Thord Fransson

Spatial, Temporal, and Species Variation in Prevalence of Influenza A Viruses in Wild Migratory Birds

Although extensive data exist on avian influenza in wild birds in North America, limited information is available from elsewhere, including Europe. Here, molecular diagnostic tools were employed for high-throughput surveillance of migratory birds, as an alternative to classical labor-intensive methods of virus isolation in eggs. This study included 36,809 samples from 323 bird species belonging to 18 orders, of which only 25 species of three orders were positive for influenza A virus. Information on species, locations, and timing is provided for all samples tested. Seven previously unknown host species for avian influenza virus were identified: barnacle goose, bean goose, brent goose, pink-footed goose, bewicks swan, common gull, and guillemot. Dabbling ducks were more frequently infected than other ducks and Anseriformes; this distinction was probably related to bird behavior rather than population sizes. Waders did not appear to play a role in the epidemiology of avian influenza in Europe, in contrast to the Americas. The high virus prevalence in ducks in Europe in spring as compared with North America could explain the differences in virus–host ecology between these continents. Most influenza A virus subtypes were detected in ducks, but H13 and H16 subtypes were detected primarily in gulls. Viruses of subtype H6 were more promiscuous in host range than other subtypes. Temporal and spatial variation in influenza virus prevalence in wild birds was observed, with influenza A virus prevalence varying by sampling location; this is probably related to migration patterns from northeast to southwest and a higher prevalence farther north along the flyways. We discuss the ecology and epidemiology of avian influenza A virus in wild birds in relation to host ecology and compare our results with published studies. These data are useful for designing new surveillance programs and are particularly relevant due to increased interest in avian influenza in wild birds.

Surveillance of influenza A virus in migratory waterfowl in northern Europe

Ducks may maintain influenza virus from 1 year to the next.

Impaired Predator Evasion in Fat Blackcaps (Sylvia atricapilla)

When birds are attacked by predators, take-off ability is crucial for the chance of survival. Recently, theoretical studies have predicted that predation risk in terms of reduced flight performance increases with body mass. However, empirical data are scarce. Because migratory birds sometimes double their body mass, mass dependent predation risk may be especially important during migratory fattening. Here we present the first study of take-off ability in relation to migratory fat load. Alarmed take-off flights of caged blackcaps (Sylvia atricapilla) induced by a simulated predator attack were analysed in terms of velocity and angle of ascent. Fat loads (percentage of fat-free body mass) of the birds ranged from 1% to 59%. An increase in fat load was found to influence both velocity and angle of ascent. From our results we calculated that blackcaps carrying 60% fat loads would have 32% lower angle of ascent and 17% lower velocity than blackcaps carrying no fat load. Even though the effect of fat load on the blackcaps was less than indicated in previous experimental studies of other species, our results suggest that the large fat loads needed for migration probably place them at increased risk of predation.

Effects of influenza A virus infection on migrating mallard ducks.

The natural reservoir of influenza A virus is waterfowl, particularly dabbling ducks (genus Anas). Although it has long been assumed that waterfowl are asymptomatic carriers of the virus, a recent study found that low-pathogenic avian influenza (LPAI) infection in Bewicks swans (Cygnus columbianus bewickii) negatively affected stopover time, body mass and feeding behaviour. In the present study, we investigated whether LPAI infection incurred ecological or physiological costs to migratory mallards (Anas platyrhynchos) in terms of body mass loss and staging time, and whether such costs could influence the likelihood for long-distance dispersal of the avian influenza virus by individual ducks. During the autumn migrations of 2002–2007, we collected faecal samples (n=10 918) and biometric data from mallards captured and banded at Ottenby, a major staging site in a flyway connecting breeding and wintering areas of European waterfowl. Body mass was significantly lower in infected ducks than in uninfected ducks (mean difference almost 20 g over all groups), and the amount of virus shed by infected juveniles was negatively correlated with body mass. There was no general effect of infection on staging time, except for juveniles in September, in which birds that shed fewer viruses stayed shorter than birds that shed more viruses. LPAI infection did not affect speed or distance of subsequent migration. The data from recaptured individuals showed that the maximum duration of infection was on average 8.3 days (s.e. 0.5), with a mean minimum duration of virus shedding of only 3.1 days (s.e. 0.1). Shedding time decreased during the season, suggesting that mallards acquire transient immunity for LPAI infection. In conclusion, deteriorated body mass following infection was detected, but it remains to be seen whether this has more long-term fitness effects. The short virus shedding time suggests that individual mallards are less likely to spread the virus at continental or intercontinental scales.

Timing and speed of migration in North and West European populations of Sylvia warblers

Timing and speed of migration within Europe and North Africa are analysed in five Sylvia warblers using North European and British ringing recoveries. Intraspecific comparisons between populations breeding in Great Britain and in Northern Europe show no difference in the timing of autumn migration but about three weeks earlier spring arrival in Great Britain, indicating that northern populations spend a shorter time on the breeding grounds. Autumn migration speed estimates based on distance and elapsed time between consecutive captures vary between 43 and 93 km d-1 depending on species and origin. High speeds of birds reported up to ten days after ringing suggest that some individuals have long flight-stages when they pass through Europe. Populations breeding in Northern Europe migrate at a higher speed than those in Great Britain. Shorter time on the breeding grounds and higher speed during autumn migration in more northern populations as well as higher speed in species undertaking longer migrations, indicate that migrants adjust their behaviour to a time shortage. Migration behaviour may thus be under selection to economize time. A compensatory increase in migration speed for late migrants, observed in some of the species, is consistent with the existence of such a selection pressure. Calculated spring migration speeds are higher than corresponding autumn speeds, but no obvious differences between northern and more southern populations are evident.

Migrating Birds and Tickborne Encephalitis Virus

During spring and autumn 2001, we screened 13,260 migrating birds at Ottenby Bird Observatory, Sweden, and found 3.4% were infested with ticks. Four birds, each a different passerine species, carried tickborne encephalitis virus (TBEV)–infected ticks (Ixodes ricinus). Migrating birds may play a role in the geographic dispersal of TBEV-infected ticks.

Predator–induced take–off strategy in great tits (Parus major)

When birds are attacked by predators the initial take–off is crucial for survival. The strategy in the initial phase of predator evasion is probably affected by factors such as body mass and presence of cover and conspecifics, but it may also be a response to the character of the predators attack. In choosing an angle of flight, birds face a trade–off between climbing from the ground and accelerating across the ground. This is, to our knowledge, the first study investigating whether the attack trajectory of a raptor affects the take–off strategy of the prey bird. First–year male great tits (Parus major) adjusted take–off angle to a model predators angle of attack. Birds attacked from a steep angle took off at a lower angle than birds attacked from a low angle. We also compared take–offs at dawn and dusk but could not find any measurable effect of the diurnal body mass gain (on average 7.9%) in the great tits on either flight velocity or angle of ascent.

High Migratory Fuel Loads Impair Predator Evasion in Sedge Warblers

During migration, many species of birds rely on stored fat for fuel. The extra mass taken on for migration entails costs (Witter and Cuthill 1993). Time and energy must be devoted to foraging to build up fat loads, and increased feeding may increase the risk of being attacked by predators. An additional cost of increased fuel loads may be higher predation risk owing to reduced ability to take off, maneuver, and climb. Mass-dependent predation risk has been the focus of several recent theoretical studies (McNamara and Houston 1990, Hedenstrdm 1992, Witter and Cuthill 1993, Brodin 2000). In species that depend on flight to escape from predators, takeoff ability is crucial because once the prey are airborne, the success rate of predators diminishes (e.g. Rudebeck 1950, Kenward 1978, Lindstrdm 1989, Cresswell 1993). Within the natural range of body mass of nonmigratory birds (ca. 10% diurnal increase in mass), mass seems to have no measurable effect on takeoff ability (Kullberg 1998, Kullberg et al. 1998, Veasey et al. 1998, van der Veen and Lindstrdm 2000). In migratory birds, fuel loads of 20 to 30% of lean mass are common (Alerstam and Lindstrbm 1990), and fuel loads may exceed 100% of lean mass when passerines are about to cross wide barriers (e.g. Fry et al. 1970, Finlayson 1981). Although fat storage is the most common explanation for mass changes in birds, mass may change because of other reversible processes, e.g. by increases or decreases in muscle mass and in various internal organs (Piersma and Lindstrdm 1997). To date, only two species of migrants have been studied with respect to takeoff ability in a predatorescape situation. Kullberg et al. (1996) calculated that Blackcaps (Sylvia atricapilla) carrying 60% of lean body mass as fuel would have an angle of ascent that was 32% lower and a velocity that was 17% lower

PATTERNS OF MIGRATORY FUELLING IN WHITETHROATS SYLVIA COMMUNIS IN RELATIONTO DEPARTURE

Whitethroats at a coastal autumn stopover site were supplied with mealworms ad libitum and their fuel accumulation rates were recorded by repeated weighings by means of a remote-controlled balance. This study focuses on two questions: (1) How does the daily fuelling rate change in relation to departure? (2) Is the decision to depart affected by weather conditions? The fuelling rates were not constant during the fuelling period. A decreasing fuelling rate close to the departure was evident in both first-year and adult birds and as many as a fourth of the birds did not gain any body mass on the last day before departure. Among possible explanations for the observed pattern are mass-dependent costs, adverse weather conditions as well as physiological changes in preparation for the flight. The decision to depart was not affected by local weather conditions (wind and cloudiness) and some individuals departed under head wind and overcast conditions. The frequency of strong head winds was, however, low during the period of departure. Weather data do not support the hypothesis that individuals that did not gain any body mass on the last day did so as a result of their departures being delayed as a consequence of adverse weather.

Migratory Birds, Ticks, and Crimean- Congo Hemorrhagic Fever Virus

TO THE EDITOR:In a recently published study, Estrada-Pena et al. reported the finding of Crimean-Congo hemorrhagic fever virus (CCHFV) in adult Hyalomma lusitanicum ticks from red deer (Cervus elap ...