systems proposed by land sparing proponents are characterized by low levels of biodiversity and low heterogeneity of agricultural landscapes . Monocultures can affect the bird species guild in different ways and deplete bird diversity . The land sparing approach assumes that current natural areas will be preserved by preventing further land use conversion to agriculture, but this theoretical assumption does not always hold due to market-driven economic incentives ,plants in pots ideas that promote land use changes linked to the expansion of bio-fuels and land-grabbing initiatives . A third approach for biodiversity conservation in agricultural landscapes proposes an integrated strategy where elements of land sparing and land sharing can be useful for conservation, depending on factors such as the levels of fragmentation, the socio-political conditions, and the level of previous disturbance of the environment . For example, spatial prioritization for conservation in South America shows that when the top 17% of priority areas were analyzed, the land sharing alternative resulted in a better conservation outcome than the land sparing alternative , although in some areas a mixed strategy better matched conservation priorities . In southeastern Australia, Michael et al. found that land sharing strategies were successful for birds, many of which are of conservation concern. However, land sharing had limited effects on conservation of other vertebrates , suggesting that mixed alternatives should be explored .Natural ecosystems provide irreplaceable biotic and abiotic conditions for birds, in particular for highly specialized forest-dependent birds, pollinators birds, migratory species, and endemics . Forest patches and fragments can contribute to higher bird diversity within the agricultural matrix and increase ecosystem services provided by birds . In Madagascar, Martin et al. compared a biological corridor of native vegetation and the surrounding agricultural matrix and found higher species richness in the agricultural mosaic of crops than in the corridor. In particular, some functional groups such as carnivores, terrestrial and sallying insectivores, and granivores were significantly more abundant within the agricultural mosaic, although the majority of these species were generalists and the endemic species remain associated to forest.
It should be emphasized that the agricultural mosaic is defined as a complex diversified system of different crops, where scattered trees, small forest patches, and other secondary habitats support various species. In a fragmented native forest in southern Chile, Carneiro et al. found that isolated native trees supported the abundance of the endemic parakeet within agricultural landscapes. Scattered trees provide key resources for refuge, roosting, nesting, feeding and connectivity within agroecosystems . Riparian corridors within a mosaic of low intensity managed crops provided significant habitat and connectivity for two forest specialist frugivorous birds in Costa Rica . Mangnall and Crowe found in South Africa that retaining native vegetation within a landscape with arable crops could increase bird species richness in comparison with monoculture crops. In the agricultural landscapes of the US Midwest, fragment size of riparian forest was positively related with the occupancy by Neotropical migratory bird species and species richness Forest edges represent ecotones between agroecosystems and native vegetation. These transition zones can host different bird species. In the North American Corn Belt Best et al. , reported that abundance of birds was higher along forest edges adjacent to corn fields in comparison with grassland edges or the center of cornfields. The same study, also stablished that bird abundance decreased in larger corn fields , which fits the patterns of land intensification suggested by Sauerbrei et al. . Similar results were recovered by Terraube et al. , who reported that the bird abundance of insectivores, under story gleaners, resident and migratory birds, cavity nesters and under story nesters increased in the interior of forest edges. Floristic composition and habitat structure were relevant for bird abundance and composition within the forest edges . Ecological and biological traits as well as natural history of different birds influence the adaptability of the different species to anthropogenic environments. For example, Figure 1 shows a number of different species enhanced by agricultural land cover in central Chile, where species composition changed between crop types but also between seasons . Examples of these varying associations of birds with crops, agricultural land cover, management, and ecosystem type are summarized in Table 1.Some bird species have a direct relationship with pastures and are considered grassland obligates, thus depending on agricultural management for their conservation . Cattle stocking at high density directly decrease habitat quality and influence the abundance of arthropods in prairie systems, which in turn influence the availability of prey for insectivorous birds . In a grazing experiment in Florida , Willcox et al. found that along with the loss of structural diversity in more intensively managed grasslands, total richness and abundance of birds decreased in monoculture grassland, although analysis by subgroups showed that some increased with the grazing intensity. Grasslands can also provide alternative feeding habitats, as in the case of the Austral Thrush in central southern Chile. Austral thrushes are considered frugivorous forest birds that, due to conversion of forest to grassland for cattle, were favored by the increase in soil annelids which complement their diet when fruit sources are scarce due to seasonal variation . In the case of the native grasslands of the southern cone of South America, the Pampas, land use change has converted most of the Pampas to rangeland or croplands . In the Pampas, vegetation structure was the main driver of the bird community composition . In terms of grazing pressure, low rates of nest destruction were found in Canada, although the nest destruction was positively correlated with grazing pressure . Silvopastoral systems combines grazing lands with trees and can be considered within the agroecological strategies of improve the agricultural matrix to support biodiversity . In Spain and Portugal ancient cork oaks known as “dehesa” and “montado” forest respectively, are used for different purposes but also can provide biodiversity and ecosystem services . In a “montado” systems, silvopastoral areas with higher heterogeneity supported high richness of bird guilds .