Spring Arrival Research Articles

Evolution of leapfrog migration: A test of competition-based hypotheses.

Leapfrog migration is a common migration pattern in birds where the breeding and wintering latitudes between populations are in reversed latitudinal sequence. Competition for wintering and breeding sites has been suggested to be an ultimate factor, and several competitor-based hypotheses have been proposed to explain this pattern. If wintering sites close to the breeding sites are favored, competitive exclusion could force subdominant individuals to winter further away. Competitive exclusion could be mediated either through body size or by prior occupancy. The alternative "spring predictability" hypothesis assumes competition for sufficiently close wintering areas, allowing the birds to use autocorrelated weather cues to optimally time spring migration departure. To test predictions and assumptions of these hypotheses, we combined morphometrics, migration, and weather data from four populations of common ringed plover breeding along a latitudinal (56-68° N) and climatic gradient (temperate to Arctic). Critical for our evaluation was that two populations were breeding on the same latitude in subarctic Sweden with the same distance to the closest potential wintering site, but differed in breeding phenology, and wintered in West Africa and Europe, respectively. Thus, while breeding on the same latitude, their winter distribution overlapped with that of an Arctic and temperate population. Body size was largest within the temperate population, but there was no size difference between the two subarctic populations. Populations wintering in Europe arrived there before populations wintering in Africa. The largest variation in the arrival of meteorological spring occurred at the temperate breeding site, while there was almost no difference among the other sites. In general, temperatures at the northernmost wintering area correlated well with each breeding site prior to breeding site-specific spring arrival. Based on these observations, we conclude that competitive exclusion through body-size-related dominance cannot explain leapfrog migration. Furthermore, the assumptions on which the "spring predictability" hypothesis is based did not match the observed wintering ranges either. However, we could not reject the hypothesis that competitive exclusion mediated by prior occupancy in the wintering area could lead to leapfrog migration, and therefore, this hypothesis should be retained as working hypothesis for further work.

Using PIT tags to infer bat reproductive status and parturition date: busy nights during lactation

Abstract Passive integrated transponders (PIT tags) can aid in the collection of important demographic data for species for which other methods, such as GPS technology, are not suitable. PIT tags can be particularly suitable to monitor small and cryptic species like bats and permit inference on their behavioral ecology. Literature for several species of bats states that females change their nightly activity patterns—going out and in of the roost only once per night during gestation compared to several times during lactation. Hence, we tested whether PIT tag detection patterns could be used to infer reproductive status and parturition date of female bats. From 2017 to 2021, we recorded detections of PIT-tagged little brown (Myotis lucifugus) and northern long-eared bats (M. septentrionalis) at the entrance of 2 maternity roosts in Québec and Newfoundland, Canada. We also used the maternity roost in Québec as a case study to further evaluate the potential of this method to link behavior and demography and investigated factors affecting parturition date. We were able to infer reproductive status for 63% to 97% of tagged individuals detected during both the gestation and the lactation periods, and parturition date for 61% to 95% of reproductive individuals, depending on the year and roost. Early spring arrival at the roost and warm spring mean temperature at night were associated with earlier parturition dates. Herein, we highlight that PIT tag systems may be useful to detect changes in activity patterns of female bats and infer individual reproductive parameters, which is on the long-term less stressful for bats and easier for researchers. We demonstrate that this approach is useful to investigate intrinsic and extrinsic factors of reproductive parameters, improving our understanding of bat population dynamics resulting in more informed population management decisions.

Snowmelt progression drives habitat selection and vegetation disturbance by an Arctic avian herbivore

AbstractArctic tundra vegetation is affected by rapid climatic change and fluctuating herbivore population sizes. Broad‐billed geese, after their arrival in spring, feed intensively on belowground rhizomes, thereby disturbing soil, mosses, and vascular plant vegetation. Understanding of how springtime snowmelt patterns drive goose behavior is thus key to better predict the state of Arctic tundra ecosystems. Here, we analyzed how snowmelt progression affected springtime habitat selection and vegetation disturbance by pink‐footed geese (Anser brachyrhynchus) in Svalbard during 2019. Our analysis, based on GPS telemetry data and field observations of geese, plot‐based assessments of signs of vegetation disturbance, and drone and satellite images, covered two spatial scales (fine scale: extent 0.3 km2, resolution 5 cm; valley scale: extent 30 km2, resolution 10 m). We show that pink‐footed goose habitat selection and signs of vegetation disturbance were correlated during the spring pre‐breeding period; disturbances were most prevalent in the moss tundra vegetation class and areas free from snow early in the season. The results were consistent across the spatial scales and methods (GPS telemetry and field observations). We estimated that 23.4% of moss tundra and 11.2% of dwarf‐shrub heath vegetation in the valley showed signs of disturbance by pink‐footed geese during the study period. This study demonstrates that aerial imagery and telemetry can provide data to detect disturbance hotspots caused by pink‐footed geese. Our study provides empirical evidence to general notions about implications of climate change and snow season changes that include increased variability in precipitation.

Multispecies fish tracking across newly created shallow and deep habitats in a forward-restored lake

BackgroundFreshwater fish communities typically thrive in heterogenous ecosystems that offer various abiotic conditions. However, human impact increasingly leads to loss of this natural heterogeneity and its associated rich fish communities. To reverse this trend, we need guidelines on how to effectively restore or recreate habitats for multiple fish species. Lake Markermeer in the Netherlands is a human-created 70,000-ha lake with a uniform 4 m-water depth, steep shorelines, high wind-induced turbidity, and a declining fish community. In 2016, a forward-looking restoration project newly created a 1000-ha five-island archipelago in this degrading lake, which offered new sheltered shallow waters and deep sand excavations to the fish community.MethodsIn 2020, we assessed how omnivorous and piscivorous fish species used these new habitats by tracking 78 adult fish of five key species across local and lake-scales. We monitored spring arrival of adult fish and assessed local macro-invertebrate and young-of-the-year fish densities.ResultsAdult omnivorous Cyprinidae and piscivorous Percidae arrived at the archipelago in early spring, corresponding with expected spawning movements. During the productive summer season, 12 species of young-of-the-year fish appeared along the sheltered shorelines, with particularly high densities of common roach (Rutilus rutilus) and European perch (Perca fluviatilis). This suggests the sheltered, shallow, vegetated waters formed new suitable spawning and recruitment habitat for the fish community. Despite highest food densities for adult fish in the shallowest habitats (< 2-m), adult fish preferred minimally 2-m deep water. After spawning most Cyprinidae left the archipelago and moved long distances through the lake system, while most Percidae remained resident. This may be related to (1) high densities of young-of-the-year fish as food for piscivores, (2) medium food densities for omnivores compared to elsewhere in the lake-system, or (3) the attractiveness of 30-m deep sand excavations that were newly created and frequently used by one-third of all tracked fish.ConclusionsNew littoral zones and a deep sand excavation constructed in a uniform shallow lake that lacked these habitat types attracted omnivorous and piscivorous fish species within four years. Both feeding guilds used the littoral zones for reproduction and nursery, and notably piscivorous fish became residents year-round.

Changes in Avian Spring Arrival Dates of 115 Species in the Central Appalachians over 127 Years

Changes in Avian Spring Arrival Dates of 115 Species in the Central Appalachians over 127 Years

Large- and Small-Scale Climate Influences Spring Migration Departure Probability of American White Pelicans

Endogenous (e.g., age and sex) and exogenous (e.g., climate and resource availability) factors influence avian migration phenology. However, little is known regarding the migration ecology of birds at the non-breeding grounds, including the American white pelican (Pelecanus erythrorhynchos). We used Global Positioning System transmitters to track the movements and migration of 51 pelicans from 2002 to 2012. We used the Kaplan–Meier model to estimate pelican spring migration probabilities to quantify partial migration with 94 spring migration events and used the Cox proportional hazards model to evaluate the effects of the North Atlantic Oscillation index (NAOI), Southern Oscillation Index (SOI), and spring daily precipitation on the propensity of pelican spring migration departures. Increases in the NAOI and SOI enhanced the propensity of pelican spring departure. The propensity of spring departure was also positively related to daily precipitation. Male pelicans have greater spring migration probabilities than female pelicans. Spring migration departure probabilities of adult pelicans are greater than those of immature pelicans. Therefore, both large-scale and local climatic conditions affect pelican spring departure probabilities. Advanced migratory phenology of pelicans caused by climate changes with warming temperature and increased precipitation may result in the mismatch of pelican spring arrival with food resource availability of breeding grounds and subsequent pelican population declines.

Migration and wintering of vulnerable adult Chinese Egrets (Egretta eulophotes) revealed by GPS tracking

Knowledge of migratory bird requirements is critical to developing conservation plans for vulnerable migratory species. This study aimed to determine the migration routes, wintering areas, habitat uses, and mortalities of adult Chinese Egrets (Egretta eulophotata). Sixty adult Chinese Egrets (31 females and 29 males) on an uninhabited offshore breeding island in Dalian, China were tracked using GPS satellite transmitters. GPS locations recorded at 2 ​h intervals from June 2019 to August 2020 were used for analysis. A total of 44 and 17 tracked adults completed their autumn and spring migrations, respectively. Compared with autumn migration, tracked adults displayed more diverse routes, higher number of stopover sites, slower migration speed, and longer migration duration in the spring. Results indicated that migrant birds had different behavioral strategies during the two migratory seasons. The spring migration duration and stopover duration for females were significantly longer than those for males. A positive correlation existed between the spring arrival and spring departure dates, as well as between the spring arrival date and stopover duration. This finding indicated that the egrets that arrived early at the breeding grounds left the wintering areas early and had a shorter stopover duration. Adult birds preferred intertidal wetlands, woodlands, and aquaculture ponds during migration. During the wintering period, adults preferred offshore islands, intertidal wetlands, and aquaculture ponds. Adult Chinese Egrets showed a relatively low survival rate compared with most other common ardeid species. Dead specimens were found in aquaculture ponds, indicating human disturbance as the main cause of death of this vulnerable species. These results highlighted the importance of resolving conflicts between egrets and human-made aquaculture wetlands and protecting intertidal flats and offshore islands in natural wetlands through international cooperation. Our results contributed to the hitherto unknown annual spatiotemporal migration patterns of adult Chinese Egrets, thereby providing an important basis for the conservation of this vulnerable species.

Sexual dimorphism and sex-differential migration of Little Buntings (Emberiza pusilla) at an East Asian stopover site

Sex differences in morphology provide key information for understanding a species' morphological adaptations in relation to the evolution of sexual selection. In migratory birds, morphological traits have adapted to long-distance travel, and sexual dimorphism is typically related to sex-differential migration phenology. Little Buntings (Emberiza pusilla) have one of the longest migrations and are the least dichromatic species among the Emberiza buntings. In this study, we measured sexual size dimorphism and sexual dichromatism of Little Buntings in relation to the spring arrival dates at a stopover site in Korea. Wing length was the most important predictor for identifying sex; the wings of males were longer than those of females. Males also had a significantly stronger chestnut color of the head feathers than females, but this color difference was more prominent in the spring than in the fall. Males arrived earlier than females by four days. Arrival dates correlated with both size and color, but unlike other bunting species previously studied in the same area, there was no clear sex-differential trend in the relationship between arrival date and morphological characteristics. Seasonal differences in the degree of sexual dichromatism suggest that chestnut plumage coloration can be used as a social or sexual signal of males in the breeding season. The correlation of size and color to early arrival regardless of sex may indicate that a preference for assortative mating exists or that a sex-differential migration strategy is not clearly defined in the early stages of northward migration. Our findings on the sexual dimorphism of Little Buntings provide insight into the evolution of the sex-differential migration of buntings in the East Asian Flyway.

A decrease in the number and the timing shift of the bird arrival in the North-Eastern Baikal Region

The article deals with the main results of a long-term study of birds in the Barguzin State Nature Biosphere Reserve (Russia). Phenological observations of the bird spring arrival have been carried out from 1938 to 2020. Monitoring of bird communities has been carried out from 1984 to 2020 on permanent counting routes in the valleys of three rivers in the area from the Lake Baikal coast to the highlands of the Barguzin Range (460–1700 m a.s.l.). We detected shifts and cyclical changes in the timing of the bird arrival and revealed a steady decrease in the abundance of the bird population after 1997–1998. The long-term series of observations (taking into account of model bird groups) made it possible to identify some responses of the biota to climatic changes in the Lake Baikal Region. Twenty-six species (40.0%) began to arrive in spring statistically significantly earlier, seven species (10.8%) significantly later, and for 32 species (49.2%) the arrival timing did not change statistically significantly. In contrary to Europe and North America, in the Baikal Region, the proportion of distant migrants in the group of early arriving bird species is higher than in the group of nearby migrants. We suggest that these differences may be associated with different wintering areas of long-distance migrants (species of the Baikal Region winter in South and Southeast Asia in contrast to African wintering areas of European birds). In the Baikal Region, the periods of high and low abundance in background species populations are probably associated with the passage of wet and dry phases of a long climatic cycle. We have identified positive trends in long-term changes in abundance for seven background species (14.0%), and a steady decline in abundance for 17 species (34.0%). In addition, we noted an equal ratio of species with a positive and negative trend in native species abundance. Negative trends of changes in the number of distant and nearby migrants prevailed over positive (increase) trends. So, we found 14 species with negative and four species with positive trends. An increase in the duration of observations makes it possible to give a more reliable assessment of processes in population dynamics, and identify mechanisms of the influence of meteorological and phenological factors on the dynamics of the abundance of bird species. This makes it possible to predict some biota responses to long-term climate changes in the absence of anthropogenic transformations of the natural environment.

Population specific annual cycles and migration strategies in a leap-frog migrant

A common migratory pattern in birds is that northerly breeding populations migrate to more southerly non-breeding sites compared to southerly breeding populations (leap-frog migration). Not only do populations experience differences in migration distances, but also different environmental conditions, which may vary spatiotemporally within their annual cycles, creating distinctive selective pressures and migratory strategies. Information about such adaptations is important to understand migratory drivers and evolution of migration patterns. We use light-level geolocators and citizen science data on regional spring arrivals to compare two populations of common ringed plover Charadrius hiaticula breeding at different latitudes. We (1) describe and characterize the annual cycles and (2) test predictions regarding speed and timing of migration. The northern breeding population (NBP) wintered in Africa and the southern (SBP) mainly in Europe. The annual cycles were shifted temporally so that the NBP was always later in all stages. The SBP spent more than twice as long time in the breeding area, but there was no difference in winter. The NBP spent more time on migration in general. Spring migration speed was lower in the SBP compared to autumn speed of both populations, and there was no difference in autumn and spring speed in the NBP. We also found a larger variation in spring arrival times across years in the SBP. This suggests that a complex interaction of population specific timing and variation of breeding onset, length of breeding season, and proximity to the breeding area shape the annual cycle and migratory strategies.Significance statementMigration distance, climate, and the resulting composition of the annual cycle are expected to influence migration strategies and timing in birds. Testing theories regarding migration behaviours are challenging, and intraspecific comparisons over the full annual cycle are still rare. Here we compare the spatiotemporal distributions of two latitudinally separated populations of common ringed plovers using light-level geolocators. We found that there was a larger long-term variation in first arrival dates and that migration speed was slower only in spring in a temperate, short-distance migratory population, compared to an Arctic, long-distance migratory population. This suggests that a complex interaction of population specific timing and variation of breeding onset, length of breeding season and proximity to the breeding area shape the annual cycle and migratory behaviours.

Effects of Environmental Conditions on Spring Arrival, the Timing of Nesting, and the Reproductive Effort of Ross’s Gull (Phodostethia rosea) in the Delta of Lena River, Yakutia

Effects of Environmental Conditions on Spring Arrival, the Timing of Nesting, and the Reproductive Effort of Ross’s Gull (Phodostethia rosea) in the Delta of Lena River, Yakutia

Nest box reuse in a migrating bird is independent of nest content

Site fidelity after successful nesting is an adaptation to spatially heterogeneous and temporally auto-correlated risk of nest predation. Cavity-nesting common goldeneye (Bucephala clangula) females use this strategy to minimize nest predation from pine marten (Martes martes), but because goldeneyes migrate they may save time when deciding where to nest by relying on information about successful nests gained in the previous year. I tested whether reuse of a nest box where the previous nest was successful is affected by the content. After a goldeneye had successfully nested, I manipulated nest box availability by offering two nest boxes; one in the original nest tree and one in a new tree for the season, each containing either old nest material from the successful nest or new nest material, i.e. wood shavings. The boxes were installed and relocated when goldeneyes were absent from the study area. The manipulation was designed to test whether goldeneyes reuse a cavity based on information conveyed by its current content, or on private or public information gained in the previous nesting season. Goldeneyes consistently reused the box in the original nest tree, independent of box content. Thus, when the information available in the current nesting season conflicted with information acquired in the previous nesting season, the goldeneyes relied on the latter rather than on information that would cost valuable time to update after arrival in spring. The common practice among ornithologists and land managers to clean nest boxes after each nesting would not affect cavity reuse in the goldeneye.

Migratory strategy drives species-level variation in bird sensitivity to vegetation green-up.

Animals and plants are shifting the timing of key life events in response to climate change, yet despite recent documentation of escalating phenological change, scientists lack a full understanding of how and why phenological responses vary across space and among species. Here, we used over 7 million community-contributed bird observations to derive species-specific, spatially explicit estimates of annual spring migration phenology for 56 bird species across eastern North America. We show that changes in the spring arrival of migratory birds are coarsely synchronized with fluctuations in vegetation green-up and that the sensitivity of birds to plant phenology varied extensively. Bird arrival responded more synchronously with vegetation green-up at higher latitudes, where phenological shifts over time are also greater. Critically, species' migratory traits explained variation in sensitivity to green-up, with species that migrate more slowly, arrive earlier and overwinter further north showing greater responsiveness to earlier springs. Identifying how and why species vary in their ability to shift phenological events is fundamental to predicting species' vulnerability to climate change. Such variation in sensitivity across taxa, with long-distance neotropical migrants exhibiting reduced synchrony, may help to explain substantial declines in these species over the last several decades.

The timing of spring migration in trans-Saharan migrants: a comparison between Ottenby, Sweden and Capri, Italy

Some migratory birds have advanced their spring arrival to Northern Europe, possibly by increasing the speed of migration through Europe in response to increased temperature en route. In this paper we compare the phenology of spring arrival of seven trans-Saharan migrants along their migration route and test for patterns indicating that migration speed varied over the season using long-term data collected on the Italian island of Capri and at Ottenby Bird Observatory, Sweden. There was a linear relationship between median arrival dates on Capri and at Ottenby. The slope was not significantly different from one. On average, the seven species arrived 15 days later at Ottenby compared to Capri. There was a (non-significant) negative relationship between the species-specific arrival dates at Capri and the differences in median arrival dates between Capri and Ottenby, possibly indicating a tendency towards faster migration through Europe later in the season. To what extent different species are able to speed up their migration to benefit from the advancement of spring events is unknown.

Hierarchy of Factors that Determine the Timing of the Arrival of Passeriformes in the Ob Forested Tundra

This paper analyzes the factors that determine the timing of the spring arrival of passerine birds in the nesting area, i.e., the Lower Ob Region. For the period 1971–2015, a reliable negative trend to an arrival shift to earlier dates for seven out of 16 species, an unreliable shift for six species, and a positive trend for three species were found. Using cluster analysis, three groups of species with similar arrival dynamics were identified. The temperature in the study area at the beginning of the arrival of all species increased with the approach to the end of the period analyzed (1971–2015) in parallel with the growing spring average monthly temperatures. Significant correlations of the starting dates of bird arrival with spring air temperatures (mainly in May), dates of ice passage along the Ob River, and the length of the migration route of the species were revealed. The relationship of the starting date of arrival in most species with the average daily air temperature directly on the day of arrival is weakly expressed. Thus, the main factors affecting the arrival dates are the average monthly spring air temperatures, primarily in May. The North Atlantic Oscillation Global Weather Index (NAO) is much less significant.

Changes in spring arrival dates of Central European bird species over the past 100 years

Over the past decades, spring temperatures have increased in temperate regions, which resulted in birds arriving earlier in spring. Nonetheless, the timing of some species’ spring migration relies on endogenous rhythms that are not affected by climate change. In this study, we analysed changes in the spring arrival dates of 36 bird species over two periods in 22 towns and villages in Southeast Hungary and West Romania. The first period covered the national spring migration counts between 1894 and 1926, while the second period took place between 2005 and 2019 and is based on our recent observation data. Our results show, that the average spring arrival dates of most long-distance migrant species have not changed significantly over the past 100 years. In contrast, in cases of medium and short-distance migrants, most species arrive earlier recently than in the past. This may be caused by the fact, that the migration habit of long-distance migrants is characterized by strong genetic determinants, so they can not react as quickly to the warmer spring weather in Europe as the medium and short-distance migrants. However, in cases of some long-distance migrants, the timing of spring migration changed due to the drying of wintering grounds.

Linking Weather and Phenology to Stopover Dynamics of a Long-Distance Migrant

For many migratory species, migration can represent a significant part of the annual cycle and the strategies used to move between the breeding and non-breeding areas vary considerably. Weather conditions are important during migration, particularly wind and temperature, and can play a crucial role in the timing of events during the annual cycle of migratory birds. When timing of specific events is important, for example spring arrival and laying dates, the effects of weather on the previous migration might lead to important fitness consequences, as it may alter migration speed. During spring, Icelandic whimbrels Numenius phaeopus islandicus display two main migratory behaviours: a direct flight from the wintering to the breeding sites (direct migration), or, more commonly, two flights with one stopover (stopover migration). We investigated how wind conditions, temperature and spring departure date may drive individuals to adopt either migratory behaviour. Interestingly, we found no differences in wind support during migratory flights, in temperature closer to Iceland or on crosswinds experienced in the region before reaching the main stopover areas. However, when individuals undertook a direct flight, departure date from the wintering sites was on average later, but this was not explained by wind patterns over a period of seven days prior to departure. In addition, we explored the variation at the individual level for three birds that changed migratory behaviour between years. The differences in all variables for these individuals reflected the variation observed at the population level. Overall, in such long migrations, it seems advantageous to perform a shorter flight to a stopover area, from where the weather conditions in the breeding areas may be assessed and avoid the risk of facing stochastic inclement weather prior to breeding, while synchronising time of arrival with conspecifics. In contrast, direct flights seem more common when individuals are time pressed.

Shifts in migration phenology under climate change: temperature vs. abundance effects in birds

In migratory birds, increasing temperatures have been linked to earlier arrival to breeding sites, enabling an earlier start of breeding and leading to changes in abundance. Long-term population trends may thus reflect a species capacity to respond to climate change. However, when a species is more abundant, it is also more easily detectable by observers, leading to an earlier detection of its arrival. Therefore, investigations of the drivers of shifts in apparent arrival dates to breeding sites and population trends remain challenging. Here, we formulate predictions aiming to disentangle the different drivers, analysing spring arrival dates and population changes of 52 migratory birds in a Central European country, the Czech Republic, from 1994 to 2017. If shifts in arrival dates are driven by increasing spring temperatures, migrants should arrive earlier in a warmer year and their abundance should increase in the subsequent year due to earlier breeding. If earlier migrant arrival results from their increased detectability caused by higher abundance, then migrants should arrive earlier in the same years when their abundance is high. We found clear support for the former prediction, indicating that climate change drives the earlier arrival of migrants irrespective of changes in their detectability. Moreover, species advancing their arrival to a greater degree had more positive population trends, and responses to rising spring temperatures in the Czech Republic became weaker with increasing migration distance. Therefore, climate change drives population trends of migratory species according to their capacity to adjust their arrival date to variations in spring temperatures.

Climatic correlates of migrant Natal long-fingered bat (Miniopterus natalensis) phenology in north-eastern South Africa

Abstract ContextFor migratory animals, particularly those with long generation times, changing weather patterns may cause a mismatch between periods of expected and actual resource availability, termed phenological mismatch. The cave-dwelling Natal long-fingered bat (Miniopterus natalensis) is a regional migrant within South Africa for which the (hitherto unknown) phenology of migration may be affected by climate. AimsTo investigate the migration phenology of the Natal long-fingered bat in relation to climate at a maternity cave in South Africa. MethodsFive years (2014–18) of echolocation data from a maternity cave site in Limpopo, South Africa, were studied. Separate stepwise General Linear Models (GLMs) were constructed for each season using photoperiod, minimum temperature, dew point, rainfall, barometric pressure, humidity and maximum wind speed. Arrival and departure dates among years were also compared. Key resultsPhotoperiod had the greatest effect on the magnitude of Natal long-fingered bat phenological patterns in activity across all seasons. Although spring (September - November) arrival at the maternity site was variable across years, summer departure dates did not differ, resulting in a shorter breeding period in the 2017–18 sample year. During the 2016–17 sample year, the magnitude of Natal long-fingered bat activity was significantly lower than in other years, which coincided with El Niño-induced drought conditions and likely impacted resources and led to a reduction in activity and population size. ConclusionsPhotoperiod is a strong predictive cue of the phenology of migration of the Natal long-fingered bat and likely cues migration for this species. The narrow departure dates of these bats from the maternity site supports these results. ImplicationsThe present study indicates that Natal long-fingered bats use photoperiod as a migration cue and do not appear to shift their spring–summer breeding season, likely making them vulnerable to phenological mismatch and population decline. The research highlights the need for systematic population monitoring for the Natal long-fingered bat.

Gonads or body? Differences in gonadal and somatic photoperiodic growth response in two vole species.

To optimally time reproduction, seasonal mammals use a photoperiodic neuroendocrine system (PNES) that measures photoperiod and subsequently drives reproduction. To adapt to late spring arrival at northern latitudes, a lower photoperiodic sensitivity and therefore a higher critical photoperiod for reproductive onset is necessary in northern species to arrest reproductive development until spring onset. Temperature-photoperiod relationships, and hence food availability-photoperiod relationships, are highly latitude dependent. Therefore, we predict PNES sensitivity characteristics to be latitude dependent. Here, we investigated photoperiodic responses at different times during development in northern (tundra or root vole, Microtus oeconomus) and southern vole species (common vole, Microtus arvalis) exposed to constant short (SP) or long photoperiod (LP). Although the tundra vole grows faster under LP, no photoperiodic effect on somatic growth is observed in the common vole. In contrast, gonadal growth is more sensitive to photoperiod in the common vole, suggesting that photoperiodic responses in somatic and gonadal growth can be plastic, and might be regulated through different mechanisms. In both species, thyroid-stimulating hormone β-subunit (Tshβ) and iodothyronine deiodinase2 (Dio2) expression is highly increased under LP, whereas Tshr and Dio3 decrease under LP. High Tshr levels in voles raised under SP may lead to increased sensitivity to increasing photoperiods later in life. The higher photoperiodic-induced Tshr response in tundra voles suggests that the northern vole species might be more sensitive to thyroid-stimulating hormone when raised under SP. In conclusion, species differences in developmental programming of the PNES, which is dependent on photoperiod early in development, may form different breeding strategies as part of latitudinal adaptation.