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Spatial Subsidies—Quantifying Linkages between Human and Natural Systems with Migratory Species

Animal migration occurs because it allows animals to exploit resources where and when they are most abundant by moving seasonally between habitats. Where humans have come to exploit, enjoy or otherwise benefit from migratory species, we too are capitalizing on the seasonal bounty of distant ecosystems. The benefits we derive from migratory species are economically and culturally important; they include food for millions of people, regulation of agricultural pests, pollination, recreation (wildlife viewing, hunting), seed dispersal, and many more. Without explicitly recognizing the benefits provided by migratory species or the places upon which they depend, we are less well equipped to manage them effectively across jurisdictional boundaries. Indeed, population declines have been observed for migratory species worldwide (Rappole and McDonald, 1994; Askins, 1995; Sanderson and others, 2006; Kirby and others, 2008; Limburg and Waldman, 2009; Brower and others, 2012; Sauer and others, 2014).

combined picture of northern pintail duck, monarch butterfly, and Mexican free-tailed bats

What Are Spatial Subsidies?

Spatial subsidies result because of mismatches between the location(s) of habitats most important for the survival of migratory species and the location(s) where humans most benefit from the species. For example, migratory ducks are most dependent on productive breeding habitat in the north where relatively few people live. Humans derive benefits from ducks primarily through hunting and wildlife viewing, which occurs largely at stopover sites during the fall migration and in southern winter habitat which are close to areas with many more people. People living in the duck's winter range are therefore receiving benefits derived from summer breeding habitat. In a sense, they are being subsidized by the availability of high-quality habitat further north.

The concept of spatial subsidies allows us to quantify the spatial ecological dependencies of coupled human-natural systems that have developed around migratory species. Quantifying these dependencies will make it possible to:

  1. Identify how and where people derive benefit from a migratory species;
  2. Establish which habitat locations are most critical for the growth and survival of a migratory population;
  3. Determine the extent to which (often distant) critical habitat subsidizes the economic and social wellbeing of people throughout the migratory range of a species;
  4. Educate decision-makers and the public about the connections between their livelihoods and/or wellbeing and distant landscapes;
  5. Reveal the value of a landscape for the role it plays in supporting migratory species;
  6. Resolve conflicts over the sustainable and equitable allocation of exploited migratory species;
  7. Facilitate cross-jurisdictional cooperative management of migratory species;
  8. Identify the magnitude and potential sources of funding that could be developed for investment in the maintenance of migratory populations;
  9. Target conservation funding to those areas most important for maintenance of migratory populations and their ecosystem services;
  10. Establish programs to incentivize conservation in ecologically important areas where people derive little to no benefit from migratory species; and
  11. Close the feedback loop for coupled human-natural systems involving migratory species.

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How Do You Calculate Subsidies?

To quantify spatial subsidies we need a combination of biological and socioeconomic information. On the biological side, we need to know how migratory species depend on the various ecosystems they visit throughout their migration. Spatially explicit population modeling can be used to estimate this proportional dependence, DS, of a species on different parts of its range (e.g. Wiederholt and others, 2013).

We have a NIMBioS working group, "Estimating area-specific contributions to the population dynamics of migratory species", starting in 2014 to further develop and refine these methods.

On the socioeconomic side we need to know how and where humans benefit from a species. This involves conducting an ecosystem services analysis to estimate the dollar value of different benefits provided by a species, VS. Benefits provided by migratory species include pollination, pest control, recreation (hunting & viewing), subsistence harvest, existence/bequest values, and others (see our list of publications, below). All sources of value must be collected and/or compiled for each part of the range of a migratory species such that the areas used to estimate economic benefits match the areas used to estimate proportional dependence.

Once estimates for the proportional dependence and ecosystem service value(s) have been obtained, the spatial subsidy, Y, can be estimated using the following equation (Semmens and others, 2011; López-Hoffman and others, 2013):


Where YA is the subsidy at location A, VS is the total value of benefits provided by a species S across its entire range, DSA is the proportional dependence of the species on location A, and VSA is the value of benefits provided by the species at location A. Positive values indicate that location A is subsidizing other parts of the migratory range and negative values indicate that it is being subsidized by other areas. When summed across all parts of a migratory species' range, the subsidy necessarily balances out to 0.

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Powell Center Working Group—Animal Migration and Spatial Subsidies: Establishing a Framework for Conservation Markets

A grant from the USGS Powell Center for Analysis and Synthesis has allowed us to convene a working group in which we pioneered calculating spatial subsidies for three well-known North American migratory species: northern pintail ducks, monarch butterflies, and Mexican free-tailed bats. These three species provide a wide range of services, from purely aesthetic cultural services to economically important regulatory services. Similarly, a wide range of markets exist for their services, from well-established markets to no markets at all. These species were selected deliberately to further develop and demonstrate the Semmens and others (2011) spatial subsidy approach for three very different types of migratory species.

Early publications from the working group have focused on range-wide, spatially explicit economic valuation of the goods and services provided by each species, and estimating the extent to which the species depends on different parts of its range for survival and reproduction at the population level. Papers presenting our final subsidy calculations for each species and synthesizing lessons learned are anticipated in 2014.

Members of the working group:

Contact Us

We are very interested in applying this methodology to new species, particularly those facing important management challenges and/or requiring coordinated international governance. Please don't hesitate to contact us with your ideas!

Darius SemmensDarius Semmens
Research Physical Scientist
Geosciences and Environmental Change Science Center
U.S. Geological Survey
Denver, Colorado

Laura Lopez-HoffmanLaura López-Hoffman
Assistant Professor
Udall Center for Studies in Public Policy
School of Natural Resources and Environment
University of Arizona, Tucson

Jay DiffendorferJay Diffendorfer
Research Ecologist
Geosciences and Environmental Change Science Center
U.S. Geological Survey
Denver, Colorado


Bagstad, K.J., and Wiederholt, Ruscena, 2013, Tourism values for Mexican free-tailed bat (Tadarida brasiliensis mexicana) viewing: Human Dimensions of Wildlife, v. 18, no. 4, p. 307-311. [doi:10.1080/10871209.2013.789573]

Diffendorfer, J.E.; Loomis, J.B.; Ries, Leslie; Oberhauser, Karen; López-Hoffman, Laura; Semmens, D.J.; Semmens, Brice; Butterfield, Bruce; Bagstad, K.J.; Goldstein, Josh; Wiederholt, Ruscena; Mattsson, B.J.; and Thogmartin, W.E.; 2013, National valuation of monarch butterflies indicates an untapped potential for incentive-based conservation: Conservation Letters. [doi:10.1111/conl.12065]

Goldstein, J.H., Thogmartin, W., Bagstad, K.J., Dubovsky. J.A., Semmens, D.J., Mattsson B.J., López-Hoffman, Laura, and Diffendorfer, J.E., in press, Replacement cost valuation of Northern Pintail (Anas acuta) subsistence harvest in Arctic and sub-Arctic North America: Human Dimensions of Wildlife.

López-Hoffman, Laura, Semmens, D.J., and Diffendorfer, J.E., 2013, How do migratory species add ecosystem service value to wilderness? Calculating the spatial subsidies provided by protected areas: International Journal of Wilderness, v. 19, p. 14-19.

López-Hoffman, Laura; Wiederholt, Ruscena; Sansone, Chris; Bagstad, K.J.; Cryan, Paul; Diffendorfer, J.E.; Goldstein, Joshua; LaSharr, Kelsie; Loomis, J.B.; McCracken, Gary; Medellín, R.A.; Russell, Amy; and Semmens, D.J.; 2014, Market forces and technological substitutes cause fluctuations in the value of bat pest-control services for cotton: PLoS ONE, v. 9, no. 2, e87912. [doi:10.1371/journal.pone.0087912]

Semmens, D.J., Diffendorfer, J.E., López-Hoffman, Laura, and Shapiro, C.D., 2011, Accounting for the ecosystem services of migratory species: quantifying migration support and spatial subsidies: Ecological Economics, v. 70, p. 2236-2242. [doi:j.ecolecon.2011.07.002]

Wiederholt, Ruscena; López-Hoffman, Laura; Cline, Jon; Medellín, R.A.; Cryan, Paul; Russell, Amy; McCracken, Gary; Diffendorfer, J.E.; and Semmens, D.J.; 2013, Moving across the border: Modeling migratory bat populations: Ecosphere, v. 4, no. 9, article 114. [doi:10.1890/ES13-00023.1]

Wiederholt, Ruscena, Mattsson, B.J., Thogmartin, W.E., Diffendorfer, J.E., Erickson, R.A., and López-Hoffman, Laura, in review, Contributions of discrete habitats to population dynamics of seasonally migrating species: Submitted to American Naturalist.


Askins, R.A., 1995, Hostile Landscapes and the Decline of Migratory Songbirds: Science, v. 267, no. 5206, p. 1956-1957.

Brower, L.P., Taylor, O.R., Williams, E.H., Slayback, D.A., Zubieta, R.R., and Ramirez, M.I., 2012, Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk?: Insect Conservation and Diversity, v. 5, no. 2, p. 95-100.

Kirby, J.S., Stattersfield, A.J., Butchart, S.H.M., Evans, M.I., Grimmett, R.F.A., Jones, V.R., O'Sullivan, John, Tucker, G.M., and Newton, Ian, 2008, Key conservation issues for migratory birds in the world's major flyways: Bird Conservation International, v. 18, p. 49-73.

Limburg, K.E., and Waldman, J.R., 2009, Dramatic declines in North Atlantic diadromous fishes: BioScience, v. 59, no. 11, p. 955-965.

Rappole, J.H., and McDonald, M.V., 1994, Cause and effect in population declines of migratory birds: The Auk, v. 111, no. 3, p. 652-660.

Sanderson, F.J., Donald, P.F., Pain, D.J., Burfield, I.J. and van Bommel, F.P.J., 2006, Long-term population declines in Afro-Palearctic migrant birds: Biol Conserv., v. 131, p. 93-105.

Sauer, J.R., Hines, J.E. and Fallon, J., 2007, The North American Breeding Bird Survey, results and analysis 1966-2007. Version 10.13.2007: U.S. Geological Survey Patuxent Wildlife Research Centre, Laurel, Maryland.

Sauer, J.R., Hines, J.E., Fallon, J.E., Pardieck, K.L., Ziolkowski, D.J. Jr., and Link, W.A., 2014, The North American Breeding Bird Survey, Results and Analysis 1966-2012. Version 02.19.2014: U.S. Geological Survey Patuxent Wildlife Research Center, Laurel, Maryland.

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