Test for physiological limitation to nutrient assimilation in a long-distance passerine migrant at a Springtime stopover site

During northward migration, blackcaps arrive at stopover sites in Israel's Negev Desert with reduced masses of organs that are important in food digestion and assimilation. Blackcaps that stay to refuel (largely on fruits) do not gain mass rapidly until after 3 d at the stopover site. We hypothesized that (1) it may take several days to rebuild these reduced organs, (2) during this recovery interval high feeding rates might not be possible, and (3) this could be the basis for the absence of immediate body mass gain in blackcaps at stopover sites. To test predictions from this hypothesis we used an established fasting protocol to create a group of blackcaps with reduced intestinal and liver mass compared with ad lib. fed controls. Migrants were captured and caged in the laboratory, where they were habituated to a fruit mash diet for 8 d. One experimental group was then fasted 2 d, one was fed at a restricted level (one-third ad lib. food intake) for 4 d, and one was held as ad lib.-fed controls. The fasted and restricted birds were then allowed to feed again ad lib. Birds that were experimentally fasted progressively increased their daily assimilation rate and achieved the highest rate (one-third higher than controls) 3 d after the end of their fast. Birds that were restricted achieved high rates immediately once ad lib. food was provided. Increased assimilation rate was achieved via hyperphagia and not increased assimilation efficiency. The response of the fasted birds supports the hypothesis that there may be physiological constraints to the rate of refueling during migratory stopover.     

Test of a digestion optimization model: effect of variable-reward feeding schedules on digestive performance of a migratory bird

Birds on migration often alternate between feeding and nonfeeding periods, in part because food resources may be patchily distributed and in part because birds on migration may adopt a risk-prone foraging strategy characterized by selection of variable rather than constant food rewards. Optimal digestion models predict that increases in intermeal interval like those encountered by some migratory birds should result in longer retention time of digesta and higher digestive efficiency if birds are maximizing their rate of energy intake. We tested these predictions by comparing residence time of digesta and extraction efficiency of lipid for captive yellow-rumped warblers (Dendroica coronata) feeding adlibitum and when we added intervals of time when the birds received no food. We increased the likelihood that the warblers were maximizing their rate of energy intake by increasing light levels during spring to induce hyperphagia (treatment birds (16L:8D light: dark cycle) ate 2.13 ± 0.14 g dry food day⁻¹ (n = 8) while control birds (10L:14D) ate 1.25 ± 0.03 g dry food day⁻¹ (n = 6)). Treatment birds offered food only every other 2–3 h ate 50% more during the 4-h test period than when they were always feeding adlibitum. Despite these differences in food intake, extraction efficiency of glycerol trioleate remained high and constant (93%), and mouth-to-anus total mean retention time (TMRT) did not change (overall mean: 54.8 ± 6.0 min). Residence time of lipid in the stomach increased whereas residence time of lipid in the intestine decreased when birds fed only every other 2–3 h compared to when birds always fed ad libitum. None of the results were consistent with the predictions of the optimal digestion model unless we assume that birds were minimizing their feeding time rather than maximizing their rate of energy gain. Furthermore, the ability of yellow-rumped warblers to maintain high extraction efficiency with no change in TMRT suggests some spare digestive capacity when food intake increases by as much as 50%. Received: 14 June 1997 / Accepted: 20 November 1997     

Anatomical and histological changes in the alimentary tract of migrating blackcaps (Sylvia atricapilla): a comparison among fed, fasted, food-restricted, and refed birds

During northward migration, blackcaps that arrive to refuel at stopover sites in Israel's Negev Desert have reduced masses of organs that are important in food digestion and assimilation. We tested several predictions from the general hypothesis that smaller organs of digestion (small intestine and pancreas) and nutrient assimilation (liver) bring about a lower capacity to consume food and that the organs must be restored before blackcaps can feed and digest at a high rate. We used a fasting protocol to create a group of blackcaps with reduced intestine and liver mass (reduced by 45% and 36%, respectively) compared with controls fed ad lib. Because most of the small intestine's biochemical digestive capacity reside in enterocytes found on villi, we predicted and found that reduced intestinal mass in fasted blackcaps related mainly to changes in enterocytes rather than other cells and tissues such as nonabsorptive crypt cells or underlying muscle. Because migrating blackcaps that stop over to feed begin to increase in body mass only 2 d after arrival, we predicted and found a similar recovery period in blackcaps that were first fasted but then refed--the organ mass, structure, function, and ability to consume food was restored after 2 d of feeding. Another group of food-restricted blackcaps (fed at one-third ad lib. level) lost similar amounts of body mass as fasted blackcaps but had much greater capacity to consume food than fasted blackcaps, and so we predicted that they would exhibit little or no reduction in alimentary organs relative to controls fed ad lib. A surprising result was that, as in fasted blackcaps, in food-restricted blackcaps, the decreases in masses of small intestine, liver, and pancreas were proportionally greater than the decreases in body mass or in masses of nonalimentary organs (heart, pectoralis). Food restriction, like fasting, caused a decrease in amount of intestinal mucosa and an alteration in the phenotype of enterocytes. These results are thus not consistent with the general hypothesis, and although they can be rationalized by assuming that blackcaps fed ad lib. have excess digestive capacity, it may also be that the physiological process or processes limiting very high feeding rate lie elsewhere than in the digestive system.     

Diet preferences of warblers for specific fatty acids in relation to nutritional requirements and digestive capabilities

During energy-demanding periods of the annual cycle such as migration or during cold days in winter, birds store fat comprised mostly of 16- or 18-carbon unsaturated fatty acids. In such situations, birds may feed selectively on foods with specific fatty acids that enable efficient fat deposition. We offered wild-caught yellow-rumped warblers Dendroica coronata paired choices between semi-synthetic diets that differed only in their fatty acid composition. Warblers strongly preferred diets containing long-chain (18:1; carbon atoms:double bonds) unsaturated, unesterified fatty acids to diets containing long-chain saturated, unesterified fatty acids (18:0) and they preferred diets containing mono-unsaturated fats (18:1) to diets containing poly-unsaturated fats (18:2). The preference for diets containing long-chain unsaturated fatty acids to diets containing long-chain saturated fatty acids was consistent in birds tested one week after capture at 21°C, one month after capture when cold-acclimated (1°C), and six weeks after capture at 21°C. Birds acclimated to a diet with 50% of the fat comprised of unesterified stearic acid (18:0) lost mass and reduced their food intake when we reduced ambient temperature from 21°C to 11°C over three days. We conclude that especially in energy-demanding situations there are limits to the yellow-rumped warblers' ability to assimilate some long-chain saturated fatty acids and that this digestive constraint can explain in part why yellow-rumped warblers prefer diets containing long-chain unsaturated fatty acids to diets containing long-chain saturated fatty acids.     

Digestive tract function in the long-distance migratory garden warbler,Sylvia borin

Digestive tract morphology and function of captive garden warblers (Sylvia borin) were measured during four stages of their endogenous circannual rhythm: before, during and after their autumn fattening prior to migration to wintering grounds in Africa, and after a partially simulated migratory flight. Food intake increased by 33% during fattening, utilization efficiency of dry matter tended to increase, and that of energy increased significantly (P0.01). This was because digestive tract capacity (measured as dry tissue mass) increased, so that mean retention time of food remained constant before, during and after fattening (80–84 min). After a 48-h period of starvation of fattened birds to partially simulate a migratory flight, food intake was lower on the first day of refeeding than on the next 4 days, and utilization efficiency was higher on that day, at least partly because of a longer mean retention time (111 min versus 78 min on the third day). Digestive tract dry tissue mass fell by 50% during starvation, and that of the small intestine by 63%. It is concluded that the garden warbler adapts to long-distance migration without feeding by rapidly reducing the size of its digestive tract, an expensive tissue to maintain, during migration in order to save weight and energy, and possibly also to supply part of the fuel and protein required for the flight. The cost of this strategy appears to be the time taken to rebuild the gut at stopover sites with food, but the low probability of finding such a site in the Sahara Desert means that this strategy is probably optimal for garden warblers.     

Basal and stress-induced corticosterone levels of garden warblers,Sylvia borin,during migration

Summary Plasma levels of the metabolically and behaviorally active corticosteroid hormone, corticosterone, were studied in garden warblers in the laboratory and in the field during the autumnal migratory phase. Garden warblers showing nocturnal migratory activity in the laboratory had elevated levels of corticosterone at the end of the dark phase and low levels during daytime. When nocturnal migratory activity was experimentally disrupted by food deprivation and subsequent refeeding or after spontaneous termination of migratory activity this rhythm was absent. Garden warblers stopping over in the Sahara desert during autumnal migration had low levels of corticosterone. Levels were negatively correlated with fat stores and body mass in birds sampled throughout the day. These levels were generally lower than those associated with stress in response to repeated handling and blood sampling. The results suggest (1) the existence of diel changes in adrenocortical hormonal activity that could be involved in regulation of migration, and (2) that garden warblers carrying large fat depots are not stressed by prolonged flight or lack of appropiate feeding areas during migration over the desert.Abbreviations ACTH adrenocorticotrope hormone - cpm counts per minute - EtOH ethanol - RIA radioimmunoassay     

Transition between moult and migration in a long-distance migratory passerine: organ flexibility in the African wintering area

Phenotypic flexibility of organs in migratory birds has been documented for a variety of species of different genera during the migratory period. However, very little is known about phenotypic mass changes of organs with respect to other events within the annual cycle. This seems particularly interesting when birds face different physiological challenges in quick succession. We investigated mass changes of 13 organs from garden warblers (Sylvia borin) during the transition from moult to migration. These long-distance migratory birds perform a complete moult within their wintering area just shortly before the onset of spring migration. Birds were sampled in three successive stages according to their moult status: group I consisted of birds with growing primary or secondary wing feathers, group II consisted of birds with completed wing moult but with still moulting body feathers, and group III consisted of birds that had completed wing moult and body moult. Size-corrected flight muscle, kidney mass, and pancreas mass differed significantly among the three groups. Flight muscle was heaviest in birds that were about to leave their wintering area (group III) compared with birds still in body moult (group II). Kidney and pancreas showed a pattern similar to each other, with the heaviest mass occurring in birds with moulting wing feathers (group I) and significantly reduced mass in birds that had completed wing moult (group II) or both wing and body moult (group III). Mass reductions of kidney and pancreas during the transition from moult to migration are considered to be related to the demands of moult, while increased flight muscle may be due to moult, migration, or both. Phenotypic mass changes of organs in birds occur during their migration, but they also occur during the transition between other phases of the annual cycle such as moult and migration and are not restricted to the flight muscle.     

Hostile encounters among spruce-woods warblers (Dendroica: Parulidae)

Intraspecific interactions were initiated with high frequency by four species of sympatric warblers (Dendroica: Parulidae) early in the breeding season. They declined during the incubation and nestling stages and then increased during the fledging stage in two species, the black-throated green (Dendroica virens) and yellow-rumped (D. coronata) warblers. Interspecific interactions occurred infrequently early in the season, but increased during the incubation and nestling stages in the black-throated green and blackburnian (D. fusca) warblers and during the fledging stage in the magnolia warbler (D. magnolia). Fights and chases predominated over supplanting attacks in both intraspecific and interspecific encounters. Male black-throated green and yellow-rumped warblers initiated hostile encounters more frequently than did their females, but male and female blackburnian and magnolia warblers did not differ in this regard. A somewhat equivocal interspecific social dominance hierarchy occurred: magnolia > black-throated green > yellow-rumped > blackburnian. Reversals to this trend were frequent and may have resulted from the strong defences initiated by these species in certain parts of their territories, particularly about their nests.     

Testicular development during long-distance spring migration

In birds, gonadal size varies between fully functional and maximally sized during reproduction and a regressed state with limited function during the non-reproductive periods. Recent findings show that testicular mass of the long-distance migratory garden warbler begins to increase during spring migration. Therefore, we sampled garden warblers during spring migration from Tanzania to Ethiopia, and finally to Egypt to determine if this mass increase is functional in terms of sperm and hormone production. In addition, we compared these birds, with garden warblers sampled after a 9-day recovery period following the crossing of the Sahara Desert (simulation of stopover) in Egypt and a group sampled in breeding condition in the laboratory. During migration there was a significant increase in testicular mass that was correlated with seminiferous tubule area and the stage of spermatogenesis. Plasma testosterone levels were low during migration, but were significantly correlated with testicular mass. LH concentration was not related to testicular mass, and, surprisingly, remained constant during migration. We suggest that previous experiments that found a tight relationship between testicular growth and LH level in the laboratory may not reflect the situation during long-distance migration where the great physical and energetic demands of migration likely affect the reproductive axis and, consequently, the relationship between testicular growth and LH titer. However, testes do develop to a considerable extent during spring migration and the present data suggest that initiation of testicular maturation during spring migration is necessary to ensure full spermatogenetic development soon after arrival at the breeding area.     

An experimental test of dietary enzyme modulation in pine warblers Dendroica pinus.

Modulation of gut function is important in an ecological and evolutionary context because it likely determines what food items an animal can and cannot eat. We examined how diet affects activity of digestive enzymes in an omnivorous bird, the pine warbler (Dendroica pinus). Pine warblers were fed insect-based, fruit-based, and seed-based diets for approximately 54 d. We then measured activity of amylase, maltase, sucrase, aminopeptidase-N, trypsin, chymotrypsin, carboxypeptidase A, carboxypeptidase B, pancreatic lipase, and carboxyl ester lipase. We predicted that carbohydrase activities would be highest in birds fed the diet highest in carbohydrates (fruit based), protease activities would be highest in those fed the diet highest in protein (insect based), and lipase activities would be highest in those fed the diets highest in lipid (insect based and seed based). Also, we predicted that pine warblers would exhibit greater dietary modulation of enzyme activity than reported for a less omnivorous congener, the yellow-rumped warbler (Dendroica coronata). All predictions were upheld, supporting the hypothesis that pine warblers modulate the activity of digestive enzymes in proportion to demand from substrates in the diet.     

Flexible remodeling of organ size during spring migration of the garden warbler (Sylvia borin)

The energetic demands of long-distance migratory birds change drastically, depending on the stage of their life cycle. Changing demands are reflected in the up and down regulation of adipose tissue and organ mass. This paper presents new data on organ size changes during different stages of spring migration of garden warblers (Sylvia borin). Phenotypic mass changes were quantified in 13 organs of birds caught in Tanzania, Ethiopia and Egypt. We also sampled birds after a simulated stopover in Egypt. Some organs increased in mass up to about 1.5-fold during migration from Tanzania to Ethiopia, while some remained unchanged or even decreased in mass. During flight across the Sahara, nearly all organ masses including heart and flight muscles were reduced. Exceptionally large reductions (approximately 50%) were observed for liver, bile, spleen, kidney and digestive tract organs. The only exceptions were the testes, which increased 4-fold in mass. During the simulated stopover in Egypt, a significant recovery was observed for kidney, liver, heart, proventriculus, and small intestine. The testes continued to increase in mass. Flexible remodeling of organ size in the course of spring migration thus comprises significant changes for all quantified organs, with a variety of organ-specific patterns. Individual organ patterns are differentially shaped by functional aspects according to the different organ requirements in the alternation of flight and stopover phases, energetics, future demands, and protein requirements. Anticipatory mechanisms account for the size change of the testes, and we suggest the same for the kidney and the gall bladder.     

Compensatory frugivory in migratory Sylvia warblers: geographical responses to season length

Seasonal shifts in the diets of Garden Warblers Sylvia borin , Blackcaps S. atricapilla and Lesser Whitethroats S. curruca at a North German site were studied from samples obtained by flushing the digestive tract of the birds. The significance of seven species of berries and pulpy fruits in the diet of these species while feeding in riparian vegetation during the premigratory and migratory seasons was assessed and compared with the pattern of frugivory shown by the same species in southern Germany. Because of the short time span between hatching and onset of migration, first-year long- and medium-distance migratory Sylvia warblers from northern Europe are forced to accelerate their juvenile development. Presumably to meet the higher nutritional demands of an accelerated development, juvenile Garden Warblers and Blackcaps in northern Germany ate relatively more fruit during premigration than Blackcaps in southern Germany. Fruit occurred in about 90% of their diet samples during both premigration and migration. However, this might not hold true for experienced adult birds. Garden Warblers accelerated the rate of fattening and reduced the time needed to prepare for migration when feeding on a mixed fruit diet. There were indications that Blackcaps directly influenced the fruit choice of Garden Warblers when fruits preferred by both species were scarce. Blackcaps and Garden Warblers showed subtle differences in their seasonal preferences for black elder Sambucus nigra and woody nightshade Solanum dulcamara .     

The autumnal fattening of the long-distance migratory garden warbler (Sylvia borin) is stimulated by intermittent fasting

To investigate the proximate influence of a changing food availability on the seasonal fattening of migratory birds, garden warblers (Sylvia borin) following postnuptial moult were food restricted once a week. Body mass, food intake, plasma hormone and metabolite levels were measured and compared to birds which always had ad libitum food access. The food-restricted birds increased their body mass significantly earlier than the controls. The accelerated fattening was initially not accompanied by hyperphagia and may be due to either an increased food utilisation efficiency or a reduced metabolic rate. An increase of basal glucagon and corticosterone and a decrease of insulin levels prior to fattening were not significant, however, they resulted in a significant decrease of the insulin:glucagon ratio. This ratio was also lower in food-restricted birds than in control birds and may account for the difference in the fattening progress. We conclude that seasonal fattening may be stimulated by a catabolic impulse which could be imposed in free-living birds by a decrease of food availability and/or by an increase of energy expenditure. A negative energy balance is hypothesised to be a common proximate factor affecting migratory as well as winter fattening. Accepted: 24 August 2000     

迁徙鸟类中途停歇期的生理生态学研究

大多数候鸟的迁徙活动由迁徙飞行和中途停歇两个部分组成。在迁徙过程中,鸟类要多次交替经历消耗能量的飞行阶段和积累能量的中途停歇阶段。从鸟类在中途停歇时期的能量积累速度、体重变化模式以及迁徙飞行中的禁食或食物限制、食物种类的改变、中途停歇的能量快速积累过程对消化器官的影响等方面,对目前迁徙鸟类的生理生态学研究成果进行回顾,并提出有待解决的问题及今后的研究方向。     

Foraging behavior of three species of songbirds during stopover in southeastern Morocco during spring migration

Investigators studying the stopover ecology of migrating birds typically use the capture–recapture method to examine important parameters such as fuel deposition rates (FDR) and stopover duration. However, such studies can be constrained by the number of recaptures. An alternative method is to calculate a regression of mass over time of day, but this method may not be reliable because patterns of mass change of individual birds through the day may not reflect that of the whole population. Given the potential constraints of these methods, using them in combination with other methods, such as behavioral observations of foraging birds, may improve our understanding of the patterns of fuelling in birds at stopover sites. We observed the foraging behavior of three songbird species, including Western Bonelli's (Phylloscopus bonelli), Subalpine (Sylvia cantillans), and Willow (Phylloscopus trochilus) warblers, from 15 March to 30 April 2011 at a small oasis at the northern border of the Sahara desert in southeast Morocco. Given the location of our study site at the northern edge of the Sahara desert, birds migrating north likely needed to replenish their energy reserves at this stage of their journey. We assessed foraging effort by determining the rate (number per unit time) at which birds pecked at substrates or made aerial forays after flying insects. Peck rates were higher for Western Bonelli's Warblers than for Subalpine and Willow warblers, suggesting either species‐specific adaptations to feeding in arid environments or differences in the motivation to feed. In addition, Western Bonelli's Warblers had FDRs that were negative or close to zero and, therefore, were apparently unable to refuel successfully (i.e., increase their fuel stores) despite greater effort, possibly indicating less efficiency in obtaining food (i.e., more unsuccessful pecks). The lower peck rates of Subalpine and Willow warblers suggest either that they were less efficient at finding prey or were simply foraging at lower rates. For all three species, peck rates were lower at higher wind speeds, suggesting that wind may alter prey availability and detectability, especially of flying insects. Interactions among species‐specific migration strategies, environmental conditions, and habitat quality ultimately define the success of migration. Our results suggest that using observational data in combination with capture data may improve our understanding of these interactions at migration stopover sites.     

Intermittent feeding in a migratory omnivore: digestion and body composition of American black duck during autumn

Birds fast intermittently during weather disturbances and migration. We tested responses of black duck to lost feeding days during autumn mass gain. Nine adult males were fed a pelleted diet (1.5% fat, 15.8% protein, and 18.3% neutral detergent fiber) and caged indoors during September and October (12 h light; 17 degrees -24 degrees C) to measure balances over 14 d when fed ad lib. each day and fasted intermittently for 2 d wk(-1) (short fast) or 4 d wk(-1) (long fast). Body mass (1,081 g), body water content, and metabolizable intakes of energy and protein were maintained as daily intakes of dry matter increased to 1.65 (short fast) and 2.35 (long fast) times the unfasted level. Intermittent feeding reduced metabolizability of dry matter, energy, protein, and acid detergent fiber. Concentrations of Mn provided similar estimates of metabolizability to direct measures in unfasted birds but underestimated measures of birds on long fasts. Fasting regimes continued outdoors for 9 wk when temperatures declined to -9 degrees C. Birds on short fasts were heavier (1,373 vs. 1,241 g) and fatter (159 vs. 58 g) than those on long fasts, while body water (894 g) and protein (316 g) were similar between groups after 5 wk. Birds on long fasts subsequently gained mass when fed daily, but those on short fasts lost mass when fed each day. Omnivorous waterfowl combine ingestive and digestive flexibility with plasticity of body lipid to contend with uncertain food availability.     

The effect of food restriction on morphological and metabolic development in two lines of growing Japanese quail chicks

To investigate whether there is a relationship between the inherent maximum growth rate of a chick and its degree of developmental plasticity, we studied the effects of food restriction on morphological and physiological development in P-line (selected for high growth rates) and C-line (nonselected) chicks of the Japanese quail between 2 and 64 d of age. In each line, three groups were created; one group in which the chicks were fed ad lib. and two other groups in which the chicks received 70% and 40% of the line-specific ad lib. feeding levels, respectively. In all three groups, chick survival rates were very high, and no relationship was detected between feeding level and chick mortality. The experimental feeding levels strongly affected the chicks' attainment of body mass at all ages. In addition, at most ages the growth of the structural components (wing, tarsus, and head) were also significantly affected by the feeding experiment but to a much smaller extent than the body mass. The feeding levels also affected the achievement of female sexual maturity such that, at the end of the experiment, most of the ad lib.-fed females and none of the females that received 40% of the ad lib. feeding level were laying eggs. In chicks of both lines that were fed ad lib., homeothermy was achieved at 7 d of age, but in chicks that received 40% of the line-specific ad lib. levels, homeothermy was achieved after 15-22 d of age. Poikilothermic chicks (P- and C-line) that were relatively heavy for their age exhibited relatively high resting metabolic rates (RMRs) and peak metabolic rates (PMRs) for their age. In addition, a positive relationship was found between the chicks' relative mass and RMR (based on mass-based predictive equations). No relationship was detected between the chicks' relative body mass and their relative PMR (relative to mass-based predictive equations). With respect to the metabolic scope (i.e., PMR-RMR), Japanese quail chicks exhibited remarkable developmental plasticity: chicks with body masses that were 50% lower than the normal growing chicks did exhibit a normal capacity of thermogenic heat production for their mass. Because no differences were found with respect to the level of plasticity of morphological and physiological development between the two strains, we conclude that the selection for high postnatal growth rates in P-strain chicks has not resulted in a in a higher vulnerability of these chicks to food restrictions.     

Energetics of fattening and starvation in the long-distance migratory garden warbler,Sylvia borin,during the migratory phase

Garden warblers (Sylvia borin) were subjected to starvation trials during their autumnal migratory phase in order to simulate a period of non-stop migration. Before, during and after this treatment the energy expenditure, activity, food intake and body mass of the subjects were monitored. Assimilation efficiency was constant throughout the experiments. The catabolized (during starvation) and deposited body tissue (during recovery) consisted of 73% fat. Basal metabolic rate was decreased during the starvation period and tended to a gradual increase during the recovery period. The reduced basal metabolic rate can possibly be attributed to a reduced size/function of the digestive system, which is consistent with the sub-maximal food intake immediately after resuming the supply of food to the experimental birds. The observed reductions in basal metabolic rate during starvation and activity during recovery can be viewed as adaptations contributing to a higher economization of energy supplies. The experimental birds were unable to eat large quantities of food directly after a period of starvation leading to a comparatively low, or no increase in body mass. Such a slow mass increase is in agreement with observations of migratory birds on arrival at stop-over sites.Abbreviations BM body mass - BMR basal metabolic rate - LBM lean body mass - RQ respiratory quotient     

Effect of match or mismatch of maternal-offspring nutritional environment on the development of offspring in broiler chickens

In mammals, maternal food restriction around conception and during pregnancy results in low birth weight and an adjusted growth trajectory of offspring. If, subsequently, the offspring are born into a food-abundant environment, they are at increased risk of developing obesity, type 2 diabetes, hypertension and renal dysfunction. Here, we show similar effects of maternal undernutrition on hatch weight, growth and fat deposition in offspring of birds (domestic chicken). Both mothers and offspring were fed either ad libitum or restricted in a two-by-two factorial design, resulting in two matched and two mismatched maternal-offspring nutritional environments. Offspring of ad libitum mothers grew heavier than those of restricted mothers, possibly due to the larger muscle mass. Ad libitum-fed offspring, especially females, of restricted mothers were lighter at hatch, and were heavier and had more abdominal fat at 6 weeks of age than daughters of ad libitum-fed mothers. These results suggest a common mechanism in mammals and birds in response to a mismatch in the maternal-offspring nutritional environment. They also indicate that the common practice of restrictive feeding of the broiler breeders and subsequent ad libitum feeding of the broilers may result in reduced growth and increased abdominal fat as compared to broilers of less restricted broiler breeders.     

Availability of water affects renewal of tissues in migratory blackcaps during stopover

Migrating blackcaps (Sylvia atricapilla) were used to test the predictions that (1) the rebuilding of the digestive tract, as reflected by mass-specific consumption of food on the first 2-3 days of a stopover, is faster in birds with access to drinking water than in birds without, and (2) that adipose tissue and pectoral muscles grow faster and to a greater extent in birds with unlimited access to water. We simulated migratory stopover in two experiments. In Experiment I, each of 31 birds was randomly assigned to one of three experimental groups for 6 days. Along with mealworms (～64% water) ad libitum, Group 1 received drinking water ad libitum; Group 2 had 0.5 h/day access to water; and Group 3 had no access to water. In Experiment II, 30 birds were offered a mixed diet for insectivorous birds (～33% water) ad libitum for 6 days, while randomly assigned to two groups: (1) Water ad libitum-control; and (2) 30 min access to water twice a day. We measured lean mass and fat mass using dual energy X-ray absorptiometry, as well as body mass (m(b)), pectoral muscle index (PMI), and daily intake of food and water. Mean daily water intake was significantly different among the groups in both experiments. However, the availability of drinking water positively affected the rates of gain of lean and fat mass only in birds fed with the mixed, relatively dry diet. Furthermore, mass-specific daily food intake was affected by the availability of drinking water only in the mixed diet experiment, in which birds with unlimited access to drinking water reached an asymptote, 1 day earlier than birds in the water-restricted group. We suggest that in birds consuming diets with low water content, the lack of sufficient drinking water may result in slower rebuilding of the digestive tract, or may influence biochemical processes in the gut that result in slower growth of tissue. Although blackcaps obtained sufficient water from preformed and metabolic water to renew lost tissues when eating mealworms, given access to water, the birds drank prodigiously. Our results also suggest that if drinking water is unavailable to migrating blackcaps, their choices are restricted to water-rich foods, which may constrain their rate of feeding and thus the rate at which they deposit fat. Consequently, drinking water may have an important influence on birds' migratory strategies with respect to habitat selection, use of energy, and the saving of time.