Migratory Destinations Research Articles

Behavioural responses of a trans-hemispheric migrant to climate oscillation.

Large-scale climatic fluctuations, such as the El Niño-Southern Oscillation, can have dramatic effects on ocean ecosystem productivity. Many mobile species breeding in temperate or higher latitudes escape the extremes of seasonal climate variation through long-distance, even trans-global migration, but how they deal with, or are affected by, such longer phased climate fluctuations is less understood. To investigate how a long-lived migratory species might respond to such periodic environmental change we collected and analysed a 13 year biologging dataset for a trans-equatorial migrant, the Manx shearwater (Puffinus puffinus). Our primary finding was that in El Niño years, non-breeding birds were at more northerly (lower) latitudes than in La Niña years, a response attributable to individual flexibility in migratory destinations. Daily time spent foraging varied in concert with this latitudinal shift, with birds foraging less in El Niño years. Secondarily, we found that in subsequent breeding, a hemisphere away, El Niño years saw a reduction in foraging time and chick provisioning rates: effects that could not be attributed to conditions at their breeding grounds in the North Atlantic. Thus, in a highly migratory animal, individuals may adjust to fluctuating non-breeding conditions but still experience cascading carry over effects on subsequent behaviour.

Spring migration strategies of Anas platyrhynchos (Mallard) necessitate individual time-energy trade-offs despite wintering origins or migratory destinations

Abstract Spring migration is hypothesized to be time-constrained because of competition for optimal nesting and brood-rearing sites. Therefore, individuals are predicted to minimize migration time to breeding destinations; however, migration strategies likely lie on a continuum based on wintering and stopover habitat quality, environmental conditions, or individual-level factors. In other words, individuals and wintering subpopulations may differentially prioritize time-energy trade-offs during migration depending on where they are from, when they leave, and where they are going. We tested these hypotheses by characterizing spatial and temporal variation in spring migration strategies in female Anas platyrhynchos (Mallards), using global positioning system (GPS) data from ~150 individuals captured across the Mississippi Alluvial Valley and Gulf Coast Chenier Plain, USA. We used principal components analysis to classify a series of migratory behaviors into distinct time- and energy-minimization migration strategies, and tested whether migration strategies were related to wintering origins (habitat quality or latitudinal differences influencing migration initiation), migratory destinations (resource predictability), and individual-level factors (age and body condition). Additionally, we estimated individual and wintering subpopulation space-use to identify geographic regions of high and overlapping use that may facilitate time- or energy-minimizing migration strategies. Our results indicated a gradient of time-minimization migration strategies but migration strategy was not influenced by wintering origins nor migratory destination. Instead, time-energy trade-offs manifested at the individual level with time-minimization depending on experience and body condition. We also revealed stopovers and migration corridors of continental importance for spring-migrating A. platyrhynchos and space-use therein suggested migration strategies varied spatially with increasing time-minimization behavior as A. platyrhynchos neared their breeding grounds. Future research should link migration strategies and settling patterns to demographic rates.

Contemporary sightings of eastern North Pacific right whales, 2006 to 2023

North Pacific right whales Eubalaena japonica once numbered in the 10s of 1000s. Today, the eastern population is one of the most endangered large whale stocks in the world. A lack of dedicated surveys and a population in the 10s of animals have resulted in considerable knowledge gaps. Here, we collate all contemporary sightings of eastern North Pacific right whales (ENPRWs) from 2006 through 2023 to investigate possible migratory routes and elucidate important habitat. Sightings in the northern Bering Sea, Gulf of Alaska, and along the west coast of North America have increased. Of the 99 sightings recorded between 2006 and 2023, 58 occurred during the few dedicated ENPRW surveys with simultaneous aerial and vessel platforms. All animals sighted were non-calves. Opportunistic sightings along the California coast were only reported in spring months (February-May). While this timing would coincide with a northward migration from lower latitudes, poor photo quality prevented matching of these animals, making it difficult to determine migratory patterns. Furthermore, there have been no sightings in Hawai’i or Mexico since 1996, and no sightings in the eastern North Pacific off the continental shelf since the 1970s. To date, only 2 animals have been photographically matched from Alaska to more southerly latitudes, and there have been no photographic matches between the Bering Sea and the Gulf of Alaska. Feeding has been observed throughout their range, suggesting right whales opportunistically feed whenever possible. While their primary migratory destinations remain unknown, these recent sightings provide insight into important ENPRW habitat in Alaska.

Diurnal activity in an insectivorous bat during migration period

Abstract Diurnal flight activity in otherwise strictly nocturnal bats has typically been linked to random disturbance from day roosts, an urgent need to balance food shortage caused by adverse weather during nighttime, or the absence of diurnal predators. However, migration may be another reason why bats fly during daylight, at least in some areas. Using community-science data collection, we obtained more than 500 records of over 15,000 bats displaying diurnal flight activity, suggesting that it is relatively common in Central Europe. The vast majority of sightings were of common noctules (Nyctalus noctula), with most records concentrated in spring and autumn. The seasonal dynamics of diurnal flights exactly coincided with migratory periods, and directional movements in autumn—when diurnal activity was most frequent and included highest numbers of observed bats—suggest that the behavior may ultimately be linked to migration ecology. The highest frequency of diurnal flights in autumn coincided with highest body mass in the studied territory, thereby refuting the hypothesis of early roost emergence due to poor body condition or decreased predation risk related to increased maneuverability. A shift from strictly nocturnal to partly diurnal activity may balance increased energetic demands imposed by migration, which is temporally synchronized with periods of cold nights when prey density is limited. Common noctule diurnal activity during the migratory period may be beneficial as they can acquire energy by foraging on daily abundant prey while saving nighttime for long endurance flights—alternatively, they may forage on the way to their migratory destination, thereby saving time. Predation risk from diurnal predators may be significantly decreased by choosing high flight altitudes, as observed particularly during autumn. We suggest that observations on the geographic distribution of diurnally flying noctules may help identify migration corridors.

Climate change drives migratory range shift via individual plasticity in shearwaters

How individual animals respond to climate change is key to whether populations will persist or go extinct. Yet, few studies investigate how changes in individual behavior underpin these population-level phenomena. Shifts in the distributions of migratory animals can occur through adaptation in migratory behaviors, but there is little understanding of how selection and plasticity contribute to population range shift. Here, we use long-term geolocator tracking of Balearic shearwaters (Puffinus mauretanicus) to investigate how year-to-year changes in individual birds' migrations underpin a range shift in the post-breeding migration. We demonstrate a northward shift in the post-breeding range and show that this is brought about by individual plasticity in migratory destination, with individuals migrating further north in response to changes in sea-surface temperature. Furthermore, we find that when individuals migrate further, they return faster, perhaps minimizing delays in return to the breeding area. Birds apparently judge the increased distance that they will need to migrate via memory of the migration route, suggesting that spatial cognitive mechanisms may contribute to this plasticity and the resulting range shift. Our study exemplifies the role that individual behavior plays in populations' responses to environmental change and highlights some of the behavioral mechanisms that might be key to understanding and predicting species persistence in response to climate change.

Migratory destinations of endangered humpback whales, Megaptera novaeangliae (Cetartiodactyla: Balaenopteridae), from El Salvador

Introduction: The study of many aspects of cetacean ecology is made possible by identifying individuals through space and time. Humpback whales (Megaptera novaeangliae) can be easily identified by photographing their ventral tail flukes’ unique shape and pigmentation patterns. The small and endangered distinct population segment (DPS) of Central America humpback whales visit El Salvador seasonally each winter; however, dedicated research has been extremely limited there. Before 2018, only 11 individual whales had been photo-identified, and the migratory destinations of Salvadoran humpback whales were unknown. In recent years, photo-identification efforts have increased, and today there are 92 individually identified humpback whales from El Salvador.
 Objective: To identify the main high-latitude feeding areas of Salvadoran humpback whales.
 Methods: Using the online matching platform Happywhale, Salvadoran whales were matched via automated image recognition to a global humpback whale fluke photo-identification catalog of 66 043 individuals.
 Results: In total, 80 (87.0 %) of the whales photographed in El Salvador were matched to individuals seen in North Pacific feeding areas. Sighting histories of Salvadoran whales resighted in feeding areas ranged from two to 29 years (average = 12.1, SD = 5.8). While we note that survey effort was likely very different between regions, the main feeding area of Salvadoran humpback whales on Happywhale was Central California (n = 70, 76.1 %). Of these whales, 21 (22.8 %) had also been sighted in Southern California, while just three (3.3 %) individual whales were registered only in Southern California. Additionally, two whales (2.2 %) were sighted in Southern British Columbia, Canada, and one whale was matched to a humpback whale from Southeast Alaska. This whale (of unknown sex) has a sighting history of 27 years but no prior documentation in a breeding area and is the first published sighting of a Southeast Alaskan humpback whale in the breeding area of the endangered Central America DPS.
 Conclusions: Our study shows that while Salvadoran humpback whales were matched to various feeding areas in the Eastern North Pacific, their primary migratory destinations are in Southern and Central California.

Migratory destinations and spatial structuring of humpback whales (Megaptera novaeangliae) wintering off Nicaragua

Understanding the migratory patterns of large whales is of conservation importance, especially in identifying threats to specific populations. Migration ecology, including migratory destinations, movements and site fidelity for humpback whales (Megaptera novaeangliae) remain poorly studied in parts of the range of the Central America population, considered endangered under the United States Endangered Species Act. This study aimed to investigate the migratory destinations of humpback whales sighted at two study sites in Nicaragua, which are part of the Central America population. A ten-year photographic database of humpback whales observed off Nicaragua was combined with citizen science contributions and sightings from dedicated research programs. The resulting image collection was compared with available historical photo identifications and databases using an automated image recognition algorithm. This approach yielded 36 years of photographic identification totaling 431 recaptures in Nicaragua (2006–2008 and 2016–2021) and 2539 recaptures (1986–2020) in both feeding and breeding grounds of 176 unique individuals sighted in Nicaragua. Our results showed that photo-identified whales were recaptured between October and April in breeding grounds and year-round in feeding grounds between British Columbia and California, with peak recaptures between June and October. Our study provided first-time evidence on fine-scale site affinity of individual humpback whales within Nicaraguan waters and to other breeding and feeding grounds.

Weather, sex and body condition affect post-fledging migration behaviour of the greater flamingo Phoenicopterus roseus

BackgroundUnderstanding which intrinsic and extrinsic factors dictate decision-making processes such as leaving the natal area or not (migratory vs resident strategy), departure time, and non-breeding destination are key-issues in movement ecology. This is particularly relevant for a partially migratory meta-population in which only some individuals migrate.MethodsWe investigated these decision making-processes for 40 juvenile greater flamingos Phoenicopterus roseus fledged in three Mediterranean colonies and equipped with GPS-GSM devices.ResultsContrary to the body size and the dominance hypotheses, juveniles in better body condition were more likely to migrate than those in worse conditions, which opted for a residence strategy. Flamingo probability of departure was not associated with an increase in local wind intensity, but rather with the presence of tailwinds with departure limited to night-time mostly when the wind direction aligned with the migratory destination. Moreover, a positive interaction between tailwind speed and migration distance suggested that juveniles opted for stronger winds when initiating long-distance journeys. In contrast to previous studies, the prevailing seasonal winds were only partially aligned with the migratory destination, suggesting that other factors (e.g., adults experience in mix-aged flocks, availability of suitable foraging areas en route, density-dependence processes) may be responsible for the distribution observed at the end of the first migratory movement. We found potential evidence of sex-biased timing of migration with females departing on average 10 days later and flying ca. 10 km/h faster than males. Female flight speed, but not male one, was positively influenced by tailwinds, a pattern most likely explained by sexual differences in mechanical power requirements for flight (males being ca. 20% larger than females). Furthermore, juveniles considerably reduced their flight speeds after 400 km from departure, highlighting a physiological threshold, potentially linked to mortality risks when performing long-distance non-stop movements.ConclusionThese results suggest that not only intrinsic factors such as individual conditions and sex, but also extrinsic factors like weather, play critical roles in triggering migratory behaviour in a partially migratory metapopulation. Furthermore, social factors, including conspecific experience, should be taken into consideration when evaluating the adaptive processes underlying migration phenology, flight performance, and final destination selection.

The migratory whale herd concept: A novel unit to conserve under the ecological paradigm

AbstractPhotographic and genetic studies have revealed the complex population structure of migratory large whales. Most research and management are geographically based, focusing on either wintering or summering areas, which in most cases fails to capture this complexity. We use examples from humpback whales (Megaptera novaeangliae) and gray whales (Eschrichtius robustus) to illustrate the concept of migratory herds, defined here as conspecific whales that migrate between the same wintering and feeding ground. In cases where individuals show strong fidelity to both feeding and wintering grounds, and therefore to a herd, dispersal between herds can be low enough to render them as demographically independent populations, where population dynamics are determined more by net internal recruitment (births minus deaths) than by immigration from outside sources. In these cases, the migratory whale herd is the appropriate unit to conserve under the ecological paradigm that focuses on groups united by demographic forces. We suggest that when addressing questions focused on ecological timescales for whale species with strong fidelity to migratory destinations, the migratory whale herd is a better initial working hypothesis rather than one based on geographically defined strata.

Songbirds initiate migratory flights synchronously relative to civil dusk

BackgroundEach spring and fall billions of songbirds depart on nocturnal migrations across the globe. Theory suggests that songbirds should depart on migration shortly after sunset to maximize their potential for nightly flight duration or to time departure with the emergence of celestial cues needed for orientation and navigation. Although captive studies have found that songbirds depart during a narrow window of time after sunset, observational studies have found that wild birds depart later and more asynchronously relative to sunset than predicted.MethodsWe used coded radio tags and automated radio-telemetry to estimate the time that nearly 400 individuals from nine songbird species departed their breeding or wintering grounds across North America. We also assessed whether each species was most likely beginning long-distance migratory flights at departure or instead first making non-migratory regional flights. We then explored variation in nocturnal departure time by post-departure movement type, species, age, sex, and season.ResultsWe found that 90% of individuals from species that were likely initiating long-distance migratory flights departed within 69 min of civil dusk, regardless of species, season, age, or sex. By contrast, species that likely first made non-migratory regional movements away from the migratory destination departed later and more asynchronously throughout the night. Regardless of post-departure movement type, 98% of individuals departed after civil dusk but otherwise showed no preference in relation to twilight phase.ConclusionsAlthough the presence of celestial orientation cues at civil dusk may set a starting point for departure each night, the fact that species likely beginning long-distance migration departed earlier and more synchronously relative to civil dusk than those first making non-migratory regional movements is consistent with the hypothesis that departing promptly after civil dusk functions to maximize the potential for nightly flight duration and distance. By studying the onset of migration, our study provides baseline information about departure decisions that may enhance our understanding of departure timing throughout migration.

Migrations of individually identified humpback whales between the Antarctic Peninsula and South America

Considerable uncertainty exists regarding the migratory destinations of humpback whales (Megaptera novaeangliae) from the Antarctic Peninsula region and the breeding grounds off the coasts of South America. Evidence is presented on the migratory patterns of Antarctic humpback whales based upon movements of individuals identified by natural markings as part of a large-scale international collaboration. Recapture rates were compared between animals from the low latitude breeding and calving areas along the northeastern (n=288) and northwestern (n=325) margins of South America with those identified in the high-latitude feeding areas in the region of the Antarctic Peninsula (n=535). The number of individuals re-sighted in the Antarctic Peninsula differed dramatically between eastern and western South America (c2=40.98, p=1.5 3 10–10). No individuals from Brazil were re-sighted in either the Antarctic Peninsula or off western South America. In contrast, 43 individuals from western South America were identified off the Antarctic Peninsula. These findings suggest that the northwest coast of South America represents an important breeding ground destination for at least some of the humpback whales that feed near the Antarctic Peninsula, but provide no support for movement between the Antarctic Peninsula and the east coast of South America.

Photo-identification confirms that humpback whales (Megaptera novaeangliae) from eastern Australia migrate past New Zealand but indicates low levels of interchange with breeding grounds of Oceania

Recent photo-identification and genetic studies have identified at least five discrete breeding populations in Australia and Oceania: western Australia (D), eastern Australia (E (i)), New Caledonia (E (ii)), Tonga (E (iii)), French Polynesia and the Cook Islands (F). Also evident are low levels of intermingling among breeding populations consistent with the degree of genetic differentiation. Photo-identification has confirmed linkages between Area V feeding areas and eastern Australia breeding grounds and one genotype match has been reported between Area V feeding areas and Oceania breeding grounds. Recent abundance estimates show strong increases in the eastern Australian population, and some recovery in the New Caledonia and Tonga populations, but with little evidence of recovery at other known Oceania breeding grounds or New Zealand. Studies to date have provided no conclusive evidence of the migratory destination of humpback whales passing through New Zealand waters en route between Antarctic feeding areas and tropical breeding grounds. Photo-identification comparisons were undertaken between humpback whale fluke catalogues from eastern Australia (EA, 1315), Oceania east (OE, 513), Oceania west (OW, 166) and New Zealand (NZ, 13). Five matches were found between OE/OW, four matches between OW/EA and three matches between NZ/EA. The data are used to investigate and discuss the migratory destination and breeding ground migratory interchange of humpback whales travelling through New Zealand waters. The data confirm that humpback whales with site fidelity to eastern Australia migrate past New Zealand including through the Cook Strait and Foveaux Strait.

Migratory destinations and timing of humpback whales in the southeastern Caribbean differ from those off the Dominican Republic

Humpback whales wintering in the entire West Indies chain are widely treated as comprising a single breeding population. However, most areas outside of Silver Bank and Samana Bay, Dominican Republic, are poorly and sporadically studied. Data is presented on the timing and movement patterns of 262 whales from the southeastern Caribbean, extending from Antigua in the north to Trinidad and Tobago in the south. Whales from the area were re-sighted in all of the major North Atlantic feeding grounds. However, of the 43 individuals re-sighted in feeding areas, animals from eastern feeding grounds were significantly over-represented, while those from western feeding areas were under-represented. This is in direct contrast to the pattern previously demonstrated in the Dominican Republic. Supporting this finding, the proportion of whales showing visible scarring on the flukes from non-lethal attack by killer whales was similar to that previously shown for Norway; yet lower than that presented from western feeding areas. The seasonal pattern of distribution in the southeastern Caribbean shows a peak of occurrence about six weeks later than in the Dominican Republic, and there is little overlap in the periods of greatest use. Sightings are uncommon before February. The peak in abundance occurs during March and April, declining during May, with some sightings extending into June. This is consistent with the pattern of sightings from historical whaling records in the southeastern Caribbean. These results suggest that the humpbacks mating and calving in this region are not a representative subset of those that winter in the Dominican Republic. Further studies will be needed to examine the spatial nature of the pattern shown here and define the nature and limits of this group, but these results suggest that some part of this breeding area represents a previously un-described distinct population segment within the North Atlantic. Given this, the widely held idea that there is a single West Indies humpback whale distinct population segment is in need of reconsideration.

Photo-identification comparison of humpback whale (Megaptera novaeangliae) flukes from Antarctic Area IV with fluke catalogues from East Africa, Western Australia and Eastern Australia

Early ‘Discovery mark’ data together with recent photo-identification, acoustic, genetic and satellite-radio tag data revealed linkages between humpback whales migrating from breeding grounds (C) off East Africa and the Area III feeding area, from Western Australian breeding grounds (D) and the Antarctic Area IV feeding area and the East Australian breeding grounds (E1) and Antarctic Area V feeding area. These data also revealed low levels of intermingling between (E1) and (D) humpback whales in the Antarctic Area IV feeding area consistent with these being separate populations. Greenpeace photographed the ventral tail flukes of 30 individual humpback whales in the Antarctic Area IV feeding area (70°E–130°E) from 2 to 9 January 2008, between 62°47’S and 64°14’S latitude and 80°00’E and 112°57’E longitude. Comparisons of the Antarctic Area IV Greenpeace fluke catalogue (n = 30) with existing reconciled fluke catalogues from East Africa (n = 842), Western Australia (n = 1,558) and Eastern Australia (n = 1,964), yielded no photo-identification matches. An analysis of the frequencies of whales seen and not seen in Antarctica, East Africa, Western Australia and Eastern Australia relative to the frequencies expected to have been seen and not seen, based on the estimated population sizes and the sizes of the catalogues, provided evidence that the Antarctic whales photographed are from a different population to the East African and East Australian populations. There was weak evidence supporting the hypothesis that the Antarctic whales are from the Western Australian population but insufficient data were available to determine a clear outcome. A comparison of the Antarctic Area IV Greenpeace catalogue (n = 30) with other existing African, Indian Ocean, Western and Eastern Australian and/or Antarctic catalogues, together with increased sampling across the humpback whale feeding season in Antarctica and along the Western and Eastern Australian coastline during their winter migration, is likely to provide further evidence of the migratory destination of these humpback whales. It will also add to our limited knowledge of the extent of population overlap within the Antarctic Area III, IV and V feeding areas.

Colombian International Migration: The Impact of Information Networks on Migration

Data from the Latin American Migration Project (LAMP) collected in Colombia between 2008 and 2015 were used to establish the scarcely studied relationship between social networks and the destinations where Colombians migrate. A logistic regression was employed to predict these migratory destinations. The contribution of this research is that it tests whether social networks tied to a destination are associated with the likelihood to migrate there. The findings support the Social Network Theory and offer an improved measure of social networks. It is shown that in migration gender matters since flow and interactions vary between men and women. There is evidence that men receive a greater benefit from social networks.

Migrants employ mixed strategies to route across the Great Lakes basin

Millions of migrants encounter the Great Lakes during spring and autumn migratory movements. How migrants behave when encountering these lakes is relatively unknown at the local and basin scales. Using seven years of radar data from 33 sites along the Great Lakes coastline, we investigated three hypotheses on migrant behavior during crepuscular and nocturnal movements. First, we hypothesized migrants’ direction is driven by local geography and its relation to the destination of migration. Second, we hypothesized migrants would move toward shore at dawn. Finally, we hypothesized that the Great Lakes would have different directional movements at lakes on the outside of the basin versus the interior. We found partial support for our first hypothesis, as well as evidence of decision making when migrants first encounter the Great Lakes. We found partial support for our second hypothesis. We found that migrants moved toward land at elevated levels at dawn compared to night during fall migration, but no effect was found during spring. We found support for our final hypothesis during spring migration, but not during fall. This pattern may be because of a combination of geographical, biological, and data bias, and will require additional work to disentangle. Taken together, we found that migrants perceive and react to the Great Lakes, and attempt to decrease risk, perceived or real, as they make their way to their migratory destination. Better understanding of directional movement has conservation implications, including mitigating anthropogenic obstacle collision risk and prioritizing stopover habitat restoration.

Sulfur stable isotope ratios provide further insight into movements of the fin whale, an oceanic long-range migrant

Stable isotope ratios have proven a valuable tool to investigate marine mammal ecology, including diet, distribution, and migratory movements. While most studies have focused on δ15N and δ13C values, δ34S values have been little used because their pattern of variation and tissue dynamics remain unclear. We examined the sequential variation of δ15N, δ13C, and δ34S values along the baleen plates from fin whales occurring off West Iceland in summer. All baleen plates exhibited fluctuations along their growing axis. A significant synchronic correlation was found between δ15N and δ34S values, while the relation of these values to the δ13C value was highly variable and inconsistent. These results were similar to those obtained in previous studies of Greenland bowhead whales, although the pattern of the oscillations in fin whales showed an increase in values during winter, while those of bowhead whales showed a decrease. Although seasonal variations in food intake and the associated cycles of protein synthesis and catabolism may have played a role in such fluctuations and the observed differences between species, we suggest that the main driver for the δ34S fluctuations reflected in baleen plates is the variation of local baselines between winter and summer grounds. This suggests ample potential for using δ34S values to study migratory movements and destinations of marine megafauna, provided that the geographic variation in δ34S baselines is clarified.

Multi-year presence of humpback whales in the Atlantic sector of the Southern Ocean but not during El Ni\xf1o

Humpback whales are thought to undertake annual migrations between their low latitude breeding grounds and high latitude feeding grounds. However, under specific conditions, humpback whales sometimes change their migratory destination or skip migration overall. Here we document the surprising persistent presence of humpback whales in the Atlantic sector of the Southern Ocean during five years (2011, 2012, 2013, 2017, and 2018) using passive acoustic data. However, in the El Niño years 2015 and 2016, humpback whales were virtually absent. Our data show that humpback whales are systematically present in the Atlantic sector of the Southern Ocean and suggest that these whales are particularly sensitive to climate oscillations which have profound effects on winds, sea ice extent, primary production, and especially krill productivity.

Decadal shift in foraging strategy of a migratory southern ocean predator.

Rapid anthropogenic environmental change is expected to impact a host of ecological parameters in Southern Ocean ecosystems. Of critical concern are the consequences of these changes on the range of species that show fidelity to migratory destinations, as philopatry is hypothesized to help or hinder adaptation to climate change depending on the circumstances. Many baleen whales show philopatry to feeding grounds and are also capital breeders that meet migratory and reproductive costs through seasonal energy intake. Southern right whales (Eubalaena australis, SRWs) are capital breeders that have a strong relationship between reproductive output and foraging success. The population dynamics of South Africa's population of SRWs are characterized by two distinct periods: the 1990s, a period of high calving rates; and the late 2010s, a period associated with lowered calving rates. Here we use analyses of stable carbon (δ13 C) and nitrogen (δ15 N) isotope values from SRW biopsy samples (n=122) collected during these two distinct periods to investigate foraging ecology of the South African population of SRWs over a time period coincident with the demographic shift. We show that South African SRWs underwent a dramatic northward shift, and diversification, in foraging strategy from 1990s to 2010s. Bayesian mixing model results suggest that during the 1990s, South African SRWs foraged on prey isotopically similar to South Georgia/Islas Georgias del Sur krill. In contrast, in the 2010s, South African SRWs foraged on prey isotopically consistent with the waters of the Subtropical Convergence, Polar Front and Marion Island. We hypothesize that this shift represents a response to changes in preferred habitat or prey, for example, the decrease in abundance and southward range contraction of Antarctic krill. By linking reproductive decline to changing foraging strategies for the first time in SRWs, we show that altering foraging strategies may not be sufficient to adapt to a changing ocean.

Exploring intraspecific variation in migratory destinations to investigate the drivers of migration

Various benefits (e.g. tracking of resources and of climate niche) and costs (e.g. distance travelled) are hypothesized to drive seasonal animal migrations. Until now, these potential factors have been investigated together at the species level, but migratory movements are made at the individual level, leading to intraspecific variability. Here, we use ringing/recovery data from 1308 individuals belonging to thirteen North American bird species to analyse patterns in intraspecific variability of migratory destinations in order to investigate which factors underpin bird migration and how individuals trade‐off among multiple factors. Our results suggest that migratory destinations have been shaped by access to resources (most important during the breeding season) and climatic niche tracking (during winter, mostly). However, the benefits of resource surpluses and climate niche tracking appear to be traded off against the cost of migratory distance, which seems to strongly constrain where individuals migrate.