General ornithology:

references, abstracts and comments. Where there is no abstract, an abstract has been written, where abstracts are too long they have been abridged. Abstracts in languages other than English have been translated into English. The comment is personal, it points out errors and possible follow-ups, it is begun: CP:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27

Bensch, S. & B. Nielsen (1999): Autumn migration speed of juvenile Reed and Sedge Warblers in relation to date and fat loads. The Condor 101: 153 - 156.

We analyzed speed of migration in two congeneric warblers, the Reed and Sedge Warbler, Acrocephalus scirpaceus and A. schoenobaenus. Sedge Warblers migrated at a higher speed than Reed Warblers. The two species showed similar rates of fat deposition at our Swedish study site, although Sedge Warblers departed with lower fat loads. The higher speed of migration in Sedge Warblers and their lower departure fat loads suggest that they encounter stopover sites which offer higher relative fat deposition rates farther south. The amount of visible fat at the time of banding was positively related to the speed of migration. Estimates of speed of migration for the two species suggest that the recoveries were situated on average 76 - 111 km farther south per (unit) increase in fat score, corresponding to 58 - 85 % of the expected distance a bird can cover by using the fuel of one unit of fat score.

Bibby, C. & R. E. Green (1981): Autumn migration strategies of Reed and Sedge Warblers. Orn. Scand. 12: 1-12.

This paper compares the patterns of migration of two congeneric warblers, moving from Britain to Africa, and aims to see how these might be influenced by the distribution of food supplies. Most Sedge Warblers fattened in southern England or northern France and overflew Iberia, while Reed Warblers paused and fattened in Portugal. The occurrence, duration of stay and rate of weight gain of Sedge Warblers depended on the abundance of the plum-reed aphid whose seasonality and distribution was broadly sufficient to predict the migration pattern. Reed Warblers showed no similar restriction of diet, did not respond to aphid abundance and were able to achievea similar rate of weight gain any time in September or October in Portugal. Migration strategies are discussed in evolutionary terms and shown to be appropriate responses to the pattern of food availability for birds with different feeding adaptations.

Blyumental, T. I. (1973): Development of the fall migratory state in some wild passerine birds (bioenergetic aspect). In: Bykhovskii, B. E. ed. Bird migrations. Ecological and physiological factors: 125-218.

Burns, J. G. (2003): Relationship of Calidris sandpiper wing shape with relative fuel load and total migration distance. The Auk : It has proven difficult to support the classic prediction of aerodynamic theory that highly migratory birds should have more pointed wings than less migratory birds. This study extends the search by testing for correlations between wing shape of Calidris sandpipers and a traditional migratory variable (total migration distance) as well as a novel variable (relative fuel load). Using phylogentically independent contrasts, it was determined that relative fuel load is a better predictor of wing shape than total migration distance.

Busse, P. & W. Kania (1970): Operation Baltic 1961 - 1967. Methods of work. Acta orn. 12: 231-267.

Busse, P. (2000): Bird Station Manual. Gdansk 2000.

CP: This must be regarded as an up-to-date version of the Operation Baltic scale. The furculum alone separates "0" from "1" and "4" from "5". The liver shows in rankings 0 - 3, intestines in rankings 0 - 2, and there is an explicit comment by Busse. Mistakes are usually made when someone has a tendency to "liberal" interpretation of rules, e.g. when the bird has a thick cover of yellow fat on the belly but part of the intestinum visible; this should be "2" but is classified "3"(...)


Connell, C. E., P. E. Odum & H. Kale (1960): The fat-free weight of birds. Auk 77: 1-9.


The fat-free weight, and also the lean dry weight, is relatively constant for birds of the same size (as indicated by wing length) and species in marked contrast to the total live weight which, in migratory species, fluctuates greatly because of the large variations in fat deposits. Accordingly, the amount of body fat of the living bird, or fresh specimen, may be accurately calculated by subtracting the fat-free weight (as a previously determined constant) from the live weight. Detailed analysis of fat-free weights of 230 Savannah Sparrows showed that sex, age, and racial differences were entirely the result of differences in basic body size as indicated by wing length. Postmigratory individuals, however, exhibited a lower fat-free weight than wintering or premigratory individuals of the same size. Fat-free weight values for males and females would provide the bird bander with a basis for a reasonably good estimate of the fat level. For a more precise estimate, fat-free weights would need to be worked out for each wing-length category, or else corrections made for individuals larger or smaller than average for the species. A table of fat-free and lean dry weights of 14 species of migratory birds is included.


Dalberg Petersen, F. (1972): Weight-changes at Hesselö in nightmigrating Passerines due to time of day, season and environmental factors. DOFT 66: 97-107.

1. In the springs og 1963, 1966 and 1971 several passerine species, especially Robins, were weighed at Hesselö. 2. All species investigated showed an increase in weight during the day. If the weight (Y) was expressed as a function of hours after sunrise (X) most distributions were better fitted by Y = a + b log X than Y = a + b X, where a and b are constants. 3. For the Robins the increase in weight is calculated for 3 different periods and compared with the rate of emigration. It is shown that the rate of emigration is largest when the increase in weight is largest, and vice versa. 4. The increase in weight is larger when the sky is clear than when the sky is covered by clouds. The number of birds present on the island has apparently no influence on the change in weight. 5. The mean weight of the Robins which leave the island is larger than the mean weight of the birds, which do not leave. 6. It is concluded that both innate and environmental factors influence the degree of emigration.

Dolnik, V. R. & V. M. Gavrilov (1973): Caloric equivalent of body weight variations in chaffinces (Fringilla coelebs). In: Bykhovskii, B. E. ed. Bird migrations. Ecological and physiological factors: 273-287.

Direct measurements of energy value (caloric equivalent - CE) of nocturnal, daily (24-hour period) and seasonal variations in body weight were made. The size of nocturnal CE is related to the seasonal and individual state of energy reserves and their relationship during oxidation, and also to the amount of water lost by respiration. Dependences of nocturnal CE on the temperature of the surrounding medium in various seasons have been established. CE of weight increase in the course of 24 hours or any weight variation in the course of several days approximates in magnitude the caloric density of fat and does not depend either on the season of the year or temperature of the environment. CE of body weight decrease in the course of 24 hours is considerably lower and is affected by numerous factors. CE of variation of average body weight of birds within a population in one season (except for the period of breeding) is constant, but has different values at different seasons. Variations of body weight during the bird's transition from one seasonal state to another, and during breeding, possess no stable CE. CE of weight loss in flight is high, indicating an insignificant loss of water through respiration during flight. The results obtained make possible the determination of the energy equivalent of body weight variations of birds in the wild and under experimental conditions, with satisfactory accuracy. Analysis of factors which determine the variations in body weight, and the corresponding CE, are given.

Dolnik, V. R. & V. M. Gavrilov (1973): Energy metabolism during flight of some passerines. In: Bykhovskii, B. E. ed. Bird migrations. Ecological and physiological factors: 288-296.

Energy expenditure resulting from losses of body weight in flight, previously measured by the authors, is determined anew on the basis of additional experiments and calculations. Energy expended in flight amounts in house martins to 0.860±0.015 kcal/hour, in chaffinches - to 4.58±0.73, in bramblings - to 4.35±0.44, in siskins - to 2.52±0.33, in bullfinches - to approximately 5.67. Expenditure of energy during flight on physiological processes unconnected with flight is equal to the value of one standard diurnal metabolism, irrespective of the environmental temperature, i.e., a bird in flight is in a state of thermoneutrality.


Ehrenroth, B. & G. Ekbohm (1979): Weight and wing length variations in Long-tailed Tits Aegithalos caudatus during autumn movements in Central Sweden. In: Ehrenroth, B. Autumn movements in Parus and Aegithalos (Passeriformes) in central Sweden. Ph. D. thesis, Uppsala.

In 1969-1976 a total of 583 Long-tailed Tits were weighed and measured at Hammarö Bird Observatory. The mean weight of all birds was 8.6 g and the mean wing length 63.5 mm. The weight increased by 0.15 g per mm wing length. There were no significant differences in the size between birds trapped in different years. Seasonal differences in size were small, although birds trapped during a pentade in the middle of October i most years had, on avergae, shorter wing lengths than birds measured later. The daily mean weight increase was calculated to 0.76 g. On the basis of wide weight ranges within different wing length categories it is supposed that many birds were comparatively fat, with fat deposits between 1 and 2 g. An analysis of variance within and between flocks showed that birds within a flock were more alike than birds from different flocks.

Ehrenroth, B. & V. Marcström (1979): Autumn lipid levels in three species of tis, Parus montanus, Parus ater, Parus caeruleus, and Goldcrest Regulus regulus.. In: Ehrenroth, B. Autumn movements in Parus and Aegithalos (Passeriformes) in central Sweden. Ph. D. thesis, Uppsala.

Lipid and water levels of 20 Willow Tits, 21 Coal Tits, 15 Blue Tits and 31 Goldcrests collected during three autumns in Central Sweden were analysed. The Willow Tits posessed the lowest mean lipid level - 4.61 % of total weight - while the corresponding values for Coal Tits, Blue TIts and freshly killed Goldcrests were 7.2, 7.5 and 8.3 % respectively. The Blue Tits, which were found dead in nets, contained less water than expected. Highly significant differences in both fat and water levels were obtained between the Goldcrests collected alive and those found dead in the nets, indicating thatthe latter were in poor condition already when they arrived to the trapping area. A comparison of total weight data from the collected birds with maximum weights recorded for ringed birds indicate that some individuals of Coal Tits, Blue Tits and Goldcrests might reach lipid levels around 20 %, while the maximum fat content in Willow Tits probably does not exceed 15 %.


Frelin, C. (1979): Physiological adaptations of blue tits (Parus caeruleus) to migration. Vogelwarte 30: 33-41.


Hedenström, A. & S. Sunada (1999): On the aerodynamics of moult gaps in birds. J. Exp. Biol. 202: 67-/76.

During the moult, birds sequentially replace their flight feathers and thus temporarily have gaps in their wings. These gaps will vary in size and position(s) during the course of the moult. We investigated the aerodynamic effects of having moult gaps in a rectangular wing by using a vortex-lattice (panel) approach, and we modelled the effect of moult gap size at the wing moult initiation position, of gap position in the primary tract and of two simultaneous gaps (as occurs during secondary feather moulting in many birds). Both gap size and gap position had a detrimental effect on aerodynamic performance as measured by lift curve slope, effective aspect ratio and the aerodynamic efficiency of the wing. The effect was largest when the moult gap was well inside the wing, because the circulation declines close to the wing tip. In fact, when the gap was at the wing tip, the performance was slightly increased because the lift distribution then became closer to the optimal elliptical distribution. The detrimental effect of moult gaps increased with increasing aspect ratio, which could help to explain why large birds have relatively slow rates of moult associated with small gaps.


Johnson, C. (1985): Patterns of Seasonal Weight Variation in Waders on the Wash. Ring. & Migr. 6: 19-32.

Analysis of weight variation, based on monthly mean weights for ten wader species occurring on the Wash demonstrating the patterns of season weight variation. For each species the trends are interpreted in terms of adaptations and responses to specific life cycle events and potential feeding difficulties which arise from winter environmental conditions.


Kaiser, A. (1993): A new multi-category classification of subcutaneous fat deposits in songbirds. J. Field Orn. 64: 246-255.

A new fat scoring technique for small birds is introduced using 31 classes (nine main classes with up to four subclasses each; Fig. 1). In contrast to many othe methods, fat score and respective fat load (as determined by the Soxhlet method) correlate very well. Furthermore, variability in the calculated regression lines for nine different species is low. This effective new method can easily be learned by handling approximatively 100 individual birds and substantially improves precision of studies on fat-deposition in migratory birds.

Klaassen, M. & Å. Lindström (1996): Departure fuel loads in time minimising migrating birds can be explained by the energy costs of being heavy. J. Th. Biol. 183: 29 - 34.

Kvist, A., Lindström, Å., Green, M., Piersma, T. & G. H. Visser (2001): Carrying large fuel loads during sustained bird flight is cheaper than expected. Nature 413: 730-732.

Birds on migration alternate betweem consuming fuel stores during flights and accumulating fuel stores during stopovers. The optimal timing and length of flights and stopovers for successful migration depend heavily on the extra metabolic power input (fuel use) required to carry the fuel stores during flight. The effect of large fuel loads on metabolic power input has never been empirically determined. We measured the total metabolic power input of a long-distance migrant, the red knot (Calidris canutus), flying for 6 to 10 h in a wind tunnel, using the doubly labelled water technique. Here we show that total metabolic power input increased with fuel load, but proportionally less than the predicted mechanical power output from the flight muscles. The most likely explanation is that the efficiency with which metabolic power input is converted into mechanical output by the flight muscles increases with fuel load. This will influence current models of bird flight and bird migration. It may also help to explain why some shorebirds, despite the high metabolic power input required to fly, routinely make nonstop flights of 4,000 km or longer.

Kvist, A. & Å. Lindström (2003): Gluttony in migratory waders - unprecedented energy assimilation rates in vertebrates. Oikos 103: 397 - 402.

Maximum energy assimilation rate has been implicated as a constraint on maximal sustained energy expenditure, on biomass production, and in various behavioural and life history models. Data on the upper limit to energy assimilation rate are scarce, and the factors that set the limit remain poorly known. We studied migratory waders in captivity, given unlimited food supply around the clock. Many of these waders assimilated energy at rates of seven to ten times basal metabolism, exceeding maximum rates reported for vertebrates during periods of high energy demand, for example during reproduction and in extreme cold. One factor allowing the high energy assimilation rates may be that much of the assimilated energy is stored and not concomitantly expended by muscles or other organs. The remarkable digestive capacity in waders is probably an adaptation to long and rapid migrations, putting a premium on high energy deposition rates. The upper limit to daily energy assimilation in vertebrates is clearly higher than hitherto believed, and food availability, total daily feeding time and, possibly, the fate of assimilated energy may be important factors to take into account when estimating limits to energy budgets in animals.


Lind, J. (2001): Escape flight in moulting Tree-Sparrows (Passer montanus). Functional Ecology 15: 29-35.

Lind, J. & S. Jakobsson (2001): Body building and concurrent mass loss: flight adaptations in tree sparrows. Proc. R. Soc. Lond. B 268: 1915 - 1919.

Environmental changes are responsible for the evolution of flexible physiology and the extent of phenotypic plasticity in the regulation of birds' organ size has not been appreciated until recently. Rapid reversible physiological changes during different life-history stages are virtually only known from long-distance migrants, and few studies have focused on less extreme aspects of organ flexibility. During moult, birds suffer from increased wing loading due to wing-area reductions, which may impair flight ability. A previous study found that tree sparrows' (Passer montanus) escape flight is unaffected during moult, suggesting compensatory aptness. We used non-invasive techniques to study physiological adaptations to increased wing loading in tree sparrows. As wing area was reduced during natural moult the ratio of pectoral-muscle size to body mass increased. When moult was completed this ratio decreased. We show experimentally a novel, strategic, organ-flexibility pattern. Unlike the general pattern, where body mass is positively coupled to pectoral-muscle size, tree sparrows responded within7 days to reductions in wing area by reducing body mass concurrently with an increase in pectoral-muscle size. This rapid flexibility in a non-migratory species probably reflects the paramount importance and long history of flight in birds.

Lind, J., Gustin, M. & A. Sorace (2004): Compensatory bodily changes during moult in Tree Sparrows Passer montanus in Italy. Ornis Fennica 81: 1-9.

Environmental changes are responsible for the evolution of flexible physiology and the extent of phenotypic plasticity in the regulation of birds' organ size has not been appreciated until recently. Rapid reversible physiological changes during different life-history stages are virtually only known from long-distance migrants, and few studies have focused on less extreme aspects of organ flexibility. During moult birds suffer from increased wing loading due to wing-area reductions, which may impair flight ability. A previous study found that tree sparrows' (Passer montanus) escape flight is unaffected during moult, suggesting compensatory aptness. We used non-invasive techniques to study physiological adaptations to increased wing loading in tree sparrows. As wing area was reduced during natural moult the ratio of pectoral-muscle size to body mass increased. When moult was completed this ratio decreased. We show experimentally a novel, strategic, organ-flexibility pattern. Unlike the general pattern, where body mass is positively coupled to pectoral-muscle size, tree sparrows responded within 7 days to reduction in wing area by reducing body mass concurrently with an increase in pectoral-muscle size. This rapid flexibility in a non-migratory species probably reflects the paramount importance and long history of flight in birds.

Lindström, Å., Bensch, S. & D. Hasselqvist (1985): Höstflyttningsstrategi hos unga blåhakar Luscinia svecica. Vår Fågelvärld 44: 197 - 206.

Autumn migration strategy of young Bluethroats, Luscinia svecica. [The study was performed at two sites: Ammarnäs (65.58 N/16.05 E) and Kvismaren (59.10 N/15.25 E).](...)The results from Ammarnäs show that the young Bluethroats leave their birthplace already from the middle of August, and that they leave without any store of fat, or with just a small amount.
(...)The weight and fat figures from Kvismaren show that Bluethroats arrive with no or little amounts of fat, and that they stay for some time and leave with considerable amounts of fat. The fattest bird had about 25 % of its body weight in fat, and several others had similar amounts of fat. A bird with a 25 % fat content can reach 800 - 1000 km, i.e. over the Baltic Sea and quite some distance into the Soviet Union, where the next resting places are presumably situated.(...)


Lindström, Å. (1986): Fat deposition in migrating birds. Introductory paper no 44, Dept of Ecology, Lund University.

Lundgren, B., Hedenström, A. & J. Pettersson (1995): Correlation between some body components and visible fat index in the Willow Warbler Phylloscopus trochilus (L.). Orn. Svec. 3: 75 - 80.


Meissner, W. (1998): Fat reserves in Dunlins Calidris alpina during autumn migration through Gulf of Gdansk. Orn. Svec. 8: 91 - 102.

To describe fat reserves in adult and juvenile Dunlins during autumn migration in the Gulf of Gdansk, multiple regression equations for estimating fat mass in Dunlins were derived. The average fat level in a particular wave of migrants depends on many factors. Low amount of accumulated fat suggests that this species migrates along the southern Baltic in small steps, similarly to the rest of Europe. The interpretation of the results is difficult because at least two distinct migration routes cross the Gulf of Gdansk region. Dunlins starting their primary moult had lower fat index than birds in advanced stages of moult. The rate of fattening in Dunlin depends on the quality of the feeding place (higher in the sewage farm than in the river estuary). Birds which stayed longer in the feeding area had, on average, lower fat mass increments than those leaving Gulf of Gdansk after a short stay. Birds with low fat mass started putting on weight immediately, whereas "fat" birds lost weight at the beginning. Those results confirmed Mascher's (1966) hypothesis about differences in body mass change rate during the first day of stay in birds with low and high fat reserves. The level of free fatty acids in the blood appears to be a factor controlling this pattern. Differences in fat accumulation between Ottenby (southern Sweden) and Gulf of Gdansk are discussed.


Newton, I. (1969): Winter fattening in the Bullfinch. Physiol. Zool. 42: 96-107.

Bullfinches in England were heavier in December/January (23 - 26 g) than in October/November (22 - 25 g). Water comprised 64 % of this weight difference, lean dry material (mainly protein) 24 %, and fat 12 %. The significance of the large seasonal changes in protein are not known.
It is unlikely that the increased fat deposits significantly improved the virds' insulation in the colder months, and the insulating potential of the plumage was no better then than in October.
The fat served mainly as an overnight energy reserve; in the colder months, with longer nights, more fat was laid down each day and more lost each night. Some Bullfinches also stored whole seeds in their gullet prior to roosting, but these contributed less than one-fourth of the overnight energy requirements in October/November and less than one-fifth in December/January.
In all four months, most birds were found to contain some fat at dawn, This fat store was greater and, in the absence of feeding, probably sufficient for several more hours of activity in December/January (when food was generally scarcer) than in October/November. After using all their fat, starving Bullfinches can live for a few hours by breaking down body protein, but at no time could the birds have fasted a whole day and survived. As a supplement to reduced food intake, stored fat could contribute to the energy requirements over only a few days, though periods of food shortage may last up to several weeks. "Winter" fat cannot therefore be regarded as a long-term reserve, and only by obtaining sufficient food each day to lay down fat for overnight use can the birds survive from one day to the next.

Nisbet, I. C. T., Drury, W. H. & J. Baird (1963): Weight-loss during migration. Part I: Deposition and consumption of fat by the Blackpoll Warbler Dendroica striata. Bird-Banding 34: 107-138.

[CP] This and the following papers are important antiques, like the above one by Newton. Blackpoll Warblers were ringed and studied in Massachusetts and again on Bermuda; from this comparison the authors drew conclusions about the energy consumption during migration flight. Values, conclusions, theoretical positions are no longer up-to-date, but any student of fat accumulation, weight loss on migration etc. should have some basic knowledge of the contents of this paper. Use more modern estimates, where such exist.

(...)3. During 3-24 September 1962, most birds caught at Round Hill, Massachusetts, weighed only 10-15 gm. Arrivals of light birds followed cold frosts. In late September and early October more heavy birds were caught; most of the birds which were caught put on weight rapidly during rainstorms and appeared to depart immediately after clearing. Immatures appeared to put on weight more slowly than adults.
4. At Drumlin farm, Massachusetts, many more very heavy birds (16-23 gm) were caught. In at least two different years a group of birds of average weight 20.8 gm has been caught in late September and early October, and three such birds have been killed during nocturnal migration at this time. It is suggested that this is the usual departure weight of the species.
(...)6. New England is an area where Blackpoll Warblers pause in their migration for several weeks to put on fat for overseas flight.
(...)8. On the nights of 2-3 October 1962, many heavy Blackpoll Warblers (average weight 17.3 gm) were attracted to the Bermuda lighthouse: these birds were part of a flight from New England which passed Bermuda without stopping. Lighter birds (11-16 gm) stopped on Bermuda on several days later in October, but these birds had not flown directly from New England.
9. Forty-five birds kept overnight in dark cages lost weight at an average rate of 0.062 gm/hour.
10. The birds which flew to Bermuda during 1-3 October 1962 lost weight at an average rate of 0.107 ± 0.013 gm/hour; this figure may be an over-estimate but is unlikely to be an under-estimate. This gives an upper limit for their average power consumption of 1.02 ± 0.13 Kcal/hour, only about 2.0 times the resting power consumption in spite of a load of 6 - 10 gm of fat. It is argued that they lost little or no water during the flight, but this needs further study.
10. Blackpoll Warblers have sufficient fat-reserves when they leave New England to fly non-stop for 105-115 hours. This is enough for a non-stop flight to the mainland of South America in the usual weather in which they migrate.

/"New England" designates the six northeastern states of USA, Maine, New Hampshire, Vermont, Massachusetts, Rhode Island and Connecticut, first colonized by Englishmen./


Nisbet, I. C. T. (1963): Weight-loss during migration. Part II: Review of other estimates. Bird-Banding 34: 139-159.


Pettersson, J. (1983): Åldersbestämning av tättingar och vadare. Rapport från Ottenby fågelstation nr 1, 2nd rev. edition.

CP: Pictures "defining" the fat rankings used in the paper below are given here. The liver still shows in rankings "4" and "5", intestines show in rankings 0 - 3, and some still in ranking "4". In addition there is a ranking for superfat birds: "6". This ranking scale has been widely applied in Sweden; Busse & Kania 1970 is quoted as source, but as a matter of fact the Ottenby scale deviates strongly from the Operation Baltic scale, unfortunately the two scales simultaneously used in the Baltic are not compatible. Pettersson is intent on continuous development, Busse & Kania on defining "catch structures" for the eye.

Pettersson, J. & D. Hasselquist (1985): Fat deposition and migration capacity of Robins Erithacus rubecula and Goldcrests Regulus regulus at Ottenby, Sweden. Ring. & Migr. 6: 66 - 76.

To investigate migration strategy we have studied the visually observable fat deposits of Robins and Goldcrests and made calculations of flight distance capacity. High fat deposits in Robins and Goldcrests after one night migrations to Ottenby suggest that these birds could migrate two or more nocturnal stages without refuelling. The long periods needed to recover depleted fat reserves could be one reason for Robins storing fat for more than one night's migration. Recoveries in the same autumn of Robins ringed at Ottenby confirm our suggested pattern of fat deposition and migration strategy.
CP: There is a good linear regression WEIGHT on RANKING with sample-sizes order of magnitude 1 - 4.000 birds. Still, it is obvious, that the relation based on the Ottenby scale is slightly bow-shaped.


Summers, R. V. & M. Waltner (1979): Seasonal variations in the mass of waders in southern Africa, with special reference to migration. Ostrich 50: 21-37.

Swaddle, J. P., Witter, M. S., Cuthill, I. C., Budden, A. & P. McCowen (1996): Plumage condition affects flight performance in Common Starlings: implications for developmental homeostasis, abrasion and moult. J. Av. Biol. 27: 103 - 111.

Variation in length and asymmetry of wing primary feathers can arise from a breakdown of developmental homeostasis, feather abrasion and incomplete growth during moult. Indirect predictions have been made concerning the impact of primary length and assymetry on the flight ability of birds, but they have not been explicitly tested. Here we provide evidence from both natural variation in primary feather condition and experimental manipulations of primary feather length and asymmetry to indicate that these factors influence aspects of flight performance in the Common Starling Sturnus vulgaris. Damaged and incompletely grown primary feathers reduce escape flight performance. Experimentally reduced primary lengths reduce take-off speed; increased primary asymmetry decreases aerial manoeuvrability. A comparison of the experimental and natural plumage data indicates that birds may be able to adapt to a change in wing morphology, perhaps reducing the effects of feather loss or damage on flight. The results from this study indicate that primary feathers are under strong stabilising selection to maximise developmental homeostasis and reduce feather asymmetry. These findings are also of ecological importance to the damage-avoidance and moult strategies of these birds. This is the first experimental evidence to indicate a quantitative reduction in flight performance with feather lengths and asymmetries typical of those observed during flight feather moult and feather damage in any species.

Swaddle, J. P. & M. S. Witter (1997): The effects of molt on the flight performance, body mass, and behaviour of European starlings (Sturnus vulgaris): an experimental approach. Can. J. Zool. 75: 1135 - 1146.

The physiological and energy costs of avian molt are well documented, but indirect consequences such as changes in flight performance have received less attention. Here, we report two experiments that investigated flight performance, body mass regulation, and behavior in captive starlings (Sturnus vulgaris) In the first experiment, we found a U-shaped change in take-off escape performance during natural molt; birds ascended at the shallowest trajectories during midmolt. Birds' body molt was also reduced during molt. In the second experiment, we manipulated the plumage of starlings to simulate different stages of flight-feather molt. This allowed us to separate the aerodynamic costs of feather loss from the physiological costs of feather associated with plumage growth. Through observations of flight (take-off, aerial maneuverability, and level flapping-flight speed) and behavioral parameters, we demonstrated that birds in simulated molt have reduced flight performance and reduced body mass. These birds also decrease the time spent performing energetically costly activities and seek areas of relative protection. In the longer term, some aspects of performance return to pretreatment levels, implying compensation for the plumage manipulations. Our results demonstrate that molt incurs significant functional costs that may play an important role in the adaptive radiation of molt strategies and molt patterns observed in avianspecies.

Swaddle, J. P., Williams, E. V. & J. M. V. Rayner (1999): The effect of simulated flight feather moult on escape take-off performance in starlings. J. Av. Biol. 30: 351 - 358.

We investigated the effects of the plumage changes associated with moult on the anti-predator take-off performance of European Starlings Sturnus vulgaris. By altering the plumage to simulate moult, we have simulated the biomechanical consequences of changes in wingform from the underlying physiological and metabolic changes that may occur during natural moult. Previous analyses of avian take-off performance have relied on descriptive observations of wingtip kinematics or dual measures of take-off speed and angle. We have developed a novel method using the energy gain per wingbeat as a measure of overall take-off performance. The advantages of this measure compared with previous approaches are that it summarises the potential trade-off between height gain and speed gain, and can be related directly to lift on the wings. Analysis of high speed (100 Hz) video tapes indicated that birds in simulated moult suffer a reduction in total energy produced during the second wingbeat of take-off, resulting in a slower take-off speed. This reduction in take-off performance is also associated with a marked change to the pattern of movement of the wingtip during flight; moult-manipulated birds appear to reverse the wingtip at the top of the downstroke although there is no associated change in wingbeat amplitude or duration. Birds appeared to be able to regain, in part, their flight performance within 6 days of the manipulations, as take-off speeds returned to pre-manipulation levels. This partial return to pre-manipulation flight performance was associated with an alteration in pattern of movement of the wingtip during take-off. The relevance of this adaptation to birds in natural moult is discussed. Any reduction in take-off performance is likely to influence directly individual behaviour and survival; hence the ability to quantify take-off in different species under a common currency is of general ecological importance and will enable predictions to be generated and tested concerning the effects of natural moult in wild birds.


Thomas, A. L. R. (1993): The aerodynamic costs of asymmetry in the wings and tail of birds: asymmetric birds can't fly round tight corners. Proc. R. Soc. Lond. B 254: 181 - 189.


Ward, P. (1963): Lipid levels in birds preparing to cross the Sahara. Ibis 105: 109-111.

Zwarts, L., B. J. Ens, M. Kersten & T. Piersma (1990): Moult, mass and flight range of waders ready to take off for long-distance migrations. Ardea 78: 339 - 364.

Wader species wintering on the Banc d'Arguin increased their body mass by about 40 % during the 4 - 6 weeks before their departure in spring. This estimate is based on 1) the empirical fact that most waders which had finished or suspended their body moult into summer plumage were heavy and thus ready to take off, and 2) the assumption that only the heaviest birds in the population left, which allowed the mass of disappearing waders to be estimated from counts and the frequency distribution of body masses in samples of captured birds. The mass gain on the Banc d'Arguin is just over 1 % per day, when expressed as a proportion of winter mass. A review of studies on waders preparing for migration shows that 1) the total migratory reserve adds 20-80 % to winter mass, 2) the rate of mass gain is 0.1-4 % per day and 3) the period of mass increase lasts four weeks on average, but longer if waders prepare for spring migration on the wintering areas. We suggest that all wader species leaving the Banc d'Arguin at the end of April and the beginning of May are able to reach SE and NW Europe without refuelling. This seems only possible if current equations to predict flight range systematically underestimate this range, even when the energetic benefits of favourable winds at high altitude are taken into account.

Åkesson, S., A. Hedenström, A. & D. Hasselquist (1995): Stopover and fat accumulation in passerine birds in autumn at Ottenby, southeastern Sweden. Orn. Svec. 3: 81-92.

Stopover duration and fat accumulation were studied during autumn migration at two sites near Ottenby, Öland, southeastern Sweden in 1985 and 1986. The species are Thrush Nightingale, Barred Warbler, Lesser Whitethroat, Whitethroat, Willow Warbler and red-backed Shrike. We captured the birds in mistnets between 10 July and 20 August and recorded visually the fat class and measured the body mass. Post juvenile moult was scored on juvenile birds. In several of the species fat class and body mass increased with day of season (Thrush Nightingale, Barred Warbler and Whitethroat), while in the Lesser Whitethroat there was a reduction in fat class and body mass with day of season. Recaptures revealed that the highest daily increase in body mass was 2.7 % in a Willow Warbler and a Red-backed Shrike, while a Barred Warbler showed a maximum daily body mass increase of 2.4 %. The duration of stopover in migrants varied between 2 and 7 days.

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