Site Tenacity Research Articles

Aspects of Breeding Performance of Scopoli’s Shearwater (Calonectris diomedea): The Case of the Largest Colony in Greece

Here we report, for the first time, aspects of the breeding performance of Scopoli’s Shearwater (Calonectris diomedea) in one of its largest colonies in Europe, i.e., in the Strofades island group. We describe the chronology of the main events in the breeding cycle of this species on Stamfani Island, the largest island of this island group, including the evaluation of breeding performance and the influence of ecological factors (nesting habitat, nest type, nest-entrance orientation, and occupation rate per nest) on breeding success. The Scopoli’s Shearwater colony of Stamfani Island exhibited a high degree of breeding synchrony and nest site tenacity. The data obtained by monitoring 472 nests during five consecutive years (2008–2012), showed a breeding success (fledging per occupied nest per year) of up to 66.6%. In addition, hatching success (chick hatched successfully per egg laid) was 76.9%, and fledging success (fledging young per chick hatched successfully) was 86.8%. We also observed annual variations in breeding performance during that period. These results seemed to be influenced positively by the breeding experience of the pair. Furthermore, the type of nest site and the nest-entrance orientation were found to have an effect on breeding success rates, whereas the nesting habitat did not, indicating low predation risk by rats.

Dear territory or dear partner? Causes and consequences of breeding dispersal in a highly territorial bird of prey with a strong pair bond

Territorial species are unlikely to show extensive movements between breeding seasons. This is especially true for long-lived species, which often have strong pair bonding and can occupy the same territory for years. However, also in such species, individuals may face situations that can lead to a territory shift. Here, we use a comprehensive dataset documenting 40 years of breeding behavior in tawny owl (Strix aluco) – a long-lived species with high site tenacity and mate fidelity – to examine the factors affecting the decisions whether or not to move to another breeding territory and how far, as well as the fitness consequences thereof. We found that the likelihood and distance of movement in either sexes is strongly associated with a change of partner, indicating that mate loss may cause breeding dispersal. Moreover, mate change, not movement to a new territory, had negative effects on subsequent reproductive performance: individuals that changed partner were more likely to skip reproduction in the subsequent year and, in those cases they bred, they produced smaller clutches and raised fewer offspring. Our findings indicate that tawny owls change territory almost exclusively when searching for a new partner and that mate change has profound consequences on their subsequent breeding performance. Overall, our study provides evidence that in tawny owls territoriality and monogamy are associated and strongly linked to fitness, but mate fidelity may be more important than site fidelity, likely because sexes are involved in specific tasks and their cooperation ensures breeding success and, consequently, increases fitness.Significance statementBreeding dispersal, the movement of individuals between breeding sites, can entail high costs for animal fitness, especially for territorial species, which display strong site fidelity. We studied the factors associated with breeding dispersal and the consequences on breeding performances in tawny owl (Strix aluco), a highly territorial species. We found that tawny owls moved more frequently to another breeding territory when the mate died. Either sexes showed an equal probability to move, but the effect was stronger in females than in males after a mate change. Moreover, owls that changed partner showed delayed reproduction, smaller clutch and a higher probability to skip reproduction. Our findings show that in tawny owls territoriality and monogamy are associated and strongly linked to fitness, but mate fidelity may be more important than site fidelity, likely because sexes share the costs of holding the territory.

Birds and the Fire Cycle in a Resilient Mediterranean Forest: Is There Any Baseline?

This study investigates the effects of recurrent wildfires on the resilience of a typical Mediterranean ecosystem. It is based on uninterrupted monitoring over 42 years of the avifauna in a cork oak forest that burned three times during this time interval. The monitoring involved two line-transect counts in spring accompanied by the simultaneous and independent estimation of the vegetation cover profile. One of the two transects was initially designed to serve as an unburned control before it also burned during the second fire. Many forest bird species were already present from the first spring postfire due to the rapid regeneration of the canopy. Some open-habitat bird species colonized the burned area during the first 2–4 years after the fire, resulting in an initial phase of high diversity. The postfire bird succession was mainly driven by sedentary species that recolonized the burned area after the first winter, whereas most migratory species present before the fire resettled as early as the first postfire spring, probably because of site tenacity. It was found that the impact of the second fire on avifauna was lower than that of the first or third fire. The return to an avifauna and forest structure successionally equivalent to the prefire control was achieved in about 15 years, which can be considered as the recovery time. Afterwards, both vegetation and avifauna in the burned areas tended to take on more forest characteristics than in the prefire control. These findings suggest that: (i) the recurrence of fire does not necessarily result in the cumulative degradation of the ecosystem at each repetition; (ii) the asymptotic resilience model is not adapted to the case of disturbances in non-mature environments; (iii) the notion of returning to an original undisturbed baseline is illusive in an area that has been under continuous human influence since ancient times.

Night Capture of Roosting Cave Birds by Neanderthals: An Actualistic Approach

Evidence is accumulating on the regular and systematic Neanderthal exploitation of birds. However, the motivations, mechanisms, and circumstances underlying this behavior remains little explored despite their potential implications on Neanderthal ecology and capabilities. Fossil remains of choughs (Pyrrhocorax, Corvidae) are among the most abundant in cave sites with Mousterian technology. We reviewed the evidence showing that Neanderthals processed choughs for food, and confirmed that it occurred frequently over a widespread spatial and temporal scale. This lead us to propose the hypothesis that the cave-like refuge is the keystone resource connecting Neanderthals and choughs captured at night in rocky shelters eventually used by both species. By adopting an actualistic approach, we documented the patterns of refuge use and population dynamics of communally roosting choughs, the strategies and technology currently used to capture them, and their behavioral response against experimental human predators at night. Actualistic experiments showed that large numbers of choughs can be captured without highly sophisticated tools at night regularly and periodically, due to their occupation year-round during long-term periods of the same nocturnal shelters, the constant turnover of individuals, and their high site tenacity at these roost-sites even after recurrent disturbance and predation. Captures even with bare hands are further facilitated because choughs tend to flee confused into the cavity in darkness when dazzled and cornered by human (experimental) predators. Given the extreme difficulty of daylight chough capturing in open country, nocturnal hunting with the help of fire in the roosting caves and consumption in situ are proposed as the most plausible explanations for the strong association of choughs and Neanderthals in fossil assemblages. Night hunting of birds has implications for the social, anatomical, technological, and cognitive capacities of Neanderthals.

Experimental playback of natural gas compressor noise reduces incubation time and hatching success in two secondary cavity-nesting bird species

Abstract Natural gas compressor stations emit loud, low-frequency noise that travels hundreds of meters into undisturbed habitat. We used experimental playback of natural gas compressor noise to determine whether and how noise influenced settlement decisions and reproductive output as well as when in the nesting cycle birds were most affected by compressor noise. We established 80 nest boxes to attract Eastern Bluebirds (Sialia sialis) and Tree Swallows (Tachycineta bicolor) to locations where they had not previously nested and experimentally introduced shale gas compressor noise to half the boxes while the other 40 boxes served as controls. Our experimental design allowed us to control for the confounding effects of both physical changes to the environment associated with compressor stations as well as site tenacity or the tendency for birds to return to the specific locations where they had previously bred. We incorporated behavioral observations with video cameras placed within boxes to determine how changes in behavior might lead to any noted changes in fitness. Neither species demonstrated a preference for box type (quiet or noisy), and there was no difference in clutch size between box types. In both species, we observed a reduction in incubation time, hatching success, and fledging success (proportion of all eggs that fledged) between quiet and noisy boxes but no difference in provisioning rates. Nest success (probability of fledging at least one young; calculated from all nests that were initiated) was not affected by noise in either species suggesting that noise did not increase rates of either depredation or abandonment but instead negatively impacted fitness through reduced hatching and fledging success. Compressor noise caused behavioral changes that led to reduced reproductive success; for Eastern Bluebirds and Tree Swallows, gas infrastructure can create an equal-preference ecological trap where birds do not distinguish between lower and higher quality territories even when they incur fitness costs.

Relating beta diversity of birds and butterflies in the Great Basin to spatial resolution, environmental variables and trait‐based groups

AbstractAimWe sought to characterize spatial and temporal beta diversity of birds and butterflies in the Great Basin (western U.S.A.) and to determine whether the magnitude of beta diversity was associated with spatial resolution, trait‐based groups or local environmental variables.LocationCentral and western Great Basin, western U.S.A.Time period1995–2014.Major taxa studiedBirds and butterflies.MethodsWe calculated temporal and spatial beta diversity of birds and butterflies at two spatial resolutions, points (birds) or transects (butterflies) and canyons (birds and butterflies). Points and transects corresponded to the spatial resolution of sampling, whereas canyons might be a more ecologically meaningful resolution. We partitioned beta diversity into turnover and nestedness components, and we calculated these components for entire assemblages and for trait‐based groups within assemblages. We used Bayesian hierarchical models to relate turnover and nestedness to spatial resolution, trait‐based groups and environmental variables.ResultsVariation in the composition of bird and butterfly assemblages was primarily associated with turnover. Species composition was more consistent at the resolution of canyons than at finer spatial resolutions. The species composition of birds changed more through space than through time, and spatial turnover of bird species tended to be higher than that of butterfly species. There were few strong associations of turnover and nestedness with environmental variables, and none with trait‐based groups.Main conclusionsOur results suggest that the identities of bird and butterfly species vary at locations within canyons among years but are less variable among canyons. Decreases in temporal turnover as spatial resolution increases suggest that, at fine spatial resolutions and among years, bird and butterfly species in the Great Basin might acquire resources somewhat opportunistically rather than via strong interspecific competition (birds and butterflies) or site tenacity to breeding territories (birds).

Consequences of natal philopatry for reproductive success and mate choice in an Alpine rodent

Quantifying the interaction between dispersal, kinship, and genetic structure can provide insights into the factors that shape kin-structured mammal societies. Here, we first employ a combination of 8 years of capture–mark–recapture and molecular data to characterize the spatial and genetic relationships among female snow voles (Chionomys nivalis) in a population located in the Swiss Alps. Subsequently, we examine the individual-level consequences of kin structure in terms of fitness and mating patterns. Behavioral data, relatedness estimates, and spatial autocorrelation analyses indicate that females show strong philopatry, with spatially clustered females being characterized by high levels of genetic relatedness, leading to significant small-scale (<30 m) spatial genetic structure (SGS). In line with selection favoring female philopatry, dispersing females had a lower fitness compared with philopatric individuals. However, we found a negative association between female reproductive success and the number of neighboring females. This suggests that female kin clustering does not constitute an adaptive strategy in this species, but rather that site tenacity is a by-product of the costs of dispersal. Although dispersal is frequently invoked as a means to avoid inbreeding, our results provide no evidence for premating inbreeding avoidance, which is in line with previous studies on mammals. Instead, in the majority of years, we observed that pairs were more-closely related than expected by chance. However, we found that both males and females with related partners had reduced reproductive success, suggesting the existence of inbreeding depression and/or postmating inbreeding avoidance mechanisms. On the whole, our results show how quantification of SGS within populations can provide insights into individual dispersal behavior and its fitness consequences, and into the ways in which social and genetic structure interacts to shape the evolution of free-living populations.

Dispersal in an extensive continuous forest habitat: Marsh Tit Poecile palustris in the Białowieża National Park

Dispersal is one of the least understood features in the life-history of organisms. Theoretical work concentrates on explaining dispersal of organisms in patchy and heterogeneous landscapes, but there are few predictions of dispersal patterns in stable, spatially extensive and largely homogenous landscapes, such as large forests. It is expected that we should observe short-distance dispersal in such places, that, to avoid competition with parents and siblings and incestuous mating, offspring should leave natal patches (natal dispersal), disperse independently in different directions, and move over distances that efficiently minimise the probability of meeting a sibling. Breeding dispersal should be very limited, site tenacity should prevail. To explore these ideas, I use observations of Marsh Tits Poecile palustris (a small passerine specialist of mature forests) made in the strictly protected part of the Bialowieza National Park (Poland) over 21 years. The birds largely followed expectations: all fledglings left their natal territories and dispersed in different directions, and males moved shorter distances than females (median = 570 vs. 1,720 m). Apart from this difference, no influence of population density, fledgling time or family size was observed. No parent–offspring pairing occurred, with just one case of sibling–sibling pairing. After first breeding, individuals remained site-tenacious, as breeding dispersal distances were very short (median ca. 100 m). Such behaviour renders Marsh Tit poorly adapted to cross barriers and undertake long-distance movements, and this is actually observed in fragmented landscapes. Understanding dispersal patterns of organisms from extensive environments would be thus of value for basic and conservation science alike.

Aggregation and site tenacity under downed logs in Salamandrella keyserlingii (Caudata: Hynobiidae)

Darhadyn Wetland, Mongolia, is located in a subarctic steppe–tundra climate, where salamanders are exposed to both extremely hot and cold environments. We hypothesized that log refugia provide an adaptive advantage to salamanders in these environments because the habitat availability hypothesis predicts that restricted habitat availability can cause aggregation that plays a role in the initial stages of the evolution of complex sociality. To test this hypothesis, we assessed whether a rare salamander species aggregated under a limited shelter resource. Many small vertebrates use terrestrial burrow refuges. While many salamander species also use burrows, Salamandrella keyserlingii at Darhadyn used only downed log refuges (i.e., restricted habitat availability). Some individuals displayed site tenacity to remain under a specific log, and one or more of the same individuals were located continually or frequently under the same logs. The majority of recapture events (96.8 %, 121/125) did not show any movements of salamanders between logs. Of the 300 capture events, 66 % were aggregating. The maximum number of individuals sharing a log refuge on the same day (i.e., sharing group size) ranged from 2 to 9. Individuals were resident nonrandomly in downed log refuges, i.e., an aggregation pattern was nonrandom. Based on these findings, we provided conservation measures such that total number of individuals captured per log over the course of the study (maximum number = 32) had a positive relationship to 1 of 7 explanatory variables (i.e., log decaying class in ascending order). Thus, the retention of decaying downed logs is important for the conservation of this species.

Genetic Structure, Diversity and Subspecies Status of Gull-billed Terns (Gelochelidon nilotica) from the United States

Gull-billed Terns (Gelochelidon nilotica) are among the most widespread, yet scarce, Charadriiformes in the world. Two subspecies are recognized in the United States: G. n. aranea breeds along the U.S. Atlantic and Gulf coasts and G. n. vanrossemi breeds in the Salton Sea and San Diego Bay of California. Conservation concerns exist for the species due to its low abundance in the United States and apparent declines in some parts of its North American range. We used nuclear microsatellite markers and mitochondrial DNA sequences to assess genetic diversity and differentiation patterns among Gull-billed Tern populations from Virginia, Texas, and California. We also tested for evidence of population bottlenecks, and evaluated the support our data provide for the North American subspecies. Genetic diversity was highest in Texas and underscored the importance of habitat in that large population. Significant population differentiation existed, but could not be consistently identified using various analytical approaches and suggested that the magnitude of differentiation was low. No evidence for bottlenecks was identified. Our data could not distinguish individuals from different subspecies and therefore do not support the current intraspecific taxonomy. Tenable explanations for many findings are related to the low site tenacity demonstrated by the species.

Movement and home range of introduced Nile perch (Lates niloticus) in Lake Nabugabo, Uganda: Implications for ecological divergence and fisheries management

Nile perch (Lates niloticus) was introduced to the Lake Victoria basin in the 1950s and 1960s and eventually became one of the most valuable commercial species of East Africa's inland fisheries. Intense fishing-induced mortality may be contributing to dramatic ecological change in this species (reductions in body size and catch rate) and reinforcing patterns of ecological divergence in some lakes in the region. We used radio telemetry to characterize Nile perch movement and home range size in Lake Nabugabo, Uganda and quantified patterns of habitat selection by Nile perch in the heavily-fished near-shore areas of this system. Nile perch exhibited high site tenacity with daily movement averaging ∼400m/day and home range size averaging 0.83km2. Body size and water temperature were both important predictors of Nile perch movement patterns. In the near-shore area of the lake, Nile perch selected regions characterized by low temperature and high oxygen conditions, and tended to prefer forest edge over wetland edge. The level of site tenacity exhibited by Nile perch suggests that ecological isolation between fish using forest and wetland ecotones may be higher than expected. These results also have important implications for development of territorial jurisdiction by Beach Management Units, the decentralized structure of fisheries management in the region.

Temporal influence on foraging strategies, territoriality and nomadic tendencies of Snail Kite, Rosthramus sociabilis (Viellot, 1817) in an urban Neotropical wetland

The foraging, territoriality and displacement of the Snail Kite were studied over 232 hours of observations in an urban lake during the dry and wet seasons. The temperature and rainfall variations were used to correlate with predation rates and the correlation coefficients were 0,39 and 0,34, respectively. Snail Kites spent more time foraging during the wet than the dry season when perching is more frequently recorded. The higher predation in the wet season can be explained by the higher abundance of apple snails and the energy demand for reproduction. In the wet season, the territories were smaller and the conspecific conflicts decreased as prey were more available. However, due to the lack of food in the dry season, intra-specific conflicts and expansion of male territories were observed and the female and immatures were expelled from their foraging area to another location. In this way, site tenacity of Snail Kites should be interpreted in relation to the variations on food and dominance gradients according to the temporal changes (time) and foraging sites (space).

Dispersal Versus Site Tenacity of Adult and Juvenile Red-Backed Salamanders (Plethodon cinereus)

In many species of amphibians that display territoriality, it is unclear at what life stage and to what extent dispersal occurs. We examined whether differences existed between life stages in dispersal and homing in red-backed salamanders (Plethodon cinereus) in continuous habitat. In a mark-recapture study, we found that juvenile and adult movements between years were not significantly different. The median distances moved by both adults (0.85-0.88 m) and juveniles (1.14-1.22 m) of P. cinereus between years were similar to the diameter of adult home ranges in this area (1.15 m). In a homing experiment, we found that, although the probability of recapture of translocated individuals under their original cover object increased with body size, both adults and juveniles successfully orientated toward their original cover objects when displaced over short distances (1.5 m and 6.25 m), but their orientation was random when displaced long distances (12.5 m and 25 m). Despite the current assumption that juveniles of P. cinereus lack territorial behaviors, our results suggest that regardless of life stage, site tenacity accounts for lack of movements. TERRITORIALITY can be defined as the defense and advertisement of an area by an animal with the goal of exclusive occupancy (Wilson, 1975). Maintenance of a territory and the site fidelity associated with such mainte- nance can be energetically expensive because they limit time available for other activities

Movement behaviour of a forest songbird in an urbanized landscape: the relative importance of patch-level effects and body condition during migratory stopover

With expansion of urban areas worldwide, migrating songbirds increasingly encounter fragmented landscapes where habitat patches are embedded in an urban matrix, yet how migrating birds respond to urbanization is poorly understood. Our research evaluated the relative importance of patch-level effects and body condition to movement behaviour of songbirds during migratory stopover within an urban landscape. We experimentally relocated 91 migrant Swainson’s thrushes (Catharus ustulatus) fitted with 0.66 g radio-transmitters to seven forest patches that differed in area (0.7–38.4 ha) and degree of urbanization within central Ohio, USA, May 2004–2007. Fine-scale movement rate of thrushes (n = 55) did not differ among urban forest sites, but birds in low energetic condition moved at higher rates, indicating an energetically mediated influence on movement behaviour. In larger sites, Swainson’s thrushes (n = 59) had greater coarse-level movement during the first 3 days and utilized areas farther from forest edge, indicating stronger influence by patch-level factors. Thrushes exhibited strong site tenacity, with only five individuals (7%) leaving release patches prior to migratory departure. Movement outside the release patch only occurred at the smallest forest patches (0.7 and 4.5 ha), suggesting that these sites were too small to meet needs of some individuals. Swainson’s thrushes exhibited edge avoidance and apparent area sensitivity within urban forest patches during stopover, implying that conservation of larger patches within urban and other fragmented landscapes may benefit this species and other migrant forest birds.

Evolution of defences against cuckoo (Cuculus canorus) parasitism in bramblings (Fringilla montifringilla): a comparison of four populations in Fennoscandia

The brood parasitic common cuckoo Cuculus canorus has a history of coevolution that involves numerous passerine hosts, but today only a subset is known to be regularly parasitised in any area. In some hosts, there is significant variation in the occurrence of parasitism between populations, but still individuals in non-parasitised populations show strong antiparasite defences. In the present study we compared the strength of egg rejection of four distant Fennoscandian brambling Fringilla montifringilla populations experiencing different levels of cuckoo parasitism (0–6%). Egg rejection ability was in general very well developed and we did not find any population differences in the relationship between egg rejection probability and similarity between host and experimental parasitic eggs. Furthermore, bramblings very rarely made errors in rejection, indicating that selection against rejection behaviour is likely to be very weak. The brambling-cuckoo system therefore differs from other well studied systems which are characterised by pronounced spatial and temporal variation in the host’s level of defence. This result is unlikely to reflect independent replication of the same evolutionary trajectory because the weak breeding site tenacity of bramblings should result in an extreme amount of gene flow within the distribution area and thus strongly impede localised responses to selection. Instead, lack of geographic variation has more likely arisen because bramblings respond to selection as one evolutionary unit, and because the average parasitism pressures have been high enough in the past to cause regional fixation of rejection alleles and evolution of clutch characteristics that facilitate cost free egg recognition.

Cohabitation patterns of the San Marcos salamander (Eurycea nana)

AbstractSocial interactions of conspecifics are a function of complex relationships involving resource defense, antipredatory tactics, and mate acquisition. Consequently, individuals often associate non-randomly with conspecifics in their habitats, with spatial distributions of adults ranging from territorial spacing to aggregations. Site tenacity and cohabitation patterns have been well studied in many species of terrestrial salamander; however, less is understood about these behaviors in aquatic species. We examined the cohabitation patterns of intrasexual and intersexual pairs of the federally threatened, paedomorphic San Marcos salamander (Eurycea nana) under artificial shelters in a laboratory setting over a 20-day period. We found that intrasexual female pairs and intersexual pairs were found cohabiting more often than intrasexual male pairs. We also assessed site tenacity by examining shelter affinity and found that both males and females inhabited one of the two shelters more often than expected from random habitation, regardless of whether they were in intersexual or intrasexual pairings. Our results indicate that although both sexes of Eurycea nana exhibit site affinity, the sex of individuals is an important determinant of cohabitation patterns.

Home-Range Size and Site Tenacity of Overwintering Le Conte's Sparrows in a Fire Managed Prairie

We evaluated home-range size and site tenacity of Le Conte's Sparrows (Ammodramus lecontii) during winter 2002–2003 at Brazoria National Wildlife Refuge, Texas. Twenty-six wintering Le Conte's Sparrows were radiomarked in 1- and 2-year post-burn units, and monitored for ∼10 days. Additionally, 1-ha plots on each 1-, 2- and 3-year (n = 15) post-burn units were flush-netted once monthly. Telemetry results indicated Le Conte's Sparrows were sedentary during winter with a 50% probability mean home-range of 2.41 ha (72% < 1 ha) and a 95% probability mean home range of 10.31 ha (44% < 1 ha and 55% < 1.5 ha). Home-range size did not differ between post-burn year 1 and 2 (P = 0.227). Le Conte's Sparrows appeared to exhibit a behavioral response to flush-netting (P < 0.001) with estimated capture probability of 0.462 and recapture probability of 0.056. Our findings suggest Le Conte's Sparrows remain fairly sedentary throughout the winter.

Movements of Alpine newts (Mesotriton alpestris) between small aquatic habitats (ruts) during the breeding season

AbstractMany species with complex life cycles, such as caudate amphibians, migrate from terrestrial to aquatic habitats for reproduction. However, movements between reproductive ponds within a breeding season have rarely been studied and are usually considered to be limited. Our aim was to determine whether this pattern occurs frequently in Alpine newts (Mesotriton alpestris) inhabiting complexes of small ruts on muddy forest tracks. We analysed capture-recapture data for individually marked newts as a function of locality, sex, body condition and hydroperiod throughout the breeding season. More than one third of the newts changed their ruts. Movements occurred more often towards ruts that did not dry during the breeding season. The body condition of males that changed ponds (but not that of females) was higher compared to that of resident newts in one of the studied populations. The relatively high frequency of movements between ruts can be seen as an adaptive strategy in unpredictable habitats which have a high probability of drying. The promiscuous pattern of newts also favours low site tenacity, because few sexual partners are available in each rut. Because of the broad occurrence of this kind of habitat, future studies should take into account these movements to better understand newt population dynamics and how to apply adequate conservation measures.

Tenacity and silk investment of two orb weavers: considerations about diversification of the Araneoidea

Orbiculariae consists of two major clades: the cribellate Deinopoidea and the much more diverse ecribellate Araneoidea. It has been hypothesized that the higher diversity of Araneoidea is a consequence of the superiority of the viscid orb web. However, this explanation seems incomplete; for example, cribellate silk may perform better than viscid silk in some contexts. Here, we consider the hypothesis that the diversification of Araneoidea was facilitated by changes in microhabitat occupation behavior due to the cheaper viscid orb web. In the present work we investigate the idea that the reduction in site tenacity caused by the emergence of the viscid orb web has led to an increase in the exploration of different resources and to a greater diversification of the Araneoidea through the evolutionary time. To test this idea, we evaluated the response of one cribellate orb web spider (Zosis geniculata Olivier 1789, Uloboridae) and one ecribellate orb web spider (Metazygia rogenhoferi Keyserling 1878, Araneidae) to abrupt prey absence. The changes in site tenacity and the day-to- day investment in web silk were evaluated. Spiders with three-dimensional webs tend to exhibit greater site tenacity than spiders making orb webs. Zosis geniculata and M. rogenhoferi show similar site tenacity when prey is ample. When prey is unavailable, the tenacity of the cribellate species increases while the tenacity of the ecribellate remains unchanged, and the silk investment of both species decreases. However, this decrease in silk investment is more extensive in Z. geniculata. These results coincide with the idea that a less costly ecribellate orb web leads to a lower tenacity and suggest that more frequent microhabitat abandonment in a context of insect radiation (Neoptera) leads to more diverse and opportunistic exploration of microhabitats that, in the long term, may be one explanation for the greater Araneoidea diversification.

Natal location influences movement and survival of a spatially structured population of snail kites

Despite the accepted importance of the need to better understand how natal location affects movement decisions and survival of animals, robust estimates of movement and survival in relation to the natal location are lacking. Our study focuses on movement and survival related to the natal location of snail kites in Florida and shows that kites, in addition to exhibiting a high level of site tenacity to breeding regions, also exhibit particular attraction to their natal region. More specifically, we found that estimates of movement from post-dispersal regions were greater toward natal regions than toward non-natal regions (differences were significant for three of four regions). We also found that estimates of natal philopatry were greater than estimates of philopatry to non-natal regions (differences were statistically significant for two of four regions). A previous study indicated an effect of natal region on juvenile survival; in this study, we show an effect of natal region on adult survival. Estimates of adult survival varied among kites that were hatched in different regions. Adults experienced mortality rates characteristic of the region occupied at the time when survival was measured, but because there is a greater probability that kites will return to their natal region than to any other regions, their survival was ultimately influenced by their natal region. In most years, kites hatched in southern regions had greater survival probabilities than did kites hatched in northern regions. However, during a multiregional drought, one of the northern regions served as a refuge from drought, and during this perturbation, survival was greater for birds hatched in the north. Our study shows that natal location may be important in influencing the ecological dynamics of kites but also highlights the importance of considering temporal variation in habitat conditions of spatially structured systems when attempting to evaluate the conservation value of habitats.