Literature Sources

Table S1. Publications included in meta-analysis with latitude (in decimal degrees), study duration (in months), habitat classification, and whether birds were excluded in winter.

Literature sources

Askenmo, C., A. von Brömssen, Ekman, J. & Jansson, C. (1977) Impact of Some Wintering Birds on Spider Abundance in Spruce. Oikos, 28, 90–94.

Atlegrim, O. (1989) Exclusion of birds from bilberry stands: impact on insect larval density and damage to the bilberry. Oecologia, 79, 136–139.

Barber, N.A. & Marquis, R.J. (2009) Spatial Variation in Top-down Direct and Indirect Effects on White Oak (Quercus alba L.). American Midland Naturalist, 162, 169–179.

Barber, N.A. & Marquis, R.J. (2011a) Light environment and the impacts of foliage quality on herbivorous insect attack and bird predation. Oecologia, 166, 401–409.

Barber, N.A. & Marquis, R.J. (2011b) Leaf quality, predators, and stochastic processes in the assembly of a diverse herbivore community. Ecology, 92, 699–708.

Böhm, S.M., Wells, K., & Kalko, E. K. V. (2010) Top-down control of herbivory by birds and bats in the canopy of temperate broad-

leave oaks (Quercus robur). PLoS one 6, e17857.

Bridgeland, W. T., Beier, P., Kolb, T. & Whitham, T.G. (2010) A conditional trophic cascade: Birds benefit faster growing trees with stronger links between predators and plants. Ecology91, 73–84.

Campbell, R.W. &Torgerson, T.R. (1983) Effect of Branch Height on Predation of Western Spruce Budworm (Lepidoptera: Tortricidae) Pupae by Birds and Ants. Environmental Entomology, 12, 697–699.

Campbell, R.W., Torgersen, T.R. & Srivastava, N. (1983) A Suggested Role for Predaceous Birds and Ants in the Population Dynamics of the Western Spruce Budworm. Forest Science, 29, 779–790.

Evelegh, N., Majer, J. & Recher, H. (2001) The effects of reducing bird predation on canopy arthropods of marri (Eucalyptus calophylla) saplings on the Swan Coastal Plain, Western Australia. Journal of the Royal Society of Western Australia, 84, 13–21.

Floyd, T. (1996) Top-down impacts on creosotebush herbivores in a spatially and temporally complex environment. Ecology, 77, 1544–1555.

Forkner, R.E. & Hunter, M.D. (2000) What goes up must come down? Nutrient addition and predation pressure on oak herbivores. Ecology, 81, 1588–1600.

Gunnarsson, B. (1996) Bird Predation and Vegetation Structure Affecting Spruce-Living Arthropods in a Temperate Forest. Journal of Animal Ecology, 65, 389–397.

Gunnarsson, B. & Hake, M. (1999) Bird predation affects canopy-living arthropods in city parks. Canadian journal of zoology, 77, 1419–1428.

Holmes, R.T., Schultz, J.C. & Nothnagle, P. (1979) Bird Predation on Forest Insects: An Exclosure Experiment. Science, 206, 462–463.

Lichtenberg, J.S. & Lichtenberg, D.A. (2002) Weak Trophic Interactions among Birds, Insects and White Oak Saplings (Quercus alba). American Midland Naturalist, 148, 338–349.

Low, C. & Connor, E.F. (2003) Birds have no impact on folivorous insect guilds on a montane willow. Oikos, 103, 579-589.

Marquis, R.J. & Whelan, C.J. (1994) Insectivorous birds increase growth of white oak through consumption of leaf-chewing insects. Ecology, 75, 2007-2014.

Mazia, C.N., Kitzberger, T. & Chaneton, E.J. (2004) Interannual changes in folivory and bird insectivory along a natural productivity gradient in northern Patagonian forests.Ecography, 27, 29–40.

Mazia, C.N., Chaneton, E.J., Kitzberger, T., & Garibaldi, L.A. (2009) Variable strength of top-down effects in Nothofagus forests: bird predation and insect herbivory during an ENSO event.Austral Ecology, 34, 359–367.

Medina, R. & Barbosa, P. (2002) Predation of small and large Orgyia leucostigma (JE Smith)(Lepidoptera: Lymantriidae) larvae by vertebrate and invertebrate predators. Environmental entomology, 31, 1097–1102.

Mols, C.M.M. & Visser, M.E. (2002) Great tits can reduce caterpillar damage in apple orchards. Journal of Applied Ecology, 39, 888–899.

Mooney, K.A. (2006) The disruption of an ant-aphid mutualism increases the effects of birds on pine herbivores. Ecology, 87, 1805–1815.

Mooney, K.A. (2007) Tritrophic effects of birds and ants on a canopy food web, tree growth, and phytochemistry. Ecology, 88, 2005–2014.

Mooney, K.A. & Linhart, Y.B. (2006) Contrasting cascades: insectivorous birds increase pine but not parasitic mistletoe growth. Journal of Animal Ecology, 75, 350–357.

Murakami, M. (1999) Effect of avian predation on survival of leaf-rolling lepidopterous larvae. Researches on population ecology, 41, 135–138.

Murakami, M. & Nakano, S. (2000) Species-specific bird functions in a forest-canopy food web. Proceedings of the Royal Society of London Series B-Biological Sciences, 267, 1597–1601.

Recher, H.F. & Majer, J.D. (2006) Effects of bird predation on canopy arthropods in wandoo Eucalyptus wandoo woodland. Austral Ecology, 31, 349-360.

Ritchie, M.E. (2000) Nitrogen limitation and trophic vs. abiotic influences on insect herbivores in a temperate grassland. Ecology, 81, 1601–1612.

Schwenk, W.S., Strong, A.M., & Sillett, T.S. (2010) Effects of bird predation on arthropod abundance and tree growth across and elevational gradient.Journal of Avian Biology, 41, 367–377.

Singer, M.S., Farkas, T.E., Skorik, C.M., & Mooney, K.M. (2012) Tritrophic interactions at a community level: Effects of host plant species quality on bird predation of caterpillars. American Naturalist, 179, 363–374.

Sipura, M. (1999) Tritrophic interactions: willows, herbivorous insects and insectivorous birds.Oecologia, 121, 537–545.

Solomon, M.E., Glen, D.M., Kendall, D.A. & Milsom, N.F. (1976) Predation of overwintering larvae of codling moth (Cydia pomonella (L.)) by birds.Journal of Applied Ecology, 13, 341–352.

Strengbom, J., Witzell, J., Nordin, A. & Ericson, L. (2005) Do multitrophic interactions override N fertilization effects on Operophtera larvae? Oecologia, 143, 241–250.

Strong, A.M., Sherry, T.W. & Holmes, R.T. (2000) Bird predation on herbivorous insects: indirect effects on sugar maple saplings. Oecologia, 125, 370–379.

Torgersen, T. & Campbell, R. (1982) Some effects of avian predators on the western spruce budworm in north central Washington. Environmental Entomology, 11, 429–431.

Wiens, J.A., Cates, R.G., Rotenberry, J.T., Cobb, N., Van Horne, B. & Redak, R.A. (1991) Arthropod dynamics on sagebrush (Artemisia tridentata): effects of plant chemistry and avian predation. Ecological Monographs,61, 299–321.

Zehnder, C.B., Stodola, K.W., Cooper, R.J., & Hunter, M.D. (2010) Spatial heterogeneity in the relative impacts of foliar quality and predation pressure on red oak, Quercus rubra, arthropod communities.Oecologia, 164, 1017–1027.

Grassland studies excluded

Belovsky, G.E. & Slade, J.B. (1993) The Role of Vertebrate and Invertebrate Predators in a Grasshopper Community. Oikos, 68, 193–201.

Bock, C.E., Bock, J.H. & Grant, M.C. (1992) Effects of Bird Predation on Grasshopper Densities in an Arizona grassland. Ecology, 73, 1706–1717.

Branson, D.H. (2005) Direct and indirect effects of avian predation on grasshopper communities in northern mixed-grass prairie.Environmental Entomology, 34, 111–1121.

Fowler, A.C., Knight, R.L., George, T.L. & McEwen, L.C. (1991) Effects of avian predation on grasshopper populations in North Dakota grasslands. Ecology, 1775–1781.

Gardner, K. & Thompson, D. (1998) Influence of avian predation on a grasshopper (Orthoptera: Acrididae) assemblage that feeds on threadleaf snakeweed. Environmental entomology, 27, 110–116.

Joern, A. (1986) Experimental study of avian predation on coexisting grasshopper populations (Orthoptera: Acrididae) in a sandhills grassland. Oikos, 243–249.

Joern, A. (1992) Variable impact of avian predation on grasshopper assemblies in sandhills grassland.Oikos, 458–463.

Table S2. Herbivore species and the censuses in which each was recorded on Q. velutina field experiment. M = May, J = July, S = September.