Timing Of Autumn Migration Research Articles

Quantifying full phenological event distributions reveals simultaneous advances, temporal stability and delays in spring and autumn migration timing in long-distance migratory birds.

Phenological changes in key seasonally expressed life-history traits occurring across periods of climatic and environmental change can cause temporal mismatches between interacting species, and thereby impact population and community dynamics. However, studies quantifying long-term phenological changes have commonly only measured variation occurring in spring, measured as the first or mean dates on which focal traits or events were observed. Few studies have considered seasonally paired events spanning spring and autumn or tested the key assumption that single convenient metrics accurately capture entire event distributions. We used 60years (1955-2014) of daily bird migration census data from Fair Isle, Scotland, to comprehensively quantify the degree to which the full distributions of spring and autumn migration timing of 13 species of long-distance migratory bird changed across a period of substantial climatic and environmental change. In most species, mean spring and autumn migration dates changed little. However, the early migration phase (≤10th percentile date) commonly got earlier, while the late migration phase (≥90th percentile date) commonly got later. Consequently, species' total migration durations typically lengthened across years. Spring and autumn migration phenologies were not consistently correlated within or between years within species and hence were not tightly coupled. Furthermore, different metrics quantifying different aspects of migration phenology within seasons were not strongly cross-correlated, meaning that no single metric adequately described the full pattern of phenological change. These analyses therefore reveal complex patterns of simultaneous advancement, temporal stability and delay in spring and autumn migration phenologies, altering species' life-history structures. Additionally, they demonstrate that this complexity is only revealed if multiple metrics encompassing entire seasonal event distributions, rather than single metrics, are used to quantify phenological change. Existing evidence of long-term phenological changes detected using only one or two metrics should consequently be interpreted cautiously because divergent changes occurring simultaneously could potentially have remained undetected.

Leave before it's too late: anthropogenic and environmental triggers of autumn migration in a hunted ungulate population.

Autumn has to a large extent been neglected in the climate effect literature, yet autumn events, e.g., plant senescence and animal migration, affect fitness of animals differently than spring events. Understanding how variables including plant phenology influence timing of autumn migrations is important to gain a comprehensive understanding of the full annual cycle of migratory species. Here we use 13yr of data from 60 male and 168 female red deer (Cervus elaphus) to identify triggers of autumn migration. We relate the timing of autumn migration to environmental variables like snow fall, temperature, and plant phenology (NDVI), and to onset of hunting, sex, and migration distance. Severe weather has been suggested as the main trigger of autumn migration, but we found that the majority of the individuals had left the summer range well before snow fall (80.3%) and frost (70.5%), and also before the peak deterioration in forage quality (71.9%). Declining temperatures were associated with a higher daily migration potential. Onset of hunting showed the largest effect on migration potential, with a marked increase during the first days of hunting. Individuals still present in the summer range when snow fall, frost, or peak forage deterioration occurred showed a significantly higher migration potential around these events. Males were less responsive to environmental cues, suggesting rutting activity, starting earlier in males, initiate movement prior to such conditions. Also, individuals with longer migration distances had a higher migration potential late in the season than individuals with shorter migration distances. Our study shows that factors beyond weather and plant phenology, such as onset of hunting, may be important triggers of autumn migration. Severe weather and forage deterioration were important triggers for the individuals experiencing this, which suggests a hierarchical response to environmental cues. The trade-off between staying longer in the summer range and increased energy expenditures if surprised by severe weather is asymmetric, and leaving well in advance can be seen as a risk-averse tactic.

Differential Migration and Phenology of Adult Red-Tailed Hawks in California

Abstract Differential migration by age and sex has been observed within several raptor species. Here, we report differential autumn migration timing between adult and juvenile Red-tailed Hawks (Buteo jamaicensis), and between adult males and females at the Golden Gate Raptor Observatory in the Marin Headlands of northern California. Because Red-tailed Hawks cannot be easily sexed in hand, we used discriminant function analysis (DFA) to identify morphometric measures useful for sexing adult Red-tailed Hawks captured during migration in the Marin Headlands and created a flowchart for in-hand field sexing of adult Red-tailed Hawks. The DFA correctly assigned sex 95% of the time, and provides an improved method for sexing adult Red-tailed Hawks in the Marin Headlands when compared to existing DFAs developed for other populations of this species in the western United States. Our ability to sex adult Red-tailed Hawks permitted examination of fall migration phenology, which differed markedly for adult and juveni...

Tracking mated pairs in a long-distance migratory songbird: migration schedules are not synchronized within pairs

In long-distance migrants, it has been hypothesized that re-pairing in spring is facilitated if, on the wintering grounds, formerly mated individuals maintain close proximity or occupy ecologically similar habitat, which then results in more synchronized spring migration schedules. For songbirds, pair members have long been thought to migrate independently, but only recently has it been possible to directly track start-to-finish migration to test this prediction. We used light-sensor geolocators to track paired versus nonpaired purple martins, Progne subis subis, that breed in North America and winter in South America. In 6 of 12 pairs, pair members departed on autumn migration within 4 days of each other, but pairs rarely occupied nearby stopover sites in Central America and were separated by an average of 560 km upon arrival in Brazil. Formerly paired birds were not significantly more similar in autumn or spring migration timing, or winter roost location, compared with nonpaired birds tracked from the same colonies and years. Formerly mated pairs who were closer together in Brazil, or who occupied regions with similar amounts of forest cover, did not have more synchronized spring migration schedules. Only 1 of 12 pairs that were tracked remated after migration. Intense competition for nesting cavities combined with disparate spring migration schedules of former pairs probably contributes to the high divorce rate.

Moult Strategies Affect Age Differences in Autumn Migration Timing in East Mediterranean Migratory Passerines.

Adult passerines renew their flight feathers at least once every year. This complete moult occurs either in the breeding areas, just after breeding (summer moult), or, in some long-distance migratory species, at the non-breeding areas, after arrival to the southern wintering area at the end of autumn migration (winter moult). The aim of this study was to relate moult strategies with the DMD, the difference in median migration date, through Israel, between juveniles and adults. Our data on autumn migration timing in juveniles and adults was based on ringing data of 49,125 individuals belonging to 23 passerine species that breed in Europe and Western Asia and migrate through Israel. We found that DMD was associated with moult timing. In all species that perform a winter moult, adults preceded juveniles during autumn. Among migrants who perform a summer moult, we found evidence of both migration timing patterns: juveniles preceding adults or adults preceding juveniles. In addition, in summer moulters, we found a significant, positive correlation between mean breeding latitude and DMD. Although previous studies described that moult duration and extent can be affected by migration, we suggest that moult strategies affect both migration timing and migration strategy. These two moult strategies (summer or winter moult) also represent two unique migration strategies. Our findings highlight the evolutionary interplay between moult and migration strategies.

Quantifying non‐breeding season occupancy patterns and the timing and drivers of autumn migration for a migratory songbird using Doppler radar

For seasonal migrants, non‐breeding regions can play different roles in the ecology of their annual cycles: as stopover habitat, overwintering habitat, or as a combination in which some individuals stop‐over and others over‐winter. Such functional variations can lead to variation in occupancy dynamics and migration phenology to these different regions. In this study, we used data from archived Doppler weather surveillance radar to compare site‐occupancy and movement dynamics of a migratory songbird (tree swallow Tachycineta bicolor) between two non‐breeding areas: southeastern Louisiana and central peninsular Florida, USA. Specifically, in each area, we 1) quantified long‐term (1996–2012) non‐breeding season occupancy dynamics, 2) quantified variation in timing of autumn migration, and 3) tested which climate variables along their respective flyways were best correlated with variation in dates of arrival. Additionally, we cross‐validated the dynamics from archived radar with data from eBird, a large‐scale citizen science database that provides an independent measure of avian occupancy. We found strong and significant correlations between radar‐estimated and eBird‐estimated occupancy dynamics in both Louisiana and Florida. Long‐term Louisiana occupancy dynamics conformed to our hypothesis that this region acts as a combined stopover and overwintering region whereas Florida occupancy dynamics were akin to a traditional winter region. Arrival to Louisiana during the study period was much earlier and took place over a much shorter arrival window than did arrival to Florida, which showed much more gradual arrival over the course of several months. At both sites, annual variation in mean arrival date was best explained by the amount of precipitation along the lower portions of their respective migration flyways.

Temporal trends in the timing of autumn migration of short- and long-distance migrating Blackcaps (Sylvia atricapilla)

Bo Beolens, Michael Watkins & Michael Grayson 2014: The Eponym Dictionary of Birds. — Bloomsbury. 624 pp.

Long‐term phenological shifts and intra‐specific differences in migratory change in the willow warblerPhylloscopus trochilus

Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life‐cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long‐term study on the willow warblerPhylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22‐yr of ringing records and two temporally separated data sets of egg‐laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg‐laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra‐specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg‐laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.

Population-specific home ranges and migration timing of Pacific Arctic beluga whales (Delphinapterus leucas)

Two populations of beluga whales (Delphinapterus leucas), the Eastern Beaufort Sea (BS) and Eastern Chukchi Sea (ECS), make extensive seasonal migrations into the Pacific Arctic. However, the extent to which these populations overlap in time and space is not known. We quantified distribution and migration patterns for BS and ECS belugas using daily locations from whales tracked with satellite-linked transmitters. Home ranges and core areas in summer (July and August) and in each month (July–November), daily displacement, dispersal from core areas, and autumn migration timing were estimated. Distinct summer and fall distribution patterns and staggered autumn migration timing were identified for BS and ECS whales. Summer home ranges for each population had less than 10 % overlap. Monthly home ranges were also relatively distinct between populations except in September (up to 88 % home range overlap). A distinct east–west shift in focal area use occurred in September that persisted into October, with the two populations essentially switching longitudinal positions. Highest daily displacements occurred during the migratory period in September for BS whales and October for ECS whales, further indicating westward fall migration was offset between populations. Sexual segregation of males and females within a population also varied monthly. Autumn migration timing as well as differences in spatial and temporal segregation between BS and ECS beluga populations may be a result of maternally driven philopatry and population-specific adaptations to dynamically available resources. Our results contribute to the management of these populations by identifying seasonal area use and differences in migration patterns.

The effects of hatching date on timing of autumn migration in partial migrants – an individual approach

Timing of spring migration and breeding and their interaction with climate change has been widely studied in recent years, but the possible changes in timing of autumn migration have gained less attention. This work focuses on autumn migration and provides the first multi‐species individual‐based study of how hatching date affects the autumn migration date and migration age by using nestling ring data and re‐trappings of the same individuals during the autumn migration at the Hanko Bird Observatory, Finland. We studied three potentially multibrooded passerines (great tit, blue tit and coal tit) and two single‐brooded birds of prey (goshawk, sparrowhawk), all partially migratory short‐distance migrants. Individuals from late broods migrated at a younger age in all tit species and also in hawks the late hatched individuals tended to migrate at a younger age than the early‐hatched individuals. Late‐hatched individuals migrated later than early‐hatched individuals in blue and coal tits, where the latest hatchers represented second brood individuals. Based on our results, the time from hatching to autumn migration is not constant even among individuals of the same population. Our study indicates that climate warming induced advancement of avian breeding may cause changes in the timing of autumn migration through the frequency of second broods.

Autumn Migration of Mississippi Flyway Mallards as Determined by Satellite Telemetry

Abstract We used satellite telemetry to study autumn migration timing, routes, stopover duration, and final destinations of mallards Anas platyrhynchos captured the previous spring in Arkansas from 2004 to 2007. Of those mallards that still had functioning transmitters on September 15 (n = 55), the average date when autumn migration began was October 23 (SE = 2.62 d; range = September 17–December 7). For those mallards that stopped for >1 d during migration, the average stopover length was 15.4 d (SE = 1.47 d). Ten mallards migrated nonstop to wintering sites. The eastern Dakotas were a heavily utilized stopover area. The total distance migrated per mallard averaged 1,407 km (SE = 89.55 km; range = 142–2,947 km). The average time spent on migration per individual between September 15 and December 15 was 27 d (SE = 2.88 d; range = 2–84 d). The state where most mallards were located on December 15 was Missouri (11) followed by Arkansas (8), while 5 mallards were still in Canada, and only 8 of 43 females and 0 of 10 males were present in Arkansas. The eastern Dakotas are a heavily utilized migration stopover for midcontinent mallards that may require more attention for migration habitat management. The reasons for so few mallards, especially male mallards, returning to Arkansas the following year deserves further research.

Repeat Tracking of Individual Songbirds Reveals Consistent Migration Timing but Flexibility in Route

Tracking repeat migratory journeys of individual animals is required to assess phenotypic plasticity of individual migration behaviour in space and time. We used light-level geolocators to track the long-distance journeys of migratory songbirds (wood thrush, Hylocichla mustelina), and, for the first time, repeat journeys of individuals. We compare between- and within-individual variation in migration to examine flexibility of timing and route in spring and autumn. Date of departure from wintering sites in Central America, along with sex and age factors, explained most of the variation (71%) in arrival date at North American breeding sites. Spring migration showed high within-individual repeatability in timing, but not in route. In particular, spring departure dates of individuals were highly repeatable, with a mean difference between years of just 3 days. Autumn migration timing and routes were not repeatable. Our results provide novel evidence of low phenotypic plasticity in timing of spring migration, which may limit the ability of individuals to adjust migration schedules in response to climate change.

Timing of migration of the Curlew Sandpiper (Calidris ferruginea) through Poland in relation to Arctic breeding conditions

Recent shifts in the timing of migration and breeding have been attributed to climate vari-ation in some migratory birds. However, the divergent patterns in the timing of autumn migration among different bird species suggest a significant role of factors other than cli-mate. Using data of constant-effort catches, determinants for the annual variation in the timing of migration were investigated in the Curlew Sandpiper Calidris ferruginea in Po-land. Variation in the timing for adult and juvenile Curlew Sandpipers was influenced by breeding success, which was in turn connected to predation pressure, and June and July temperatures on the species’ breeding grounds in the Arctic region. Median date of pas-sage of adults was significantly later in good than in poor breeding years. The migration of adults was earlier by 2.3 days for every 1°C increase in average June temperature in the Arctic breeding grounds. Median migration date of juveniles was positively correlated with predation and negatively with June temperature in the Arctic breeding grounds. Me-dian migration date of adults advanced by a factor of –0.59 days/year, which translates into 10 days from 1984–2000. These results suggest that conditions on breeding grounds can affect the timing of subsequent events within the annual cycle. Circumstantial evi-dence also suggests that climate change may have increased the predation on young Cur-lew Sandpipers, increasing the frequency of poor breeding years and modifying the tim-ing of autumn migration in these waders.

Obligate and facultative migration in birds: ecological aspects

This paper is concerned mainly with the differences between obligate and facultative migration in birds. Obligate migration is considered “hard-wired”, in that the bird seems pre-programmed to leave its breeding area at a certain time each year, and to return at another time. Timing, directions and distances are relatively constant from year to year. This type of migration is thus characterised by its regularity, consistency and predictability. It is found in both short-distance and long-distance migrants, but mainly in the latter. In contrast, facultative migration is considered optional, occurring in response to conditions at the time. Individuals may migrate in some years but not in others, depending on the prevailing food supplies or weather conditions. The timing of autumn migration, and the distance travelled, can be highly variable between individuals and, at the population level, between years. Facultative migration is typical of many partial migrants, but is found in its most extreme form in so-called irruptive migrants. While individual obligate migrants typically return to the same breeding localities year after year, and sometimes also to the same wintering localities, individual irruptive migrants typically breed or winter in widely separated areas in different years, wherever conditions are favourable. It is suggested that these two types of migration are best considered not as distinct, but as lying at opposite ends of a continuum of variation in bird migratory behaviour. Both systems are adaptive; one to conditions in which resource levels vary regularly and predictably in space and time, and the other to conditions in which resource levels vary unpredictably. Suggestions are made for experimental work on captive irruptive species.

Delayed autumn migration in northern European waterfowl

Climate change is causing phenological shifts in the environment. Among birds, increasing temperatures have been shown to advance the spring migration and breeding, which in turn affect individual reproductive success. The autumn migration phenology has, however, been largely overlooked. Here, we study long-term changes in the timing of autumn migration in 15 northern European waterfowl species during 1979–2009. We hypothesised that waterfowl should delay their migration since they winter north of the Sahara desert. Our results show that 6 (Greylag Goose Anser anser, Eurasian Wigeon Anas penelope, Eurasian Teal Anas crecca, Tufted Duck Aythya fuligula, Velvet Scoter Melanitta fusca, and Common Goldeneye Bucephala clangula) of the 15 studied species have delayed at least one of the three phases of migration examined. The most marked delay in median migration dates was by more than a month over the past 31 years. Only the Bean Goose Anser fabalis exhibited an advanced beginning of its migration. We also analyse the timing of the entire waterfowl migration and show that the median and end of the migration have been significantly delayed. The results support our predictions and highlight how rapid phenological responses to climate change may be. Such delayed departures may be the cause for recently observed northward shifts of wintering ducks. Our results suggest that waterfowl to be a good indicator group for climate change. Changing migration times can also have population-level consequences due to differential hunting and natural predation pressures over the waterfowl flyway.

Long-Term Shifts in Autumn Migration by Songbirds at a Coastal Eastern North American Stopover Site

Abstract We investigated long-term trends in mean autumn capture dates of 19 species of migratory passerines including 11 long-distance migrants and eight short-distance migrants. Birds were captured between 1960 and 2007 at a banding station in southern Rhode Island. We detected annual trends in the highest ranked models with mean capture dates of seven species significantly delayed by an average of 3.0 days per decade; 38% of long-distance migrants and 50% of short-distance migrants studied significantly delayed migration. We found no evidence of long-term shifts in autumn migration timing for seven species and mean capture dates of five species exhibited non-linear annual trends. Mean autumn temperature was an important factor in explaining annual trends for eight species. Changes in annual capture rates for some species may have an equal or greater role than year or temperature in explaining long-term trends in autumn migration timing. Our analysis suggests that some migratory bird species are now dep...

Timing of seasonal migration in mule deer: effects of climate, plant phenology, and life-history characteristics

Phenological events of plants and animals are sensitive to climatic processes. Migration is a life-history event exhibited by most large herbivores living in seasonal environments, and is thought to occur in response to dynamics of forage and weather. Decisions regarding when to migrate, however, may be affected by differences in life-history characteristics of individuals. Long-term and intensive study of a population of mule deer (Odocoileus hemionus) in the Sierra Nevada, California, USA, allowed us to document patterns of migration during 11 years that encompassed a wide array of environmental conditions. We used two new techniques to properly account for interval-censored data and disentangle effects of broad-scale climate, local weather patterns, and plant phenology on seasonal patterns of migration, while incorporating effects of individual life-history characteristics. Timing of autumn migration varied substantially among individual deer, but was associated with the severity of winter weather, and in particular, snow depth and cold temperatures. Migratory responses to winter weather, however, were affected by age, nutritional condition, and summer residency of individual females. Old females and those in good nutritional condition risked encountering severe weather by delaying autumn migration, and were thus risk-prone with respect to the potential loss of foraging opportunities in deep snow compared with young females and those in poor nutritional condition. Females that summered on the west side of the crest of the Sierra Nevada delayed autumn migration relative to east-side females, which supports the influence of the local environment on timing of migration. In contrast, timing of spring migration was unrelated to individual life-history characteristics, was nearly twice as synchronous as autumn migration, differed among years, was related to the southern oscillation index, and was influenced by absolute snow depth and advancing phenology of plants. Plasticity in timing of migration in response to climatic conditions and plant phenology may be an adaptive behavioral strategy, which should reduce the detrimental effects of trophic mismatches between resources and other life-history events of large herbivores. Failure to consider effects of nutrition and other life-history traits may cloud interpretation of phenological patterns of mammals and conceal relationships associated with climate change.

Timing of autumn migration of young Corncrakes Crex crex

Knowledge of the timing of migration of young Corncrakes is required for effective implementation of conservation measures. Forty Corncrake chicks were radiotracked during the period between independence and departure from the natal area to determine the age and time at which fledged juveniles depart on migration. Departure occurred between early August and mid‐September at a mean age of 44 days, around the age at which growth of the primary feathers ceases. Chicks from later broods are exposed to greater risk of being killed during mowing, but provision of late mowing options in conservation schemes could enhance their survival.

Impact of Climate and Predation on Autumn Migration of the Curlew Sandpiper

Using constant-effort catch data, causes of annual variation in the timing of migration of Curlew Sandpipers (Calidris ferruginea) migrating through Ottenby, Sweden, as well as the trend in timing of migration from 1946–2005, was investigated. Variation in the timing of autumn migration of adult and juvenile Curlew Sandpipers was influenced by breeding success connected to predation pressure on the Arctic breeding grounds. Median migration date of adult birds was significantly later in good breeding years compared with poor breeding years while the migration of juveniles was earlier in good breeding years compared with poor breeding years. Also, adults migrated earlier when the average temperature in June was warmer. Median migration dates of adults have advanced by 23 days from 1946–2005, but the migration dates of juveniles have remained unchanged. Unchanged migration dates of juveniles indicate that earlier departure of the adult Curlew Sandpipers from the breeding grounds was not due to earlier breeding. Evidence suggests that declining breeding productivity as a result of increasing predation on broods of shorebirds might, over the years, be the reason for the observed pattern of early departure of adults from the breeding grounds. One possible consequence of earlier migration is a mismatch between timing of migration and periods of food abundance on migration routes and at the wintering grounds, leading to a decline in adult and juvenile survival and population size.

Change in migration phenology and biometrics of two conspecific Sylvia species in Hungary

The distribution area and the timing of migration of many bird species have recently changed, presumably due to climatic factors. In our study, we estimated the effect of climate change on migration phenology and biometrics of two sister Sylvia species: the medium-distance migrant Blackcap (Sylvia atricapilla) and the long-distance migrant Garden Warbler (Sylvia borin). We used the data of 52,440 Blackcaps and 6,943 Garden Warblers caught and ringed at the Ocsa Bird Ringing Station (47°15′N, 19°15′E) in Hungary between 1984 and 2008. The age and in case of Blackcaps the sex groups were handled separately. The timing of the spring migration of Garden Warblers shifted earlier, whereas it did not change in Blackcaps during the study period. We presume—in accordance with other observations concerning Blackcaps in West-Europe—that it probably has changed earlier than the 1980s. The timing of autumn migration shifted about 2 weeks later in all age and sex groups of Blackcaps. We found significant correlation in the timing of autumn migration of sex groups, the sign of the differences between the timing of males and females changed. Juvenile Garden Warblers shifted their autumn migration 13 days later, but adults did not. Mean body mass decreased while mean wing length increased suggesting a change in the composition of the trans-migrant population. We hypothesise that due to climate change the breeding range of these species expanded northwards, producing an increased ratio of long-winged northern individuals in the trans-migrant populations.