Climate change relaxes the time constraints for late-born offspring in a long-distance migrant

Adaptation to climate change through dispersal and inherited timing in an avian migrant

Many organisms fail to adjust their phenology sufficiently to climate change. Studies have concentrated on adaptive responses within localities, but little is known about how latitudinal dispersal enhances evolutionary potential. Rapid adaptation is expected if dispersers from lower latitudes have improved synchrony to northern conditions, thereby gain fitness and introduce genotypes on which selection acts. Here we provide experimental evidence that dispersal in an avian migrant enables rapid evolutionary adaptation. We translocated Dutch female pied flycatchers (Ficedula hypoleuca) and eggs to Sweden, where breeding phenology is ~15 days later. Translocated females bred earlier, and their fitness was 2.5 times higher than local Swedish flycatchers. We show that between-population variation in timing traits is highly heritable, and hence immigration of southern genotypes promotes the necessary evolutionary response. We conclude that studies on adaptation to large-scale environmental change should not just focus on plasticity and evolution based on standing genetic variation but should also include phenotype-habitat matching through dispersal as a viable route to adjust.

Postnatal growth rate varies with latitude in range-expanding geese: The role of plasticity and day length

The postnatal growth period is a crucial life stage, with potential lifelong effects on an animal's fitness. How fast animals grow depends on their life-history strategy and rearing environment, and interspecific comparisons generally show higher growth rates at higher latitudes. However, to elucidate the mechanisms behind this gradient in growth rate, intraspecific comparisons are needed. Recently, barnacle geese expanded their Arctic breeding range from the Russian Barents Sea coast southwards, and now also breed along the Baltic and North Sea coasts. Baltic breeders shortened their migration, while barnacle geese breeding along the North Sea stopped migrating entirely. We collected cross-sectional data on gosling tarsus length, head length and body mass, and constructed population-specific growth curves to compare growth rates among three populations (Barents Sea, Baltic Sea and North Sea) spanning 17° in latitude. Growth rate was faster at higher latitudes, and the gradient resembled the latitudinal gradient previously observed in an interspecific comparison of precocial species. Differences in day length among the three breeding regions could largely explain the observed differences in growth rate. In the Baltic, and especially in the Arctic population, growth rate was slower later in the season, most likely because of the stronger seasonal decline in food quality. Our results suggest that differences in postnatal growth rate between the Arctic and temperate populations are mainly a plastic response to local environmental conditions. This plasticity can increase the individuals' ability to cope with annual variation in local conditions, but can also increase the potential to re-distribute and adapt to new breeding environments.

Experimental manipulation of photoperiod influences migration timing in a wild, long-distance migratory songbird

Previous laboratory studies have demonstrated the role of photoperiod in cueing the migration timing of small land birds; however, how migration timing of young birds in wild environments develops in relation to these cues have rarely been investigated. Such investigations can make important contributions to our developing understanding of the phenotypic plasticity of migration timing to new conditions with climate change, where changes in the timing of nesting may expose juvenile birds to different photoperiods. We investigated the impact of manipulating photoperiod during nestling development in a long-distance migratory songbird on the timing of post-breeding movements in the wild. Using programmable lighting installed in the nest-boxes of purple martins (Progne subis), we exposed developing nestlings, from hatch to fledge date, to an extended photoperiod that matched the day length of the summer solstice in Manitoba, Canada. We found that birds with a simulated, earlier photoperiod had a longer nesting period and later fledge and autumn departure dates than control group birds. This study demonstrates the phenotypic plasticity of first-year birds to the ontogenetic effect of their hatch date in the formation of the timing of their first post-breeding movements. Further, we discuss how these results have implications for the potential use of assisted evolution approaches to alter migration timing to match new conditions with climate change.

Migration distance and maternal resource allocation determine timing of birth in a large herbivore

Birth timing is a key life‐history characteristic that influences fitness and population performance. For migratory animals, however, appropriately timing birth on one seasonal range may be constrained by events occurring during other parts of the migratory cycle. We investigated how the use of capital and income resources may facilitate flexibility in reproductive phenology of migratory mule deer in western Wyoming, USA, over a 5‐yr period (2015–2019). Specifically, we examined how seasonal interactions affected three interrelated life‐history characteristics: fetal development, birth mass, and birth timing. Females in good nutritional condition at the onset of winter and those that migrated short distances had more developed fetuses (measured as fetal eye diameter in March). Variation in parturition date was explained largely by fetal development; however, there were up to 16 d of plasticity in expected birth date. Plasticity in expected birth date was shaped by income resources in the form of exposure to spring green‐up. Although individuals that experienced greater exposure to spring green‐up were able to advance expected birth date, being born early or late with respect to fetal development had no effect on birth mass of offspring. Furthermore, we investigated the trade‐offs migrating mule deer face by evaluating support for existing theory that predicts that births should be matched to local peaks in resource availability at the birth site. In contrast to this prediction, only long‐distance migrants that paced migration with the flush of spring green‐up, giving birth shortly after ending migration, were able to match birth with spring green‐up. Shorter‐distance migrants completed migration sooner and gave birth earlier, seemingly trading off more time for offspring to grow and develop over greater access to resources. Thus, movement tactic had profound downstream effects on birth timing. These findings highlight a need to reconsider classical theory on optimal birth timing, which has focused solely on conditions at the birth site.

Integrating Causal and Evolutionary Analysis of Life-History Evolution: Arrival Date in a Long-Distant Migrant

In migratory species, the timing of arrival at the breeding grounds is a life-history trait with major fitness consequences. The optimal arrival date varies from year-to-year, and animals use cues to adjust their arrival dates to match this annual variation. However, which cues they use to time their arrival and whether these cues actually predict the annual optimal arrival date is largely unknown. Here, we integrate causal and evolutionary analysis by identifying the environmental variables used by a migratory songbird to time its arrival dates and testing whether these environmental variables also predicted the optimal time to arrive. We used 11 years of male arrival data of a pied flycatcher population. Specifically, we tested whether temperature and normalized difference vegetation index (NDVI) values from their breeding grounds in the Netherlands and from their wintering grounds in Ivory Coast explained the variation in arrival date, and whether these variables correlated with the position of the annual fitness peak at the breeding grounds. We found that temperature and NDVI, both from the wintering and the breeding grounds, explained the annual variation in arrival date, but did not correlate with the optimal arrival date. We explore three alternative explanations for this lack of correlation. Firstly, the date of the fitness peak may have been incorrectly estimated because a potentially important component of fitness (i.e., migration date dependent mortality en route or directly upon arrival) could not be measured. Secondly, we focused on male timing but the fitness landscape is also likely to be shaped by female timing. Finally, the correlation has recently disappeared because climate change disrupted the predictive value of the cues that the birds use to time their migration. In the latter case, birds may adapt by altering their sensitivity to temperature and NDVI.

Identifying climate refugia and its potential impact on Tibetan brown bear (Ursus arctos pruinosus) in Sanjiangyuan National Park, China

Climate change has direct impacts on wildlife and future biodiversity protection efforts. Vulnerability assessment and habitat connectivity analyses are necessary for drafting effective conservation strategies for threatened species such as the Tibetan brown bear (Ursus arctos pruinosus). We used the maximum entropy (MaxEnt) model to assess the current (1950-2000) and future (2041-2060) habitat suitability by combining bioclimatic and environmental variables, and identified potential climate refugia for Tibetan brown bears in Sanjiangyuan National Park, China. Next, we selected Circuit model to simulate potential migration paths based on current and future climatically suitable habitat. Results indicate a total area of potential suitable habitat under the current climate scenario of approximately 31,649.46 km2, of which 28,778.29 km2 would be unsuitable by the 2050s. Potentially suitable habitat under the future climate scenario was projected to cover an area of 23,738.6 km2. Climate refugia occupied 2,871.17 km2, primarily in the midwestern and northeastern regions of Yangtze River Zone, as well as the northern region of Yellow River Zone. The altitude of climate refugia ranged from 4,307 to 5,524 m, with 52.93% lying at altitudes between 4,300 and 4,600 m. Refugia were mainly distributed on bare rock, alpine steppe, and alpine meadow. Corridors linking areas of potentially suitable brown bear habitat and a substantial portion of paths with low-resistance value were distributed in climate refugia. We recommend various actions to ameliorate the impact of climate change on brown bears, such as protecting climatically suitable habitat, establishing habitat corridors, restructuring conservation areas, and strengthening monitoring efforts.

Climate warming may affect the optimal timing of reproduction for migratory geese differently in the low and high Arctic

Rapid climate warming is driving organisms to advance timing of reproduction with earlier springs, but the rate of advancement shows large variation, even among populations of the same species. In this study, we investigated how the rate of advancement in timing of reproduction with a warming climate varies for barnacle goose (Branta leucopsis) populations breeding at different latitudes in the Arctic. We hypothesized that populations breeding further North are generally more time constrained and, therefore, produce clutches earlier relative to the onset of spring than southern populations. Therefore, with increasing temperatures and a progressive relief of time constraint, we expected latitudinal differences to decrease. For the years 2000–2016, we determined the onset of spring from snow cover data derived from satellite images, and compiled data on egg laying date and reproductive performance in one low-Arctic and two high-Arctic sites. As expected, high-Arctic geese laid their eggs earlier relative to snowmelt than low-Arctic geese. Contrary to expectations, advancement in laying dates was similar in high- and low-Arctic colonies, at a rate of 27% of the advance in date of snowmelt. Although advancement of egg laying did not fully compensate for the advancement of snowmelt, geese laying eggs at intermediate dates in the low Arctic were the most successful breeders. In the high Arctic, however, early nesting geese were the most successful breeders, suggesting that high-Arctic geese have not advanced their laying dates sufficiently to earlier springs. This indicates that high-Arctic geese especially are vulnerable to negative effects of climate warming.

Identifying potential refugia and corridors under climate change: A case study of endangered Sichuan golden monkey (Rhinopithecus roxellana) in Qinling Mountains, China

Climate change threatens endangered species and challenges current conservation strategies. Effective conservation requires vulnerability assessments for species susceptible to climate change and adaptive strategies to mitigate threats associated with climate. In this paper, we used the Maxent to model the impacts of climate change on habitat suitability of Sichuan golden monkey Rhinopithecus roxellana. Our results showed that (i) suitable habitat for Sichuan golden monkey was predicted to decrease by 37% in 2050s under climate change; (ii) the mean elevations of suitable habitat in the 2050s was estimated to shift 160 m higher; (iii) nature reserves protect 62% of current suitable habitat and 56% of future suitable habitat; and (iv) 49% of current suitable habitat was predicted to be vulnerable to future climate change. Given these results, we proposed conservation implications to mitigate the impacts of climate change on Sichuan golden monkey, including adjusting range of national park, establishing habitat corridors, and conducting long‐term monitoring.

Timing manipulations reveal the lack of a causal link across timing of annual-cycle stages in a long-distance migrant

Organisms need to time their annual-cycle stages, like breeding and migration, to occur at the right time of the year. Climate change has shifted the timing of annual-cycle stages at different rates, thereby tightening or lifting time constraints of these annual-cycle stages, a rarely studied consequence of climate change. The degree to which these constraints are affected by climate change depends on whether consecutive stages are causally linked (scenario I) or whether the timing of each stage is independent of other stages (scenario II). Under scenario I, a change in timing in one stage has knock-on timing effects on subsequent stages, whereas under scenario II, a shift in the timing of one stage affects the degree of overlap with previous and subsequent stages. To test this, we combined field manipulations, captivity measurements and geolocation data. We advanced and delayed hatching dates in pied flycatchers (Ficedula hypoleuca) and measured how the timing of subsequent stages (male moult and migration) were affected. There was no causal effect of manipulated hatching dates on the onset of moult and departure to Africa. Thus, advancing hatching dates reduced the male moult-breeding overlap with no effect on the moult-migration interval. Interestingly, the wintering location of delayed males was more westwards, suggesting that delaying the termination of breeding carries over to winter location. Because we found no causal linkage of the timing of annual-cycle stages, climate change could shift these stages at different rates, with the risk that the time available for some becomes so short that this will have major fitness consequences.

Migration triggers in a large herbivore: Galápagos giant tortoises navigating resource gradients on volcanoes

To understand how migratory behavior evolved and to predict how migratory species will respond to global environmental change it is important to quantify the fitness consequences of intra- and inter-individual variation in migratory behavior. Intra-individual variation includes behavioral responses to changing environmental conditions and hence behavioral plasticity in the context of novel or variable conditions. Inter-individual variation determines the degree of variation on which selection can act and the rate of evolutionary responses to changes in average and extreme environmental conditions. Here we focus on variation in the partial migratory behavior of giant Galápagos tortoises (Chelonoidis spp.) and its energetic consequences. We evaluate the extent and mechanisms by which tortoises adjust migration timing in response to varying annual environmental conditions, and integrate movement data within a bioenergetic model of tortoise migration to quantify the fitness consequences of migration timing. We find strong inter-individual variation in the timing of migration, which was not affected by environmental conditions prevailing at the time of migration but rather by average expectations estimated from multi-annual averaged conditions. This variation is associated with an average annual loss in efficiency of ~15% relative to optimal timing based on year-specific conditions. These results point towards a limited ability of tortoises to adjust the timing of their migrations based on prevailing (and, by extension, future) conditions, suggesting that the adaptability of tortoise migratory behavior to changing conditions is predicated more by past "normal" conditions than responses to prevailing, changing conditions. Our work offers insights into the level of environmental-tuning in migratory behavior and a general framework for future research across taxa.

Climate change leads to differential shifts in the timing of annual cycle stages in a migratory bird

Shifts in reproductive phenology due to climate change have been well documented in many species but how, within the same species, other annual cycle stages (e.g. moult, migration) shift relative to the timing of breeding has rarely been studied. When stages shift at different rates, the interval between stages may change resulting in overlaps, and as each stage is energetically demanding, these overlaps may have negative fitness consequences. We used long-term data of a population of European pied flycatchers (Ficedula hypoleuca) to investigate phenological shifts in three annual cycle stages: spring migration (arrival dates), breeding (egg-laying and hatching dates) and the onset of postbreeding moult. We found different advancements in the timing of breeding compared with moult (moult advances faster) and no advancement in arrival dates. To understand these differential shifts, we explored which temperatures best explain the year-to-year variation in the timing of these stages, and show that they respond differently to temperature increases in the Netherlands, causing the intervals between arrival and breeding and between breeding and moult to decrease. Next, we tested the fitness consequences of these shortened intervals. We found no effect on clutch size, but the probability of a fledged chick to recruit increased with a shorter arrival-breeding interval (earlier breeding). Finally, mark-recapture analyses did not detect an effect of shortened intervals on adult survival. Our results suggest that the advancement of breeding allows more time for fledgling development, increasing their probability to recruit. This may incur costs to other parts of the annual cycle, but, despite the shorter intervals, there was no effect on adult survival. Our results show that to fully understand the consequences of climate change, it is necessary to look carefully at different annual cycle stages, especially for organisms with complex cycles, such as migratory birds.

The effect of climate change on the duration of avian breeding seasons: a meta-analysis

Many bird species are advancing the timing of their egg-laying in response to a warming climate. Little is known, however, of whether this advancement affects the respective length of the breeding seasons. A meta-analysis of 65 long-term studies of 54 species from the Northern Hemisphere has revealed that within the last 45 years an average population has lengthened the season by 1.4 days per decade, which was independent from changes in mean laying dates. Multi-brooded birds have prolonged their seasons by 4 days per decade, while single-brooded have shortened by 2 days. Changes in season lengths covaried with local climate changes: warming was correlated with prolonged seasons in multi-brooded species, but not in single-brooders. This might be a result of higher ecological flexibility of multi-brooded birds, whereas single brooders may have problems with synchronizing their reproduction with the peak of food resources. Sedentary species and short-distance migrants prolonged their breeding seasons more than long-distance migrants, which probably cannot track conditions at their breeding grounds. We conclude that as long as climate warming continues without major changes in ecological conditions, multi-brooded or sedentary species will probably increase their reproductive output, while the opposite effect may occur in single-brooded or migratory birds.