Agriculture

crop dusting

HOME| connecting populations | seasonal interactions | climate change | disease | urbanization

energy extraction | agriculture | invasive species | air strikes

Pesticides and herbicides

Chemical toxins are the most common way to control agricultural pests like insects, rodents, and fungi. However, these toxins also have serious detrimental effects on wildlife, including migratory species.

  • Hawks, owls, and geese can be killed by rodenticides which cause internal hemorrhage

For sedentary populations, it is relatively simple to discern the causes and effects of toxic exposure. But for migratory populations, symptoms might not be observed until the animals have traveled far away from where the initial exposure occurred.

  • A complete understanding of migratory connectivity is needed to understand the carry-over effects of chemical exposure and the ultimate causes of population declines.
  • Chemicals like DDT are still used outside the United States, and can reduce the lifespan and reproductive success of species that are familiar summer breeders in the USA.
  • In the 1990s, fewer and fewer Swainson’s hawks returned from winter migration. Wintering ground activities were the likely culprit, but nobody knew exactly where this was. In 1995, the hawks were tracked to Argentina, where 20,000 hawks were found dead or dying from pesticide-laden grasshoppers. Conservation efforts could not begin to succeed without migratory connectivity knowledge.
  • Declines in dickcissel populations could not be addressed until their wintering locations were discovered in Venezuela, where it became known that local farmers killed thousands annually hoping to reduce crop damage.

The hazards of mechanization

Modern technology has made it possible to mechanize almost every aspect of agriculture from planting to harvesting. Unfortunately, mechanical farming is extremely dangerous for birds that are prone to nesting in agricultural fields.

  • Every year, tens of thousands of tricolored blackbird chicks are killed by silage harvesting just before they fledge.
  • Bobolinks and many other grassland species are also killed during harvest.
  • Mechanized applications expand the use of chemical pest control, reducing food supplies for breeding birds.
  • It is essential to know where breeding populations winter to accurately estimate carry-over effects.

Landscape fragmentation

The conversion of native habitat to monocultured fields homogenizes vegetation, protective cover, and food resources. Domesticated grazing animals also wreck havoc on many types of habitat, including ecologically important riparian zones. Land conversion and fragmentation has negative consequences at all stages of a migratory animal’s annual cycle.

  • Loss of important stop-over habitat during migration may force populations to graze in cultivated fields, increasing exposure to pesticides
  • Loss of wintering grounds can mean death for populations of the monarch butterfly, or negative carry-over effects for birds.
  • Changes in migratory behavior can weaken the condition of migrating individuals and contribute to population decline.

Migratory connectivity knowledge helps managers protect the most important landscapes and mitigate long-term effects of habitat fragmentation on connected populations.

Aquaculture

  • Fish farm effluents contain excrement and chemicals and can cause severe declines in water quality of pristine rivers and lakes
  • When wild salmon fry migrate past fish farms, they are at risk of contracting deadly parasites
  • Some fish farms completely block important migratory headwaters

References

  1. Basili, G.D. and S.A. Temple. 1999. Dickcissels and crop damage in Venezuela: Defining the problem with ecological models. Ecological Applications 9:732–739.
  2. Bock, C.E., V.A. Saab, T.D. Rich, and D.S. Dobkin. 1993. Effects of livestock grazing on neotropical migratory landbirds in western North America. In: Finch, Deborah M.; Stangel, Peter W. (eds.). Status and management of neotropical migratory birds: September 21-25, 1992, Estes Park, Colorado. Gen. Tech. Rep. RM-229. Fort Collins, Colo.: Rocky Mountain Forest and Range Experiment Station, U.S. Dept. of Agriculture, Forest Service: 296-309.
  3. Brower, L.P. 1995. Understanding and misunderstanding the migration of the monarch butterfl (Nymphalidae) in north America: 1857-1995. Journal of the Lepidopterists Society 49: (4) 304-385.
  4. Conway, C.J., G.V.N. Powell, and J.D. Nichols. 1995. Overwinter survival of Neotropical migratory birds in early-successional and mature tropical forests. Conservation Biology 9: (4) 855-864.
  5. Geluso, K.N., J.S. Altenbach, and D.E. Wilson. 1976. Bat mortality: pesticide poisoning and migratory stress. Science 194: (4261) 184-186.
  6. Henny, D.J., F.P. Ward, K.E. Riddle, and R.M. Prouty. 1982. Migratory peregrine falcons, Falco peregrinus, accumulate pesticides in Latin America during winter. Canadian Field-Naturalist 96: (3) 333-338.
  7. Heske, E.J., S.K. Robinson, and J.D. Brawn. 1999. Predator activity and predation on songbird nest on forest-field edges in est-central illinois. Landscape Ecology 14: (4) 345-354.
  8. Jensen, R.A., M.S. Wisz, and J. Madsen. 2008. Prioritizing refuge sites for migratory geese to alleviate conflicts with agriculture. Biological Conservation 141: (7) 1806-1818.
  9. Jones, J.G. 1990. Pollution from fish farms. Water and Environment Journal 4: (1) 14-18.
  10. Klemens, J.A., R.G. Harper, J.A. Frick, A.P. Capparella, H.B. Richardson, and M.J. Coffey. 2000. Patterns of organochlorine pesticide contamination in Neotropical migrant passerines in relation to diet and winter habitat. Chemosphere 41: (1) 1107-1113.
  11. Krkošek, M., A. Gottesfeld, B. Proctor, D. rolston, C. Carr-Harris, and M.A. Lewwis. 2007. Effects of host migration, diversity, and aquaculture on sea lice threats to Pacific salmon populations. Proceedings of the Royal Society for Biological Sciences 274: (1629) 3141-3149.
  12. Moore, A., N. Lower, I. Mayer, and L. Greenwood. 2007. The impact of a pesticide on migratory activity and olfactory function in Atlantic salmon (Salmo salar L.) smolts. Aquaculture 273: (2-3) 350-359.
  13. Robinson, S.K., F.R. Thompson III, T.M. Donovan, d.R. Whitehead, and J. Faaborg. 1995. Regional forest fragmentation and the nesting success of migratory birds. Science 267: (5206) 1987-1990.
  14. Rodenhouse, N.L., L.B. Best, R.J. O’connor, and E.K. Bollinger. 1993. Effects of temperate agriculture on neotropical migrant landbirds. In: Finch, Deborah M.; Stangel, Peter W. (eds.). Status and management of neotropical migratory birds: September 21-25, 1992, Estes Park, Colorado. Gen. Tech. Rep. RM-229. Fort Collins, Colo.: Rocky Mountain Forest and Range Experiment Station, U.S. Dept. of Agriculture, Forest Service: 280-295.

HOME| connecting populations | seasonal interactions | climate change | disease | urbanization

energy extraction | agriculture | invasive species | air strikes