Reciprocal subsidies refer to the dynamic interdependence between terrestrial and aquatic food webs, where energy and resources are exchanged across habitats. In a deciduous forest and stream ecotone, aquatic insect emergence peaks in spring when terrestrial invertebrate biomass is low, while terrestrial invertebrate input to the stream occurs primarily in summer when aquatic invertebrate biomass is low. These reciprocal prey fluxes subsidize both forest birds and stream fishes, accounting for 25.6% and 44.0% of their annual energy budgets, respectively. Seasonal contrasts between allochthonous prey supply and in situ prey biomass determine the importance of reciprocal subsidies. A regional landscape is a heterogeneous collection of habitats with varying environmental properties. Despite apparent separation, local food webs can be tightly linked by energy flux across habitat interfaces. Across-habitat transfers of materials or organisms often exert critical influences on communities. Theoretical models suggest energy generally flows from more to less productive habitats, but empirical studies have mainly focused on one-sided subsidies. However, productivity in local habitats fluctuates seasonally, and peak productivities in juxtaposed habitats can be asynchronous. If these fluctuations reverse the productivity gradient and the direction of energy transfer, local communities in both habitats could be reciprocally subsidized. Reciprocal subsidies may be important between forest and streams in northern temperate latitudes, where temperature and light, two principal determinants of primary productivity, change dramatically with season. Forest and stream food webs are widely viewed as energetically coupled, with considerable edge-mediated effects. Inputs of particulate organic matter from riparian forests represent an important energy source of stream production. Accidental inputs of terrestrial invertebrates are known to be a major prey category directly available for stream consumers such as fish. Conversely, riparian forests generally support greater species diversity and population abundance of terrestrial consumers than adjacent upland habitats, although the mechanisms responsible for this edge effect have remained poorly understood. Riparian consumers, such as birds, bats, and spiders, may benefit from energy transfers gained from aquatic insects emerged from streams. Net flux direction, however, can change seasonally. In this study, field studies were conducted in a forest plot along the Horonai Stream in the Tomakomai Experimental Forest, Japan, from May 1997 to June 1998. The forest was dominated by deciduous tree species, and the stream had stable discharge. Consumers included insectivorous birds and salmonids. Prey abundance was surveyed in both the forest plot and stream reach every month. Terrestrial invertebrates on the foliage were collected quantitatively, and stream invertebrates were collected using a Surber net sampler. Across-habitat prey fluxes, including both the accidental inputs of terrestrial invertebrates to and the emergence of aquatic insects from the study reach, were simultaneously estimated. The annual contribution of allochthonous prey to the total energy budget was estimated for each assemblReciprocal subsidies refer to the dynamic interdependence between terrestrial and aquatic food webs, where energy and resources are exchanged across habitats. In a deciduous forest and stream ecotone, aquatic insect emergence peaks in spring when terrestrial invertebrate biomass is low, while terrestrial invertebrate input to the stream occurs primarily in summer when aquatic invertebrate biomass is low. These reciprocal prey fluxes subsidize both forest birds and stream fishes, accounting for 25.6% and 44.0% of their annual energy budgets, respectively. Seasonal contrasts between allochthonous prey supply and in situ prey biomass determine the importance of reciprocal subsidies. A regional landscape is a heterogeneous collection of habitats with varying environmental properties. Despite apparent separation, local food webs can be tightly linked by energy flux across habitat interfaces. Across-habitat transfers of materials or organisms often exert critical influences on communities. Theoretical models suggest energy generally flows from more to less productive habitats, but empirical studies have mainly focused on one-sided subsidies. However, productivity in local habitats fluctuates seasonally, and peak productivities in juxtaposed habitats can be asynchronous. If these fluctuations reverse the productivity gradient and the direction of energy transfer, local communities in both habitats could be reciprocally subsidized. Reciprocal subsidies may be important between forest and streams in northern temperate latitudes, where temperature and light, two principal determinants of primary productivity, change dramatically with season. Forest and stream food webs are widely viewed as energetically coupled, with considerable edge-mediated effects. Inputs of particulate organic matter from riparian forests represent an important energy source of stream production. Accidental inputs of terrestrial invertebrates are known to be a major prey category directly available for stream consumers such as fish. Conversely, riparian forests generally support greater species diversity and population abundance of terrestrial consumers than adjacent upland habitats, although the mechanisms responsible for this edge effect have remained poorly understood. Riparian consumers, such as birds, bats, and spiders, may benefit from energy transfers gained from aquatic insects emerged from streams. Net flux direction, however, can change seasonally. In this study, field studies were conducted in a forest plot along the Horonai Stream in the Tomakomai Experimental Forest, Japan, from May 1997 to June 1998. The forest was dominated by deciduous tree species, and the stream had stable discharge. Consumers included insectivorous birds and salmonids. Prey abundance was surveyed in both the forest plot and stream reach every month. Terrestrial invertebrates on the foliage were collected quantitatively, and stream invertebrates were collected using a Surber net sampler. Across-habitat prey fluxes, including both the accidental inputs of terrestrial invertebrates to and the emergence of aquatic insects from the study reach, were simultaneously estimated. The annual contribution of allochthonous prey to the total energy budget was estimated for each assembl