Autumn Migrants Research Articles

Blackaps Sylvia atricapilla stopping over at the desert edge; physiological state and flight‐range estimates

Migrating Blackcaps Sylvia atricapilla were mist netted at the desert edge in northern Israel and in Elat (southern Israel) during spring and autumn migrations between 1970 and 1991. Birds in spring in northern Israel were representative of birds that had completed the crossing of the Sahara, while those in Elat still had to cross the 150 km of the Negev Desert, which separates Elat and northern Israel. In autumn, birds captured in northern Israel were representative of those about to cross the Sahara Desert, while those in Elat had already started to cross the desert. The data allowed analysis of seasonal and location differences in the physiological state of Blackcaps before and after crossing the Sahara. Data analysed included body mass, visible fat score and calculated fat content. Autumn migrants were in better physiological condition than spring migrants at both locations, probably as a consequence of their migration route through fertile areas in autumn compared with the crossing of the Sahara in spring. Body mass was less variable after the Sahara crossing in spring than before the crossing in autumn. In spring, 71% and 67% of the birds were fat depleted (fat scores 0 and 1) at Elat and in northern Israel, respectively, while in autumn 34% and 42% were fat depleted. Blackcaps at Elat were 1.6 g lighter than those in northern Israel in autumn and 1.9 g lighter in spring. Potential flight ranges were estimated on the basis of meteorological conditions and flight altitude of passerines above the Negev in Israel (northern Sahara edge) during migration and on a simulation model that considered both energy and water as potential limiting factors for flight duration and distance. The simulation model predicted that half of the Blackcaps that stopped over in Elat and the majority of those that stopped over in northern Israel could not make a nonstop flight over the Sahara Desert in autumn without the assistance of at least an 8 m per s tailwind. Such a wind would still not be sufficient for 34% of the birds in Elat and 42% in northern Israel, and clearly they had insufficient fat reserves to cross the Sahara in a single flight. Although the fattest Blackcaps had accumulated sufficient fat to enable them to traverse the Sahara in a single flight, they probably faced dehydration by at least 12% of their initial body mass when they reached the southern Sahara edge. These birds should use intermittent migration with stopovers at sites with drinking and feeding potential. Their decision to stop over during the day in the desert at sites with shade but without food and water would be beneficial if the meteorological conditions during daytime migration imposed greater risks of dehydration than at night. Spring migrants could not reach their breeding areas in Europe without feeding, but those examined in Elat could cross the remainder of the desert in a single flight.

Spring and Autumn Migration in Arctic Shorebirds: Same Distance, Different Strategies

The Arctic is an extremely inhospitable region for most of the year, but during the summer months it bursts with life. A major proportion of avian species nesting in the Arctic are shorebirds (order Charadriiformes; suborder Charadrii). They migrate thousands of kilometers from their wintering grounds to take advantage of abundant food resources each summer and display a variety of migratory strategies. In an attempt to classify this variation, not only between spring and autumn migration, but within a migration, we present four categories. These relate to the distance a species generally flies between stopovers: short distance bout, intermediate distance bout, long distance bout, and combinations. We then explore further differences between spring and autumn migration. Spring migrants experience poor weather and decreased food availability as they fly north. Many cope with huge flocks, which serve as protection from predators, but may also reduce foraging efficiency and increase aggression. In contrast, autumn migrants generally encounter favorable weather and ample food. Flock sizes are usually smaller, thus foraging efficiency is higher and aggression lower than during spring migration. Physiologically, spring migrants are preparing for breeding and reproductive hormones are secreted. In the Western Sandpiper ( Calidris mauri ), luteinizing hormone levels are higher for spring than autumn migrants. Late spring migrants have higher testosterone levels than either early spring migrants or autumn migrants. Corticosterone levels are also higher in spring vs . autumn migrants. Although spring and autumn migrants travel similar distances, their strategies differ behaviorally and physiologically.

Growth and Survival of Newly Parasitic Sea Lampreys at Representative Winter Temperatures

Abstract Larval sea lampreys Petromyzon marinus begin to metamorphose into their parasitic phase in July and migrate to the Great Lakes either in autumn, when they immediately feed on fish, or in spring after overwintering in the stream substrate. Survival and growth of newly parasitic autumn migrants (mean weight, 4.18 g) differed significantly between temperature treatments when sea lampreys were held over winter and allowed to feed on longnose suckers Catostomus catostomus at either the maximum available temperature (˜4°C) or normal surface temperature (minimum <1°C) in the Great Lakes during winter. Survival from December 1990 to June 1991 was 60% for the animals held in the warmer water but only 30% for the animals held in the colder water until 23 April. The average increase in weight was 8.23 g for the 35 survivors in the warmer water but only 5.15 g for the 17 survivors in the colder water. Average increases in weight from December to May for sea lampreys at both temperatures were 3.8 to 6.6 times...

Diurnal and Nocturnal Patterns of Activity in Resident and Migrant SilvereyesZosterops lateralis

This study examined diurnal and nocturnal activity patterns from 40 hours of continuous activity recordings of individually caged resident and migrant Silvereyes Zosterops lateralis. Elevated night activity (= Zugunruhe) was displayed by migrants in autumn and spring but not by residents. Zugunruhe commonly commenced in the dark portion of the morning and continued to about 2-3 h beyond the onset of light. Migrants were more night restless than residents in winter and in the migratory seasons of autumn and spring. They were also more diurnally active in the winter months than residents. The increase in diurnal activity in the latter period is related to winter migratory movements.

Altitude choice by night migrants in a desert area predicted by meteorological factors

The height distribution of nocturnal migrants in southern Israel was determined by con‐ically scanning the sky with the pencil‐beam of an X‐band radar at different elevation angles. Altitudinal profiles of meteorological parameters were derived from radio sondes launched at midnight and from pilot balloons launched every 4 h. A model to predict the height distribution of birds by means of meteorological variables was developed by assuming that the observed proportions of birds within a height zone, compared with the neighbouring height zones, reflect the degree of the birds' preference for that height zone. Only one among the variables included in the multiple regression analysis proved to have a significant influence on the height distribution of migrants: the difference of tailwind speed between height zones. Simulations with 1000 birds choosing altitudes by means of the night's altitudinal profile of tailwind speed closely traced the observed distributions. The fact that all the other meteorological factors which were previously suggested to have an influence on the flight range in trans‐desert migration were not selected as relevant factors is discussed. The following basic information on nocturnal bird migration in the Negev is provided as a background for the statistical analysis: Directions of migration are within very narrow limits. During the first hour after take‐off, 60% of autumn migrants and 75% of spring migrants are climbing, with vertical speeds of 0.1–2 m per s and 0.1–4 m per s, respectively. During the rest of the night, climbing and descending birds are in nearly equal proportions. Thus, there is a high potential of sampling atmospheric conditions at different altitudes. Height distributions in spring and autumn show the influence of the trade wind situation, autumn migrants making use of the northerly winds at low levels in spite of high temperatures, while spring migrants tend to reach the southwesterly winds at higher levels.

Differences in Age and Sex Ratio among Migrating and Wintering Raptors in Southern Sweden

-In order to test hypotheses explaining intraspecific differences in migration patterns of birds, a four-year field study of migrant raptors in southernmost Sweden was undertaken. The age and sex ratios among autumn migrants departing from the province of Scania at Falsterbo were compared to the corresponding ratios among birds of the same species that stayed in Scania the following winter. In most species (Red Kite [Milvus milvus], White-tailed Eagle [Haliaeetus albicilla], Northern Harrier [Circus cyaneus], Goshawk [Accipiter gentilis], Sparrowhawk [A. nisus], Common Buzzard [Buteo buteo] and Eurasian Kestrel [Falco tinnunculus]), the proportion of adults was distinctly higher among wintering birds than among the migrants. A marked exception was the Rough-legged Hawk (B. lagopus), which had significantly more juveniles among the wintering birds. In most species where the sexes could be separated more females were found among the wintering birds than among the migrants (Northern Harrier, Goshawk, Sparrowhawk and Rough-legged Hawk). The Eurasian Kestrel, however, showed the reverse pattern with a higher proportion of males among wintering birds. The results support the social-dominance hypothesis, where the dominant adults and the larger sex (in raptors the female) generally winter furthest north. That juveniles are driven away from the breeding territories is suggested by a significantly higher proportion of juvenile Common Buzzards wintering in marginal coastal regions as compared to the inland portion of Scania. The results are also in general agreement with Bergmann's rule. The higher proportion of male Eurasian Kestrels among wintering birds is most likely explained by the importance of early arrival at the breeding territory. Received 6 July 1992, accepted 25 November 1992. AMONG BIRDS we find a mixture of migration strategies from completely resident species to long-distance migrants travelling thousands of kilometers between summer and winter quarters each year. Migration can be expected to occur in populations where birds survive in greater numbers if they leave their breeding areas for the nonbreeding season than if they remain there for the whole year (Lack 1954). Even within species there may be great variation. In the Common Buzzard (Buteo buteo), birds breeding in northeast Europe are long-distance migrants spending the winter in southern Africa, while birds breeding in most parts of Scandinavia are short-distance migrants wintering on the European mainland, and breeding birds in southern and western Europe are residents (Cramp et al. 1980). Within species, various categories of birds (e.g. age and sex classes) clearly have different migration patterns. This so-called differential migration has attracted the attention of several authors (Gauthreaux 1982, Ketterson and Nolan 1983, Lundberg 1988). Several hypotheses have been put forward to explain interand especially intraspecific differences in migratory and wintering patterns in birds. Compilations have been made by Gudmundsson (1988) and Kerlinger (1989) and a short summary follows: (1) The body-size hypothesis, closely related to Bergmann's rule (Salomonsen 1955), states that large birds are able to winter further north since they are better able to tolerate cold surroundings (Searcy 1980). As a result, smaller individuals can be expected to undertake longer migrations than larger ones. (2) The social-dominance hypothesis (Cox 1968, Mueller et al. 1977, Gauthreaux 1978, 1982) proposes that, in short-distance migrants, subordinate individuals are forced to migrate from the breeding grounds (and/or the best wintering areas) because of competition from more dominant birds. (3) The arrival-time hypothesis (King et al. 1965, Myers 1981) indicates that, if there is competition for breeding resources, birds returning earlier to the breeding grounds do better. Therefore, it is advantageous to winter as close to the breeding area as possible. (4) The character-divergence hypothesis (Koplin 1973) explains differences in winter habitat as being a result of character displacement due to

Homing of Atlantic salmon ( Salmo salar L.) to a tributary spawning stream in a major river catchment

At the Girnock Burn, a tributary of the River Dee in Scotland, a substantial part of the annual production of migrant juvenile salmon ( Salmo salar L.) leaves the stream in autumn rather than in spring. Previously, the status of the autumn migrants was uncertain because Carlin tagging indicated that they returned to the stream with a lower frequency than smolts tagged in spring. The difference was not attributable to the smolting of autumn migrants outside of the Girnock Burn and their homing to these new locations since adults tagged as autumn parr were also under-represented in fisheries distant from the home stream. Instead, the differences were probably artifactual and attributable to a seasonal effect of the Carlin tagging procedure itself. When juveniles were tagged instead with wire microtags, recapture rates were similar for autumn and spring migrants. This is consistent with the hypothesis that the autumn migration is an aspect of smolting. Microtagging of all juvenile migrants (paired with adipose fin clipping) indicated that the homing of adult spawners to the Girnock Burn was substantially accurate. Over the period of study 45% of fish of the sea-age classes that were expected to bear adipose fin clips did so.

Breeding and Wintering riverine birds at the Aurland river, western Norway during post-regulation conditions

The riverine bird community of the river Aurland was studied in 1989 and 1990 during post-regulation conditions, focusing on both the breeding bird community and the winter bird community. Although regulation has strongly reduced the spring and summer flow, the riverine bird community is within the normal range for the region with regard to both species composition and the population density along the rivers. During the breeding season three species, the dipper, white wagtail and the common sandpiper, are the regular breeders. The three species, all of which are benthic insect feeders, exhibited population densities above the average for rivers in western Norway, based on a comparison with population from 38 other rivers in three counties. As wagtails and sandpipers disappear during late summer and early autumn (migrants), they are replaced by two new species over the wintertime, grey heron and goosanders, both of which are piscivorous. Moreover, the winter community is species poor, but this is normal fo...

Do host alternating aphids know which plant they are on?

Abstract. To determine whether an aphid is ‘aware’ of which plant it is on, clones of a host alternating aphid, Cavariella aegopodii Scop., reared on its primary (Salix) or secondary (Daucus) host, were subjected to autumnal conditions. Old clones produced males and egg laying females when exposed to autumnal conditions on the primary host but autumnal migrants and males when on the secondary host. Unlike some other host alternating aphids, Cavariella did not have to spend a period on the secondary host or go through the spring migrant stage before producing sexuals. The adaptive significance of a host alternating aphid being ‘aware’ of which host plant it is on is discussed in the light of these results.

Patterns of growth and smolting in autumn migrants from a Scottish population of Atlantic salmon, Salmo salar L.

In late November 1990 salmon parr, Salmo salar L., from the Girnock Burn in northern Scotland were either caught on their feeding territories (n=25) or trapped during downstream migration (n= 18). They were then housed in a laboratory rearing tank and their food intake and growth rates were tracked, until their smolting status was ascertained in the following May. Female fish were predominant in both groups; although the range of ages was the same, the total age of migrants was 2+ while that of residents was 1+. In November, compared to resident fish of the same year class, migrants were larger, heavier and in better condition. Although growth rates dropped during the winter in both groups before increasing in spring, migrants ate more and consistently grew faster than residents. In seawater tolerance tests conducted in May, more residents than migrants failed to adapt. These results confirm the suggestion that autumn migrants smolt in the following spring and suggest that they represent the faster‐growing component of their cohort.

Fat deposition and theoretical flight range of small autumn migrants in southern Germany

From 1987 to 1989, 11 passerine species caught during their autumn migration on the Mettnau peninsula at Lake Constance (SW Germany) were examined for weight, visible fat deposition and actual fat load using a Soxhlet extraction. From the amount of fat deposited, mean theoretical flight ranges were calculated. Visible stored fat is only deposited in large quantities towards the end of the migration period. Before migration, the mean fat content stored in relation to fat-free dry weight ranges from 9–12%, whereas during migration it ranges from 13–30%. There is no difference between long- and short-distance migrants. A weight change cannot be accounted for exclusively by fat deposition. The mean weight of first-captures was low in all species. Only 5 of the 11 species studied gained weight more or less extensively during the migration period. All species showed an increase in fat deposition during migration. Since 1972, a marked annual decrease in average body weight during migration was found in the Reed ...

Radar observations of passerine migration over Frankfurt and Hannover, Germany

The direction of the autumn and spring migration of short- and long-distance migrants over Frankfurt and spring migration of short-distance migrants over Hannover were studied by radar. For long-distance migrants, a comparison with results obtained from the Swiss Lowland revealed no difference in the direction of autumn migration but a 35° difference in the direction of spring migration. In Frankfurt the migration was more northerly. The difference in the migratory direction of short-distance migrants between central Germany and the Swiss Lowland ranged from 10° to 15° in spring and to 9° in autumn. The direction of spring migration can be understood as a simple 180° reversal of autumn migration in short-distance migrants, but not in long-distance migrants. The difference in the direction of the migratory axis (about 30°) among long-distance migrants between autumn and spring indicates that such birds follow different routes during their two seasonal, migratory journeys. The short- and long-distance migrants flew a similar direction in autumn. In spring, the short-distance migrants flew considerably more easterly compared to long-distance migrants. Wind influences, because of the seasonality of cyclonic weather systems, was much more likely to affect the migration of short-distance migrants in both autumn and spring. The effect of strong crosswinds on the direction of spring migration was examined.

Flight behaviour of the bird cherry aphid, Rhopalosiphum padi

Abstract Seasonal winged forms of the bird cherry aphid, Rhopalosiphum padi L., were flown in an automated flight chamber. During their maiden flights, autumn migrants (gynoparae) had a greater initial rate of climb than summer (exules) and spring migrants (emigrants). Autumn migrants, presented with a laterally‐positioned green‐illuminated target for 2.5 s during each minute of flight, flew for a longer period before responding to the target (110 min) than summer migrants (36 min), while spring migrants responded after an intermediate time (72 min). This period is equivalent to the migratory phase of flight. The summer migrants were maximally responsive to targets illuminated by green monochromatic light (X, 555 nm). Targets illuminated with ultraviolet (γλ 360 nm) were attractive during the migratory and green‐responsive phases of flight, but infrared (γλ700 nm) wavelengths were not attractive. The results are discussed with respect to aphid behaviour in the field.

Behavioral and electrophysiological responses of Aphids to host and nonhost plant volatiles

Alate and apterous virginoparae ofAphis fabae Scop, and alate virginoparae ofBrevicoryne brassicae (L.), walking in a linear track olfactometer, were attracted by odor from leaves of their host plants.A. fabae responded to odor from undamaged but not damaged bean leaves. Gynoparae (autumn migrants) ofA. fabae, however, did not respond to their host plant (spindle,Euonymus europaeus) odor. Odors of certain nonhost plants masked the attractiveness of the host plant leaves, but tansy (Tanacetum vulgare) and summer savory (Satureja hortensis) volatiles repelledB. brassicae andA. fabae, respectively. 3-Butenyl isothiocyanate attractedB. brassicae andLipaphis erysimi (Kalt.), the latter species being more sensitive in both behavioral and electrophysiological studies. Isothiocyanate receptors were found on the antennae ofA. fabae, which was repelled by these compounds, 4-pentenyl isothiocyanate being the most active.

Differential Colonization of Resistant and Susceptible Host Plants: Pemphigus and Populus

Plants show extensive intrapopulational variation in quality as hosts for herbivores. Adaptive discrimination among individual host plants depends on the availability of plant traits that are present when plants are colonized and that are correlated with quality. Here, we examine the ability of colonizers to select appropriate hosts when colonization occurs long before feeding, and when traits available as cues may be least associated with host quality. In such systems the precision of host selection may be limited by a lack of appropriate cues at the time of colonization. In the life cycle of the aphid Pemphigus betae, autumn migrants select among host trees (Populus angustifolia and natural hybrids with P. fremontii) far in advance of the spring feeding stages, while trees are in a very different physiological condition. In order to estimate host quality, we censused successful and aborted galls on 34 trees in a Utah canyon during seven consecutive years, thus obtaining tree—specific rates of stem—mother survivorship. We estimated attractivity of these trees by censusing autumn migrants during 3 yr. Both survivorship and attractivity varied among trees, and differences among trees persisted across years. Tree—specific colonization rates were positively related to gall establishment. These results indicate that the actual colonization pattern is more adaptive than a random colonization process; however, the ability to select better hosts is far more perfect. To determine how migrants might use cues evident during colonization and correlated with quality, we examined the relationships between tree attributes in autumn and colonization rate and between these same attributes and stem—mother survivorship. One attribute, degree of leaf retention in autumn, was positively correlated with both colonization and subsequent progeny survival. Thus, the tendency to colonize trees retaining leaves longer in autumn may contribute to P. betae's limited ability to preferentially colonize better hosts. The results support the hypothesis that, in life cycles in which colonization and feeding are separated, the evolution of adaptive host discrimination may be constrained by the availability of appropriate cues.

Migratory and targeted flight in seasonal forms of the black bean aphid, Aphis fabae

ABSTRACT. Adult winged forms of Aphis fabae Scop., the spring migrants (fundatrigeniae; alate virginoparae), the summer migrants (alate virginoparae) and the autumn migrants (gynoparae), were flown in an automated vertical wind tunnel, with a small green target presented every 60 s. On average, targeted flight developed in the spring and summer migrants after 19 and 15 min, respectively. However, in autumn migrants targeted flight occurred after 184 min of flight. No evidence of target approach was found up to 30 min prior to this time, although some movement towards the target was observed in the 30 min before the first response of autumn migrants, suggesting that a gradual change from migratory to targeted flight occurred. No correlation was found between aphid weight and the time to first response for spring or summer migrants, but a positive correlation was found for autumn migrants. Flight patterns of autumn migrants, in the absence of a target, are described and compared with flight patterns previously reported for summer migrants.

A method for separating summer and autumn migrants of host‐alternating aphids

Chez de nombreuses especes d'aphides changeant de plante hote les femelles migrantes d'ete et d'automne sont morphologiquement identiques bien qu'elles different par leur comportement et leur reproduction.Une methode d'identification rapide et fiable est presentee

Spatial Pattern of Abundance of the Black Bean Aphid, Aphis fabae, in Britain

(1) Populations of Aphisfabae Scop. were monitored in Britain on its primary winter host, Euonymus europaeus L., on the two principal secondary summer crop hosts, springsown Viciafaba L. and sugar beet, and during the spring, summer and autumn migrations. This unique year-round monitoring was used to examine the spatial dynamics of the aphid in 1969-86. (2) Changes in the mean spatial pattern of abundance of the aphid during a single annual cycle reflect a sequence of changing host plants. (3) The longer-term dynamics and survival of the aphid depend on the spatial pattern of abundance in the non-crop environment. Thus, the wide distribution of wild hosts in late summer affects the numbers of autumn migrants, and the regional variation in abundance of E. europaeus affects the success of the aphid in finding sites for overwintering eggs. (4) Spatial patterns of abundance of other aphid pest species are compared with that of A. fabae. (5) The implications of varying spatial patterns of abundance are discussed in relation to pest forecasting.

The dilemma of cross-desert migrants—stopover or skip a small oasis?

Insectivorous passerines tend to stopover in a desert oasis on their way to their wintering grounds (autumn), but to skip the oasis on their way to their breeding grounds, having crossed the greater part of the Sahara (spring). Stopping-over spring migrants stayed shorter periods, gained less weight and suffered heavier mortality than stopping-over autumn migrants. It is proposed that a selective advantage to reach breeding territories early overrides tendencies to stopover due to weather, for refuelling or for rest close to the termination of a strenuous desert crossing.

Visual responses of flying aphids and their chemical modification

Abstract. Five winged forms of the black bean aphid, Aphis fabae, were subjected to 30 min of free flight in a recently designed, automated wind tunnel (David &amp; Hardie, 1988). A circular green target, on the side of the chamber, was illuminated for 2.5 s of each minute of flight. Half of the fundatrigeniae (‘spring migrants’) and all of the virginoparous ‘summer migrants’ responded by flying towards the illuminated target while gynoparae (‘autumn migrants’) induced by short days over two generations in uncrowded conditions were unresponsive. 27% of generation 1 gynoparae, induced by crowded conditions and short days over one generation, responded to the target as did 50% of males.Anaesthetization of adult gynoparae with nitrogen and carbon dioxide, but not ether, induced targeted flights. However, the effect of carbon dioxide was transient over the first 10 min whereas the effect of nitrogen continued throughout the 30‐min experimental period. In addition, treatment of late fourth instar larvae, but not young adults, with Juvenile Hormone I provoked target responses. The results are discussed with reference to settling behaviour and the endocrine control of polyphenism.