Repeatability of chick growth and food provisioning in Manx shearwaters Puffinus puffinus

In animals that produce few offspring during their lifetime, the ability to raise high-quality offspring through the provision of parental care is particularly important for individual fitness. In this paper, we use repeatability analysis of data from two separate time-periods, in the 1970s and the 1990s, to examine parental and environmental effects on chick growth and food provisioning in a long-lived seabird, the Manx shearwater Puffinus puffinus . We test the hypothesis that asymptotic body masses of chicks are most strongly influenced by an individual's genotype, with growth rates intermediate and food provisioning rates most strongly affected by environmental conditions during growth. Peak body masses of chicks raised by the same parents showed significant repeatability in both samples, whereas mass growth rates up to the attainment of peak mass showed significant repeatability only in the 1970s. Several different measures of food provisioning by parents showed no individual consistency in either time-period, in keeping with our predictions. Food provisioning rate was a major determinant of annual variation in chick growth, and so it may seem surprising that Manx shearwaters showed repeatable patterns of chick growth but not of food provisioning, and several possible explanations for this pattern are discussed.     

Sex differences in provisioning rules: responses of Manx shearwaters to supplementary chick feeding

Sex differences in food provisioning have been found in a numberof socially monogamous birds with biparental care, but the reasonsremain unclear. In Manx shearwaters, males provide 40–50%more food for chicks than do females, and previous empiricaldata have suggested that this difference could arise becausefemales are able to regulate food delivery by reducing the provisioningof well-nourished chicks, whereas males are not (hypothesis1). Alternatively, however, males may be as capable as femalesof assessing and responding to the variation in the nutritionalrequirements of their chick but have a higher threshold forreducing food delivery to well-nourished chicks (hypothesis2). To test these two hypotheses, we used supplementary feedingto manipulate the nutritional status of chicks and then examinedthe responses of male and female parents and their offspring.Supplementary feeding significantly reduced both the beggingbehavior of chicks and the frequency and sizes of meals deliveredby parents. Males and females reduced their overall provisioningrates to a similar extent (males by 38%, females by 42%), somaintaining the same difference in contributions to provisioningin the control group (males 58%, females 42%) and the experimentaltreatment (males 59%, females 41%). These data strongly supporthypothesis 2. Supplementary feeding of chicks resulted in fewervisits by parents and a higher proportion of long trips in bothsexes (4 days for males, 5–7 days for females). However,maximum trip durations were unchanged, suggesting that supplementaryfeeding of chicks had no effect on the foraging ranges or overallfood-provisioning strategies of parents.     

Sex differences in provisioning rules and honest signalling of need in Manx shearwaters, Puffinus puffinus

Sex differences in provisioning rules have been found in a number of bird species, but the reasons remain unclear. Studies of begging in species with single-chick broods exclude the influence of nestling competition and may provide especially useful models for the study of signalling during parent-offspring conflict. We tested whether sex differences in provisioning rules occur in a species with an obligate brood size of one, the Manx shearwater. We found that chicks conveyed information about their body condition through begging, but male and female parents responded differently to that information. Females varied meal sizes according to the begging intensity of the chick and adjusted subsequent trip duration according to the chick's body condition after feeding, but males did not alter meal size or adjust trip duration. We discuss these findings in the context of recorded differences in the contributions to food provisioning by male and female parents, and we discuss why females may respond more sensitively than males to changes in chicks' nutritional requirements.     

Parental food provisioning is related to nestling stress response in wild great tit nestlings: implications for the development of personality

Background

Variation in early nutrition is known to play an important role in shaping the behavioural development of individuals. Parental prey selection may have long-lasting behavioural influences. In birds foraging on arthropods, for instance, the specific prey types, e.g. spiders and caterpillars, matter as they have different levels of taurine which may have an effect on personality development. Here we investigated how naturally occurring variation in the amounts of spiders and caterpillars, provisioned to nestlings at day 4 and 8 after hatching, is related to the response to handling stress in a wild passerine, the great tit (Parus major). Broods were cross-fostered in a split-brood design allowing us to separate maternal and genetic effects from early rearing effects. Adult provisioning behaviour was monitored on day four and day eight after hatching using video recordings. Individual nestlings were subjected to a handling stress test at an age of 14 days, which is a validated proxy for exploratory behaviour as an adult.

Results

Variation in handling stress was mainly determined by the rearing environment. We show that, contrary to our predictions, not the amount of spider biomass, but the amount of caterpillar biomass delivered per nestling significantly affected individual performance in the stress test. Chicks provisioned with lower amounts of caterpillars exhibited a stronger stress response, reflecting faster exploratory behaviour later on in life, than individuals who received larger amounts of caterpillars.

Conclusions

These results suggest that natural variation in parental behaviour in wild birds modulates the developmental trajectories of their offspring's personality via food provisioning. Since parental provisioning behaviour might also reflect the local environmental conditions, provisioning behaviour may influence how nestlings respond to these local environmental conditions.

     

Nestling obesity in procellariiform seabirds: temporal and stochastic variation in provisioning and growth of short-tailed shearwaters Puffinus tenuirostris

Procellariiform seabirds such as short-tailed shearwaters Puffinus tenuirostris accumulate large quantities of lipid during the nestling period. The functional significance of this pattern of development remains unclear, but has been related both to temporal variation in feeding conditions around the colony and to stochastic variation in the foraging success of individual parents. This paper examines temporal and age-specific variation in the pattern of food delivery to nestling short-tailed shearwaters, which have one of the lowest provisioning rates of any procellariiforms and are known to experience occasional long intervals between feeds. We assess whether variation in the provisioning rates of chicks was associated primarily with temporal variation in food delivery at the level of the colony or with stochastic variation in food delivery at the level of the individual. We then discuss this variability in the context of nestling obesity. For all but the youngest chick age-classes, individual meals delivered by adults averaged 141 g, which was 25% of adult body mass. The proportion of chicks fed each night was low (49%) and highly variable (coefficient of variation = 82%), which means that occasional long intervals between feeds would be expected to arise simply by chance. In keeping with this, intervals between feeding events for individual chicks followed a negative exponential distribution with a mean of 2 nights and a maximum interval of 13 nights. There was significant temporal variation in food delivery, but deviations from expected values for both feeding frequency and meal size were restricted to a small number of nights, included values both higher and lower than expected and did not persist for more than 2 nights in succession. These data suggest that even among those species with very low feeding frequencies and occasional long intervals between feeds, nestling obesity in Procellariiformes should be regarded as a response to chronic stochastic variability in food delivery at the level of the individual chick rather than as insurance against sporadic temporal variation at the level of the colony. Received: 3 March 1997 / Accepted: 10 May 1997     

Begging, food provisioning, and nestling competition in great tit broods infested with ectoparasites

Ectoparasites are a ubiquitous environmental component of breedingbirds, and it has repeatedly been shown that hematoph-agousectoparasites such as fleas and mites reduce the quality andnumber of offspring of bird hosts, thereby lowering the valueof a current brood. Selection acting on the hosts will favorphysiological and behavioral responses that will reduce theparasites' impact. However, the results of the few bird studiesthat addressed the question of whether parasitism leads to ahigher rate of food provisioning are equivocal, and the beggingresponse to infestation has rarely been quantified. A changein begging activity and parental rate of food provisioning couldbe predicted in either direction: parents could reduce theirinvestment in the brood in order to invest more in future broods,or they could increase their investment in order to compensatefor the parasites' effect on the current brood. Since the nestlingsare weakened by the ectoparasites they may beg less, but onthe other hand they may beg more in order to obtain more food.In this study we show experimentally that (1) hen fleas (Ceratophyllusgallinae) reduce the body mass and size of great tit (Parusmajor) nestlings, (2) nestlings of parasitized broods more thandouble their begging rate, (3) the male parents increase thefrequency of feeding trips by over 50%, (4) the females do notadjust feeding rate to the lowered nutritional state of nestlings,and (5) food competition among siblings of parasitized broodsis increased. Ultimately the difference in the parental feedingresponse may be understood as the result of a sex-related differencein the trade-off of i0vesting in current versus future broods.     

Food limitation in asynchronous bluethroat broods: effects on food distribution, nestling begging, and parental provisioning rules

Scramble competition models of begging predict that junior nestlingswill be more affected by food limitation than seniors. Thesemodels assume that food allocation is under offspring controland, hence, predict that this change in food distribution iscaused by a differential behavioral response by seniors andjuniors. By using the bluethroat (Luscinia svecica svecica)as our model species, we induced food limitation by removingthe male parent temporarily. We found that, as predicted, fooddistribution became more biased in disfavor of juniors whenfood was limited. However, there was no significant differencein the behavioral responses of seniors and juniors (i.e., positioningin the nest or begging postures) to food limitation that couldexplain the change in food distribution. Hence, there was noevidence that seniors controlled food distribution. As predictedif parents preferentially fed seniors, nestling rank affectedfood distribution when controlling for variation in nestlingbehaviors. Furthermore, as expected if the increased skew infood distribution under food limitation was caused by activefood allocation by parents, nestling rank had a greater effecton food distribution under food limitation than under normalconditions. The present study suggests that food distributionin passerine birds is determined not only by nestling behaviors(begging posture and positioning) alone but also by parentalpreferences for seniors based on nonsignaling cues, such asbody size.     

Chick‐provisioning behaviour of two shearwaters breeding in south‐eastern Australia

The chick‐provisioning behaviour of the short‐tailed shearwater Puffinus tenuirostris and the wedge‐tailed shearwater Puffinus pacificus was investigated in a mixed colony on Montague Island, New South Wales, Australia, over two breeding seasons. This colony is located at opposite edges of the breeding distribution of the two species. Frequent weighing techniques were used to determine chick feeding frequency, feed timing, meal size, chick weight loss and indices of food conversion efficiency of the chicks. Short‐tailed shearwater parents fed their chicks larger more infrequent meals than wedge‐tailed shearwater parents. Short‐tailed shearwater chicks demonstrated higher food conversion efficiencies and lower weight loss than wedge‐tailed shearwater chicks, indicating either differences in diet or metabolic rates. The feeding frequency in wedge‐tailed shearwaters also fluctuated more widely than for short‐tailed shearwaters over the two breeding seasons. Despite the fact that the timing of the breeding cycle on Montague Island is almost identical for the two species, these differences in chick provisioning are probably a result of differences in prey type and location, so they may help explain variations in annual breeding success and limits to the distribution of the two species.     

Breeding biology and provisioning of nestling snow buntings in the Canadian High Arctic

We examined basic breeding biology, as well as the effects of parental sex, brood size, nestling age, and nest habitat on foraging distances and parental food delivery rates of snow buntings (Plectrophenax nivalis) on Devon Island, NT, Canada, in the summers of 2003–2006. Clutch sizes and initiation dates were similar to those found in previous studies, although nest density was much higher. Feeding rates and foraging distances of buntings differed depending on the size and age of the brood, but were similar between nest habitats. Unlike in earlier studies, we found that male buntings made fewer feeding visits, but traveled longer distances to forage for food than females. Whether these differences between the sexes relate to reducing competition for prey, or to differing sex roles in parental care due to the poorly insulated nest cavities of this species, remains to be determined.     

Parental influence upon the provisioning schedules of nestling Short-tailed Shearwaters Puffinus tenuirostris

The single young of shearwaters grows slowly and is fed at long, often highly variable, intervals. We monitored the growth patterns of nestling Short-tailed Shearwaters Puffinus tenuirostris exchanged between nests in order to assess whether the patterns of parental visits or the demands of their young determined the rate of food provisioning in this species. These cross-fostering trials indicate a strong parental influence upon the rate of food delivery, but did not exclude the possibility of a minor influence from chicks.     

Parental provisioning, nestling departure decisions and prefledging mass recession in Cassin's auklets

We investigated how parental provisioning and nestling departure behaviour interact to produce prefledging mass recession in Cassin's auklets, Ptychoramphus aleuticus. Under our hypothesis, auklet parents are reluctant provisioners and should be increasingly likely to terminate or reduce provisioning of their single nestling as it matures. For the nestling, remaining in the nest presents a risk of losing mass (if the parent does not provision) but also a possibility of additional provisioning. As the nestling matures and becomes increasingly capable of independence, the benefits of remaining in the nest decrease and nestlings should be increasingly likely to fledge. Nestlings also should be more likely to fledge when the expectation of additional provisioning is low. Data on parental provisioning (based on growth increments) and nestling departure were consistent with our hypothesis. Older and heavier nestlings had smaller growth increments than younger and lighter nestlings, suggesting that parents were reluctant to provision old and heavy nestlings. Older and heavier nestlings also were increasingly likely to fledge. We hypothesized that nestlings might use the intensity of mass loss to gauge parental reluctance to provision, and accordingly, nestlings were increasingly likely to fledge after experiencing a greater amount of mass loss. Copyright 1999 The Association for the Study of Animal Behaviour.     

Carotenoid diet and nestling provisioning in urban and rural great tits Parus major

Considering the importance of dietary constraints for the widely held view of carotenoid pigmentation as an honest quality indicator, there is surprisingly little data on carotenoid availability in different natural diets or along environmental gradients. Here we investigate the carotenoid availability in the main diet of breeding great tits Parus major , living in urban and rural environments with known differences in carotenoid pigmentation. Carotenoid availability for nestling great tits was investigated in two respects: (1) quantity and quality of diet (i.e., caterpillar abundance and their carotenoid concentration), and (2) parental feeding frequency. First, caterpillars were generally more abundant in the urban environment and the four common Lepidoptera (i.e., caterpillars) genera studied were also heavier here. Second, as determined by HPLC analysis of the caterpillar genera, carotenoid concentration was significantly lower in the urban caterpillars. Furthermore, all except one of the caterpillar genera had higher lutein/zeaxanthin ratio in urban areas, which is in accordance with earlier studies of carotenoid composition in great tit yolk. Third, parental feeding frequency was about twice as high to urban broods compared to rural broods. This result may simply reflect the higher caterpillar abundance (shorter search time) in the urban environment. Poor food quality (low carotenoid concentration) seems therefore to be compensated by quantity in the urban environment. As a consequence the carotenoid availability seems to be similar for nestlings in the two environments.     

Table scraps: inter-trophic food provisioning by pumas

Large carnivores perform keystone ecological functions through direct predation, or indirectly, through food subsidies to scavengers or trophic cascades driven by their influence on the distributions of their prey. Pumas (Puma concolor) are an elusive, cryptic species difficult to study and little is known about their inter-trophic-level interactions in natural communities. Using new GPS technology, we discovered that pumas in Patagonia provided 232 ± 31 kg of edible meat/month/100 km(2) to near-threatened Andean condors (Vultur gryphus) and other members of a diverse scavenger community. This is up to 3.1 times the contributions by wolves (Canis lupus) to communities in Yellowstone National Park, USA, and highlights the keystone role large, solitary felids play in natural systems. These findings are more pertinent than ever, for managers increasingly advocate controlling pumas and other large felids to bolster prey populations and mitigate concerns over human and livestock safety, without a full understanding of the potential ecological consequences of their actions.     

Habitat quality, nestling diet, and provisioning behaviour in great tits Parus major

Variation in early nutrition is often a strong predictor of offspring condition and fitness. In the case of woodland passerine birds, nestling diet is determined by the spatiotemporal distribution of prey items such as caterpillars during the nestling period, and is usually quantified as differences in provisioning behaviour between habitats. However, the habitat level does not account for variation between individual territories, the level at which competition and selection are assumed to operate. Here we use nestbox cameras and Radio Frequency Identification technology (RFID) to simultaneously assess variation in both nestling diet (components) and provisioning rates (quantity) among a sample (n=22) of different quality great tit Parus major territories selected from a larger breeding population (n=310 fledged broods) in a single year. Caterpillars were by far the most numerous item provisioned to nestlings (mean=75% of prey items), as expected given the known importance of this food source for this species. Broods raised close to an oak tree, or far from the woodland edge, were provisioned the highest proportion of caterpillars. Provisioning rates declined seasonally and there was a weak association between low provisioning rates and caterpillar rich diets. During the first week of the nestling stage, nestling condition was unrelated to the proportion of caterpillars in the diet, provisioning rates and oak proximity. Condition at fledging was slightly improved in broods fed a higher proportion of caterpillars in the diet and in broods raised close to an oak tree. However, in our data early breeding was the only predictor of recruitment success, although power was low for this test. Analyses of long‐term data (41 years) from the same population confirmed a relationship between oak proximity and fledgling mass, but not recruitment success. Our results suggest that territory level environmental variation can affect offspring condition, probably through observed changes in nestling diet, but that such variation does not necessarily produce discernable effects on offspring fitness.