Diurnal space use and nocturnal roost‐site selection by male Cerulean Warblers during the breeding season

Detailed information about space use during the breeding season is limited for most Nearctic‐Neotropical migratory species of songbirds because of their small size and often cryptic behaviors. We monitored male Cerulean Warblers (Setophaga cerulea), a species of conservation concern, using radio‐telemetry during the 2006–2008 breeding seasons in northern Alabama to better understand their space use and habitat selection. We estimated diurnal home range and core areas using information theoretic criteria, located nocturnal roost sites, and related day and evening locations to surrounding landscape habitat, including features representative of canopy disturbances. Mean home range size was 6.7 ha (N = 10), and home ranges included an average of at least 2 core areas encompassing 0.7 ha. We located 53 nocturnal roost sites that were an average 159.0 m from the center of the nearest core area. More than one‐third (36.6%) of roost sites were located outside the diurnal home ranges of male Cerulean Warblers; only 13.6% were located in core areas. Males in our study moved much farther than reported in previous studies, with some singing in areas > 300 m from previously used song perches, a behavior suggesting pursuit of extra‐pair copulations. Cerulean Warblers in our study preferentially selected a heavily forested landscape composed of mesic, floodplain bottomlands with little man‐made disturbance. Within their home ranges, diurnal locations of males in core areas were located significantly closer to a creek than locations outside of core areas. Our results suggest that male Cerulean Warblers require much larger areas than previously reported and underscore the importance of a predominately forested landscape in their habitat selection process. Although edge habitats appeared to influence space use by male Cerulean Warblers in our study, the extent to which this is an essential requirement is unclear. Our results and those of previous studies suggest that specific habitat requirements of this species can vary at the local scale throughout its breeding range.     

Cerulean Warblers in the Ozark region: habitat selection,breeding biology,survival, and space use

Cerulean Warblers (Setophaga cerulea) are a species with declining populations that exhibit regional variation in habitat selection and demographic rates. The Ozark region of the south‐central United States likely provides important habitat for Cerulean Warblers, but little is known about their breeding biology in that region. We studied Cerulean Warblers in riparian forests of the Ozarks of Arkansas from 2018 to 2020. We assessed multi‐scale habitat selection for vegetative and topographic features, documented their breeding biology, estimated within‐season and annual apparent survival, and estimated territory sizes. We found that Cerulean Warblers selected riparian habitat characterized by large‐diameter trees across all spatial scales. Contrary to the results of previous studies, males appeared to avoid white oaks (Quercus spp., Section Quercus) at the territory scale, but this avoidance may reflect an underlying preference for riparian habitat. Our logistic‐exposure estimate of nest survival (0.32; 85% confidence interval: 0.21–0.46) was similar to the median of estimates reported in previous studies. Our results indicate that maintaining riparian forests with large trees is important to provide suitable habitat for Cerulean Warblers in the Ozark region. Because of similarities in habitat selection among regions, some management practices from other populations, including retaining large trees and promoting a heterogeneous canopy structure, may be useful for managing for Cerulean Warblers in riparian areas of the Ozarks. However, selection for topography and tree species by Cerulean Warblers in our study also suggests that region‐specific management strategies will be beneficial. Finally, our demographic rate estimates for this population should prove valuable in future full‐annual‐cycle population modeling efforts.     

Habitat and body condition influence American Redstart foraging behavior during the non‐breeding season

Insectivorous birds may adjust their foraging strategies to exploit changes in resource distributions. Arthropod prey strongly influence habitat‐specific persistence of long‐distance migrant passerines in their wintering areas, and arthropods are strongly affected by rainfall. However, the effect of drought on the dynamics of avian foraging ecology as resources shift is not well understood. We captured female American Redstarts (Setophaga ruticilla) and studied their foraging behavior in high‐quality (evergreen black mangrove) and low‐quality (deciduous scrub) habitat in Jamaica during the winter of 1995–1996. As is typical in southwestern Jamaica, conditions became drier as spring approached and many trees in scrub lost most of their leaves; mangrove trees maintained most of their leaf cover. Birds in scrub lost more mass than those in mangrove, and scrub birds shifted to using more aerial (and fewer near‐perch) maneuvers. In scrub, but not in mangrove, the proportion of wing‐powered movements and aerial foraging maneuvers was positively correlated with mass corrected by body size. In both habitats, attack rate was negatively correlated with body condition. Therefore, redstarts in scrub that maintained body condition were likely better able to use energetically expensive aerial maneuvers and wing‐powered search movements to exploit large, calorie‐rich flying arthropods. As the scrub dried over the course of the winter, the shift in foraging tactic may have allowed some birds to forage more efficiently (i.e., lower attack rate), likely facilitating maintenance of good body condition.     

Geolocators reveal migratory connectivity between wintering and breeding areas of Golden‐winged Warblers

The conservation of migratory songbirds is often impeded by a lack of understanding of how populations in breeding and wintering areas are geographically linked (migratory connectivity). In recent years, light‐level geolocators have improved our understanding of migratory connectivity. Such information is valuable for evaluating how conservation efforts align between the breeding and non‐breeding areas of at‐risk species, and help to more effectively prioritize the allocation of conservation funding. Golden‐winged Warblers (Vermivora chrysoptera) are imperiled migratory songbirds, but the extent to which conservation efforts in their breeding and non‐breeding areas coincide with patterns of migratory connectivity are not well known. We used light‐level geolocators to evaluate the extent to which conservation actions targeting Golden‐winged Warblers in Nicaragua and in their breeding range in North America align with patterns of migratory connectivity. We recovered six of 22 geolocators that had been deployed on male Golden‐winged Warblers at the El Jaguar Reserve during the winter of 2015–2016. All six males migrated to breeding areas in the western Great Lakes region that includes eastern Minnesota, northern Wisconsin, southwestern Ontario, and Michigan's Upper Peninsula. All six males also had similar migration routes, with spring stopovers in southern Mexico, Guatemala, and Belize, a trans‐Gulf flight, and a stopover in the region of Louisiana, Arkansas, eastern Oklahoma, and Texas. Our results, in combination with those of previous studies, demonstrate strong migratory connectivity between portions of the breeding and winter distributions of Golden‐winged Warblers currently targeted for conservation. However, additional studies are needed to improve our understanding of the stopover ecology of Golden‐winged Warblers, especially in areas where they remain for extended periods of time. Finally, patterns of migratory connectivity revealed in our study should be used in combination with existing demographic parameters for Golden‐winged Warblers in the western Great Lakes and Nicaragua to help inform full life cycle population models for this imperiled songbird.     

Recent population declines in Afro‐Palaearctic migratory birds: the influence of breeding and non‐breeding seasons

Aim

Recent, rapid population declines in many Afro‐Palaearctic migratory bird species have focussed attention on changing conditions within Africa. However, processes influencing population change can operate throughout the annual cycle and throughout migratory ranges. Here, we explore the evidence for impacts of breeding and non‐breeding conditions on population trends of British breeding birds of varying migratory status and wintering ecology.

Location

Great Britain (England & Scotland).

Methods

Within‐ and between‐species variation in population trends is quantified for 46 bird species with differing migration strategies.

Results

Between 1994 and 2007, rates of population change in Scotland and England differed significantly for 19 resident and 15 long‐distance migrant species, but were similar for 12 short‐distance migrant species. Of the six long‐distance migrant species that winter in the arid zone of Africa, five are increasing in abundance throughout Britain. In contrast, the seven species wintering in the humid zone of Africa are all declining in England, but five of these are increasing in Scotland. Consequently, populations of both arid and humid zone species are increasing significantly faster in Scotland than England, and only the English breeding populations of species wintering in the humid zone are declining.

Main conclusions

Population declines in long‐distance migrants, especially those wintering in the humid zone, but not residents or short‐distance migrants suggest an influence of non‐breeding season conditions on population trends. However, the consistently less favourable population trends in England than Scotland of long‐distance migrant and resident species strongly suggest that variation in the quality of breeding grounds is influencing recent population changes. The declines in humid zone species in England, but not Scotland, may result from poorer breeding conditions in England exacerbating the impacts of non‐breeding conditions or the costs associated with a longer migration, while better conditions in Scotland may be buffering these impacts.

     

Influence of climate change and postdelisting management on long‐term population viability of the conservation‐reliant Kirtland's Warbler

Rapid global climate change is resulting in novel abiotic and biotic conditions and interactions. Identifying management strategies that maximize probability of long‐term persistence requires an understanding of the vulnerability of species to environmental changes. We sought to quantify the vulnerability of Kirtland's Warbler (Setophaga kirtlandii), a rare Neotropical migratory songbird that breeds almost exclusively in the Lower Peninsula of Michigan and winters in the Bahamian Archipelago, to projected environmental changes on the breeding and wintering grounds. We developed a population‐level simulation model that incorporates the influence of annual environmental conditions on the breeding and wintering grounds, and parameterized the model using empirical relationships. We simulated independent and additive effects of reduced breeding grounds habitat quantity and quality, and wintering grounds habitat quality, on population viability. Our results indicated the Kirtland's Warbler population is stable under current environmental and management conditions. Reduced breeding grounds habitat quantity resulted in reductions of the stable population size, but did not cause extinction under the scenarios we examined. In contrast, projected large reductions in wintering grounds precipitation caused the population to decline, with risk of extinction magnified when breeding habitat quantity or quality also decreased. Our study indicates that probability of long‐term persistence for Kirtland's Warbler will depend on climate change impacts to wintering grounds habitat quality and contributes to the growing literature documenting the importance of considering the full annual cycle for understanding population dynamics of migratory species.     

Isotopic (δ2Hf) evidence of “loop migration” and use of the Gulf of Maine Flyway by both western and eastern breeding populations of Blackpoll Warblers

Declining numbers of Blackpoll Warblers (Setophaga striata) have been documented at long‐term migration monitoring sites as well as in breeding areas. However, the “loop migration” of Blackpoll Warblers makes it difficult to ascribe population change at migration monitoring sites to specific breeding populations. Individuals from all populations across the breeding range of Blackpoll Warblers concentrate in fall along the Atlantic coastline of eastern North America prior to initiating a transoceanic flight to wintering areas. In spring, Blackpoll Warblers return along a different route, moving north into the southeastern United States where birds from eastern and western breeding populations then diverge during migration to reach their respective breeding areas. To monitor breeding populations outside of breeding areas and identify factors potentially affecting those populations, we must be able to identify where birds captured during migration breed and map seasonal variation in population‐specific flyways. To “map” population‐specific migration movements of Blackpoll Warblers, we used feather deuterium (δ²H_f) values and a spatially explicit model to assign molt origins of 289 Blackpoll Warblers moving through sites in the Gulf of Maine (GOM) region and at three locations further west and south (northern Great Lakes area, Pennsylvania, and Florida). The assignment method was validated with feather samples from 35 birds captured during the breeding season at Churchill, Manitoba, Canada. As predicted, the spatial pattern of movement within and between seasons reflected “loop migration.” Blackpoll Warblers captured during fall migration in the GOM region included birds from across their breeding range, whereas birds captured during the spring were exclusively from northeastern populations. During fall migration, Blackpoll Warblers captured at two sites west of the GOM were from breeding areas further northwest than those from western Canada that were captured in the GOM. Blackpoll Warblers captured in eastern Florida during spring migration were assigned exclusively to breeding areas in the northeast, suggesting that eastern and western populations diverge soon after entering the United States. Finally, most Blackpoll Warblers sampled at Manomet Bird Observatory originated from breeding populations in Alaska and western Canada that have shown a similar (70–90%) decline over the same period. Our results, therefore, not only document the “loop migration” pattern of Blackpoll Warblers, but, by mapping patterns of connectivity between breeding and non‐breeding areas, may help target conservation efforts for breeding populations of Blackpoll Warblers where most needed.     

Longer ice-free seasons increase the risk of nest depredation by polar bears for colonial breeding birds in the Canadian Arctic

Northern polar regions have warmed more than other parts of the globe potentially amplifying the effects of climate change on biological communities. Ice-free seasons are becoming longer in many areas, which has reduced the time available to polar bears (Ursus maritimus) to hunt for seals and hampered bears’ ability to meet their energetic demands. In this study, we examined polar bears’ use of an ancillary prey resource, eggs of colonial nesting birds, in relation to diminishing sea ice coverage in a low latitude region of the Canadian Arctic. Long-term monitoring reveals that bear incursions onto common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) nesting colonies have increased greater than sevenfold since the 1980s and that there is an inverse correlation between ice season length and bear presence. In surveys encompassing more than 1000 km of coastline during years of record low ice coverage (2010–2012), we encountered bears or bear sign on 34% of eider colonies and estimated greater egg loss as a consequence of depredation by bears than by more customary nest predators, such as foxes and gulls. Our findings demonstrate how changes in abiotic conditions caused by climate change have altered predator–prey dynamics and are leading to cascading ecological impacts in Arctic ecosystems.     

Foraging behavior of migrant warblers in mixed‐species flocks in Venezuelan shade coffee: interspecific differences,tree species selection,and effects of drought

Shade coffee has been identified as an important habitat for Nearctic‐Neotropical migrants during the non‐breeding season, including species of conservation concern such as Cerulean Warblers (Setophaga cerulea). To better understand habitat features important for migrants in shade coffee, we studied the foraging behavior of migrants in mixed‐species flocks at six shade‐coffee farms in the Cordillera de Merida, Venezuela, in 2008–2009 and the El Niño drought year of 2009–2010. We examined interspecific differences in foraging behavior and tree species selection of three foliage‐gleaning migrants, Blackburnian (Setophaga fusca), Cerulean, and Tennessee (Oreothlypis peregrina) warblers, and aerial‐foraging American Redstarts (Setophaga ruticilla). For morphologically similar Blackburnian and Cerulean warblers, we also examined factors influencing foraging rates (attack and movement rates), capture of large prey, and maneuver/substrate type. We found that aerial‐foraging American Redstarts foraged lower, used more aerial maneuvers, showed no tree species selection, and were less likely to forage in flocks than foliage‐gleaners. Although foraging rates were similar for Blackburnian and Cerulean warblers, the three foliage‐gleaners differed in foraging height and use of maneuvers. Cerulean Warblers foraged lower than the other two species, whereas Blackburnian Warblers used the greatest proportion of woody gleans. All three foliage‐gleaners selected Inga spp. (a commonly planted shade tree in shade‐coffee farms) for foraging, and Blackburnian and Cerulean warblers captured a greater proportion of large prey in Inga spp. than in other tree species. During the drought year, Blackburnian and Cerulean warblers captured half as many large prey and used a greater proportion of woody‐gleans. We found that interactions among behavioral, floristic, and environmental drivers influenced the foraging behavior of migrants wintering in shade coffee. Our results support those of previous studies suggesting that migrants partition resources behaviorally during the non‐breeding season, that foliage‐gleaners may benefit from the presence of shade trees, especially Inga spp., in agroforestry systems, and that drought may influence the foraging behavior of foliage‐gleaning migrants, presumably due to reduced prey availability.     

Distribution and at‐sea behavior of Bermudan White‐tailed Tropicbirds (Phaethon lepturus catesbyi) during the non‐breeding season

The movements and behavior of many taxa of seabirds during the non‐breeding season remain poorly known. For example, although studies conducted in the Pacific and Indian oceans suggest that White‐tailed Tropicbirds (Phaethon lepturus) seldom fly more than a few thousand kilometers from nest colonies after breeding, little is known about the post‐breeding movements and behavior of a subspecies of White‐tailed Tropicbirds (P. l. catesbyi) that breeds on islands in the North Atlantic Ocean. Our objective, therefore, was to use light‐based geolocators to identify the ranges and pelagic activities of White‐tailed Tropicbirds from Bermuda during the non‐breeding periods in 2014–2015 (N = 25) and 2015–2016 (N = 16). Locations were estimated based on changes in light intensity across time, and pelagic activities were determined based on whether geolocators attached to leg bands were wet (i.e., birds resting on the water's surface) or dry (i.e., birds in flight). In 2014, birds spent late summer (July–September) near Bermuda and the British Virgin Islands; by mid‐September, most (N = 17; 68%) birds took a direct easterly route to the Sargasso Sea. In 2015, most post‐breeders (N = 15; 94%) flew east from Bermuda and to the Sargasso before the end of late summer. For both years combined, fall and winter (October–February) ranges extended as far west as North Carolina and as far east as the mid‐Atlantic Ridge. In both years, all birds were located between Bermuda and the British Virgin Islands during the spring (April–May). All birds then flew north to Bermuda in both years, with variations in timing, during April and May. We also found extensive overlap in the ranges of males and females during the non‐breeding season in both years. During the non‐breeding season, White‐tailed Tropicbirds spent 5% of night periods and 41% of day periods in flight in 2014; in 2015, birds spent 8% and 42% of night and day periods, respectively, in flight. Tropicbirds spent more time flying during the day because they hunt by day, detecting prey on the wing by sight. Overall, our results suggest that White‐tailed Tropicbirds that breed in Bermuda are diurnal, nomadic wanderers that range over an extensive area of the Atlantic Ocean during the non‐breeding season.     

Long‐distance movements and evidence of post‐breeding elevational movements by Cassin’s Vireos

Bird migration is often framed as a straightforward journey between one breeding site and one wintering site, but recent research has shown that the reality is often more complex. Many species of birds undertake short‐distance movements separate from long‐distance migration. Such movements appear to be common in species that breed in western North America, where mountainous terrain creates a mosaic of habitats and climatic conditions. However, individual‐based tracking studies have disproportionately focused elsewhere, leaving gaps in our understanding of the year‐round movements of western species. I used tracking data from light‐level geolocators and citizen science data from eBird to study the movements of Cassin’s Vireos (Vireo cassinii) breeding in the Sierra Nevada mountains of California, USA. During three breeding seasons (2013–2015), my observations suggested that Cassin’s Vireos vacate their breeding territories during the post‐breeding period in July and August. In April and May 2016, I tagged 22 Cassin’s Vireos with light‐level geolocators and, in April and May 2017, recaptured four that had retained their geolocators. Geolocator data showed that these four birds remained in the same geographic region as their breeding territories (likely the same mountain range) during the post‐breeding period in July and August 2016, ruling out the possibility of long‐distance movements during this time. Analysis of eBird citizen science data suggested that Cassin’s Vireos undertake short‐distance molt‐migration to higher elevations in the Sierra Nevada Mountains during the post‐breeding period. Geolocator data revealed that long‐distance fall migration took place in September and spring migration in April or May, and the four birds spent the winter in different parts of the Mexican winter range of Cassin’s Vireos. These results add to the body of literature on the complex movements of migratory songbirds breeding in the mountains of western North America, an understanding that will be important for effective conservation in the future.     

Feeding preferences of an invasive Ponto‐Caspian goby for native and non‐native gammarid prey

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Body condition and feather molt of a migratory shorebird during the non‐breeding season

Migratory shorebirds have some of the highest fat loads among birds, especially species which migrate long distances. The upland sandpiper Bartramia longicauda makes long‐distance migrations twice a year, but variation in body condition or timing of feather molt during the non‐breeding season has not been studied. Molt is an important part of the annual cycle of migratory birds because feather condition determines flight performance during migration, and long‐distance movements are energetically costly. However, variation in body condition during molt has been poorly studied. The objective of our field study was to examine the timing and patterns of feather molt of a long distance migratory shorebird during the non‐breeding season and test for relationships with body size, fat depots, mass, and sex. Field work was conducted at four ranches in the Northern Campos of Uruguay (Paysandú and Salto Departments). We captured and marked 62 sandpipers in a 2‐month period (Nov–Jan) during four non‐breeding seasons (2008–2012). Sex was determined by genetic analyses of blood samples taken at capture. Molt was measured in captured birds using rank scores based on published standards. Body mass and tarsus length measurements showed female‐biased sexual size dimorphism with males smaller than females. Size‐corrected body mass (body condition) showed a U‐shaped relationship with the day of the season, indicating that birds arrived at non‐breeding grounds in relatively good condition. Arriving in good body condition at non‐breeding grounds is probably important because of the energetic demands due to physiological adjustments after migration and the costs of feather molt.     

Foraging behaviour of the social caterpillar Eutachyptera psidii (Sallé) (Lepidoptera: Lasiocampidae) during a prolonged period of food and water deprivation

Abstract 1. Colonies of the social caterpillar Eutachyptera psidii (Sallé) (Hymenoptera: Lasiocampidae) occurring on oak (Quercus) in upland forests of Mexico endure periods as long as 6 weeks, with little or no food or water between the time host trees shed their leaves in April and produce new leaves in June. 2. By monitoring the activity of both field and laboratory colonies with infrared activity monitors and data loggers, it was found that although colonies remain active during the period of deprivation, their foraging activity shifts from once nightly when food is available to once every second night when food‐deprived. 3. Over a period of absolute food and water deprivation of 18 days, caterpillars lost an average of 36% of their initial mass but none perished. On average, the caterpillars regained their pre‐starvation mass within a few days after food was provided and continued to grow thereafter. During the period of starvation, caterpillars were observed to chew on dead and dried leaves in the field and on sheets of paper in the laboratory. 4. To the authors’ knowledge, there is no other documented instance of a species of caterpillar that exhibits the physiological capacity to engage in a similar level of persistent activity when forced to endure a prolonged period with neither food nor water.     

Shift down,look up: A test of the non‐linearity and fear hypothesis in a non‐vocal skink

The non‐linearity and fear hypothesis predicts that certain non‐linear sounds are one way to evoke antipredator responses in both birds and mammals. This hypothesis, however, has not been studied in non‐vocal species or in reptiles. Such a study would be important because if non‐linear sounds are evocative even in a species that does not produce sounds, then there may be generally salient cues of risk in these sounds. We asked whether non‐vocal lizards, white‐bellied copper‐striped skinks (Emoia cyanura), respond to experimentally broadcast non‐linearities. This species is ideal to ask the question in because prior research has shown that they respond to predator sounds and alarm calls of other species even though they are not vocal. We conducted playback experiments with three computer‐generated simulated non‐linearities to assess whether or not skinks increased antipredator behavior after hearing them. We controlled for novelty by broadcasting a 3‐kHz, 500‐ms pure tone and tropical kingbird (Tyrannus melancholicus) song. Our treatments consisted of a 3‐kHz, 400‐ms pure tone followed by a frequency shift up to 5‐kHz for 100‐ms, a 3‐kHz, 400‐ms pure tone to frequency shift down to 1‐kHz for 100‐ms, and a pure tone followed by 100‐ms of white noise. Following a total of 222 playbacks, we categorized responses into looking, locomotion, and high locomotion, focusing on how skinks changed their rates of time allocation from baseline. We examined 95% confidence intervals to identify whether skinks responded to playbacks and fitted general linear models followed by pairwise comparisons to ask whether skinks discriminated between broadcast stimuli. We found that skinks were especially responsive to frequency downshifts: They significantly increased looking and locomotion, consistent with our predictions based on the non‐linearity and fear hypothesis. Surprisingly, they decreased rates of looking behavior after hearing frequency upshifts, possibly suggesting an increase in relaxed behavior. While skinks responded to noise by increasing their rate of locomotion, this response was not significantly different from controls. We conclude that skinks increase antipredator behavior after hearing downshifts more than any other type of non‐linearity. This provides some support for the non‐linearity and fear hypothesis; even non‐vocal species may respond fearfully to specific types of non‐linear sounds.     

Guiding lights: Foraging responses of juvenile nocturnal orb‐web spiders to the presence of artificial light at night

The reach of artificial light at night (ALAN) is growing rapidly around the globe, including the increasing use of energy‐efficient LED lights. Many studies document the physiological costs of light at night, but far fewer have focused on the potential benefits for nocturnal insectivores and the likely ecological consequences of shifts in predator–prey relationships. We investigated the effects of ALAN on the foraging behaviour and prey capture success in juvenile Australian garden orb‐web spiders (Eriophora biapicata). Laboratory experiments demonstrated that juvenile spiders were attracted to LED lights when choosing foraging sites, but prey availability was a stronger cue for remaining in a foraging site. Field experiments revealed a significant increase in prey capture rates for webs placed near LED lights. This suggests that any physiological costs of light at night may be offset by the foraging benefits, perhaps partially explaining recently observed increases in the size, fecundity and abundance of some orb‐web spider species in urban environments. Our results highlight the potential long‐term consequences of night lighting in urban ecosystems, through the impact of orb‐web spiders on insect populations.     

Polyandrous females provide sons with more competitive sperm: Support for the sexy‐sperm hypothesis in the rattlebox moth (Utetheisa ornatrix)

Given the costs of multiple mating, why has female polyandry evolved? Utetheisa ornatrix moths are well suited for studying multiple mating in females because females are highly polyandrous over their life span, with each male mate transferring a substantial spermatophore with both genetic and nongenetic material. The accumulation of resources might explain the prevalence of polyandry in this species, but another, not mutually exclusive, possibility is that females mate multiply to increase the probability that their sons will inherit more‐competitive sperm. This latter “sexy‐sperm” hypothesis posits that female multiple mating and male sperm competitiveness coevolve via a Fisherian runaway process. We tested the sexy‐sperm hypothesis by using competitive double matings to compare the sperm competition success of sons of polyandrous versus monandrous females. In accordance with sexy‐sperm theory, we found that in 511 offspring across 17 families, the male whose polyandrous mother mated once with each of three different males sired significantly more of all total offspring (81%) than did the male whose monandrous mother was mated thrice to a single male. Interestingly, sons of polyandrous mothers had a significantly biased sex ratio of their brood toward sons, also in support of the hypothesis.     

Comparison of invertebrate herbivores on native and non‐native Senecio species: Implications for the enemy release hypothesis

The enemy release hypothesis posits that non‐native plant species may gain a competitive advantage over their native counterparts because they are liberated from co‐evolved natural enemies from their native area. The phylogenetic relationship between a non‐native plant and the native community may be important for understanding the success of some non‐native plants, because host switching by insect herbivores is more likely to occur between closely related species. We tested the enemy release hypothesis by comparing leaf damage and herbivorous insect assemblages on the invasive species Senecio madagascariensis Poir. to that on nine congeneric species, of which five are native to the study area, and four are non‐native but considered non‐invasive. Non‐native species had less leaf damage than natives overall, but we found no significant differences in the abundance, richness and Shannon diversity of herbivores between native and non‐native Senecio L. species. The herbivore assemblage and percentage abundance of herbivore guilds differed among all Senecio species, but patterns were not related to whether the species was native or not. Species‐level differences indicate that S. madagascariensis may have a greater proportion of generalist insect damage (represented by phytophagous leaf chewers) than the other Senecio species. Within a plant genus, escape from natural enemies may not be a sufficient explanation for why some non‐native species become more invasive than others.