Leaf litter quality affects aquatic insect emergence: contrasting patterns from two foundation trees

Reciprocal subsidies between rivers and terrestrial habitats are common where terrestrial leaf litter provides energy to aquatic invertebrates while emerging aquatic insects provide energy to terrestrial predators (e.g., birds, lizards, spiders). We examined how aquatic insect emergence changed seasonally with litter from two foundation riparian trees, whose litter often dominates riparian streams of the southwestern United States: Fremont (Populus fremontii) and narrowleaf (Populus angustifolia) cottonwood. P. fremontii litter is fast-decomposing and lower in defensive phytochemicals (i.e., condensed tannins, lignin) relative to P. angustifolia. We experimentally manipulated leaf litter from these two species by placing them in leaf enclosures with emergence traps attached in order to determine how leaf type influenced insect emergence. Contrary to our initial predictions, we found that packs with slow-decomposing leaves tended to support more emergent insects relative to packs with fast-decomposing leaves. Three findings emerged. Firstly, abundance (number of emerging insects m^?2 day^?1) was 25 % higher on narrowleaf compared to Fremont leaves for the spring but did not differ in the fall, demonstrating that leaf quality from two dominant trees of the same genus yielded different emergence patterns and that these patterns changed seasonally. Secondly, functional feeding groups of emerging insects differed between treatments and seasons. Specifically, in the spring collector-gatherer abundance and biomass were higher on narrowleaf leaves, whereas collector-filterer abundance and biomass were higher on Fremont leaves. Shredder abundance and biomass were higher on narrowleaf leaves in the fall. Thirdly, diversity (Shannon’s H′) was higher on Fremont leaves in the spring, but no differences were found in the fall, showing that fast-decomposing leaves can support a more diverse, complex emergent insect assemblage during certain times of the year. Collectively, these results challenge the notion that leaf quality is a simple function of decomposition, suggesting instead that aquatic insects benefit differentially from different leaf types, such that some use slow-decomposing litter for habitat and its temporal longevity and others utilize fast-decomposing litter with more immediate nutrient release.     

Strong land‐use effects on the dispersal patterns of adult stream insects: implications for transfers of aquatic subsidies to terrestrial consumers

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Increasing donor ecosystem productivity decreases terrestrial consumer reliance on a stream resource subsidy

Because nutrient enrichment can increase ecosystem productivity, it may enhance resource flows to adjacent ecosystems as organisms cross ecosystem boundaries and subsidize predators in recipient ecosystems. Here, we quantified the biomass and abundance of aquatic emergence and terrestrial spiders in a reference and treatment stream that had been continuously enriched with nitrogen and phosphorus for 5 years. Because we previously showed that enrichment increased secondary production of stream consumers, we predicted that aquatic emergence flux would be higher in the treatment stream, subsequently increasing the biomass and abundance of terrestrial spiders. Those increases were predicted to be greatest for spiders specializing on aquatic emergence subsidies (e.g., Tetragnathidae). By adding a ¹⁵N stable isotope tracer to both streams, we also quantified nitrogen flow from the stream into the riparian community. Emergence biomass, but not abundance, was higher in the treatment stream. The average body size of emerging adult insects and the relative dominance of Trichoptera adults were also greater in the treatment stream. However, spider biomass did not differ between streams. Spiders also exhibited substantially lower reliance on aquatic emergence nitrogen in the treatment stream. This reduced reliance likely resulted from shifts in the body size distributions and community composition of insect emergence that may have altered predator consumption efficiency in the treatment stream. Despite nutrient enrichment approximately doubling stream productivity and associated cross-ecosystem resource flows, the response of terrestrial predators depended more on the resource subsidy’s characteristics that affected the predator’s ability to capitalize on such increases.     

Longitudinal and seasonal pattern of insect emergence in alpine streams

Prevailing water sources and/or regional climate are known to have an important influence on hydromorphology and chemistry of high alpine streams, affecting biology and phenology of aquatic insects considerably. Seven reaches in two different stream types (glacial and non-glacial) in the European Central Alps were investigated along a longitudinal gradient above the tree line to elucidate community structure and emergence patterns of aquatic insects. Aquatic insect emergence was dominated by chironomid taxa in both streams (95.0% in the glacial vs. 90.5% in the spring-fed stream). Emergence rate was much higher in the non-glacial stream, with Chironomidae 638.9 ind. m⁻² d⁻¹ and EPT (Ephemeroptera, Plecoptera, Trichoptera) 20.3 ind. m⁻² d⁻¹ (annual mean), compared to the glacial stream (Chironomidae 132 ind. m⁻² d⁻¹ and EPT 7.0 ind. m⁻² d⁻¹). Whereas, in the glacial stream a richer and more diverse species composition was found at lower elevations, emergence rate and emerging taxa numbers were higher at higher altitude in the non-glacial stream. Seasonal comparisons also showed a significant difference between the two streams. In the glacial stream maximum emergence was in April/May, whereas, in the non-glacial stream in July. A comparison with similar studies carried out in alpine streams showed that abundance and biomass of emerging insects were relatively low in the glacial stream. The continuous emergence throughout the summer is another example of insect life-cycle adaptation to the harsh environmental conditions in glacial streams: most likely, emergence during the warmer summer months, where the probability of experiencing favourable climate conditions on land is higher than for the rest of the year, was an evolutionary advantage for many glacial stream taxa.     

Land‐use effects on terrestrial consumers through changed size structure of aquatic insects

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Leaf breakdown in streams differing in catchment land use

1. The impact of changes in land use on stream ecosystem function is poorly understood. We studied leaf breakdown, a fundamental process of stream ecosystems, in streams that represent a range of catchment land use in the Piedmont physiographic province of the south‐eastern United States. 2. We placed bags of chalk maple (Acer barbatum) leaves in similar‐sized streams in 12 catchments of differing dominant land use: four forested, three agricultural, two suburban and three urban catchments. We measured leaf mass, invertebrate abundance and fungal biomass in leaf bags over time. 3. Leaves decayed significantly faster in agricultural (0.0465 day^?1) and urban (0.0474 day^?1) streams than in suburban (0.0173 day^?1) and forested (0.0100 day^?1) streams. Additionally, breakdown rates in the agricultural and urban streams were among the fastest reported for deciduous leaves in any stream. Nutrient concentrations in agricultural streams were significantly higher than in any other land‐use type. Fungal biomass associated with leaves was significantly lower in urban streams; while shredder abundance in leaf bags was significantly higher in forested and agricultural streams than in suburban and urban streams. Storm runoff was significantly higher in urban and suburban catchments that had higher impervious surface cover than forested or agricultural catchments. 4. We propose that processes accelerating leaf breakdown in agricultural and urban streams were not the same: faster breakdown in agricultural streams was due to increased biological activity as a result of nutrient enrichment, whereas faster breakdown in urban streams was a result of physical fragmentation resulting from higher storm runoff.     

Adult aquatic insects: Potential contributors to riparian food webs in Australia's wet–dry tropics

Abstract Changes in the abundance and biomass of aquatic and terrestrial aerial insects with distance (mid‐stream, 0, 10–15 and 160 m) from lowland streams were examined across the dry season landscape in Kakadu National Park, northern Australia. Malaise traps and sticky intercept traps were used to sample the insects at four streams, spaced over an area of 1650 km². Malaise and intercept catches were dominated by Diptera (flies and midges), both numerically and by biomass. Chironomid midges were the most abundant taxon, making up 43.4 and 51.0% of the malaise and intercept trap catches, respectively. However, most chironomids were small (less than 3 mm body length), contributing 34.9% to intercept trap biomass, but only 5.2% in malaise traps. Ceratopogonid midges and caddisflies (Trichoptera) accounted for most of the remaining adult aquatic insects. Major terrestrial components were Diptera and Hymenoptera in malaise traps and Coleoptera and Diptera in intercept traps. The total abundance and biomass of insects were much greater over streams and along the water's edge than in riparian (10–15 m) and savanna (160 m) habitats primarily because of the presence of large numbers of adult aquatic insects. The abundance and biomass of terrestrial insects in malaise traps showed no relationship with distance, but intercept trap catches suggested slightly greater abundances over the water and at the water's edge. The great abundance of aquatic insects relative to terrestrial insects close to streams suggests that they have the potential to be an important component of the diets of riparian insectivores, and predation may be an important pathway by which aquatic nutrients and energy are moved into terrestrial food webs.     

Preliminary estimation of the export of omega-3 polyunsaturated fatty acids from aquatic to terrestrial ecosystems in biomes via emergent insects

Some terrestrial consumers may be limited by food quality, namely by contents of essential polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (20:5n−3, EPA) and docosahexaenoic acid (22:6n−3, DHA) in their food. Since EPA and DHA are mainly produced in aquatic ecosystems, for future estimating of the potential limitation by food quality in global scale, the water-land fluxes of these PUFA with the biomass of emergent aquatic insects in several biomes were calculated. The water /land area ratios for each biome were calculated by dividing the water area of each biome by its terrestrial area. Data on insect emergence from water bodies (g of dry mass m⁻² year⁻¹), were summarized and averaged for each biome. From available data, EPA and DHA contents (mg g⁻¹dry mass), in the biomass of emergent aquatic insects were calculated first so that annual fluxes of PUFA to land area via aquatic insect emergence could be estimated for each biome. PUFA fluxes occurred between the biomes, ranging from 0.04 to 4.39 mg m⁻² year⁻¹. In this study, the aquatic PUFA supply to land area appeared to be significantly lower than estimated earlier. This suggests that terrestrial consumers may experience food quality limitations mediated by shortage of PUFA compounds.     

Latitudinal patterns of aquatic insect emergence driven by climate

Aim

Emerging aquatic insects link aquatic and terrestrial ecosystems across the Earth. Their diversity, abundance and functional importance means their emergence is an important phenological event. Nevertheless, aquatic insect emergence is understudied at a global scale compared to other phenological events, despite changing phenology being one of the most significant ecological responses to climate change. Here, we quantitatively describe the global patterns, and key proposed drivers, of seasonal aquatic insect emergence, to further understand how these patterns might change in the future.

Location

Global.

Time Period

1950–2018.

Major Taxa Studied

Emerging aquatic insects.

Methods

We extracted monthly emergence data from 86 studies across 163 sites to construct 1053 annual emergence curves. We parameterized the curves using two complementary metrics of seasonality, which were modelled against geographical and climatic variables to determine the direct and indirect relationships between them.

Results

We found clear global trends in aquatic insect emergence patterns across latitude and underlying climates. Between-month variation and temporal restriction of emergence increased from the equator to the poles, going from small, aseasonal fluctuations in the warm, thermally stable tropics to large, seasonal peaks at cooler, thermally unstable higher latitudes. While emergence trends were associated with gradients of precipitation, temperature was the dominant climatic driver of the latitudinal trend.

Main Conclusions

These findings suggest that with climate warming, aquatic insects will emerge over longer periods, diluted in abundances and displaying less seasonal emergence patterns with smaller between-month fluctuations. This may result in disruption of ecosystem functions seasonally dependent on aquatic insects, such as riparian predation, pollination and disease transmission. The cross-ecosystem life cycle of aquatic insects means changes to their seasonal patterns of emergence will have impacts in both aquatic and terrestrial ecosystems.     

Shifts in reciprocal river‐riparian arthropod fluxes along an urban‐rural landscape gradient

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Emerging aquatic insects as predators in terrestrial systems across a gradient of stream temperature in North and South America

1. Empirical and theoretical research over the past decade has demonstrated the widespread importance of aquatic subsidies to terrestrial food webs. In particular, adult aquatic insects that emerge from streams and lakes are prey for terrestrial predators. While variation in the magnitude of this subsidy is clearly important, the potential top‐down effects of the predatory adults of some aquatic insects in terrestrial food webs are largely unknown. 2. I used published data on benthic insect density (as a proxy for emergence) in North and South America to explore how the proportion of benthic insects that are predatory as adults varies across a gradient of mean annual stream temperature. 3. The proportion of benthic insects that are predatory as adults varied widely across sites (0–12% by abundance; 0–86% by biomass). There was a positive relationship between mean annual stream temperature and the proportion of predatory adults across all sites, driven largely by the greater abundance/biomass of predatory taxa (e.g. odonates), relative to non‐predators (e.g. midges, mayflies, caddisflies), in tropical than in temperate streams. 4. The ‘trophic structure’ (i.e. the proportion of predators) of emerging adult aquatic insects is an understudied source of variation in aquatic–terrestrial interactions. Incorporation of trophic structure in future studies is needed to understand how future modification of fresh waters may affect adjacent terrestrial food webs through both bottom‐up and top‐down effects.     

Regional-Level Inputs of Emergent Aquatic Insects from Water to Land

Emergent aquatic insects can provide inputs to terrestrial ecosystems near lentic and lotic waterbodies, producing ecosystem linkages at the aquatic–terrestrial interface. Although aquatic insect emergence has been examined for individual sites, the magnitude and spatial distribution of this phenomenon has not been examined at regional spatial scales. Here, we characterize this cross-habitat linkage for the state of Wisconsin, USA (169,639 km²). We combined GIS hydrological data with empirical data and predictive models of aquatic insect production to estimate annual aquatic emergence for the state of Wisconsin. Total emergence (lentic + lotic) was estimated to be about 6,800 metric tons of C y^?1. Lentic systems comprised 79% of total estimated insect emergence, primarily due to the large amount of lake surface area relative to streams. This is due to both basic ecosystem geometry and the overall abundance of lakes in Wisconsin. Spatial variation was high: insect emergence in southwestern Wisconsin was dominated by streams, whereas for most of the rest of the state insect emergence was dominated by lakes. Lentic inputs to land were highly concentrated (relative to lotic inputs) because lakes have a high ratio of surface area to buffer area. Although less concentrated, the spatial extent of lotic influence was greater: statewide, four times more land area fell within the 100 m buffer zones of streams compared to lakes. Large waterbodies (almost all of which were lakes) were hotspots of insect emergence and input to land. Aquatic insect inputs exceed estimated terrestrial secondary production in 13% of buffer area, and by a factor of 100 or more adjacent to large lakes (>50,000 ha). The model sensitivity analysis showed that the simplifying assumptions and sources of potential error in the input variables had a minor impact on the overall results.     

Fluxes of terrestrial and aquatic carbon by emergent mosquitoes: a test of controls and implications for cross-ecosystem linkages

Adult aquatic insects are a common resource for many terrestrial predators, often considered to subsidize terrestrial food webs. However, larval aquatic insects themselves consume both aquatic primary producers and allochthonous terrestrial detritus, suggesting that adults could provide aquatic subsidy and/or recycled terrestrial energy to terrestrial consumers. Understanding the source of carbon (aquatic vs. terrestrial) driving aquatic insect emergence is important for predicting magnitude of emergence and effects on recipient food web dynamics; yet direct experimental tests of factors determining source are lacking. Here, we use Culex mosquitoes in experimental pools as an exemplar to test how variation in general factors common to aquatic systems (terrestrial plant inputs and light) may alter the source and amount of energy exported to terrestrial ecosystems in adult aquatic insects that rely on terrestrial resources as larvae. We found strong sequential effects of terrestrial plant inputs and light on aquatic insect oviposition, diet, and emergence of Culex mosquitoes. Ovipositing mosquitoes laid ~3 times more egg masses in high terrestrial input pools under low light conditions. This behavior increased adult emergence from pools under low light conditions; however, high input pools (which had the highest mosquito densities) showed low emergence rates due to density-dependent mortality. Mosquito diets consisted mainly of terrestrial resources (~70–90 %). As a result, the amount of aquatic carbon exported from pools by mosquitoes during the experiment was ~18 times higher from low versus high light pools, while exports of terrestrial carbon peaked from pools receiving intermediate levels of inputs (3–6 times higher) and low light (~6 times higher). Our results suggest that understanding the interplay among terrestrial plant inputs, light availability and biotic responses of aquatic insects may be key in predicting source and magnitude of emergence, and thus the strength and effects of aquatic–terrestrial linkages in freshwater systems.     

Growth and loss of distal tissue in blades of Lessonia nigrescens and Lessonia trabeculata (Laminariales)

Meristematic growth and loss of distal tissue from blades of two ecologically important species in the south-east Pacific, Lessonia nigrescens and Lessonia trabeculata, was evaluated during 1 year. Comparative growth was determined by a hole-punch method, loss of distal tissue from the blades was determined by subtracting final blade length (with loss) from expected blade lengths (without loss); growth and tissue loss were transformed to fresh biomass units for calculation of inter-algae differences. The results showed that blade elongation rate increased at the beginning of spring, and declined towards the end of summer, with mean values between 0.40 and 0.08 cm day⁻¹ for L. nigrescens, and 0.65–0.17 cm day⁻¹ for L. trabeculata. Loss of distal tissue varied seasonally when examined as length units for both species; with mean values between 0.24 and 0.10 cm day⁻¹ for L. nigrescens, and 0.51–0.25 cm day⁻¹ for L. trabeculata. Variations in fresh biomass units were only observed in Lessonia trabeculata, increasing in spring, with mean values to 0.13 g (fresh weight) day⁻¹. Annual growth and loss of distal tissue were higher in L. trabeculata (0.41 and 0.39 cm day⁻¹, respectively) than in L nigrescens (0.19 and 0.15 cm day⁻¹). When growth and tissue loss were considered as fresh biomass, monthly gains significantly outweighed loss of distal tissue in both species, but parallel results based on length data followed a different trend. L. trabeculata released about 50% of its growth biomass as particulate organic matter, while the comparative value for L. nigrescens was about 20%.     

Flow regime alters body size but not the use of aquatic subsidies in a riparian predatory arthropod

Alterations to river flow conditions have wide impacts on riparian organisms in terms of behavior and biomass. However, little is known about natural flood impacts on prey use and individual growth of riparian predators. Using stable carbon isotope analysis, we investigated flood impacts on aquatic-prey use and the size structure of an orb-web spider, Nephila clavata, during 3 years under different flood conditions in a black locust forest in the middle reaches of the Chikuma River. Large floods depressed aquatic-prey abundance, but did not affect terrestrial-prey abundance in the riparian forest. Consequently, spider growth was stunted after large floods. Spider body size was positively correlated with the body sizes of both aquatic and terrestrial insects in spider webs, where terrestrial insects were significantly larger than aquatic insects. The δ¹³C of aquatic insects was about 8‰ higher than that of terrestrial insects, and the δ¹³C of both insect groups did not vary significantly between months or among years. A negative relationship was found between body size and δ¹³C in spiders under different subsidies levels. Our results showed that flow regime altered spider growth through changes in aquatic subsidies level, but not aquatic-prey use by the spiders due to relative body sizes of predators and prey. Changes in relative body sizes of predator and prey may be an important factor in understanding nutrients, materials, and energy flows in aquatic and terrestrial linkages in the context of flow regime.     

High within-stream replication is needed to predict litter fluxes in wet–dry tropical streams

1. Streams draining forested landscapes are fuelled by terrestrial plant litter, which can be transported downstream or retained and broken down locally. However, fluxes of plant litter in streams can vary at multiple spatio-temporal scales, affecting the availability of this key resource in heterotrophic stream food webs.
2. To explore this question we quantified several processes related to litter dynamics (i.e. litter inputs, storage, losses by transport and losses by breakdown) by sampling litter at multiple sites in three streams of the Brazilian Cerrado biome (which has a tropical wet–dry climate) for 2 years. We assessed the relative contribution of different spatial (among and within streams) and temporal scales (annual, seasonal and monthly) to total variability of these processes (hereafter fluxes).
3. Spatial and temporal variability of fluxes were both high, but spatial variation was 1.67-fold greater than temporal variation (61 versus 37%, respectively), especially at the within-stream scale (50% overall); an exception was litterfall, which varied less spatially than temporally (24 versus 76%). Temporal variation of litter storage (and hence availability to consumers) was mostly seasonal and due to differences in net transport.
4. Inputs and transport were higher in the wet than the dry season (wet versus dry season, 1.45 versus 0.92 and 1.43 versus 0.06 g litter m⁻² day⁻¹), while breakdown was similar between both seasons (0.88 versus 0.94 g litter m⁻² day⁻¹). Storage (i.e. accumulation) rate was positive and negative in the dry and wet season, respectively, indicating that litter was stored in the dry season and exported in the wet season. The transitional dry–wet season showed the highest inputs, breakdown and storage (3.21, 1.63 g litter m⁻² day⁻¹ and 145 g litter m⁻²), while the wet–dry season showed lower inputs (as in the dry season), higher transport (as in the wet season) and lower breakdown and storage than the other seasons (0.93, 0.65, 0.31 g litter m⁻² day⁻¹ and 24 g litter m⁻²).
5. Our results underscore the role of variation in biophysical drivers of litter fluxes within streams (e.g. pool–riffle configuration, substrate features, biological communities), and suggest that high within-stream replication is necessary to study litter fluxes at larger scales and over time. The seasonal patterns suggested potential changes in litter dynamics under future climate scenarios in the tropics, including increased storage due to reduced transport in a drier climate.

     

Climate change modifies the size structure of assemblages of emerging aquatic insects

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Selective foraging on terrestrial invertebrates by rainbow trout in a forested headwater stream in northern Japan

The important contribution of terrestrial invertebrates to the energy budget of drift-foraging fishes has been well documented in many forested headwater streams. However, relatively little attention has been focused on the behavioral mechanisms behind such intensive exploitation. We tested for the hypothesis that active prey selection by fishes would be an important determinant of terrestrial invertebrates contribution to fish diets in a forested headwater stream in northern Japan. Rainbow trout, Oncorhynchus mykiss, were estimated to consume 57.12 mg m^–2 day^–1 (dry mass) terrestrial invertebrates, 77% of their total input (73.89 mg m^–2 day^–1), there being high selectivity for the former from stream drift. Both the falling input and drift of terrestrial invertebrates peaked at around dusk, decreasing dramatically toward midnight. In contrast, both aquatic insect adults and benthic invertebrates showed pronounced nocturnal drift. Because the prey consumption rates of rainbow trout were high at dawn and dusk, decreasing around midnight, the greater contribution of terrestrial invertebrates to trout diet was regarded as being partly influenced by the difference in diel periodicity of availability among prey categories. In addition, selectivity also depended upon differences in individual prey size among aquatic insect adults, and benthic and terrestrial invertebrates, the last category being largest in both the stream drift and the trout diets. We concluded that differences in both the timing of supplies and prey size among the three prey categories were the primary factors behind the selective foraging on terrestrial invertebrates by rainbow trout.     

Seasonal variation in the trophic structure of a spatial prey subsidy linking aquatic and terrestrial food webs: adult aquatic insects

Research over the past decade has established spatial resource subsidies as important determinants of food web dynamics. However, most empirical studies have considered the role of subsidies only in terms of magnitude, ignoring an important property of subsidies that may affect their impact in recipient food webs: the trophic structure of the subsidy relative to in situ resources. This may be especially important when subsidies are composed of organisms, as opposed to nutrient subsidies, because the trophic position of subsidy organisms may differ from in situ prey. I explored the relative magnitude and trophic structure of a cross-habitat prey subsidy, adult aquatic insects, in terrestrial habitats along three streams in the south–central United States. Overall, adult aquatic insects contributed more than one-third of potential insect prey abundance and biomass to the terrestrial habitat. This contribution peaked along a permanent spring stream, reaching as high as 94% of abundance and 86% of biomass in winter. Trophic structure of adult aquatic and terrestrial insects differed. Nearly all adult aquatic insects were non-consumers as adults, whereas all but one taxon of terrestrial insects were consumers. Such a difference created a strong relationship between the relative contribution of the prey subsidy and the trophic structure of the prey assemblage: as the proportion of adult aquatic insects increased, the proportion of consumers in the prey assemblage declined. Specific effects varied seasonally and with distance from the stream as the taxonomic composition of the subsidy changed, but general patterns were consistent. These findings show that adult aquatic insect subsidies to riparian food webs not only elevate prey availability, but also alter the trophic structure of the entire winged insect prey assemblage.     

Cascading Ecological Responses to an In‐Stream Restoration Project in a Midwestern River

River restoration projects are increasingly common, but assessments of ecological responses and overall success of the vast majority of efforts are lacking. Information on potential positive ecological effects of restoration efforts can be used to justify further projects and refine methods. We examined responses of multiple trophic levels, aquatic insects and riparian birds, to a series of rock weirs installed in an Illinois river to stabilize the channel. We quantified adult insect emergence and performed weekly point counts of birds in spring at four weir and four non‐weir (control) sites. Emerging insect abundance was higher at control sites, but species richness and diversity were higher at weir sites. Total insect emergence production did not differ between site types, but emergence production of larger‐bodied taxa was higher at weir sites. Ordinations and analysis of similarity indicated differences in insect and bird assemblages between site types. Birds showed a positive numerical response to large‐bodied emerging insects, and total bird abundance was higher at weir sites. Clutch size and feeding rates of a focal bird species, Prothonotaria citrea (Prothonotary Warbler), did not differ between sites, but the number of hatchlings and fledglings was higher at control sites. Molothrus ater (cowbird) parasitism was higher at weir sites, likely because of increased edge habitat associated with weir construction activities. Results show positive ecological impacts of in‐stream restoration and provide justification for further efforts. However, forest disturbance associated with construction could offset some benefits to some species, and thus refinements to procedures may be necessary.