Availability Of Nest Sites Research Articles

Woodpecker excavations suitability for and occupancy by cavity users in the boreal mixedwood forest of eastern Canada

In the boreal forest, where tree cavities are mainly excavated by woodpeckers, many holes are incomplete excavations that are not suitable cavities for most other cavity users that form nest webs. We assessed cavity suitability for and use by a community of primary excavators and secondary users in managed and unmanaged landscapes in the boreal mixedwood forest of eastern Canada. We compared ground surveys of tree holes with direct inspections of the inside of potential cavities in remnant habitats surrounded by cutover areas and in large tracts of unharvested forest. We found that ground surveys overestimated suitable cavity abundance: only 38% of the potential cavities detected by ground surveys were suitable for nesting in both managed and unmanaged landscapes. Ground surveys of active nests correctly detected a greater proportion of primary (93%) than secondary cavity nesters (48%). In nest webs such as those of the boreal forest, where cavities are mainly created by woodpeckers, our results indicate that a large proportion of holes detected from the ground are not suitable for cavity nesters, thus overestimating the actual availability of nest sites. Furthermore, when nest cavities are active, ground surveys are satisfactory for detecting primary cavity nesters, but they are inadequate for detecting secondary cavity nesters.

Decision making in burrowing birds: Sediment properties in conflict with biological variables

Distribution and properties of loess deposits were recently suggested to drive the presence of burrowing birds: sand martins Riparia riparia, European bee-eaters Merops apiaster, and kingfishers Alcedo spp. Packing density with very low CN (such as those of loess) was suggested to be the most suitable for sand martins and bee-eaters. Correlating the distribution range of particular sediments with nesting areas of the particular burrowing bird species is a great argument in a recent discussion on whether the availability of nest sites is limiting or not. However, biological variables should be also taken into account. Each of the particular species tends to occupy its own ecological niche, avoiding direct competition for space, food, or other resources. Tight adherence to loessic slopes would severely limit two of the three Central European burrowing bird species in their distribution range, even though they are physiologically adapted to utilize a broader range of nest bank substrates. While the European bee-eaters (and perhaps most of the other bee-eater species) are limited to the fine-grained loess and silt, the other two species utilize broader textural range requiring either sufficiently high penetration resistance (Eurasian kingfisher Alcedo atthis) or digging nest holes of limited cross-sectional area (sand martins).

Long‐term change of ant community structure in cacao agroforestry landscapes in Indonesia

Abstract Land‐use change and agricultural intensification can strongly affect biodiversity in agricultural landscapes. Although many studies investigate management impacts, data on the long‐term change of species communities in agroecosystems are scarce. We analysed the long‐term change in diversity and composition of ant communities in cacao agroforestry systems in Central Sulawesi, Indonesia and attempted to disentangle the driving factors of this change. Ant communities were resampled in 2009 from sites for which previous surveys had been conducted either in 2001 (the rainforest‐poor Palolo region) or 2003 (the rainforest‐rich Kulawi region) using insecticide fogging. Ant community composition changed significantly over time in Palolo and Kulawi. The change in ant species richness differed between regions. Species richness increased in Kulawi, probably due to the increasing availability of nest sites and microhabitats as trees grow larger and older. In the Palolo region, species richness decreased, suggesting that the high local intensification and landscape‐wide changes may have counteracted the effects of tree age. Changes in ant communities over time were significant, but were more difficult to explain than expected, despite clear difference in management changes within and between regions. The findings suggest that the landscape‐scale differences between the two study regions play a more important role for species diversity and its composition than changes in local management. This highlights the importance of long‐term studies across contrasting landscapes for better understanding the consequences land‐use intensification has on tropical biodiversity.

Roadway mortality of barn owls in Idaho, USA

AbstractWe examined the temporal, spatial, and demographic factors that influenced roadway mortality of barn owls (Tyto alba) along a 248‐km stretch of Interstate 84 in southern Idaho using systematic road surveys. Counts of dead animals from surveys can be underestimated because of sampling biases; therefore, we also conducted experiments to assess the effects of search and removal bias on the estimates of roadway mortality of owls. We conducted surveys every 2 weeks over a 2‐year period and detected 812 dead barn owls (unadjusted mortality rate of 1.64 owls/km/yr). After adjusting this estimate for search and removal bias, we documented mortality rates of up to 5.99 owls/km/year. Owl mortality was not random in relation to sex, age class, or location along the highway. Females and juveniles, which represent individuals more likely to disperse long distances, were killed more frequently than males and adults. During the nonbreeding season, owls were killed more often near agricultural lands than in shrub‐steppe, but this pattern was not apparent during the breeding season. Owls were also killed more often on portions of the roadway closer to the Snake River canyon, perhaps because of the availability of nest and roost sites. Mortality rates differed markedly between the 2 years of study, which could have been related to variability in weather and its subsequent effect on owl productivity. Our data suggest that barn owls in this region may not persist under this level of mortality without significant immigration or management. Thus, roadway management to reduce or prevent owl use of roadways, reduce rodent populations near major roads, alert motorists to the presence of owls, or otherwise reduce the chances that vehicles and owls collide would improve barn owl survival and population persistence. © 2012 The Wildlife Society.

Provisioning habitat with custom‐designed nest‐boxes increases reproductive success in an endangered finch

AbstractManipulating resource availability to assess the strength and effects of resource limitation on an animal population is relatively straightforward, and thus, common in the scientific literature. Resource quality, however, is rarely manipulated, as this requiresa prioriknowledge of a relationship between some measurable variation in the resource and individual preference and/or fitness. Recent research on nest‐site selection was used to inform the design of custom‐built nest‐boxes for an endangered hollow‐nester, the Gouldian finch (Erythrura gouldiae). By provisioning breeding populations with these ‘high quality’ artificial nest sites over 3 years, we experimentally investigated the strength and effects of nest‐site limitation in this species. Breeding pairs using nest‐boxes initiated nesting earlier, produced larger clutches and fledged more offspring per season than those in natural hollows. Total and mean reproductive output also increased in nest‐box provisioned sites over the duration of the study. All of these effects were predominantly driven by pairs initiating clutches earlier, potentially because of the reduced intra‐ and interspecific competition for nest sites at optimal breeding times. Our findings suggest that reproduction in wild Gouldian finch populations may be limited by the availability of high quality nest sites in the landscape, and that nest‐boxes could be used as a tool for enhancing reproduction in recovering populations. Furthermore, we conclude that resource quality is equally, if not more important than quantity when supplementing resource‐limited habitats.

Responses to experimental reduction and increase of cavities by a secondary cavity-nesting bird community in cavity-rich Pyrenean oak forests

Cavity shortage limits secondary cavity-nesting birds (SCN) assemblages in intensively-managed forests with few cavities, but whether cavity availability limits SCN in cavity-rich forests remains unclear. To address this issue, we used a replicated before-after-control-impact design in which the availability of cavities was experimentally reduced and increased in cavity-rich Quercus pyrenaica forests. Cavity-blocking and nest-box addition led to reduction by 66% and increase by 185%, respectively, of nest densities of blue (Cyanistes caeruleus) and great (Parus major) tits. Analysis of cavity characteristics suggests that tits occupied less suitable cavities in blocking plots compared to control and nest-box addition plots after treatments, further indicating that the availability of suitable nest-sites may limit tit populations. No effect of cavity manipulation was found for short-toed treecreepers (Certhia brachydactyla) and Eurasian nuthatches (Sitta europaea), which defend larger territories than tits and whose numbers may be more influenced by territoriality than by nest-sites. Alternatively, high plasticity in nest-site use of treecreepers may enable them to cope with reductions in cavity availability and increased interspecific competition. Spotless starlings (Sturnus unicolor) were little affected by cavity manipulation. Often foraging on pastures, starlings may be more limited through reduced foraging opportunities in this forested landscape than by nest-sites. In addition, starlings may exclude other species from their preferred cavities to cope with reductions in numbers of suitable cavities. Community responses to the variation in cavity abundance in cavity-rich Pyrenean oak forests may therefore vary considerably among species, depending on their plasticity in nest-site use, behavioral dominance, foraging conditions or social structure. Thus, management actions aimed to increase cavity abundance and suitability for SCN communities in cavity-rich forests should consider inter-specific interactions and species-specific characteristics of the targeted species.

Avian predators as a biological control system of common vole (Microtus arvalis) populations in north‐western Spain: experimental set‐up and preliminary results

Ecologically based rodent pest management using biological control has never been evaluated for vole plagues in Europe, although it has been successfully tested in other systems. The authors report on the first large-scale replicated experiment to study the usefulness of nest-box installation for increasing the breeding density of common kestrels (Falco tinnunculus) and barn owls (Tyto alba) as a potential biological control of common vole (Microtus arvalis) abundance in agricultural habitats in north-western Spain. The results show that: (1) population density of both predator species increased in response to both nest-site availability and vole density; (2) voles are a major prey for the common kestrels during the breeding period; (3) vole density during the increase phase of a population cycle may be reduced in crop fields near nest boxes. The installation of nest boxes provides nesting sites for barn owls and kestrels. Kestrel populations increased faster than in areas without artificial nests, and the common vole was one of their main prey during the breeding season. The results suggest that local (field) effects could be found in terms of reduced vole density. If so, this could be an environmentally friendly and cheap vole control technique to be considered on a larger scale.

Relating Microclimate to Epiphyte Availability: Edge Effects on Nesting Habitat Availability for the Marbled Murrelet

Industrial timber harvesting typically creates forest edges with altered microclimate regimes, causing reduced growth and survival of some canopy epiphytes. This process has implications for the marbled murrelet (Brachyramphus marmoratus), a threatened seabird that nests on moss platforms in old-growth forests of the coastal Pacific Northwest in North America. We investigated microclimate and epiphyte availability in old-growth forests of southwestern British Columbia, Canada. We contrasted mean and maximum temperature, mean humidity, mean vapor pressure deficit (VPD) and mean epiphyte cover and platform tree density between forest edge and interior plots at hard edges (recent clearcuts), soft edges (regenerating forest) and natural edges (rivers and avalanche chutes). Differences measured in VPD and epiphyte availability varied due to edge proximity and edge-type. Hard edges had fewer trees with suitable marbled murrelet nest platforms relative to adjacent interiors, and hard-edged patches had the lowest epiphyte cover overall. This suggests that microclimate edge effects and substrate availability can negatively impact epiphyte growth and survival, and may reduce the availability of marbled murrelet nest sites. These negative effects may decrease with time as forests regenerate, as edge effects were lower in magnitude at soft-edged patches. In contrast, natural-edged patches had the greatest levels of epiphyte cover and platform tree density, suggesting that these areas provide an abundant source of potential nest sites. Minimizing the ratio of anthropogenic edge to suitable interior habitat, and maintaining natural edges will limit negative edge effects on moss availability and provide nesting habitat for marbled murrelets.

Restoration of Nontarget Species: Bee Communities and Pollination Function in Riparian Forests

Nontarget species such as pollinators may be of great importance to the restoration process and the long‐term functioning of restored habitats, but little is known about how such groups respond to habitat restoration. I surveyed bee communities at five equal‐aged restored sites, paired with five reference sites (riparian remnants) along the Sacramento River, California, United States. Flower availability and bee visitation patterns were also measured to examine the restoration of pollination function. Restoration of structural vegetation allowed diverse and abundant native bee communities to establish at the restoration sites; however, the composition of these important pollinator communities was distinct from that in the remnant riparian sites. Differences did not arise primarily from differences in the composition of the flowering‐plant community; rather there must be other physical characteristics of the restored sites or differences in nesting site availability that led to the different pollinator communities. Because sites were spatially paired, the differences are unlikely to be driven by landscape context. Bee life‐history and other biological traits may partially explain the differences between bee communities at restored and remnant sites. Patterns of visitation to native plant species suggest that pollination function is restored along with pollinator abundance and richness; however, function may be less robust in restored habitats. An examination of interaction networks between bees and plant species found at both restored and remnant riparian sites showed less redundancy of pollinators visiting some plants at restored habitats.

Assessing the efficacy of artificial domiciles for bumblebees

Bumblebees have suffered declines as a result of reduction in habitat availability associated with agricultural intensification. Although several conservation strategies for bumblebees address forage availability, other aspects of bumblebee ecology are often ignored. Availability of sufficient nest sites is a key requirement of bumblebee populations and since nesting habitat is likely to have become reduced on intensively farmed land, lower nest site availability may contribute to bumblebee declines. The use of artificial domiciles for bumblebees has been proposed as a potentially useful tool for conservation and for improving pollination services for crops, providing a method of boosting nest site availability where it is otherwise limiting. Here, six different artificial domiciles for bumblebees are trialled in different habitats in southern England and central Scotland. Of these, only one domicile design at one particular site achieved reasonable uptake rates, whilst all other combinations of domicile and site achieved low success. Overall, only 23 of 736 domiciles deployed were occupied by bumblebees (3.1%). Based on current knowledge, attempts to use domiciles for conservation or research in the UK are likely to be ineffective. Commercially available domiciles for bumblebees performed poorly in these trials and the implications of these findings for manufacturers are discussed.

Plasticity in reproductive behaviour in two populations of the peacock blenny

Summary In the peacock blenny (Salaria pavo) the reproductive behaviour is described to vary between two populations that differ in nest availability. At the Gulf of Trieste (GT), Italy, where nest availability is high, conventional sex roles are present and males adopting an alternative parasitic reproductive tactic are rare. Conversely, at Ria Formosa (RF), Portugal, where nest site availability is low, females are the courting sex and a high percentage of parasitic males occur. Laboratory experiments were used to study the degree of plasticity of the reproductive behaviours used by females and by the two male morphs in both populations. Nesting males were sequentially presented with a female and a female-like parasitic male and the reproductive behaviours of all fish were quantified. Under similar laboratory conditions, nesting males from both populations did not differ in sexual or agonistic displays towards females or parasitic males, showing that males from the sex-reversed population are also able to express significant levels of courtship. In contrast, females followed the typical population pattern, with females from RF courting nesting males more and more readily than females from GT. We hypothesised that apparent differences in behavioural plasticity between nesting males and females were a consequence of the perception of the presence of eggs in the nest. Nesting males from both populations received an empty nest during test trials and, thus, had to court females in order to receive a first spawn. On the other hand, females were probably unaware of the presence or absence of eggs when presented to the nesting male and assumed the population typical courtship profile. Interestingly, the parasitic males’ behaviour towards

Is there enough habitat for reintroduced populations of the Lesser Kestrel? A case study in eastern Spain

SummaryThe Lesser Kestrel Falco naumanni is one of the most endangered birds in Europe. Spanish populations have suffered large declines and disappeared from large areas of former distribution, thus leading to many reintroduction programmes. One of the main factors that could affect the population growth of reintroduced populations is the availability of suitable habitat for breeding and foraging. We investigated whether nest site availability is a limiting factor for a newly established population of Lesser Kestrels in eastern Spain. We developed univariate models to understand the relationship between building characteristics (area, height, roof condition, etc.) and occupancy and abundance of Lesser Kestrels, and multivariate models to predict the availability of nest-sites. Our results showed that the species selected medium-sized buildings with extensive land use in the surrounding area and an absence of trees. In addition, Lesser Kestrel abundance was explained by roof condition and distance to the nearest building. Multivariate models predicted that most of the buildings were not suitable for nesting by Lesser Kestrels and thus population growth may be limited due to lack of nest sites. Lack of suitable nest sites, conspecific attraction and Allee effects are all processes that may be limiting, resulting in the low population and colony sizes that were found and predicted. Based on this, we recommend the provision of nest boxes, the use of special tiles and the construction of breeding towers to improve building quality and therefore increase colony size. We also critically question the use of reintroduction projects to restore locally extinct populations for two reasons. First in this case the reintroduced population is near some larger colonies and there is a strong tendency for Lesser Kestrels to move from small to large colonies. Secondly, in a general strategy for the conservation of Lesser Kestrels, conservation of the main colonies is the priority rather than dedicating human and economic resources on manipulative actions for the establishment of new colonies.

Social information in nest colonisation and occupancy in a long-lived, solitary breeding bird

Recent work increasingly reveals the importance of social information in individual dispersal decisions, population dynamics and conservation. Much of the knowledge gained to date comes from studies on short-lived and/or densely breeding species. In contrast, our understanding of the processes involved in nest-site selection for long-lived, solitary breeding species is insufficient. We increased nest-site availability by nest-box supplementation over a 5-year period in a population of a long-lived, solitary, secondary-cavity nesting bird, the European roller Coracias garrulus, breeding in natural cavities and human constructions. We tested the nest limitation and the inadvertent conspecific social information hypothesis in order to study the dynamics and mechanisms of abandonment of previously used nests and the colonisation of new ones. Our data lend support to the nest-limitation hypothesis both in terms of quantity-population and the size of breeding clusters increased, and suitability--the majority of pairs used and re-occupied nest-boxes. Nevertheless, the use of natural cavities did not decrease after 5 years. At the between-patch scale, rollers were revealed to colonise nest-boxes based on conspecific social attraction, namely distance to the nearest neighbour in the same season. Despite the unpredictability of patch productivity, at the within--patch scale, the selection of previously unoccupied cavities was consistent with the performance-based conspecific attraction hypothesis. Philopatry could account for the repeated use of cavities, because nests that were used for two successive years were more likely to also be reused in the subsequent season.

The value of agri‐environment schemes for macro‐invertebrate feeders: hedgehogs on arable farms in Britain

AbstractAgri‐environment schemes have been introduced in countries throughout the world in an attempt to reverse the negative impacts of agricultural intensification on biodiversity and the environment. There have been some investigations into the effectiveness of such schemes, which show mixed outcomes but little is known with regard to mammals. The hedgehog is a generalist predator and preys on, among others, an array of macro‐invertebrates, prey important for many other taxa. For a non‐volant species, it is highly mobile in the environment and should thus be less susceptible to negative effects of habitat fragmentation caused by agricultural intensification. However, it has recently been included in the UK Biodiversity Action Plan, as a result of evidence of a significant decline. We studied the importance of agri‐environment schemes for hedgehogs using radio‐tracking on arable farms. Both agri‐environment field margins and hedgerows appear to be very valuable for hedgehogs. Both habitat types were intensively utilized by hedgehogs; higher food availability/accessibility on agri‐environment field margins and higher food or nest site availability along edges and/or lower predation risk by badgers in arable areas may explain these preferences. Badger predation of hedgehogs was high in the study site and the main cause of death. Our study emphasizes the importance of natural habitat in an agricultural landscape and shows that agri‐environment schemes can be beneficial to this generalist macro‐invertebrate feeder. The implementation of agri‐environment schemes that include wide field margins and dense, well‐established hedgerows on farmland could significantly contribute to the viability of hedgehog populations in intensive arable‐farming landscapes, and by implication benefit other macro‐invertebrate feeders.

The influence of nest availability on the abundance and diversity of twig-dwelling ants in a Papua New Guinea forest

Tropical ant communities are frequently diverse, but highly patchy in nature. The availability of suitable nest sites may be a regulating force in structuring litter ant communities. Our aim was to examine ant resource utilization in naturally occurring twigs, and to modify the availability of these resources in order to quantify the influence of nest availability on ant communities in a Papua New Guinean forest. First, we compared ant communities that assemble in artificial twigs (drilled, wooden dowels), naturally occurring twigs, and the leaf litter. A total of 55 ant species were captured: 33 from the leaf litter, 29 from naturally occurring twigs, and only 12 from artificial nests. Significantly different communities formed in each of the three nest types. Second, we examined how the density of natural or artificial nest material influenced the ant abundance and species richness. Plots had between 5 and 96 potential nest sites. An average of only 11.2% of these twigs was colonized. Both species richness and the total abundance of adult ants were significantly positively correlated with increasing naturally occurring twig density. Conversely, increasing the availability of artificial nests from 5 to 20 per plot had no significant effect on the proportion of artificial nests colonized, species richness, or the colony size. We observed that ant species richness and abundance increased with natural twig density, at least for naturally occurring communities. But why so many twigs remain vacant and available for ant colonization remains unknown. Other biotic and abiotic factors likely influence the use of nesting habitat in these ant communities.

Differential Fledgling Production for Tree Swallows Using Nest Boxes in Two Artificial and Seemingly Different Environments in Western Washington

(Tsuga mertensiana) zone (Smith and others 1997). Other habitat descriptions for Washington, Oregon, and California emphasize the close association of nesting with freshwater (Verner and Boss 1980; Csuti and others 2001; Wahl and others 2005). Local populations of Tree Swallow appear to be limited by the availability of nest sites, which makes the use of nest boxes a means to augment populations by providing more nesting opportunities (Holroyd 1975). I installed and monitored nest boxes at 2 sites in western Washington to determine if a wetland constructed to

Nest-Site Limitation of Secondary Cavity-Nesting Birds in Even-Age Southern Pine Forests

I used a randomized, replicated, controlled study design to test the hypothesis that nest-site availability limits breeding densities of secondary cavity nesting species in even-age southern pine (Pinus spp.) forests. Breeding densities of secondary cavity nesters increased significantly on treated plots after nest boxes were introduced. Total number of nesting attempts also increased several fold post-treatment. These data indicate nest-site availability was a limiting factor for breeding densities of secondary cavity nesting species. The response of individual species to nest boxes ranged from moderately high (Great Crested Flycatcher [Myiarchus crinitus]), to low (Tufted Titmouse [Baeolophus bicolor], Eastern Bluebird [Sialia sialis]) to no response (Carolina Wren [Thryothorus ludovicianus]). At least three factors accounted for interspecific differences in this study: different levels of reliance on cavities excavated in snags, different body sizes, and differences in local population densities. The large number of unoccupied nest boxes (only 9% were used for nesting) suggests secondary cavity nesters were not limited solely by cavity availability but also by habitat quality. Prescribed burning appeared to facilitate discovery and use of nest boxes by birds in this study, consistent with the hypothesis that nest-site limitation is mitigated by habitat structure.

Spatial Ecology of Northern Map Turtles (Graptemys geographica) in a Lotic and a Lentic Habitat

Lentic (i.e., lake) and lotic (i.e., river) environments differ in several biotic and abiotic variables such as water velocity, productivity, thermal regimes, and depth. These variables can interact with important factors such as sex, body size, and life-history stage to shape the spatial ecology of aquatic animals such as freshwater turtles. We used radio-telemetry to study seasonal movement patterns and home-range size of juvenile and adult Northern Map Turtles (Graptemys geographica) both in a small lake and in a large river in eastern Ontario, Canada. Adult females in the lotic environment moved longer distances and had larger home ranges than conspecifics from the lentic environment. Males and juvenile females at each site had similar patterns of space use. A seasonal effect on movement was only apparent for adult females in the lotic environment in which adult females moved longer distances during the nesting season. Differences in swimming abilities resulting from a larger body size, in natal homing, or in nest site availability are potential factors explaining the site difference in the spatial ecology of adult females. Our findings illustrate the complexity of interactions shaping patterns of space use by aquatic reptiles.

Influence of fish-farming management on duck breeding in French fish pond systems

Fish ponds host a relatively important share of the breeding population of waterfowl in Europe. The objective of this study was to investigate the influence of fish-farming management on the distribution of dabbling and diving duck breeding, in 103 fishponds from four regions important for duck breeding in France. Duck breeding in fish ponds was apparently influenced by food resource and nesting site availability. Dabbling duck pair density was generally higher when invertebrates were abundant in macrophytes beds and when competition for food with carps Cyprinus carpio was potentially decreased by lower fish stock biomass. Diving duck pair abundance seemed to be negatively influenced by low invertebrates biomasses in pond sediment and by the absence of large reed beds at the edge of waterbodies. The difference between dabbling and diving ducks was also confirmed by a study of the variation in brood numbers standardized by pair numbers. This brood:pair ratio corresponded to a measure of nesting success and the possible attraction of fish ponds for some broods hatched in neighbouring waterbodies. Dabbling duck brood:pair ratio was lower in one of the study regions where most of meadow areas surrounding fish ponds have been transformed into cereal crops in the past few decades. Diving duck brood:pair ratio was positively linked to pond fertilization due to fish farming. Fish farming, therefore, influenced duck breeding by an interaction between carp density and fertilization. We hypothesize that fertilization increases zooplankton density, thereby decreasing the competition between carps and waterfowl for benthic prey.

Environmental modulation of androgen levels and secondary sex characters in two populations of the peacock blenny Salaria pavo

Morphology and endocrinology were studied in two populations of the peacock blenny Salaria pavo, with different regimes of sexual selection imposed by differences in nest site availability. The peacock blenny is a small, sexually dimorphic benthic fish that presents exclusive paternal care of the clutch and inhabits rocky shores of the Mediterranean and adjacent Atlantic areas. In a population from the Gulf of Trieste (Northern Adriatic sea) inhabiting rocky shores where nest sites are abundant, male–male competition for nests is low, males court females and a low frequency of alternative reproductive tactics (small, parasitic female-mimicking sneaker males that change tactic into nest holders in subsequent breeding seasons) occurs. Conversely at Ria Formosa, a coastal lagoon in Southern Portugal, where nest sites are scarce and highly aggregated, male–male competition for nests is very high, there is sex-role reversal with female courtship and a high frequency of alternative reproductive tactics is observed. Concomitantly, at Ria Formosa nest holder males are larger and present more developed secondary sex characters and higher levels of 11KT than at the Gulf of Trieste. However, the gonads of nest holders and parasitic males were larger in the Gulf of Trieste population. Competition for nests at Ria Formosa seems to promote more developed secondary sex characters in nest site scarcity conditions, while competition for females at the Gulf of Trieste seems to be spurring sperm competition among males in populations where nest sites are more abundant. 11KT was thus associated with the development and expression of secondary sex characters in contrasting environments. These results exemplify how the modulation of behavioral plasticity and secondary sex characters by the social environment can be mediated by androgens.