Terrestrial Breeding Research Articles

Seabird inputs drive changes in Cladocera assemblages in freshwater ponds

Seabirds are biovectors that transport large concentrations of nutrients from their marine feeding areas to terrestrial breeding grounds. Here, we used subfossil cladoceran assemblages to assess if, and how, changes in the world’s largest colony of Leach’s Storm Petrels affected the structure of Cladocera assemblages over the past ~1700 years. Using sediment cores from four ponds impacted by Leach’s Storm-Petrel colonies on Baccalieu Island (NL, Canada), we observed a consistent transition in cladoceran assemblages from benthic/littoral to pelagic taxa in association with high seabird presence. This shift aligns with previously published limnological changes that tracked the growth of the colony. Compared to trends in sedimentary chlorophyll-a, pelagic cladoceran taxa lagged behind algal shifts driven by seabird activity. The main drivers of cladoceran assemblage shifts were likely alterations to the physical habitat structure and food availability driven by seabird inputs. Furthermore, deposition of calcium from seabirds may have also contributed to changing the composition of cladoceran communities. Our study provides information on food web shifts associated with seabird-driven eutrophication, which can be compared to future paleoecological studies.

Flexible oviposition behavior enabled the evolution of terrestrial reproduction

Among vertebrates, nearly all oviparous animals are considered to have either obligate aquatic or terrestrial oviposition, with eggs that are specialized for developing in those environments. The terrestrial environment has considerably more oxygen but is dry and thus presents both opportunities and challenges for developing embryos, particularly those adapted for aquatic development. Here, we present evidence from field experiments examining egg-laying behavior, egg size, and egg jelly function of 13 species of Central and South American treefrogs in the genus Dendropsophus, which demonstrates that flexible oviposition (individuals laying eggs both in and out of water) and eggs capable of both aquatic and terrestrial development are the likely factors which enable the transition from aquatic to terrestrial reproduction. Nearly half of the species we studied had previously undescribed degrees of flexible oviposition. Species with obligate terrestrial reproduction have larger eggs than species with aquatic reproduction, and species with flexible reproduction have eggs of intermediate sizes. Obligate terrestrial breeding frogs also have egg masses that absorb water more quickly than those with flexible oviposition. We also examined eight populations of a single species, Dendropsophus ebraccatus, and document substantial intraspecific variation in terrestrial oviposition; populations in rainy, stable climates lay fewer eggs in water than those in drier areas. However, no differences in egg size were found, supporting the idea that the behavioral component of oviposition evolves before other adaptations associated with obligate terrestrial reproduction. Collectively, these data demonstrate the key role that behavior can have in facilitating major evolutionary transitions.

Seabird transported contaminants are dispersed in island ecosystems

Seabirds are long-range transporters of nutrients and contaminants, linking marine feeding areas with terrestrial breeding and roosting sites. By depositing nutrient-rich guano, which acts as a fertiliser, seabirds can substantially influence the terrestrial environment in which they reside. However, increasing pollution of the marine environment has resulted in guano becoming similarly polluted. Here, we determined metal and metalloid concentrations (As, Cd, Cr, Cu, Hg, Pb) in Flesh-footed Shearwater (Ardenna carneipes) guano, soil, terrestrial flora, and primary consumers and used an ecological approach to assess whether the trace elements in guano were bioaccumulating and contaminating the surrounding environment. Concentrations in guano were higher than those of other Procellariiformes documented in the literature, which may be influenced by the high amounts of plastics that this species of shearwater ingests. Soil samples from shearwater colonies had significantly higher concentrations of all metals, except for Pb, than soils from control sites and formerly occupied areas. Concentrations in terrestrial primary producers and primary consumers were not as marked, and for many contaminants there was no significant difference observed across levels of ornithogenic input. We conclude that Flesh-footed Shearwaters are transporters of marine derived contaminants to the Lord Howe Island terrestrial environment.

When slow explorers are fast: Personality‐related differences in timing of migration in Red Knots (Calidris canutus)

The timing of migration varies significantly among individuals, even within populations sharing breeding sites. Consistent individual behavioural differences, known as personality traits, have been linked to variation in movement behaviour. However, little attention has been given to investigating whether personality traits can explain such variation in the timing of migration. We studied post‐breeding migration of Red Knots Calidris canutus islandica breeding in the High Arctic and wintering in European coastal areas. We captured Red Knots in the Dutch Wadden Sea, a main non‐breeding and moulting site, and assessed their exploration behaviour, a personality trait, before releasing them with colour‐rings. We first investigated whether arrival timing in marine areas was associated with exploration speed. Secondly, we asked whether slow explorers were more likely to fly non‐stop to the Wadden Sea compared with fast explorers, as faster explorers were expected to move more and visit more staging sites. To determine arrival timing in marine non‐breeding areas and non‐stop flights to the Wadden Sea, we analysed isotope signatures in blood samples collected after capture, as these differ between the terrestrial breeding grounds (arthropod diet) and marine non‐breeding and moulting sites (benthic invertebrate diet). Thirdly, we estimated arrival time in the Wadden Sea based on primary moult progress, allowing us to examine the relationship between arrival timing estimated from isotope values and the onset of moult. Our findings revealed that slower exploring Red Knots departed earlier from the breeding site and were more likely to fly non‐stop to the Wadden Sea than were faster exploring individuals. Arrival timing to marine areas as estimated from isotope analyses predicted arrival timing in the Wadden Sea (via moult progress) but this relationship exhibited significant variation, possibly due to individual differences in the use of staging sites en route. By migrating early, slower explorers can better outpace the aerial predators also arriving at the Wadden Sea moulting site and thereby reduce mortality risk due to predation.

A new cryptic species of terrestrial breeding frog of the Pristimantisdanae Group (Anura, Strabomantidae) from montane forests in Ayacucho, Peru.

Based on morphological and molecular characters, we describe a new species of terrestrial breeding frog of the Pristimantisdanae Group from montane forests of La Mar Province, Ayacucho Department in southern Peru, at elevations from 1200 to 2000 m a.s.l. The phylogenetic analysis, based on concatenated sequences of gene fragments of 16S rRNA, RAG1, COI and TYR suggests that the new species is a sister taxon of a clade that includes one undescribed species of Pristimantis from Cusco, Pristimantispharangobates and Pristimantisrhabdolaemus. The new species is most similar to P.rhabdolaemus, which differs by lacking scapular tubercules and by its smaller size (17.0-18.6 mm in males [n = 5], 20.8-25.2 mm in females [n = 5] in the new species vs. 22.8-26.3 mm in males [n = 19], 26.0-31.9 mm in females [n = 30] of P.rhabdolaemus). Additionally, we report the prevalence of Batrachochytriumdendrobatidis (Bd) in this species.

The transformation of river ecosystems caused by mining affects bird breeding in indigenous riparian habitats

Our study considered the excavation of sand and gravel, which modifies the landscapes of riparian ecosystems. It promotes the creation of water bodies with surrounding vegetation, but it also results in the loss of natural habitats.We investigated the species richness, composition, and abundance of aquatic and terrestrial breeding birds and their interaction with three habitat types: managed and abandoned flooded pits, and oxbow lakes. We surveyed 117 sites in medium-sized river valleys in the foreground of the Bohemian Massif (Czech Republic), and in the Carpathian Mountains (Poland, Slovakia) in 2022.Flooded pits were suitable for open-water and colonial birds. Managed flooded pits were also suitable for early successional land birds, but they did not provide habitat for birds that use marshes and wet meadows, or riparian woodlands. The majority of species preferred to breed in oxbow lakes with riparian forests and these areas hosted the highest number of threatened species.We concluded that high levels of disturbance in riparian ecosystems promoted some birds (e.g. colonial or breeding in early-successional habitats), but it negatively affected the overall bird diversity, and it led to a species composition shift with the elimination of taxa associated with indigenous riparian habitats. The importance of flooded pits increases with subsequent plant succession. Our results indicate that gravel or sand mine pits, although beneficial for some taxa, are not substitutes for natural habitats in riparian ecosystems, as they do not support birds breeding in indigenous riparian habitats. Natural oxbow lakes with riparian forests are habitats that need to be preserved to effectively promote local biodiversity.

Use of dead tree-fern trunks as oviposition sites by the terrestrial breeding frog Leiopelma archeyi

Use of dead tree-fern trunks as oviposition sites by the terrestrial breeding frog Leiopelma archeyi

Nearby large islands diminish biodiversity of the focal island by a negative target effect.

The Equilibrium Theory of Island Biogeography postulates that larger and closer islands support higher biodiversity through the dynamic balance of colonization and extinction processes. The negative diversity-isolation (i.e. the distance to the mainland) relationship is derived based on the assumption that the mainland is the only source pool for island biotas. However, nearby islands could also act as species sources for focal islands via a source effect. In this study, we move a further step and hypothesize that nearby islands may reduce bird colonizers of the focal island and diminish its biodiversity, resulting in a negative target effect. To test our hypothesis, we assessed the effects of island area and isolation (metrics considering both the mainland and nearby islands) on taxonomic (i.e. species richness), functional and phylogenetic diversity of terrestrial breeding birds on 42 islands in the largest archipelago of China, the Zhoushan Archipelago. Furthermore, we compared the predictive power of the distance to the large island under a set of relative area thresholds and the relative area of nearby islands on species richness under a set of distance thresholds to explore the role of nearby islands as a source and/or target island. We found that island area had a positive effect on species richness, phylogenetic diversity and functional diversity, while the distance to the mainland had a negative effect only on species richness. Species richness on the focal island increased with increasing distance to the nearest larger island, indicating the negative target effect. Furthermore, the negative target effect depended on the area of nearby islands relative to the area of the focal island. Our finding of the negative target effect suggests islands located between the mainland and the focal island can be not only sources or stepping stones, but also colonization targets. This result demonstrates the importance of considering multiple geographical attributes of islands in island biogeographic studies, especially the characteristics related to source and/or target effects.

Dissipation of seabird‐derived nutrients in a terrestrial insular trophic web

AbstractHighly mobile organisms can transport nutrients and energy among distinct ecosystems, such as between oceanic foraging areas and terrestrial breeding sites. Seabirds are great nutrient carriers and potentially play a key role in the maintenance of trophic webs on islands. In this study, we assessed three dimensions of marine nutrient dissipation—horizontal, temporal and vertical—on the tropical Meio Island of Fernando de Noronha Archipelago, Brazil. For this, C3 and C4 plants, ants and spiders found in a 100 m long transect between colonies of masked (Sula dactylatra) and red‐footed boobies (Sula sula) were sampled during the rainy (the masked booby breeding period) and dry seasons (the red‐footed booby breeding period). The marine contribution to the terrestrial trophic web was analysed using Bayesian mixing models from a carbon and nitrogen stable isotope data set. The main findings indicate that marine nutrients in the terrestrial trophic web dissipated horizontally as the distance from the colony increased, which was more marked during the rainy season. On the vertical axis, the relative contribution of marine nutrients in terrestrial consumers was strongly related to food habits but not necessarily to the trophic level, dissipating rather than increasing, due to variable omnivory and the use of terrestrial food sources. The breeding strategy of the masked booby (i.e. incubating eggs on the ground), in addition to a larger body size and larger colony, could produce a more concentrated pulse of nutrients in comparison to seabirds nesting sparsely on trees, contributing more efficiently to the enrichment of marine nutrients on land. The importance of seabirds for the maintenance of interconnected ecosystems has been demonstrated, and the role of marine‐derived nutrients in the enrichment of nutrient‐poor tropical islands.

The influence of seabirds on their breeding, roosting and nesting grounds: A systematic review and meta-analysis.

Seabird species world‐wide are integral to both marine and terrestrial environments, connecting the two systems by transporting vast quantities of marine‐derived nutrients and pollutants to terrestrial breeding, roosting and nesting grounds via the deposition of guano and other allochthonous inputs (e.g. eggs, feathers).We conducted a systematic review and meta‐analysis and provide insight into what types of nutrients and pollutants seabirds are transporting, the influence these subsidies are having on recipient environments, with a particular focus on soil, and what may happen if seabird populations decline.The addition of guano to colony soils increased nutrient levels compared to control soils for all seabirds studied, with cascading positive effects observed across a range of habitats. Deposited guano sometimes led to negative impacts, such as guanotrophication, or guano‐induced eutrophication, which was often observed where there was an excess of guano or in areas with high seabird densities.While the literature describing nutrients transported by seabirds is extensive, literature regarding pollutant transfer is comparatively limited, with a focus on toxic and bioaccumulative metals. Research on persistent organic pollutants and plastics transported by seabirds is likely to increase in coming years.Studies were limited geographically, with hotspots of research activity in a few locations, but data were lacking from large regions around the world. Studies were also limited to seabird species listed as Least Concern on the IUCN Red List. As seabird populations are impacted by multiple threats and steep declines have been observed for many species world‐wide, gaps in the literature are particularly concerning. The loss of seabirds will impact nutrient cycling at localized levels and potentially on a global scale as well, yet it is unknown what may truly happen to areas that rely on seabirds if these populations disappear.

Fluctuations in serum steroid hormone concentrations and body mass during growth and sexual maturation in captive northern fur seals (Callorhinus ursinus).

Northern fur seals (Callorhinus ursinus) have a distinct life history pattern comprising annual terrestrial breeding and oceanic migration, and the physiological changes associated with these patterns are of particular interest for understanding their environmental adaptations. However, owing to their oceanic distribution, limited information is available on the reproductive physiology of wild individuals during the immature stage and the winter migration period. This study aimed to determine the relationships among the seasonal hormone profiles, body growth, age, and pregnancy using monthly serum samples collected over 3–5 years from two male and two female captive individuals during pubescence and sexual maturation. Small increases in the serum testosterone signaled puberty in males aged 3 and 4 years. Thereafter, males showed considerable increases in testosterone during breeding seasons, indicating sexual maturity. Immature female serum progesterone was maintained at low levels, but after pubescence, females showed an increase in serum progesterone in August, the month next to the peak of delivery, followed by a decrease. In non-pregnant females, progesterone did not increase significantly until the next breeding season, but in pregnant females, they increased again from February to March and then gradually decreased. Immature males increased body mass constantly and reached puberty when their body mass exceeded 20 kg, and they showed seasonal weight fluctuations after puberty. These results provide fundamental information for determining sexual maturity and pregnancy in this species based on sex steroid hormones and body mass measurements.

Incorporating Geographical Scale and Multiple Environmental Factors to Delineate the Breeding Distribution of Sea Turtles

Temperature is often used to infer how climate influences wildlife distributions; yet, other parameters also contribute, separately and combined, with effects varying across geographical scales. Here, we used an unoccupied aircraft system to explore how environmental parameters affect the regional distribution of the terrestrial and marine breeding habitats of threatened loggerhead sea turtles (Caretta caretta). Surveys spanned four years and ~620 km coastline of western Greece, encompassing low (<10 nests/km) to high (100–500 nests/km) density nesting areas. We recorded 2395 tracks left by turtles on beaches and 1928 turtles occupying waters adjacent to these beaches. Variation in beach track and inwater turtle densities was explained by temperature, offshore prevailing wind, and physical marine and terrestrial factors combined. The highest beach-track densities (400 tracks/km) occurred on beaches with steep slopes and higher sand temperatures, sheltered from prevailing offshore winds. The highest inwater turtle densities (270 turtles/km) occurred over submerged sandbanks, with warmer sea temperatures associated with offshore wind. Most turtles (90%) occurred over nearshore submerged sandbanks within 10 km of beaches supporting the highest track densities, showing the strong linkage between optimal marine and terrestrial environments for breeding. Our findings demonstrate the utility of UASs in surveying marine megafauna and environmental data at large scales and the importance of integrating multiple factors in climate change models to predict species distributions.

Tadpoles' Resistance to Desiccation in Species of Leptodactylus (Anura, Leptodactylidae)

Desiccation may increase egg and tadpole mortality of anurans that reproduce in temporary ponds. Tadpoles of some species, however, can survive temporarily out of water. Among leptodactylids, desiccation-resistant tadpoles were reported only for species that use terrestrial foam nests for reproduction. To test whether Leptodactylus tadpoles' ability to survive out of water represents an exclusive trait of species with terrestrial nests, we compared survival and resistance to hydric stress of tadpoles of six different species of the Leptodactylus groups and one Physalaemus. We also present an exploratory discussion about the evolutionary association between dehydration-tolerant tadpoles, egg-laying microhabitat, and nitrogen excretion type. Tadpoles were divided into two groups, one staying in 100 mL of water and another subjected to hydric stress on moist paper substrate. Our results indicate that tadpoles resistant to desiccation are not common for all species tested, as only the species with terrestrial nests survived longer and lost less body mass than the other related species. As an estimate, tadpoles of terrestrial-nesting frogs were seven times more resistant to desiccation than those with eggs/nests placed directly into the water. A possible dehydration-resistance mechanism is the premetamorphosis ureotelism that has been shown in terrestrial breeding species with tadpoles that survive some time out of water. Therefore, the capacity of tadpoles to survive a few days after pool drying probably arose from the evolutionary association between terrestrial reproduction and the tadpole ability to prevent body dehydration by a mechanism such as ureotelism.

Conspecific attraction for conservation and management of terrestrial breeding birds: Current knowledge and future research directions

Abstract Conspecific presence can indicate the location or quality of resources, and animals settling near conspecifics often gain fitness benefits. This can result in adaptive conspecific attraction during breeding habitat selection as demonstrated in numerous terrestrial, territorial birds. There is growing interest in using simulated conspecific social cues (e.g., decoys, broadcasted vocalizations) to manage bird distributions, yet it remains unclear when this approach is likely to succeed. We reviewed published studies to evaluate whether the strength of conspecific attraction in terrestrial birds is mediated by characteristics of species (life history traits), simulated cues (e.g., timing and duration), sites (e.g., quality), and how conspecific attraction was measured. We identified 31 experiments that simulated social cues and compared conspecific settlement between treatment and control sites. We then used phylogenetically controlled meta-regression to assess the impacts of 19 moderators on settlement. Nearly all species included in these experiments were migratory passerines, and social cues generally had a strong, positive influence on their settlement decisions, as the odds of site occupancy were 3.12× (95% CI: 0.81–11.69) greater in treatment sites relative to control sites. Within this group, conspecific attraction was evolutionarily conserved with ≥25.5% (95% CI: 5.1%–65.4%) of the variance in treatment effects explained by phylogenetic relatedness. However, we found no evidence that any covariates influenced the response to social cues, and we posit this stems from limited research specifically designed to identify the mechanisms mediating conspecific attraction. We therefore developed a research agenda that provides a framework for testing mechanistic hypotheses regarding how cue characteristics, species traits, and spatial contexts may mediate attraction to conspecifics. Evaluating these hypotheses will greatly advance the field by helping managers understand when, where, and why simulating social cues can be used to enhance populations of species that are of conservation concern.

Geolocators link marine mercury with levels in wild seabirds throughout their annual cycle: Consequences for trans-ecosystem biotransport

Seabirds are widely used as indicators of marine pollution, including mercury (Hg), because they track contaminant levels across space and time. However, many seabirds are migratory, and it is difficult to understand the timing and location of their Hg accumulation. Seabirds may obtain Hg thousands of kilometers away, during their non-breeding period, and deposit that Hg into their terrestrial breeding colonies. We predicted that Hg concentration in rectrices reflects exposure during the previous breeding season, in body feathers reflects non-breeding exposure, and in blood collected during breeding reflects exposure during current breeding. To test this hypothesis, we measured total Hg concentration in these three tissues, which reflect different timepoints during the annual cycle of rhinoceros auklets (Cerorhinca monocerata) breeding on both sides of the North Pacific (Middleton Island in Alaska and Teuri Island in Hokkaido), and tracked their wintering movement patterns with biologging devices. We (i) identify the wintering patterns of both populations, (ii) examine Hg levels in different tissues representing exposure at different time periods, (iii) test how environmental Hg exposure during the non-breeding season affects bird contamination, and (iv) assess whether variation in Hg levels during the non-breeding season influences levels accumulated in terrestrial plants. Individuals from both populations followed a figure-eight looping migration pattern. We confirm the existence of a pathway from environmental Hg to plant roots via avian tissues, as Hg concentrations were higher in plants within the auklet colonies than at control sites. Hg concentrations of breast feathers were higher in Alaskan than in Japanese auklets, but Hg concentrations in rectrices and blood were similar. Moreover, we found evidence that tissues with different turnover rates could record local anthropogenic Hg emission rates of areas visited during winter. In conclusion, Hg was transported across thousands of kilometers by seabirds and transferred to local plants.

Small ponds support high terrestrial bird species richness in a Mediterranean semiarid region

Ponds are among the world’s most endangered freshwater ecosystems. A comprehensive knowledge of pond biodiversity is urgently required to inform effective pond management and conservation actions. Most studies about pond biodiversity focus on aquatic taxa, while the terrestrial biodiversity, especially of birds, has been little studied. Moreover, the few studies existing on pond biodiversity do not account for different detection rates of species, thus yielding biased results. Here, we apply a hierarchical Bayesian modelling technique to data obtained from visual censuses to estimate bird species richness associated with small ponds in a semiarid region, considering the imperfect detection of species. The model incorporates specific responses to site characteristics (pond typology), landscape (environmental heterogeneity) and at regional scale (mean annual precipitation). The studied ponds were used by two thirds of the terrestrial breeding bird community of the study region. Our modelling approach increased by an average of 7.5 species the observed site-specific richness. Drinking troughs supported a greater richness than other pond types. Environmental heterogeneity was positively related with species richness, whereas no clear relation was observed between richness and precipitation. In addition to ecosystem services provided by ponds to human welfare, our results suggest these small isolated habitats may act as key landscape elements for terrestrial birds in semiarid regions.

Sex differences in response to environmental and social breeding cues in an amphibian

Abstract The relative influence of climatic and social factors on sex-specific variation in reproductive behaviour remains poorly understood. Here, we examine the influence of multiple climatic cues in combination with a social cue on the reproductive behaviours of males and females in a terrestrial breeding toadlet (Pseudophryne coriacea). Over a 115-day breeding season, arrival patterns of each sex, and male calling activity, were recorded daily, while climatic variables were logged continuously. Multivariate analysis showed that arrival of males at the breeding site, as well as male nightly calling activity, were most strongly influenced by a climatic variable (rainfall). By contrast, female arrival was strongly correlated with a social variable (male calling activity), with abiotic conditions having no influence, other than a moderate influence of lunar phase (lunar illumination). These results suggest that cues used for breeding are sex specific and provide new evidence that combinations of climatic and social cues can be integrated into breeding decisions.

Nest site selection in a terrestrial breeding frog: interrelationships between nest moisture, pH and male advertisement

In resource defence mating systems where males control nest sites, complex interrelationships between nest characteristics and nest advertisement are likely to influence female mate choice. Surprisingly, however, we know little about the influence of such relationships on female mating decisions. In terrestrial-breeding oviparous species, one character likely to have a major influence on female nest site selection is nest moisture. In addition to influencing the susceptibility of eggs to desiccation, nest moisture also stands to influence nest pH and offspring fitness, as well as the hydration state of resident males, and their potential to advertise. Together, such interrelationships could strongly influence female mating decisions. The aim of this study was to use a long-term field study combined with a multivariate approach to investigate the combined influence of nest moisture, nest pH and male acoustic advertisement on female nest site selection in a wild population of red-backed toadlets, Pseudophryne coriacea. We found that females deposited more eggs in wetter and less acidic nests, and that these variables were positively correlated. Moreover, nest moisture and pH in combination were positively related to the calling potential of resident males, and nests that were advertised more often received more eggs. These results suggest that nest site selection in red-backed toadlets is influenced by a complex interplay between covarying nest characteristics that together influence male sexual signalling and nest advertisement. More broadly our findings highlight the potential for nesting behaviour to be mechanistically intertwined with mate choice.

Marine subsidies mediate patterns in avian island biogeography

The classical theory of island biogeography, which predicts species richness using island area and isolation, has been expanded to include contributions from marine subsidies, i.e. subsidized island biogeography (SIB) theory. We tested the effects of marine subsidies on species diversity and population density on productive temperate islands, evaluating SIB predictions previously untested at comparable scales and subsidy levels. We found that the diversity of terrestrial breeding bird communities on 91 small islands (approx. 0.0001–3 km2) along the Central Coast of British Columbia, Canada were correlated most strongly with island area, but also with marine subsidies. Species richness increased and population density decreased with island area, but isolation had no measurable influence. Species richness was negatively correlated with marine subsidy, measured as forest-edge soil δ15N. Density, however, was higher on islands with higher marine subsidy, and a negative interaction between area and subsidy indicates that this effect is stronger on smaller islands, offering some support for SIB. Our study emphasizes how subsidies from the sea can shape diversity patterns on islands and can even exceed the importance of isolation in determining species richness and densities of terrestrial biota.

Male-male competition and repeated evolution of terrestrial breeding in Atlantic Coastal Forest frogs.

Terrestrial breeding is a derived condition in frogs, with multiple transitions from an aquatic ancestor. Shifts in reproductive mode often involve changes in habitat use, and these are typically associated with diversification in body plans, with repeated transitions imposing similar selective pressures. We examine the diversification of reproductive modes, male and female body sizes, and sexual size dimorphism (SSD) in the Neotropical frog genera Cycloramphus and Zachaenus, both endemic to the Atlantic rainforest of Brazil. Species in this clade either breed in rocky streams (saxicolous) or in terrestrial environments, allowing us to investigate reproductive habitat shifts. We constructed a multilocus molecular phylogeny and inferred evolutionary histories of reproductive habitats, body sizes, and SSD. The common ancestor was small, saxicolous, and had low SSD. Terrestrial breeding evolved independently three times and we found a significant association between reproductive habitat and SSD, with shifts to terrestrial breeding evolving in correlation with decreases in male body size, but not female body size. Terrestrial breeding increases the availability of breeding sites and results in concealment of amplexus, egg-laying, and parental care, therefore reducing male-male competition at all stages of reproduction. We conclude that correlated evolution of terrestrial reproduction and small males is due to release from intense male-male competition that is typical of exposed saxicolous breeding.