Breeding success in a Houbara Bustard Chlamydotis [undulata] macqueenii population on the eastern fringe of the Jungar Basin, People's Republic of China

Nesting success and chick survival of a migratory population of Houbara Bustard Chlamydotis [undulata] macqueenii were studied during three consecutive years (1998–2000) in the Xinjiang province of north‐west China. A total of 45 nests was monitored and 85 broods comprising 227 chicks were captured, of which 82 chicks were radio‐tracked. Start of laying varied between 6 and 17 April between years but the laying mode fell consistently between 26 and 30 April. Mean clutch size was 4.0 (sd = 0.8) (range 2–6) for early clutches and 3.3 (sd = 1.1) for late clutches (range 2–5). The average nesting success was 0.588 (sd = 0.270) but great variations were observed between years –0.882 in 1998, 0.530 in 1999 and 0.351 in 2000. This was related to increased predation in 1999 and 2000, which is reflected by increased predator density (chiefly Corsac Fox Vulpes corsac and Long‐legged Buzzards Buteo rufinus). The overall hatchability, defined as the proportion of eggs hatched in successful nests was 0.839 sd = 0.238). The average brood size at hatching varied from 2.9 (sd = 0.8) to 3.3 (sd = 0.9) according to years, and no significant decrease in brood size was observed in the first 5 days post‐hatching. In 1999 and 2000 the brood size diminished sharply (14% and 27%, respectively) in prefledging chicks. A further severe decrease (37%) was observed in fledglings in 2000, probably due to predation by raptors. For the 3 years of the study, a successful female Houbara would bring on average 2.3 (sd = 0.9) chicks to fledging and would have lost 30.2% (sd = 14.9%) of its brood to adversity during the rearing process. The proportion of females that lost their entire brood was 0.181 in 1998, 0.708 in 1999 and 0.453 in 2000. For the 3 years of the study, only 55.3% (sd = 26.3%) of the females hatching eggs brought chicks to fledging. The overall chick production was 0.827 per breeding female per year and the probability of an egg laid producing a fledgling of 8 weeks old was 0.190.     

Early-season river entry of adult Atlantic salmon: its dependency on environmental factors

River entry of adult Atlantic salmon Salmo salar into the River Tornionjoki, monitored during three migration seasons (1997–1999) by horizontal split-beam hydroacoustics, started early in June when water temperature was c . 9° C and when the discharge varied between 1700 and 2000 m³ s⁻¹. In 1997 and 1999, migration peaked during the latter half of June, 17 days after the peak flood, at water temperatures ranging from 11· 5 to 18·2° C. Few statistically significant correlations were observed between river entry and six measured environmental factors and those that were significant were not persistent over the years. The strongest correlation (  r  = −0·60) was between the number of upstream migrants and seawater level, with a time lag of 1 day in 1998. In 1998 and 1999, no clear diurnal migration pattern was observed, although in 1997 the intensity of midday migration was higher than that of the midnight migration. It is concluded that environmental factors have little effect on river entry of Atlantic salmon in a large pristine river located at high latitude.     

Natural incidence of Cladosporium spp. as a bio-control agent against whiteflies and aphids in Egypt

Abstract:   Five species of entomopathogenic fungi were tested against whiteflies and aphids. Cladosporium spp. showed a high incidence on the two insect species tested (81% of the total isolated species). However, C. uridenicola was the predominant species isolated from both insect species during the two successive seasons of 1998 and 1999. Natural infection by Cladosporium ranged from 18.19 to 44.38% and 16.4 to 45.27% in 1998 and 1999, respectively, according to insect species and the host plant. Statistical analysis revealed a high correlation ( R  = 0.8759 ± 0.093) between the total investigated and total infected of each insect species during the two successive years of the study. The natural infection of Cladosporium to whitefly life stages was higher on whitefly nymphs (87.8%) than adults (8.08%) and eggs (4.15%) in 1998 and 1999. The results showed that the seasonal distribution of Cladosporium occurred all year around, but rates were higher during the period from June until November which coincided with the high populations of whiteflies and aphids. The weather had a significant effect on infection of insects and had no effect on other fungi species . The laboratory tests showed a higher pathogenicity of the candidate on Aphis gossypii , Aphis craccivora and Bemisia agrentifollii than other reported fungi.     

Possible roles for corticosterone and critical size in the fledging of nestling pied flycatchers

Our study was designed to see whether corticosterone (B) rises abruptly in the blood of nestling pied flycatchers (Ficedula hypoleuca) at the time they fledge, as reported recently for kestrels, and if so, why. We measured the growth and blood levels of B and selected nutrients of nestlings in broods of five, seven, and nine chicks during 1998 and 1999. In half of the broods, we clipped selected wing and tail feathers of both parents with the intention of making it more difficult for them to provide their chicks with food. We collected blood samples when the chicks were six to 10 d old (period of rapid growth) and 15 d of age or older (0-5 d before fledging). B increased substantially several days before the chicks left the nest and then declined somewhat. We found no differences in rates of growth or blood levels of B, nutrients, and hematocrit as a function of either brood size or parental handicapping. Nestlings within a day of fledging appear to have been food deprived in 1998; their glucose was significantly reduced, and B, free fatty acids, and glycerol were significantly elevated compared to levels in chicks 1-4 d younger. Such changes did not occur in 1999. Blood levels of B were significantly correlated with brood size near the day of fledging, but not earlier, in both years of the study. It was possible to predict the day on which chicks would leave the nest, using their wing length when 12 d old. These results suggest that high blood levels of B associated with food restriction and sibling competition induce chicks to fledge, provided they have reached a critical size, and that the importance of fasting, sibling competition, and B may vary from year to year.     

Growth and energetics of a small shorebird species in a cold environment: the little stint Calidris minuta on the Taimyr Peninsula, Siberia

The little stint Calidris minuta is one of the smallest shorebird species breeding in the Arctic (weighing 4.3  g on hatching). Their chicks are small and have a high surface area-to-volume ratio. We determined prefledging growth, energy expenditure and time budgets for little stint chicks in northwestern Taimyr, Siberia. A modified power curve was introduced to model the relationship between daily energy expenditure and body mass. Total metabolisable energy, TME, over the 15-d prefledging period was 107% greater than the allometric prediction for a bird the size of a little stint. Their growth rate coefficient was 14% greater than the prediction for a bird their size. The growth of young chicks was reduced in cool weather, possibly due to a reduction in foraging time in order to be brooded and reduced food availability which impact foraging efficiency. We did not detect weather effects on energy expenditure of chicks, but lack of temperature variation during energy expenditure measurements may have prevented this. In sum, both growth rate coefficient and energy expenditure of little stint chicks were greater than predicted and this is similar to that observed in other arctic shorebird species.     

Copulation behaviour and paternity in shy albatrosses (Thalassarche cauta)

We investigated the mating system of shy albatrosses Thalassarche cauta by combining behavioural observations during the pre-laying period with genetic paternity analysis. Genetic data on the mating systems of several procellariiform seabirds have recently become available, but data on the reproductive behaviour of these species are rarely obtained. Our main aims were to describe the copulatory behaviour of this species and identify how males achieve within-pair and extra-pair paternity (EPP). Most copulations occurred on the nest, were unforced and were within-pair. Females controlled the success of copulations and were observed soliciting extra-pair matings. Within-pair and extra-pair copulations were behaviourally similar. A low frequency (7–10%, n =29 chicks) of EPP was detected despite male use of frequent copulation as a paternity guard. The pre-laying foraging exodus of female shy albatrosses differed from that in other albatrosses: it was relatively short in length, lasting c . 2 days, and within-pair copulations occurred after the female's return 2 days before laying. This may reflect the close proximity of feeding grounds to the breeding colony.     

Cryopreservation of houbara semen: A pilot study

The potential of producing viable houbara bustard Chlamydotis undulata undulata progeny with cryopreserved semen was investigated during the 1998 breeding season. Houbara semen was diluted and rapidly frozen into pellet form in LN₂ using dimethylacetamide (DMA) as a cryoprotectant. Thawed semen exhibited 24.86± 10.61% recovery of fresh sperm motility levels and 36.44±16.17% of fresh viability counts. Two second‐year females were inseminated on two and three occasions, respectively, with thawed semen. One female laid four eggs between two clutches and the second female laid two eggs in a single clutch. All eggs were fertile; two developed to 18–21days but failed to pip; one chick died at pip and three chicks hatched. This is the first documented occasion that houbara bustard chicks were conceived with cryopreserved semen and it demonstrates the feasibility of using a rapid, simple, and relatively inexpensive methodology to achieve this result. Zoo Biol 18:147–152, 1999. © 1999 Wiley‐Liss, Inc.     

Limited effects of egg size on chick growth in the chinstrap Penguin Pygoscelis antarctica

We studied the effect of egg size on chick growth in the chinstrap penguin under natural non-manipulative, conditions. The influence of egg size on chick mass at hatching, 15 and 45 days of age was analysed controlling for the effect of hatching date, as hatching date has been repeatedly associated with chick growth in this species. Egg volume explained 20% of the variation in the body mass of chicks at hatching. Its effect disappeared as chicks grew, being statistically not significant at the age of 15 and 45 days. Egg volume asymmetry also had no role in determining chicks' growth asymmetries. Accepted: 6 June 1998     

Hand-rearing,growth, and development of the red bird of paradise (Paradisaea rubra) at the New York Zoological Park

Growth and development of six hand-reared red bird of paradise chicks was documented at the New York Zoological Park from March 1988 to May 1989. A total of 16 eggs were laid, of which 10 were fertile. Clutches consisted of two eggs and the female left the next infrequently during incubation. Two chicks left in the nest were apparently victims of parental abuse. Eggs were subsequently removed from the nest after 10–14 days, candled, and if fertile, were artificially incubated. The average incubation period was 16.6 days. Newly hatched chicks were without down and their eyes remained closed until approximately 6 days of age. Hand-reared chicks were maintained in Air Shield Infant Isolettes. The weight of newly hatched chicks was about 8 g, and the weight typically doubled during the first week. Ratios of food intake to body weight were highest between day 4 and 10. Pin feathers were visible on the wings after 4 days, and after 3 weeks, the chicks were fully feathered. Analysis of the diet revealed acceptable levels of iron, but vitamin A and E levels were higher than recommended for poultry chicks. This paper documents the first successful hand-rearing of any species of birds of paradise from hatching to fledging.     

Adult Brünnich's Guillemots Uria lomvia balance body condition and investment in chick growth

To investigate the covariation of adult body condition and nestling growth, we weighed adult Brünnich's Guillemots Uria lomvia rearing chicks at Coats Island, Nunavut, Canada, each year between 1988 and 2002. We estimated chick mass at 14 days for a sample of chicks reared in the same years. Adult mass and chick mass at 14 days were highly correlated, suggesting that, as feeding conditions deteriorate, adults compromise by reducing their own body reserves, while at the same time delivering less food to their offspring. We compared the prediction of the least-squares regression for the Coats Island data with observations made at Digges Island, a much larger colony about 300 km away, where birds are similar in linear body measurements to those at Coats Island and have a similar body mass while incubating. Adult mass at Digges Island averaged 11% less during chick-rearing than during incubation, compared with only a 5% difference at Coats Island. Mean chick mass at 14 days at Digges Island was lower in all years than was observed for chicks at Coats Island in any year. The observed 14-day chick masses at Digges Island in two years were close to values predicted by adult mass and somewhat lower in two other years (those when chick growth was slowest). At Digges Island, the distribution of mass for brooding adults was right skewed and suggested a lower threshold at 800–850 g, below which Brünnich's Guillemots terminate breeding. We conclude that the correlation between adult and chick mass represents a dynamic equilibrium in which adults simultaneously adjust their own energy reserves and their delivery rate to the chick. This compromise must be based on behavioural choices made by individual birds and is unlikely to be a passive consequence of fluctuating conditions.     

Great Green Macaws and the annual cycle of their food plants in Ecuador

ABSTRACT.   The Great Green Macaw ( Ara ambiguus ) is one of the largest New World parrots and is considered endangered with extinction. Their precarious decline in western Ecuador has been attributed to food scarcity, among other pressures. To understand the effects of food abundance on macaw behavior, phenological patterns of a community of food plants were documented in a dry tropical forest in southwest Ecuador from June 1999 to May 2000. Edible biomass was estimated weekly for 100 trees representing 10 species of macaw food plants. Simultaneously, we conducted a census of macaws. Of the plants studied, little food was produced during nearly 4 consecutive months (February–May). Food availability was unrelated to macaw abundance, but was positively correlated with the amount of time macaws spent in the study area. One plant species ( Cynometra bauhiniifolia ) produced more food than nine other species combined and was responsible for the correlation. Additional study of macaws foraging on C. bauhiniifolia and other plant species is needed, with special attention paid to those species with both large crops and large seeds. Although the diet of Great Green Macaws remains poorly known, our study illustrates the potential importance of quantifying differences in food production by plant species consumed by threatened granivores.     

Complex patterns of food allocation in asynchronously hatching broods of crimson rosellas

In birds, asynchronous hatching typically leads to lower growth and survival of last-hatched chicks. However, all crimson rosella Platycercus elegans, chicks grow at the same rate, although first-hatched chicks can be as much as seven times heavier than last-hatched chicks at the end of hatching. We examined the delivery and distribution of food to 18 rosella broods by videotaping feeds and simultaneously recording mass changes in the nestbox using a digital balance. Parents visited the nest infrequently and delivered loads of up to 25% of their body weight during a feeding visit. Male rosellas consistently delivered larger loads and consequently had higher feeding rates (g/h) than females. Parents distributed food between chicks by direct regurgitation in a series of up to 51 food transfers. Overall, chicks of all hatching ranks received equal numbers of transfers, but parents differed in how they distributed food within the brood. Males fed first-hatched chicks more than last-hatched chicks, whereas females distributed food equally to all chicks. Selective feeding of small chicks might be costly to females since they delivered food more slowly than males and spent more time in the nestbox. Thus female rosellas may invest more in current reproduction than males. Parents also distributed food differently to male and female chicks. Large males were fed more than all other nestlings, while female nestlings were fed equally irrespective of size. This study confirms that complex patterns of parental allocation occur in wild populations. Copyright 1999 The Association for the Study of Animal Behaviour.     

Dark-bellied Brent Geese Branta bernicla bernicla, as recorded by satellite telemetry, do not minimize flight distance during spring migration

Nine Dark-bellied Brent Geese Branta bernicla bernicla were equipped with satellite transmitters during spring staging in the Dutch Wadden Sea in 1998 and 1999. The transmitters (in all cases less than 3% of body mass) were attached to the back by a flexible elastic harness. One juvenile female was tracked to the Yamal peninsula in 1998. Eight adult males were selected from a single catch of 75 to span the range of body mass observed on the date of capture (11 May 1999) and all but the lightest individual completed the first lap of the migratory flight to the White Sea, Russia, according to the time schedule normal for the species. Six birds were successfully tracked to Taymyr for a total distance averaging 5004 km (range 45775164) but judging from later movements none bred (although 1999 was a breeding year). Although the routes chosen during spring migration were closely similar, none of the tagged birds migrated together. On average the geese used 16 flights to reach their summer destinations on Taymyr. The longest uninterrupted flights during the first half of the journey (Wadden Sea to Kanin) covered 1056 km (mean of seven adult males, range 7681331), while the corresponding value for the second half of the migration (KaninTaymyr) was only 555 km (mean of six adult males). Only 7% of total time during spring migration was spent in active flight, as contrasted to c.  80% at long-term stopovers. Overall average travelling speed was 118 km/day (range 97148). Including fattening prior to departure the rate of travel falls to 62 km/day (range 4970), in keeping with theoretical predictions. Routes followed deviated from the great circle route, adding at least 700 km (16%) to the journey from Wadden Sea to Taymyr, and we conclude that the coastal route is chosen to facilitate feeding, drinking and resting en route instead of minimizing total flight distance.     

Reproductive biology and ecology of white‐winged trumpeters (Psophia leucoptera) and recommendations for the breeding of captive trumpeters

The reproductive biology and ecology of a wild population of white‐winged trumpeters (Psophia leucoptera) were studied in southeastern Peru from 1983 to 1987. Because little information is available about any of the trumpeter species and because trumpeters have proven difficult to breed in captivity, information relevant to breeding and management of captive trumpeters is reported in this paper. White‐winged trumpeters lived in territorial social groups that ranged in size from four to 13 individuals. A typical territorial group contained three adult males, two adult females, and several sexually immature offspring, but smaller temporary groups sometimes formed for the duration of the breeding season. Only the dominant female contributed eggs to the clutch, and all adult males in the group competed to obtain copulations with her. Eggs were laid in elevated nesting cavities and no nest was constructed. The average clutch size was three eggs and incubation was not begun until the final egg was laid. The dominant male and female shared most of the incubation duties, but subordinate males covered approximately 15% of the incubation shifts. Eggs hatched approximately 27 days after incubation was begun and chicks left the nesting cavity the day after they hatched. Chicks were completely dependent on older birds to feed them for their first 3 weeks and then gradually began to feed themselves more and more food. The subordinate adult males fed chicks the most food, the dominant male and female and older offspring fed chicks an intermediate amount, and the subordinate adult female fed chicks the least. Young chicks behaved aggressively toward each other but were separated by adults before they injured each other. If at least one chick from the clutch survived, trumpeters did not breed again until the beginning of the next breeding season the following year. Zoo Biol 19:65–84, 2000. © 2000 Wiley‐Liss, Inc.     

Reproductive cycles and spawning periods of two Lessepsian siganid fishes on the Lebanese coast

A total of 1048 specimens of Siganus rivulatus and Siganus luridus were collected from the Batrun area of the Mediterranean Sea from January 1999 to August 2000. The sex-ratio in both species did not differ significantly from 1 : 1 between size classes or months. For S. rivulatus , the estimated mean length at first maturity ( L _T50) was 132·5 mm for males and 136·5 mm for females, and 139·0 and 142·0 mm, respectively, for male and female S. luridus . Spawning occurred in June in S. rivulatus and from May to July in S. luridus . High temperature in summer appeared to be a limiting factor in the gonadal development of both siganid species, which have reduced their breeding seasons on the Lebanese coast compared to their native Red Sea.     

Early lysine deficiency in young broiler chicks

The carry-over effect of a pre-starter diet (0 to 3 days of age) deficient in lysine on subsequent growth and body composition (3 to 10 days) was examined in two experiments on male broiler chicks raised in cages. In experiment 1, lysine deficiency was applied from 3 to 10 days after providing a balanced pre-starter control feed (D+, 1.40% lysine) or a lysine deficient feed (D−) during the first 3 days. Three levels of deficiency (A = 0.63%, B = 0.72%, C = 0.82%) were tested. Growth and feed intake were higher in D+ than in D− chicks ( P < 0.001). However, the feed conversion ratio from 3 to 10 days of age was higher in D+ chicks ( P < 0.001); pre-starter and starter feeds interacted ( P < 0.04) with the feed conversion of treatment D+/A = 2.07 being better than treatment D+/A = 2.61 ( P < 0.05). This suggests that chicks deficient from hatching exhibit a relatively lower sensitivity to lysine deficiency than chicks started on a control diet. In experiment 2, performance, slaughter parameters and body composition were analysed at 3 and 10 days of age, in chicks having received a lysine deficient feed (D0, 0.72% lysine), a control feed (D+, 1.40% lysine) or having been pair fed with control feed adjusted to D0 intake (PF) from 0 to 3 days of age, and then fed D0 ad libitum from 3 to 10 days of age. At 3 days, PF chicks had a higher body weight ( P < 0.05) than D0, and thus a better feed conversion. Body composition in relative values was little or not affected by dietary treatments, but the breast muscle weight at 3 days was higher in D+ and PF chicks compared with D0 ( P < 0.05) and this effect was even accentuated at 10 days of age. The present work confirms that early nutrition can have subsequent consequences on the adjustment of fast growing broiler chicks to their nutritional conditions. It also suggests that breast muscle development is a more reactive parameter than whole body composition in this kind of experiments.     

GRAZER-INDUCED DEFENSE IN SCENEDESMUS OBLIQUUS (CHLOROPHYCAEA)

Porphyra pendula Dawson is an endemic species of the mid-intertidial zone in the Gulf of California. Based on surveys from the Phycological Herbarium of UABCS since 1994, we found an extensive population of this species in Punta Coyote, south of La Paz. Here, we assess the phenology of the gametophyte phase from December of 1998 to June of 1999 with visits every 2 weeks. Our results show significant temporal and spatial changes in length and width of the plant, with some quadrants displaying two peaks in development ( January and March) and other quadrants with a peak only in January. A significant correlation existed between length and width of the blade and is linked with plant maturation, observations which strongly support the isometric growth rate of the species. No differences between exposed and protected areas were observed suggesting stronger differences between quadrants. Differences plants in length and in color existed between male and female plants; the males were smaller and yellow and females/carposporophyte were larger and red-purple. Most of the thalli were reproducing during the study, with a greater proportion of females than males (ca. 2:1). Our results suggest that the morphological changes in this species may be related with temperature and day length.     

Parental behaviour of Spanish Imperial Eagles Aquila adalberti: sexual differences in a moderately dimorphic raptor

Capsule The sexes make significantly different contributions in the tasks of nest-building, incubation and food provisioning to chicks.

Aims To determine the division of parental activities during breeding (nest-building, incubation, brooding, food provisioning and feeding).

Methods Between 1991 and 1998 focal observations were made at nests using 20–60× telescopes. During the incubation period, 11 pairs were studied involving a total of 2812 observation hours over 269 days. During the chick-rearing period, seven pairs were studied involving a total of 5499 observation hours spread over 503 days. The birds were sexed and identified individually on the basis of size, position during copulation, vocalization and plumage differences.

Results Significant differences were found between the sexes in parental behaviour. Males scarcely participated in incubation and contributed significantly more than the females only in food provisioning, both during incubation (food transfers to feed the female) and during chick-rearing (to feed the chicks). Females were responsible for most of the incubation, nest-building (during incubation and chick-rearing), brooding, shading and feeding of chicks. Nest attendance by females decreased over time. In both sexes, food provisioning increased with brood size.

Conclusion Intersexual differences are discussed in the context of the reversed sexual size dimorphism and parental investment strategies. We suggest that in Spanish Imperial Eagles reversed sexual size dimorphism is best explained by the prey capture difficulty hypothesis, than by parental role division during reproduction.     

Navigational ability in the domestic fowl (Gallus gallus domesticus)

Little is known about the navigational abilities of domestic fowl. The question of how chickens represent and orient in space becomes relevant when they are kept in non-cage systems. Since the sun is known to be the dominant spatial organiser in other diurnal bird species, we started our investigation of the chicken’s spatial abilities by subjecting them to a food-searching task with the sun as the only consistent visual cue. In an additional experiment we tried to rule out the use of auditory cues in finding a food reward.

Eight ISA Brown chicks were housed in outdoor pens. A separate test arena comprised an open-topped, opaque-sided wooden octagon (2 m wide and 1.5 m high). Eight goal boxes with food pots were attached to each of the arena sides; a wooden barrier inside each goal box prevented the birds from seeing the food pot before entering. After habituation we tested during five daily 5 min trials whether the chicks were able to find food in a systematically allocated goal direction. Food residue in every foot pot controlled for the use of olfactory cues and no external landmark cues were visible. Every day each box was unpredictably moved to a randomly assigned side of the arena and the side to face north was also randomly allocated, to prevent the chicks from using cues other than the sun’s position. Circular statistics were used to determine whether birds moved in a non-random direction and if so, if they significantly oriented goalwards. The results showed that seven of the eight birds moved significantly in the goal direction. It seems likely that the chicks used the sun to orient. Due to weather constraints only four chicks received the same treatment on a new location, to rule out the use of auditory cues. Two of these four chicks significantly moved in the goal direction.

The results from our experiments show that domestic chicks use spatial memory to orient towards a hidden goal. Moreover, their orientation is most likely to be based on sun cues opening up the possibility that the sun compass may dominate even in this ancestrally predominantly ground-living forest bird.     

Between-lake differences in the diet and provisioning behaviour of Black-throated Divers Gavia arctica breeding in Scotland

Surveys at 23 Black-throated Diver breeding lakes in Scotland showed large between-lake differences in the species and size range of potential prey. The study lakes were classified into four types according to the main size-taxa prey classes present. Type 1 lakes lacked small fish, Type 4 lacked salmonids < 300 mm and Types 2 and 3 both had all four of the main prey classes. Diver diet for 30 families at the study lakes was quantified from 7943 prey items seen fed to chicks, and 153 items seen eaten by adults, during 662 h of observations. At all lake types adults mostly ate salmonids of 120–240 mm in length, especially Brown Trout Salmo trutta , and European Eels Anguilla anguilla up to c.  350 mm. The prey eaten by chicks ranged widely, from c.  0.03 g to 300 g, with important implications for feeding behaviour. Young chicks (days 1–8) rejected items greater than 70 mm long. The diet of young chicks consisted mostly of small fish, either Three-spined Sticklebacks Gasterosteus aculeatus (Type 2 lakes) or Minnow Phoxinus phoxinus (Type 3 and Type 4 lakes). At other lakes (Type 1) it consisted mostly of mayfly larvae (Ephemeroptera); invertebrates were the only abundant potential small prey in these lakes. At all lakes the chick diet became more similar to that of adults as chicks grew. Adults provisioning chicks used two foraging strategies. In 'excursion foraging', adults hunted away from the chicks and carried prey back for them; in 'attendance foraging', the chicks accompanied the foraging adult(s). Excursion foraging was used mostly before day 4 and was strongly and positively correlated with the abundance of fish < 80 mm in length. This behaviour is probably adaptive, but is probably tenable only where small fish are relatively abundant. Young chicks fed mainly on small fish had higher survival rates than those fed on invertebrates.