Karen Oberhauser

Karen Oberhauser

Professor and Director of the UW-Arboretum

UW Arboretum
1207 Seminole Highway
Madison, WI 53711-3726
608-262-2748

Ph.D. University of Minnesota, 1989 (Ecology and Behavioral Biology)
MS University of Wisconsin, Madison, 1981 (Natural Science Education)
BS Harvard University, 1979  (Biology)


My students and I conduct research on several aspects of monarch butterfly (Danaus plexippus) ecology, including reproductive ecology, host-parasite interactions, factors affecting the distribution and abundance of immature monarch stages, habitat management and availability, and risks posed by global climate change and pest control practices to monarch butterflies. Our research employs traditional lab and field techniques, as well as contributions of a variety of other audiences through citizen science. I have a strong interest in engaging K-12 students and teachers in inquiry-based science and promoting a citizenry with a high degree of scientific and environmental literacy.  To this end, I have developed a comprehensive science education program called Monarchs in the Classroom, which involves courses and workshops for teachers, opportunities for youth to engage in research and share their findings with broad audiences, a nationwide Citizen Science project called the Monarch Larva Monitoring Project, and curriculum development.

I am passionate about the conservation of the world’s biodiversity, and believe that the connections my projects promote between monarchs, humans, and the natural world will help to promote conservation actions. I chair the Steering Committee of the Monarch Joint Venture, am an officer and founding member of the Monarch Butterfly Fund, and am a member of state and national organizations that are focused on pollinator conservation, and citizen science.



Richard C. Newman Teaching Award. University of Minnesota, 2011
Richard C. Newman Community Impact Award. University of Minnesota, 2008


Director of UW-Madison Arboretum
Founder and Director: Monarch Larva Monitoring Project. 1996-present.
Xerces Society for Invertebrate Conservation; Board of Advisors. 2014-present.
Editorial board of the Journal Citizen Science: Theory and Practice.


Professional Societies:

Entomological Society of America

Publications, Since 2000
Refereed Primary Journal Articles and Book Chapters:

  • Oberhauser, K.S., D. Elmquist, J. M. Perilla-López, I. Gebhard, L. Lukens, J. Stireman. 2017. Tachinid fly (Diptera: Tachinidae) parasitoids of Danaus plexippus (Lepidoptera: Nymphalidae). Annals of the Entomological Society of America. in press.
  • Thogmartin, W.E., R. Wiederholt, K. Oberhauser, R. Drum, J.E. Diffendorfer, S. Altizer.6, O.R. Taylor, J. Pleasants, D. Semmens, B. Semmens, R. Erickson, K. Libby, L.Lopez-Hoffman 2017. Threats associated with the decline of the monarch butterfly. R. Soc. Open Sci. 4(9):170760. doi: 10.1098/rsos.170760
  • Thogmartin, W.E., L. López-Hoffman, J. Rohweder, J. Diffendorfer, R. Drum, D. Semmens, S. Black, I. Caldwell, D. Cotter, P. Drobney, L.L. Jackson, M. Gale, D. Helmers, S. Hilburger, E. Howard, K.S. Oberhauser, J. Pleasants, B. Semmens, O. Taylor, P. Ward, J.F. Weltzin, R. Wiederholt. 2017. Restoring monarch butterfly habitat in the Midwestern U.S.: All hands on deck. Environmental Research Letters. 12 10.1088/1748-9326/aa7637
  • Lewandowski, E. J., K.S. Oberhauser. 2017. Contributions of citizen scientists and habitat volunteers to monarch conservation. Human Dimensions of Wildlife. 22:55-70. DOI: 10.1080/10871209.2017.1250293
  • Lewandowski, E. J., W.J. Caldwell, D. C. Elmquist, K.S. Oberhauser. 2017. Public perceptions of citizen science. Citizen Science: Theory and Practice. 2(1), p.3. DOI: http://doi.org/10.5334/cstp.77
  • Saunders, S.P., L. Ries, K.S. Oberhauser, W. Thogmartin, E.F. Zipkin. 2017. Local and cross-seasonal associations of climate and land use with abundance of monarch butterflies (Danaus plexippus). Ecography in press.
  • Thogmartin, W. E., J. E. Diffendorfer, L. Lopez-Hoffman, K. Oberhauser, J. Pleasants, B. X. Semmens, D. Semmens, O. R. Taylor, and R. Wiederholt. 2017. Density estimates of monarch butterflies overwintering in central Mexico. PeerJ 5:e3221 https://doi.org/10.7717/peerj.3221.
  • Kasten, K., C. Stenoien, W. Caldwell, K.S. Oberhauser. 2016. Can roadside habitat lead monarchs on a route to recovery? Journal of Insect Conservation DOI 10.1007/s10841-016-9938-y
  • Stenoien, C., K.R. Nail, J. Zalucki, H. Parry, K.S. Oberhauser, M. Zalucki. 2016. Monarchs in decline: a collateral landscape level effect of modern agriculture. Insect Science. DOI 10.1111/1744-7917.12404
  • Oberhauser K.S., R. Wiederholt, J.E. Diffendorfer, D. Semmens, L. Ries, W.E. Thogmartin, L. Lopez-Hoffman, B. Semmens. 2016. A trans-national monarch butterfly population model and implications for regional conservation priorities. Ecological Entomology. DOI: 10.1111/een.12351
  • Lewandowski, E. J., K.S. Oberhauser. 2016. Butterfly citizen science projects support conservation activities among their volunteers. Citizen Science: Theory and Practice, 1(1): 6, pp. 1–8, DOI: http://dx.doi.org/10.5334/cstp.10
  • McCoshum, S.M., S.L. Andreoli, C. Stenoien, K.S. Oberhauser, K.A. Baum. 2016. Species distribution models for natural enemies of monarch butterfly (Danaus plexippus) larvae and pupae: distribution patterns and implications for conservation. Journal of Insect Conservation DOI 10.1007/s10841-016-9856-z
  • Semmens B.X., D.J. Semmens, W.E. Thogmartin, R. Wiederholt, L. López-Hoffman, J.E. Diffendorfer, J.M. Pleasants, K.S. Oberhauser, O.R. Taylor. 2016. Quasi-extinction risk and population targets for the Eastern migratory population of monarch butterflies (Danaus plexippus). Nature Reports 6, 23265; doi: 10.1038/srep23265
  • Brower, L. P., D. A. Slayback, P. Jaramillo-López, I. M. Ramirez, K. S. Oberhauser, E. H. Williams, and L. S. Fink. 2016. Illegal logging of 10 hectares of forest in the Sierra Chincua monarch butterfly overwintering area in Mexico.  American Entomologist Summer 2016:92-97 (Featured article)
  • Saunders, S.P., L. Ries, K.S. Oberhauser, E.F. Zipkin. 2016. Evaluating confidence in population-level predictions from climate impacts on the migratory monarch butterfly. Global Ecology and Biogeography DOI: 10.1111/geb.12461.
  • Pleasants, J. M., E.H. Williams, L.P. Brower, K.S. Oberhauser, and O.R Taylor. 2016. Conclusion of no decline in summer monarch population not supported. Annals of the Entomological Society of America doi: 10.1093/aesa/sav115.
  • Stenoien, C., S. McCoshum, W. Caldwell, A. De Anda, and K.S. Oberhauser. 2015. New reports that monarch butterflies (Lepidoptera: Nymphalidae, Danaus plexippus Linnaeus) are hosts for a pupal parasitoid (Hymenoptera: Chalcidoidae, Pteromalus cassotis Walker). Journal of the Kansas Entomological Society 88:16-26.
  • Lewandowski, E., K.S. Oberhauser. 2016. Butterfly citizen scientists in the United States increase their engagement in conservation. Biological Conservation http://dx.doi.org/10.1016/j.biocon.2015.07.029.
  • Nail K.R., Stenoien C., Oberhauser K.S. 2015. Immature monarch survival: Effects of site characteristics, density, and time. Annals of the Entomological Society of America. doi: 10.1093/aesa/sav047
  • Stenoien, C., K. Nail, and K.S. Oberhauser. 2015. Habitat productivity and temporal patterns of monarch butterfly egg densities in the Eastern U.S. Annals of the Entomological Society of America. doi: 10.1093/aesa/sav054
  • Ries, L., D. J. Taron, E. Rendon-Salinas, K.S. Oberhauser. 2015. Connecting eastern monarch population dynamics across their migratory cycle. pp. 268-282 in Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly. Cornell University Press, Ithaca, NY.
  • Oberhauser, K.S., L. Ries, S. Altizer, R.V. Batalden, J, Kudell-Ekstrum, M. Garland, E. Howard, S. Jepsen, J. Lovett, M. Monroe, G. Morris, E. Rendón-Salinas, R.G. RuBino, A. Ryan, O.R. Taylor, R. Treviño Ulloa, F.X. Villablanca, and D. Walton. 2015. Contributions to monarch biology and conservation through citizen science: 70 years and counting. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly, Chapter 2. Cornell University Press, Ithaca, NY.
  • Oberhauser, K.S., M. Anderson, S. Anderson, W. Caldwell, A.P. De Anda, M.D. Hunter, M. Kaiser, and M.J. Solensky. 2015. Lacewings, wasps and flies – oh my: insect enemies take a bite out of monarchs. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly, Chapter 6. Cornell University Press, Ithaca, NY.
  • Nail, K.R., R.V. Batalden, and K.S. Oberhauser. 2015. What’s too hot and what’s too cold? Lethal and sub-lethal effects of extreme temperatures on developing monarchs. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic butterfly, Chapter 8. Cornell University Press, Ithaca, NY.
  • De Anda, A., and K.S. Oberhauser. 2015. Invertebrate natural enemies and stage-specific mortality rates of monarch eggs and larvae. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic insect, Chapter 5. Cornell University Press, Ithaca, NY.
  • Batalden, R., and K.S. Oberhauser. 2015. Potential changes in Eastern North American monarch migration in response to an introduced milkweed, Asclepias curassavica. In Oberhauser, K.S., K.R. Nail, and S.M. Altizer, eds. Monarchs in a changing world: biology and conservation of an iconic insect, Chapter 19. Cornell University Press, Ithaca, NY.
  • Ries, L., K.S. Oberhauser. 2015. A citizen-army for science: quantifying the contributions of citizen scientists to our understanding of monarch butterfly biology. Bioscience 65:419-420.
  • Oberhauser, K.S., O. R. Taylor, S. M. Reppert, H. Dingle, K. R. Nail, R. M. Pyle, C. Stenoien. 2013. Are monarch butterflies true navigators? The jury is still out. Proceedings of the National Academy of Sciences 110(39):E3680.
  • Diffendorfer J.E., Loomis J.B., Ries L., Oberhauser K.S., Lopez-Hoffman L., Semmens D., Semmens B., Butterfield B., Bagstad K., Goldstein J., Wiederholt R., Mattsson B., Thogmartin W.E. 2013. National valuation of monarch butterflies indicates an untapped potential for incentive-based conservation. Conservation Letters 7:253-262.
  • Zipkin, E., L. Ries, R. Reeves, J. Reetz, K.S. Oberhauser. 2012. Tracking climate impacts on the migratory monarch butterfly. Global Change Biology 18:3039–3049
  • Barve N., Bonilla A.J., Brandes J., Brown J.C., Brunsell N., Cochran F.V., Crosthwait R.J., Gentry J., Gerhart L.M., Jackson T., Kern A.J., Oberhauser K.S., Owens H.L., Peterson A.T., Reed A.S., Soberón J., Sundberg A.D., Williams L.S. 2012. Climate change and mass mortality events in overwintering monarch butterflies. Revista Mexicana de la Biodiversidad. 83: 817-824. DOI:10.7550/rmb.26460
  • Pleasants, J., K.S. Oberhauser. 2013. Milkweed loss in agricultural fields because of herbicide use: Effect on the monarch butterfly population. Insect Conservation and Diversity. 6:135-144.
  • Oberhauser, K.S. 2012. Tachinid flies and monarch butterflies: Citizen Scientists document parasitism patterns over broad spatial and temporal scales. American Entomologist 58:19-22.
  • Bartel, R.E., K.S. Oberhauser, J.C. De Roode, S.M. Altizer. 2011. Monarch migration, seasonal habitat use and parasite transmission in eastern North America. Ecology 92(2): 342-351.
  • Fargione, J.E., T.R. Cooper, D.J. Flaspohler, J. Hill, C. Lehman, T. McCoy, S. McLeod, E.J. Nelson, K.S. Oberhauser, D. Tilman. 2009. Bioenergy and wildlife: Threats and opportunities for grassland conservation. Bioscience 59:767-777.
  • Lindsey, E., M. Mudresh, V. Dhulipala, K.S. Oberhauser, S. Altizer. 2009. Crowding and disease: effects of host density on response to infection in a butterfly-parasite interaction. Ecological Entomology 34:551–561.
  • Solensky, M.S., K.S. Oberhauser. 2009. Sperm precedence in monarch butterflies (Danaus plexippus). Behavioral Ecology 20 (2):328-334
  • Solensky, M.S., K.S. Oberhauser. 2009. Male monarch butterflies (Danaus plexippus) adjust their ejaculates in response to risk and intensity of sperm competition. Animal Behavior 77:465-472.
  • Oberhauser, K.S., S. Manweiler, R. Lelich, M. Blank, R. Batalden, A. De Anda. 2009. Impacts of ULV resmethrin applications on non-target insects. Journal of the American Mosquito Control Association 25:83–93.
  • Batalden, R., K.S. Oberhauser, A.T. Peterson. 2007. Ecological niches in breeding generations of Eastern North American monarch butterflies. Environmental Entomology 36:1365-1373.
  • Brower, L., K. Oberhauser, M. Boppré, A.V.Z. Brower, R.I. Vane-Wright. 2007. Monarch sex: Ancient rites, or recent wrongs? Antennae 31:12-18.
  • Oberhauser, K.S., I. Gebhard, C. Cameron, S. Oberhauser. 2007. Parasitism of monarch butterflies (Danaus plexippus) by Lespesia archippivora (Diptera: Tachinidae). American Midland Naturalist 157:312-328.
  • Oberhauser, K.S., S.J. Brinda, S. Weaver, R.D. Moon, S.A. Manweiler, N Read. 2006. Growth and survival of monarch butterflies (Lepidoptera: Danaidae) after exposure to permethrin barrier treatments. Environmental Entomology 35 (6): 1626-1634.
  • Szymanski, J., J.A. Shuey, K. Oberhauser. 2004. Population structure of the endangered Mitchell’s Satyr, Neonympha mitchellii mitchellii (French). American Midland Naturalist 152(2):304-322.
  • Lavoie, B., K.S. Oberhauser. 2004. Compensatory feeding in Danaus plexippus (Lepidoptera: Nymphalidae) in response to variation in host plant quality. Environmental Entomology 33:1062-1069.
  • Borland, J., C. Johnson, T. Crumpton, T. Thomas, S. Altizer, K. Oberhauser. 2004. Characteristics of fall migratory monarch butterflies, Danaus plexippus, in Minnesota and Texas. Pp. 97-104. In Oberhauser, K.S. & M.J. Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Altizer, S.M., K.S. Oberhauser , K.A. Geurts. 2004.  Transmission of the protozoan parasite Ophyocystis elektroscirrha in monarch butterfly populations: implications for prevalence and population-level impacts. Pp. 203-218. In: Oberhauser, KS, MJ Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Solensky, M.J., K.S. Oberhauser.  2004.  Behavioral and genetic components of male mating success in monarch butterflies. Pp. 61-68. In: Oberhauser, KS, MJ Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Oberhauser, K.S. 2004. Effects of female age, female mass and nutrients from males on monarch egg mass. Pp. 21-26. In: Oberhauser, KS, MJ Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Goehring, L., K.S. Oberhauser. 2004. Environmental factors influencing postdiapause reproductive development in monarch butterflies.  Pp. 187-198. In: Oberhauser, KS, MJ Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Prysby, M., K.S. Oberhauser. 2004. Temporal and geographical variation in monarch densities: Citizen scientists document monarch population patterns.  Pp. 9-20 in: Oberhauser, KS, MJ Solensky (Eds.). The Monarch Butterfly: Biology and Conservation.  Cornell University Press. Ithaca NY.
  • Oberhauser, K.S., E.R.L. Rivers. 2003. Monarch butterfly (Danaus plexippus) larvae & Bt corn pollen: A review of ecological risk assessment for a non-target species. AgBiotechNet 5:1-7.
  • Oberhauser, K.S., T. Peterson. 2003. Modeling current and future potential wintering distributions of Eastern North American monarch butterflies. Proceedings of the National Academy of Science 100:14063-14068.
  • York, H., K.S. Oberhauser. 2002. Effects of duration and timing of heat stress on monarch butterfly (Lepidoptera: Danaidae) development.  Journal of the Kansas Entomological Society 75:290-298.
  • Goehring L., K.S. Oberhauser. 2002. Effects of photoperiod, temperature and host plant age on induction of reproductive diapause and development time in Danaus plexippus. Ecological Entomology 27:674-685.
  • Oberhauser, K.S., M.D. Prysby, H.R. Mattila, D.E. Stanley-Horn, M.K. Sears, G. Dively, E. Olson, J.M. Pleasants, W.F. Lam, R. Hellmich. 2001. Temporal and spatial overlap between monarch larvae and corn pollen. Proceedings of the National Academy of Science 98(21):11913-11918.
  • Sears, M.K., R.L. Hellmich, D.E. Stanley-Horn, K.S. Oberhauser, J.M. Pleasants, H.R. Mattila, B.D. Siegfriedi, G.P. Dively. 2001. Impact of Bt corn pollen on monarch butterfly populations: A risk assessment. Proceedings of the National Academy of Science 98(21):11937-11942.
  • Altizer, S.M., K.S. Oberhauser, L.P. Brower. 2000. Associations between host migration and the prevalence of a protozoan parasite in natural populations of monarch butterflies.  Ecol. Entomol. 25:125-139. (received Royal Entomological Society’s Excellence in Ecological Entomology Reward.  See: Leather, S. 2002. Excellence in ecological entomology- the Royal Entomological Society’s awards for scientific writing. Ecological Entomology 27:513)

Books or Monographs:

  • Oberhauser, K.S., K.R. Nail, and S.M. Altizer (Eds). 2015. Monarchs in a changing world: biology and conservation of an iconic butterfly. Cornell University Press, Ithaca, NY.
  • Oberhauser, K.S., R. Batalden, E. Howard. 2009. Monarch monitoring in North America: Overview of initiatives and protocols. Commission on Environmental Cooperation. Montreal, Canada.
  • Oberhauser, K.S., D. Cotter, D. Davis, R. Décarie, A.E. Behnumea, C. Galino-Leal, M.P. Gallina Tessaro, E. Howard, J. Lauriault, W. Macziewski, S. Malcolm, F. Martínez, J.M. González, M. McRae, D. Nernberg, I. Pisanty Baruch, I. Ramírez, J.J. Reyes, A. Wilson. 2008. North American Monarch Conservation Plan. Commission on Environmental Cooperation. Montreal, Canada.
  • Oberhauser, K.S., M.J. Solensky (Eds.).  2004.  The Monarch Butterfly: Biology and Conservation.  Cornell University Press, Ithaca NY. (248 pp).

Biological Research

I have most recently focused broadly on ways in which human activities affect monarch butterfly habitats in Canada, the US and Mexico. This includes empirical research focused on potential impacts of climate change, and both bottom-up and top-down regulation of monarch populations attributable to natural enemies and plant defenses. The MLMP, which involves hundreds of volunteers throughout North America, provides spatially and temporally extensive data to address these issues, and my students and I also conduct field and lab experiments. I am very interested in synthesizing data from many other sources collected during all stages of monarchs’ annual cycle of breeding, migrating and overwintering. This has led to collaborations with researchers throughout the world, and several meetings and presentations at national and international conferences. I was a co-PI on a working group funded by the National Center for Ecological Analysis and Synthesis (NCEAS) that used data from a variety of monitoring programs to study monarch population dynamics; was involved with a USGS Powell Center working group studying contributions of different habitats to population recruitment in three model migratory species; and help to lead the Monarch Conservation Science Partnership, a group of researchers from agencies and universities that has written synthetic papers to inform ongoing monarch conservation efforts.

Climate change: My work on monarchs and climate change began with a study almost 15 years ago that used point occurrence data for monarchs wintering in Mexico to define ecological parameters of their wintering niche, and to predict whether and where this niche would be available in 2050 (Oberhauser and Peterson 2003). Since then, we have used similar techniques and data from the MLMP to address similar questions for the summer breeding population (Batalden et al. 2007). More recently, I have published collaborative papers using a variety of modeling techniques to understand monarchs’ relationship to climate (Saunders et al. 2017, Saunders et al. 2016, Nail et al. 2015, Batalden and Oberhauser 2015, Zipkin et al. 2012, Barve et al. 2012).

Monarch predators and parasitoids: The abundance of insect herbivores like monarchs can be regulated by interactions with their host plants, their natural enemies (predators, parasitoids, and parasites), and abiotic factors. While several researchers have studied how host-plant defenses and temperature affect monarch larval survival, the effect of natural enemies is less well known. Using field studies, experimental lab work, and data from the MLMP, we are working to understand selective pressures exerted on monarchs by natural enemies and the life stage at which these enemies have their greatest effect.

Analysis of 17 years’ data from MLMP volunteers allowed us to assess temporal and spatial variation in mortality due to the generalist parasitoid flies in the family Tachinidae. (Oberhauser et al. 2007, Oberhauser 2012, Oberhauser et al. 2015, Oberhauser et al. 2017). I have also worked with other researchers to understand the impacts of a protozoan parasites (Lindsey et al. 2009, Bartel et al. 2011), and overviews of monarch natural enemies and the stages at which they impact monarch populations (Oberhauser et al. 2015), and synthesize the cumulative impacts of natural enemies using an intensive field observation study (De Anda and Oberhauser 2015).

Population dynamics: I have worked with other researchers to synthesize monitoring data collected during all stages of the monarchs’ annual cycle of breeding, migrating and overwintering, using MLMP data and data from several other Citizen Science projects. Data from many of these projects have not been analyzed or shared broadly, so much of my work has focused on bringing together groups and individuals who collected them. These efforts have resulted in several synthetic papers that addressed threats to monarchs, density estimates at the monarch wintering sites, the need for an “all-hands-on-deck” approach to monarch conservation (Thogmartin et al. 2017a, b, c), and contributions to monarch numbers from different regions (Oberhauser et al. 2016).

Impacts of insecticides and agricultural practices on monarchs: In collaboration with many colleagues and students, I have studied the impacts of the pyrethroid insecticides used to control adult mosquitoes on monarch butterflies and other non-target insects (Oberhauser et al. 2007, Oberhauser et al. 2009). I am also continuing to study the impacts of genetically modified crops that tolerate post-emergence herbicide applications, resulting in a drastic reduction of weeds, including milkweed, in row crops. I have recently worked with a colleague at the University of Iowa to document the correlation between the increased use of herbicide tolerant crops and declining monarch numbers (Pleasants and Oberhauser 2012), and am working on a summary paper on the impacts of changing agricultural practices in general (Pleasants et al. in prep).

Extension and Outreach Research

I have conducted research on the impacts and implications of my extension and outreach work. I have published papers documenting connections of natural science volunteers to nature (Guiney and Oberhauser 2009); and using insects to promote conservation awareness (Guiney and Oberhauser 2008). I have also studied the educational and behavioral impacts of engagement in citizen science (Oberhauser and Prysby 2008; Kountoupes and Oberhauser 2008; Oberhauser and Lebuhn 2012; Lewandowski and Oberhauser 2016a, b; 2017a, b; Oberhauser et al. 2015; Koomen et al. 2014, 2016, in press).