Poor Food Supply Research Articles

Living deep-sea benthic foraminifera from the warm and oxygen-depleted environment of the Sulu Sea

The semi-enclosed, oligotrophic Sulu Sea is characterised by warm (ca. 10 °C) and oxygen-depleted ( 32 μm) from 56 samples (from surface down to 5 cm). The stained foraminiferal assemblages of the Sulu Sea comprised 285 species, including 137 agglutinated and 148 calcareous species. Standing stock values ranged from 595 individuals/10 cm2 on the continental slope to 100 individuals/10 cm2 in the abyssal zone. Generally, in the low-productivity and low-oxygen environment of the Sulu Sea, stained assemblages are characterized by low-standing stock values, moderate dominance and low diversity. The combination of poor rates of C org flux and low dissolved oxygen content in bottom waters are the main factors controlling the deep-sea benthic fauna in the Sulu Sea. The foraminiferal abundances in the upper bathyal zone respond to both food fluxes and oxygen concentrations. Most of the epifaunal, oxyphilic species have their lower limit of occurrence at a water depth of approximately 2000 m (dissolved oxygen <1.25 ml/l) in the Sulu Sea. At constantly dysoxic (<1 ml/l O2) sites from the lower bathyal and abyssal zone, the assemblages comprised low-oxygen tolerant species and are more dependant on C org fluxes. The correlations between benthic foraminiferal faunas and C org flux and dissolved oxygen values are very good, with correlation coefficients of r2=0.956r2=0.956 and 0.88, respectively. The living deep-sea foraminiferal assemblages consisted mainly of agglutinated tests, with dominant species such as Lagenammina difflugiformis, Ammoscalaria tenuimargo, various Reophax species, and small (<70 μm) trochamminaceans like Portatrochammina wiesneri. Stained individuals of the calcareous Parrelloides bradyi (type 2) occurred in low numbers at oxygen-poor sites, down to a depth of 5 cm in the sediment column. The only stained, calcareous, infaunal species found deeper than 4000 m was Valvulineria mexicana (average living depth of 3 cm). The general microhabitat preferences of common species were consistent with those from other studies, although due to the unique combination of poor food supply and dysoxic conditions, most of the infaunal species had shallower average living depths than those reported from other dysoxic locations.

Tawny Owls Strix aluco with reliable food supply produce male‐biased broods

Tawny Owls Strix aluco have been reported to skew the sex ratio of their offspring towards males when facing food shortage during the nestling period (and vice versa), because female fitness is more compromised by food shortage during development than male fitness. To test the generality of these results we used a DNA marker technique to determine the sex ratio in broods of Tawny Owls in Danish deciduous woodland during two years of ample food supply (rodent population outbreak) and two years of poor food supply. Of 268 nestlings, 59% were males (95% CI: 53–65%). This proportion was higher than previously reported for the species (49% in Northumberland, UK, and 52% in Hungary), but consistent with Fisherian sex allocation, which predicts a male bias of c. 57% based on inferred differences in energy requirements of male and female chicks. Contrary to previous results, brood sex ratios were not correlated with the resource abundance during the breeding seasons, despite considerable variation in breeding frequency, brood size or hatching date across years. Brood sex ratios were unaffected by brood reduction prior to DNA sampling, and nestling mortality rates after DNA sampling were not related to gender. The inconsistency between the sex ratio allocation patterns in our study and previous investigations suggests that adaptive sex allocation strategies differ across populations. These differences may relate to reproductive constraints in our population, where reproductive decisions seem primarily to concern whether to lay eggs at all, rather than adjust the sex ratio to differences in starvation risk of nestlings.

Mobilization and recovery of energy stores in traíra, Hoplias malabaricus Bloch (Teleostei, Erythrinidae) during long-term starvation and after re-feeding

In some neotropical environments, fishes often experience periods of poor food supply, especially due to extreme fluctuations in rainfall regime. The fish species that experience periods of drought such as the traíra Hoplias malabaricus (Bloch 1794), may stand up to long-term food deprivation. In this study, experiments were performed in order to determine the dynamic of utilization of endogenous reserves in this species during starvation. Adult traíra were both fasted for 30-240 days and re-fed for 30 days following 90 and 240 days of fasting. Glycogen and perivisceral fat were primary energy substrates consumed. During the first 30 days, fish consumed hepatic and muscular glycogen, without exhausting these reserves, and used lipids from perivisceral fat. Hepatic lipids were an important energy source during the first 60 days of starvation and perivisceral fat were consumed gradually, being exhausted after 180 days. Protein mobilization was noticeable after 60 days of fasting, and became the major energy source as the lipid reserves were decreased (between 90 and 180 days). Following the longest periods of food deprivation, fish had utilized hepatic glycogen again. Fish re-fed for 30 days after 90 and 240 days of fasting were able to recover hepatic glycogen stores, but not the other energy reserves.

Predators control post‐fledging mortality in tawny owls,Strix aluco

Despite its recognition as an important source of variation in recruitment probability, the ecological processes leading to mortality between fledging and independence are poorly studied. Accordingly, the proximate and ultimate impact of bottom‐up (food limitation) and top‐down factors (predators, pathogens) for individual survival as well as population productivity is largely unknown in most terrestrial birds. Survival and behaviour of 131 radio‐tagged tawny owls (Strix aluco) during the post‐fledging dependency period were studied for each of three years with high food abundance and three years of poor food supply in Danish deciduous woods. To identify the effects of food limitation, 32 young received extra food 2–3 weeks prior to fledging, as opposed to 99 young that were fed by their parents only. Thirty‐six percent of the young from control broods died between fledging and independence, primarily due to predation from raptors and mammals (predominantly foxesVulpes vulpes). Predation by mammals occurred within the first few days after fledging, with young leaving the nest at an early age being at particularly high risk. Young that had received extra food as nestlings were also at higher risk of being preyed upon by mammals, possibly because they were easier to locate on their smell. Total mortality risk (control broods) increased with fledging date from 14% in April to &gt;58% in June due to an increasing raptor predation risk. Individual attributes such as sex, condition, immunocompetence or prevalence of blood parasites did not predict total or cause‐specific mortality risk. Survival during the post‐fledging dependency period was therefore primarily a function of variation in predation pressures, particularly from raptors. Increasing raptor predation of late broods appears to be an important selective agent for early breeding in the tawny owl.

Maerl grounds provide both refuge and high growth potential for juvenile queen scallops ( Aequipecten opercularis L.)

Human damage to biogenic substrata such as maerl has been receiving increasing attention recently. Maerl forms highly biodiverse and heterogeneous habitats composed of loose-lying coralline red algae, which fulfil nursery area prerequisites for queen scallops ( Aequipecten opercularis) and other invertebrates. The benefits obtained by queen scallops utilising maerl were poorly understood, so we used both laboratory predation and field tethering experiments to investigate the refuge and growth potential provided by pristine live maerl (PLM) grounds over other common substrata. In aquaria, more juvenile queen scallops (<35 mm shell height) survived on PLM than on gravel substrata in the presence of the crab Carcinus maenas or the starfish Asterias rubens. Field tethering experiments indicated similar survivorship of juvenile queen scallops on PLM than gravel; additionally, their growth rates were similar on both substrata. PLM allows scallops to seek refuge from predators and position themselves to optimise their food supply. Other bivalve refugia have been shown to provide poor food supply as a consequence of their high heterogeneity, yet maerl grounds provide a ‘win–win’ scallop nursery area coupling refuge availability with high food supply.

Effects of hypoxia on principal prey and growth of flathead flounder Hippoglossoides dubius in Funka Bay, Japan

Effects of hypoxia on the prinCipal prey and growth of flathead flounder Hippog/os­ soides dubius were studied in Funka Bay. Of the three dominant year-classes that occurred in recent years, the 1995 year-class was small in total length at age :2: 3 and low in condition factor at age :2: 2. Ophiuroids (almost Ophiura sars/), which were the dominant prey in the 1980s, were of little impor­ tance and instead, crustaceans such as mysids, natant decapods and pelagic amphipods, bivalves and fish were important prey items for H. dubius in 2000-2001. In addition, the feeding intensity of H. dubius in 2000-2001 was lower than that in the 1980s. These facts are closely related to a reduction of prey abundance, particularly ophiuroids. It seems that the hypoxia that occurred in the central part of the bay during the summer and autumn of 1995-1997 caused the poor food supply and low growth rate at ages 2-4 of the 1995 year-class.

A Case of Cooperative Polyandry in the Common Tern

Abstract The first case of cooperative polyandry in the Common Tern (Sterna hirundo) is reported. During the breeding season of 2000 two males, originating from the same brood, bred together with a female, who was paired in the previous season with one of the males. Both males copulated with the female. All three terns incubated the eggs, brooded and fed the chicks, but in different proportions. Despite poor food supply and bad weather conditions during the breeding season 2000, this polyandrous trio reared two fledglings, one of which has returned to the native colony in 2002. In another case, a two-year old, unrelated male incubated a clutch belonging to a pair of terns for a few days. Possible reasons for this deviation from the common monogamous mating system are discussed.

Forest management is associated with physiological stress in an old-growth forest passerine.

We investigated how physiological stress in an area-sensitive old-growth forest passerine, the Eurasian treecreeper (Certhia familiaris), is associated with forest fragmentation and forest structure. We found evidence that the concentrations of plasma corticosterone in chicks were higher under poor food supply in dense, young forests than in sparse, old forests. In addition, nestlings in large forest patches had lower corticosterone levels and a better body condition than in small forest patches. In general, corticosterone levels were negatively related to body condition and survival. We also found a decrease in corticosterone levels within the breeding season, which may have been a result of an increase in food supply from the first to the second broods. Our results suggest that forest fragmentation may decrease the fitness of free-living individual treecreepers.

Benthic recruitment of zooplankton in an acidic lake

In recent years, most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic–pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20 °C. Maximum heliozoan recruitment was 23 (±9 S.E.) individuals cm −2 day −1 (40% initial standing stock daily) in the winter 20 °C incubation. Maximum rhizopod recruitment was 6 (±2 S.E.) individuals cm −2 day −1 in the summer 20 °C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5 °C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 (±2 S.E.) individuals cm −2 day −1 during the winter 5 °C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20 °C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic–pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.

INFLUENCES OF FOOD AVAILABILITY AND PREDATION ON SURVIVAL OF KITTIWAKES

Life history theory predicts a trade-off between current reproduction and survival to maximize fitness. In long-lived seabirds, one might expect adults not to jeopardize survival by excessive reproductive investment when environmental conditions for breeding are adverse. Some environmental factors have reduced the fecundity of Black-legged Kittiwakes (Rissa tridactyla) breeding in Shetland, UK, a metapopulation that has declined substantially during the last two decades. Two hypotheses are proposed to explain this decrease: (1) reduced availability of sandeels (the main prey for kittiwakes), which has occurred since the late 1980s; and (2) increased predation by Great Skuas (Catharacta skua), the main predator of kittiwakes. Detailed data on food supply (sandeel stock size, by age groups), kittiwake body condition and breeding success, and diet and productivity of Great Skuas allowed us to assess the influence of each of these factors on adult kittiwake survival from 1986 through 1997. Capture–recapture models were constructed to examine correlations between local adult survival rate and environmental parameters. Body condition at the end of the breeding season and availability of 0-group (juveniles ≤ 1 yr old) sandeels positively influenced adult survival, whereas survival was lower when Great Skua productivity was high. Adult survival varied greatly during the study, from 0.53 ± 0.04 to 0.98 ± 0.01 (mean ± 1 sd), and was independent of sex. Both hypotheses were supported. Contrary to predictions of life history theory, kittiwakes did not refrain from breeding in years of poor food supply or high predator activity to buffer their survival at the cost of not rearing chicks. Although 0-group sandeel availability affected breeding success of kittiwakes, its influence on adult survival was also significant. The discovery that food supply affects adult survival rate has important implications for fisheries management to minimize impacts on seabirds.

The effect of age and year on the survival of breeding adult Great SkuasCatharacta skuain Shetland

The survival rates of breeding adult Great SkuasCatharacta skuawere examined at Foula, the largest colony in the world, where numbers have been declining since the late 1970s. Resightings of colour‐ringed breeding adults over a 12‐year period were analysed using Cormack‐Jolly Seber models to estimate survival rates. Annual survival rates averaged 0.89 but varied among years between 0.82 and 0.93, with annual variations being temporally associated with variations in sandeel abundance during the breeding season. Most birds appeared to die outside the breeding season and so it is possible that nutritional stress and reproductive costs of breeding in years of poor food supply affect survivorship on migration or in the wintering range. Survival rates of adult Great Skuas were affected by their age according to a quadratic equation, with survival increasing significantly with age from 0.73 in 5‐year‐old‐birds to between 0.85 and 0.96 in birds from 7 to 22 years old, with a sharp decline to between 0.75 and 0.87 in birds over 22 years old. Year effects were evident when controlling for age, indicating that annual variations in survival rates are not explained by changes in age‐composition of the marked population among years.

A dynamic model of hypothermia as an adaptive response by small birds to winter conditions.

We present a dynamic programming model which is used to investigate hypothermia as an adaptive response by small passerine birds in winter. The model predicts that there is a threshold function of reserves during the night, below which it is optimal to enter hypothermia, and above which it is optimal to rest. This threshold function decreases during the night, with a particularly sharp drop at the end of the night, representing the time and energy costs associated with returning to normal body temperature. The results of the model emphasise the trade-off between energy and predation, not just between foraging options, but also between foraging during the day and entering hypothermia at night. The value of being able to use hypothermia represents not just energy savings, but also reduced predation risk due to changes in the optimal foraging strategy. Conditions which give a high value of hypothermia are short photoperiod, variable food supply, low temperatures, poor and scarce food supplies.

Assessment of the Particulate Food Supply Available for Mussel (Mytilus spp.) Farming in a Semi-enclosed, Northern Inlet

Temporal variability in the quantity, organic content, and phytoplankton composition of the particulate food supply available to a cultured mussel population was assessed for a 3-year period in a small inlet of Notre Dame Bay, Newfoundland, Canada. The study site had a restricted flushing rate estimated at 1–2·75 timeswk−1for a complete water exchange. The quantity of both total (TPM) and organic (POM) seston varied temporally from 0·7–23·7mgl−1and 0·05–1·97mgl−1respectively during the 3-year sampling period. TPM typically remained relatively high (>10mgl−1) through the winter and spring period. Most of the seasonal variation in total seston was due to seasonal variability in the PIM component. Both PIM and POM concentrations were seasonally lowest during summer. The organic fraction of the seston (POM/TPM ratio) was seasonally low in winter and increased steadily through spring and summer to reach its maximum in the autumn. The living phytoplankton component of the seston was typically dominated, both numerically and in biomass, by a variety of diatom and autotrophic nanoflagellate species in the 2– 20-μm diameter size range. Discrete diatom population blooms occurred in the autumn of all three years and largely consisted of a single species, Skeletonema costatum. Phytoplankton:detritus ratios were significantly lower during winter. Total phytoplankton biomass levels were seasonally low during winter and summer and were associated with seasonal variation in diatom biomass. We conducted modelling simulations of relationships among seston organic food levels, their temporal variability, tidal flushing rates, cultured mussel biomass and production indices, and estimates of mussel maintenance ration requirements to predict the adequacy of northern inlets to sustain commercial-scale mussel farm development. We conclude from these simulations that small, semi-enclosed, northern inlets likely frequently experience periods when naturally occurring organic seston levels are insufficient to meet basic mussel stock maintenance ration requirements when such inlets are stocked to commercial-scale densities. We infer that periods of food-limited mussel growth and/or production are likely to occur at these high mussel population levels, particularly during summer. Qualitatively poor (low POM:TPM ratio; low phytoplankton:detritus ratio) food supply during winter may also be a further limiting factor. The implications of our conclusions in relation to aquaculture industry development and environmental management are discussed.

Food limitation explains most clutch size variation in the Nazca booby

Summary Natural selection is expected to optimize clutch size, but intrapopulation variation is maintained in many bird species. The Nazca booby provides a simple system in which to investigate clutch size evolution because clutch size and brood size are decoupled due to obligate siblicide. The indirect effect of brood size on clutch size evolution can therefore be eliminated. In Nazca boobies, second eggs provide insurance against the failure of the first egg or early death of the first hatchling, but approximately half of all females lay only one egg. We tested the hypothesis that one‐egg clutches result from food limitation by providing female Nazca boobies with supplemental food. A higher proportion of supplemented females produced two‐egg clutches than did control females. Supplemented females produced larger second‐laid eggs than did control females, but not first‐laid eggs. Laying date and laying interval were not affected. Comparisons of clutch size and egg volume between years indicated that the supplemental feeding experiment was not conducted in a year with a poor natural food supply. Thus supplemented females produced larger clutch sizes despite apparently normal natural food levels. This experiment nearly completes our understanding of clutch size variation in the Nazca booby, and indicates that food limitation and the costs of egg‐laying should be considered carefully in studies of clutch size evolution.

Metabolism and circadian rhythms of the European blind cave salamander Proteus anguinus and a facultative cave dweller, the Pyrenean newt (Euproctus asper)

Comparisons of circadian rhythmicity, behavior, and metabolism between surface- and cave-dwelling salamanders allow evolutionary trends in these processes to be elucidated. The proteid Proteus anguinus, an obligate cave-dweller, showed no apparent daily rhythm of activity or resting metabolic rate. In contrast, the salamandrid Euproctus asper, a surface-dweller/facultative cave-dweller, had a circadian resting metabolic rate and activity cycle. These circadian rhythms had an endogenous component. The lives of both studied salamanders were characterized by long periods of inactivity punctuated by bouts of foraging or exploratory/predatory behavior. Proteus anguinus had reduced resting metabolic and spontaneous activity rates (considerably lower than those of most surface-dwelling amphibians), and therefore appears to be a good example of a vertebrate as a low-energy system. The low metabolic and activity rates of P. anguinus are interpreted as adaptations to a subterranean environment, where a poor and discontinuous food supply and (or) intermittent hypoxia may be present for long period

In situ comparison of activity in two deep-sea scavenging fishes occupying different depth zones

The activity of two scavenging deep-sea fishes occupying the same niche in overlapping depth zones were compared by in situ measurements of swimming speeds, tail-beat frequencies and by arrival time at baits. At 4800 m on the Porcupine Abyssal Plain, the grenadier Coryphaenoides (Nematonurus) armatus was the dominant scavenger, arriving at baits after 30 min, and swimming at relatively slow speeds of 0.17 body lengths (BL) sec-1. At 2500 m in the relatively food rich Porcupine Seabight both C. (N.) armatus and the blue-hake, Antimora rostrata, were attracted to bait, but A. rostrata was always the first to arrive and most of the bait was consumed before the C. (N.) armatus arrived. A. rostrata swam at mean speeds of 0.39 BL sec-1, similar to related shallow water species at equivalent temperatures. Observations on tail-beat frequency from video sequences confirmed the greater activity of A. rostrata. The data indicate that, given sufficient food supply, high pressure and low temperature do not limit activity levels of demersal deep-sea fishes. Low activity of C. (N.) armatus is an adaptation to poor food supply in the abyss, where these fishes dominate, but prevents it competing with the more active A. rostrata in shallower depths.

Natal dispersal in the western gull: proximal factors and fitness consequences

1. Natal dispersal distance (NDD; the distance between natal site and recruitment site) was studied in relation to proximal factors including sex, cohort, recruitment age, nesting density, nest site quality; and also within‐colony movements of prospecting prebreeders among 133 recruits of two cohorts (1979–80) in a large, dense colony of western gulls Larus occidentalis (Audubon) on South‐east Farallon Island, California. NDD was also studied in relation to ultimate factors, assessed from total number of chicks fledged to 1994, survival of breeding adults, and fitness‐related life history traits, including brood size and hatching date. The Farallones colony is an unusual case in that it includes 50% of the species population and 90% of all western gulls breeding within a radius of 1000 km. Hence, potential recruits could choose between locations within the Farallones colony, but had limited choice to recruit at other colonies. 2. Among prebreeders, distance from natal site to prospecting site increased with age among gulls aged 2 to 4 years, and stabilized in 4‐ to 8‐year‐olds. Most 2‐year‐olds prospected on their natal sites. 3. Compared to other bird species, natal philopatry was strongly developed in both sexes, but was significantly greater in males (median distance between natal and recruitment site among males, 17 m; median distance among females, 50 m). 4. More philopatric males nested in areas of higher density and with a tendency for more nest cover (P = 0·080, when controlling for the effect of density). A non‐linear relation between NDD and recruitment age among males resulted from shorter NDD in 4‐, 5‐ and 6‐year‐olds compared to 3‐year‐olds and males older than 6 years. There was no relation between NDD and recruitment age in females. 5. Males who had hatched early in the season (individuals who were, on average, more dominant, with higher prebreeder survival and recruitment probability; Spear &amp; Nur 1994) had shorter NDD than males who hatched later. 6. Fitness costs associated with natal philopatry were detected in both sexes. More philopatric males survived significantly less well than did less philopatric males. Average number of chicks fledged among experienced females (6–11 years breeding experience) was significantly lower among more philopatric compared to less philo patric individuals, as was cumulative number of chicks fledged for all females (as of 1994). 7. Thus, whilst philopatry was well developed in these gulls, the trait appeared maladaptive. This paradoxical result may be related to an extended period of poor food supply (1989–94) in the Gulf of the Farallones. We hypothesize that fitness costs associated with philopatry reflect different life history strategies where high philopatry may be part of a high effort strategy characterized by higher reproductive effort and lower survival. These results are consistent with the view that relative advantages and disadvantages between life history strategies could lead to selective equilibrium, depending on environmental conditions.

Development, prevention and treatment of iron deficiency in women

Iron deficiency is the most common nutritional deficiency in the world. Women of childbearing age are at particular risk of developing iron deficiency due to the iron losses associated with menstruation and childbirth. Women in less developed countries are often unable to obtain adequate dietary iron for their needs due to poor food supplies and inadequate bioavailable iron. In this situation, fortification and supplementation of the diet with extra iron is a reasonable approach to the prevention and treatment of iron deficiency. In Western countries however, food supply is unlikely to be an issue in the development of iron deficiency, yet studies have shown that many women in these countries receive inadequate dietary iron. Research has shown that the form of iron and the role of enhancers and inhibitors of iron absorption may be more important than total iron intake in determining iron status. Despite this, very little research attention has been paid to the role of diet in the prevention and treatment of iron deficiency. Dietary modification would appear to be a viable option for the prevention and treatment of iron deficiency in Western women, especially if the effects of enhancers/inhibitors of absorption are considered. While dietary modification has the potential to address at least part of the cause of iron deficiency in women of childbearing age, its efficacy is yet to be proven.

Effects of Supplementary Feeding on Provisioning and Growth Rates of Nestling Puffins Fratercula arctica: Evidence for Regulation of Growth

We used a supplementary feeding experiment to investigate the existence of a causal relationship between the nutritional status of nestling Puffins and the subsequent rates of food provisioning by their parents. Chicks given supplementary food received less frequent meals than controls, with the effect that the total amount of food received by the experimental group (parental delivery plus supplementary food) was similar to the amount delivered by parents in the control group. This indicated compensatory regulation of provisioning by parents in the experimental group. Increases in body size and body mass were virtually identical in the two groups until shortly before fledging, when supplemented chicks attained higher body mass than controls. This difference appeared to result mainly from the fact that unmanipulated chicks normally receive little food from their parents towards the end of the nestling period; supplements thus constituted a large proportion of chicks' normal daily food intake over this period, and compensatory reduction in food delivery by parents did not completely match the extra food given to chicks in the supplemented group. If growth rates of chicks were usually limited by poor food supply and adults delivered food to the chick at the maximum rate permitted by food availability irrespective of the chick's immediate nutritional requirements, then regulation of food delivery by parents would not be expected. The fact that adults were regulating food delivery to their offspring below the maximum attainable rate suggests that in this study at least, nestling growth rate was not limited by a scarce and unpredictable food supply.

Food availability and the male's role in parental care in double‐brooded Treecreepers Certhia familiaris

The aim of this work was to examine differences in paternal and maternal care in a double‐brooded, monogamous species, the Treecreeper Certhia familiaris, in relation to food availability. As a measure of parental care, we recorded the hourly feeding activity of parents when the nestlings from their first and second breeding attempts were 7 and 12 days old. Feeding frequency of the first brood increased with the age of the nestlings and also with the brood size when 12 days old. While the feeding activities of the females were similar with respect to the first and second broods, the males were less active and failed to provide any food to their nestlings in 15 cases out of 28 second broods. In spite of this, the fledglings from the second broods were heavier than those in the first. Such a pattern of male behaviour was possible without being a disadvantage to the chicks because the food supply increased during the breeding season and the female could provide food for the young alone. Thus paternal care was particularly important in times of poor food supply, i.e. during the first brood, where the extent of these males' activity in feeding the 7‐day‐old nestlings was positively correlated with the average mass of the nestlings. Our results support the idea that the male of monogamous, altricial bird species often makes important contributions to raising the young, especially during periods when it is difficult for the female to do so alone. Males show flexibility in their pattern of parental care, and male Treecreepers change their contribution to the first and second broods within the same season.