Feeding Trips Research Articles

The Annual Mortality Rate of Black-Legged Kittiwakes in NE England from 1954 to 1998 and a Recent Exceptionally High Mortality

-Annual mortality rates of breeding Black-legged Kittiwakes (Rissa tridactyla) have been measured from 1954 to 1998 at colonies near the mouth of the River Tyne in NE England, with most annual values in the 1530% range. Over the period, mortality rates tended to increase progressively until the mid 1980s, when they briefly fell to the levels observed in the first ten years of the study. This was followed in 1997 and 1998 by the highest mortality rates recorded, reaching 39% and 58% respectively. No other species were involved. These high mortality rates, and those in 1984-1987, appeared to be caused by toxin-producing algal blooms. The toxin is extremely poisonous, killing birds away from the colony during a single feeding trip and affected significantly more females than males (possibly because of different feeding areas or methods between the sexes). Bodies floated ashore only when on-shore winds occurred. Birds died in several spring and summer months during each of three years and in the same restricted area about seven km off-shore and in, or close to, an area used to dump human sewage. Circumstantial evidence suggests that the nutrients from the sewage may have been responsible for larger than normal blooms of algae. As a result of the mortality, colonies in the immediate area, particularly at Marsden, have declined dramatically (43% during 1992-1997 and an additional 50% during 1997-1998). In 1998, over a quarter of the remaining occupied nests were frequented by males only. Received 30 November 1998, accepted 11 January 1999

Experimental evidence for the relationship between food supply, parental effort and chick survival in the Lesser Black‐backed Gull Larus fuscus

We studied breeding success, chick growth, parental effort and chick behaviour in two groups of Lesser Black‐backed Gulls Larus fuscus whose chicks were provided with additional food until 7 days after hatching or until fledging. These data were compared with those from control pairs which we studied simultaneously to test the hypotheses that food was in short supply during the chick stage at the colony site and that in such circumstances the behaviour of adults and young is mainly responsible for the low success. Pairs whose chicks were fed with additional food until fledging showed a higher fledging success than control pairs (intermediate for pairs of first experimental group). During the first week after hatching, experimental adults of both groups were present together at the territory for longer than control pairs. In adult females of experimental pairs, the length of feeding trips was shorter than in females of control pairs, whilst the rate of chick feeding was more frequent in the experimental broods. After the chicks were 7 days old, differences were significant only for the experimental pairs whose chicks were provided with additional food until fledging. Chicks fed until fledging showed a higher daily mass and wing‐length increments and reached a higher fledging mass at an earlier age than both control chicks and chicks which were provided with additional food until day 7. Starvation occurred only in control chicks and in chicks of the first experimental group after we had stopped providing food. When food was in short supply, fledging success of gulls was adversely affected as a result of both starvation (because of the lower feeding rates of chicks) and a higher predation rate (arising from changes in behaviour of both adults and chicks).

Luxury in freshwater and stress at sea? The foraging of the Common Tern Sterna hirundo

We compared the foraging strategies of Common Terns Sterna hirundo in freshwater (Lake Jeziorsko, Brzeg, Poland) and marine environments (Minsener Oldeoog, German Wadden Sea). Body mass changes, nest relief and duration and number of feeding trips per day were studied by automatically weighing the adults, using electronic balances under the nests. At the freshwater site, adults were lighter both before and after feeding and gained less mass during a trip. in the Wadden Sea, single feeding trips lasted longer than at the freshwater site and the terns made fewer trips per day. To achieve the same mass gain per day as in birds in freshwater, trips at sea had to be longer and food intake per trip was higher. The daily duration of absence for feeding and the daily mass gain were about the same in both areas. The limnetic feeders finished foraging earlier in the evening than the terns foraging at sea. These differences are consistent with the hypothesis that limnetic prey availability was consistent, whereas the tides limited the availability of marine prey. In consequence, foraging over freshwater presents several advantages, such as higher colony attendance, better mate coordination and better parental care.

Fledgling care and male parental effort in the Hooded Warbler (Wilsonia citrina)

We followed family groups of Hooded Warblers (Wilsonia citrina) from hatching through to fledgling independence to determine (i) the duration and extent of parental care of fledglings, (ii) the extent of brood division, and (iii) whether male parental effort in caring for nestlings predicts male effort in caring for fledglings. The 9-day nestling period of Hooded Warblers was followed by 4 – 6 weeks of further parental care of fledged young. Parental feeding rates increased from hatching to when the young fledged from the nest, and males fed nestlings significantly more than females did. At the fledgling stage feeding rates to fledglings were significantly higher than at the nestling stage, but there was no difference in feeding rates between the parents. Parents usually divided the brood of fledglings equally, so that each parent assumed full and exclusive care of a subset of the brood. However, many females (45%) initiated a second brood and the male assumed care of the entire first brood at the time when his mate began incubating. The proportion of feeding trips to nestlings made by the male was not predictive of his subsequent effort in the care of fledglings. Exclusion of the fledgling care period in studies of parental investment may give a biased picture of overall investment on the part of both male and female parents.

Costs and benefits of parental care in eastern kingbirds

We manipulated brood sizes of eastern kingbirds (Tjrannus tyrannus) to measure the costs and benefits of parental care and to test whether kingbirds showed evidence of individual optimization of reproductive effort. We found that the number of feeding trips (trips/h) increased and that per capita feeding rates (trips/nestling/h) declined as brood size increased. The decline in per capita feeding rates was mostly due to high feeding rate* to broods of one: parents made roughly equal number of trips to feed each nestling in broods of two to five. Nonetheless, nestling mass declined with brood size, probably because large broods were fed more small prey. Nesding condition (mass adjusted for structural size) differed only between broods of one and five. After controlling for effects of brood size, feeding rates had no supplementary influence on either nesding size or condition, but productivity and feeding rate were positively and significantly related. Adult male condition did not vary with brood size, manipulated brood size, or total feeding rate, but declined as the pair's per capita feeding rates increased. In addition, males that returned to breed were in better condition before leaving for migration than those that failed to return. Female condition tended to decline, and the probability of returning to breed dropped when broods were enlarged. However, female condition was independent of the probability of returning. Our results show that high feeding rates were costly, but that they carried benefits (greater productivity). Some evidence for individual optimization of reproductive effort existed: variability in nestling and adult female condition were better explained by changes in brood* size than by the actual number of young in the nest. However, most evidence supported die alternative that increased brood size was equally costly for all birds.

Male Song Complexity and Parental Care in the European Starling

Female European starlings prefer to mate with males that have large song repertoires, and those males will, on average, be older birds. We tested the hypothesis that female European starlings (Sturnus vulgaris) that choose males with large song phrase repertoires benefit by obtaining more experienced mates that will provide better parental care. Contrary to the hypothesis, males with large repertoires did not spend more time incubating nor did they make more feeding trips to the nestlings than did males with small repertoires. After controlling for the effects of brood size and age on feeding rates, there was no correlation between the nestling feeding rates of males and females. The possibility that the benefit of mating with large repertoire males is that these males are of higher genetic quality is discussed.

Egg laying, chick growth and food of kittiwakes Rissa tridactyla at Hopen, Svalbard

In 1984, kittiwakes at Hopen laid eggs ca. 14 days later than previously found in North Norway and on the Kola Peninsula. The mean clutch size, egg volume, and hatching success were otherwise very similar to those documented on the mainland. Although feeding trips were very long, a rapid chick growth and high rate of chick survival suggested that food availability was not a limiting factor in 1984. In contrast to other sites at Svalbard where polar cod Boreogadus saida and crustaceans dominate kittiwake diets, the diets of chicks at Hopen consisted mainly of capelin Mallotus villosus which the adults probably collected at or beyond the polar front southeast of the island.

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

Ectoparasites are a ubiquitous environmental component of breeding birds, and it has repeatedly been shown that hematoph-agous ectoparasites such as fleas and mites reduce the quality and number of offspring of bird hosts, thereby lowering the value of a current brood. Selection acting on the hosts will favor physiological and behavioral responses that will reduce the parasites' impact. However, the results of the few bird studies that addressed the question of whether parasitism leads to a higher rate of food provisioning are equivocal, and the begging response to infestation has rarely been quantified. A change in begging activity and parental rate of food provisioning could be predicted in either direction: parents could reduce their investment in the brood in order to invest more in future broods, or they could increase their investment in order to compensate for the parasites' effect on the current brood. Since the nestlings are weakened by the ectoparasites they may beg less, but on the other hand they may beg more in order to obtain more food. In this study we show experimentally that (1) hen fleas (Ceratophyllus gallinae) reduce the body mass and size of great tit (Parus major) nestlings, (2) nestlings of parasitized broods more than double their begging rate, (3) the male parents increase the frequency of feeding trips by over 50%, (4) the females do not adjust feeding rate to the lowered nutritional state of nestlings, and (5) food competition among siblings of parasitized broods is increased. Ultimately the difference in the parental feeding response may be understood as the result of a sex-related difference in the trade-off of i0vesting in current versus future broods.

Fitness consequences of helping behavior in the western bluebird

We examined the fitness consequences of helping behavior in the western bluebird (Sialia mexicand) at Hastings Reservation in Carmel Valley, California, USA, and tested hypodieses for how helpers benefit from engaging in alloparental behavior. Both juvenile and adult western bluebirds occasionally help at the nest. During a 12 year period, all adult helpers and most juvenile helpers were male. Helpers usually fed at nests of both their parents and rarely helped when only one parent was present. The frequency of pairs with adult helpers was only 7%, but nearly one-third of adult males helped among those with both parents on the study area. At least 28% were breeders whose nests failed. The propensity to help appears to depend upon parental survival, male philopatry, and die breeding success of potential helpers. Feeding rates were not increased at nests with juvenile helpers, apparendy because breeding males reduced their feeding rates. In contrast, adult helpers increased die overall rates of food delivery to die nest in spite of a reduction in die number of feeding trips made by both male and female parents. Helpers did not derive any obvious direct fitness benefits from helping, but diey had greater indirect fitness than nonhelpers due to increases in nesding growdi rates and fledging success at dieir parents' nests. Helpers fledged fewer offspring in their first nests dian did nonhelpers, suggesting diat they were birds widi reduced reproductive potential. Aldiough we have not yet measured the effect of extrapair fertilizations on die fitness benefits of helping, we calculated die difference in fitness between helpers and nonhelpers as a function of die potential helper's paternity when breeding independendy and his fadier's paternity in die nest at which he might help. In conjunction with constraints on breeding and indirect fitness benefits, we predict that relatedness of males to die young in dieir own as well as dieir parents' nests will influence helping behavior in western bluebirds.

Incubation and brooding performance of the Antarctic Petrel Thalassoica antarctica at Svarthamaren, Dronning Maud Land

Antarctic Petrel Thalassoica antarctica incubation and brooding effort was studied at Svarthamaren, Dronning Maud Land, during the austral summer of 1991–1992. The females probably left the nest site shortly after egg laying. The duration of incubation and brooding shifts as well as the daily weight loss (absolute and proportionate) were comparable with those of other similar‐sized procellariform species. Males spent more time incubating and brooding than did females, suggesting higher female energy stress due to egg laying. Incubating birds which were below average weight were likely to desert the nests before their mates returned from feeding trips. Both males and females lost approximately one‐fifth of their body‐weight during their first incubation shifts. Nevertheless, they increased their initial weights from egg laying to hatching and had their highest initial weights when they returned to start the shift during which the egg hatched. No factors related to adult body‐weight explained the duration of the incubation shifts. Both males and females gained weight at a higher rate when at sea than they lost it during incubation, and it is suggested that factors unrelated to food availability or individual feeding skills may be important in regulating the duration of the incubation shifts and the stay at sea.

Paternity and paternal behaviour in the red-winged blackbird, Agelaius phoeniceus

The relationship between paternity and male parental behaviour was investigated in an eastern population of red-winged blackbirds. Data collected over four seasons revealed substantial variation in paternity and the frequency of male provisioning. The feeding of nestlings by males increased non-linearly with the age of the nestlings but did not differ within or between seasons. Average relative provisioning by males to individual nests was not associated with the proportion of nestlings sired by the territory owner (determined through multi-locus DNA fingerprinting), either in a bivariate analysis or a multivariate analysis with those variables found to be associated with male parental care in other studies of red-winged blackbirds. Males provisioned significantly less frequently at nests of older females, but paternity was not associated with female age. The later in the season a female settled, the higher her mate's paternity in her brood, yet male provisioning was not associated with female settlement date. Estimated total provisioning by males (sum of all feeding trips over all nests in each male's territory) was not associated with average paternity in bivariate and multivariate analyses. Total provisioning by males was positively associated with the number of days in the season the male had a brood in a bivariate test, but not with male age, the number of females nor male condition in either bivariate or multivariate analyses. The lack of a relationship between paternity and paternal effort fits predictions of recent theory on the potential effects of reduced paternity on paternal behaviour given (1) the lack of consistent patterns of paternity among nests of different order, time of season and male and female age and (2) generally weak associations between possible behavioural cues about paternity and actual paternity.

Parental Care at Nests of Two Age Classes of Male American Redstart: Implications for Female Mate Choice

We compared food provisioning at nests of two age classes of male American Redstarts (Setophaga ruticilla). Older male redstarts are more likely to obtain a mate than yearling males. We hypothesized that females actively choose older males as mates because of direct benefits due to increased rates of nestling provisioning. Lack of foraging experience or low food availability on their territories might cause yearling males and their mates to deliver less food to their nestlings. Our results did not support this hypothesis. Nestling provisioning rates did not differ between nests of yearling and older males in number of feeding trips per hour, average load size, estimated mass delivered per hour, nor prey taxa. Direct benefits to the female (at least with regard to nestling provisioning) do not explain why older male redstarts are more likely to obtain a mate. We discuss alternative hypotheses that might explain the lower mating success of yearling male redstarts.

Mass change in fasting immature male northern fur seals

Immature male northern fur seals (Callorhinus ursinus) lost an estimated 20–30% of their body mass while fasting during the breeding season on St. Paul Island, Alaska. This is somewhat less than the mass loss reported for territorial adult male pinnipeds. During fasting, absolute rates of mass change (averaging −0.68 kg∙day−1) were positively correlated with initial mass. Mass-specific rate of change (averaging 2%∙day−1) did not vary with age or initial mass. Although they lose large amounts of mass while fasting, immature male fur seals achieve a net increase in mass during the breeding season by making feeding trips to sea. We postulate that the capability for prolonged fasting in immature males facilitates the development of social and sexual skills that are likely to increase future reproductive success.

The attendance and absence of adult Kittiwakes Rissa tridactyla from the nest site during the chick stage

In recent years there have been indications that the attendance of Kittiwakes Rissa tridactyla at the nest whilst containing young has changed, possibly influenced by food shortage. This paper examines the attendance of parents at the nest at North Shields, England, at a time when the breeding success was high and there was no indication of food shortage. It was evident that there was considerable variation in the attendance of individual parents, and chicks were left alone for the first time between 9 and over 40 days after hatching. Chicks were left alone overnight more frequently than during the day; this is related to the much longer overnight feeding trips by the parents.The recording method used in this study gave a continuous trace of the presence of each adult, and it has been used to calculate the errors made from spot observations.

Temporal and spatial pattern of common tern (Sterna hirundo) foraging in the Wadden Sea.

In 1989, 313 foraging flights of common terns in the Wadden Sea were radio-tracked. The feeding trips lasted on average 115 min covering about 30 km per flight. Completely tracked flights had a mean radius of 6.3 km. The terns preferred distinct foraging areas in the Wadden Sea. These were visited at site-specific phases of the tidal cycle resulting in a temporal and spatial pattern of foraging, caused by the site-specific and tide-related fluctuations of food availability.

Patterns of Parental Provisioning by Eastern Phoebes

We compared patterns of male and female provisioning to nestlings in first and second broods of Eastern Phoebes (Sayornis phoebe). Female Eastern Phoebes made more trips to the nest throughout the nestling cycle. Male and female feeding rates increased with nestling age in parallel until day 11 and decline slightly to day 14 (nestlings leave the nest at approx. day 17). The median total number of feeding trips per nestling did not differ between broods for either sex. We manipulated brood sizes, within the limits of naturally occurring brood sizes, and found that the per-nestling feeding rates of both sexes were unaffected. The increasing food requirements of older or larger broods caused male and female Eastern Phoebes to increase their per-nestling feeding rates in a similar pattern. Because of similarities between the sexes in size and foraging behavior, additional costs of feeding imposed by older or enlarged broods are expected to affect members of the sexes equally.

Activity budgets, diet and breeding success of KittiwakesRissa tridactylaon the Isle of May

We collected data on activity patterns (brood attendance, durations of feeding trips and feeding rates) of parent Kittiwakes Rissa tridactyla and the food fed to chicks in 2 breeding seasons at the same colony. In 1989, trip duration increased markedly towards the end of the nestling period. Pairs attempted to increase the feeding rate of their young by both adults foraging simultaneously rather than alternately. This response was more pronounced in pairs with two chicks (b/2s), i.e. those with greater food requirements. Estimates of the energy value of food delivered by the pair to the brood suggested that, particularly for b/2s at the end of the season, amounts were insufficient to meet the chicks' requirements. However, despite this shortfall most chicks survived to fledging. In 1990, Kittiwakes fed their young on smaller sandeels Ammodytes spp which had a lower energy density than those in 1989. Feeding rates were also low. We estimated that for most of the chick rearing period energy intakes for the young were below those required. Breeding success was only 0.17 chicks fledged/completed nest, the lowest value for at least 10 years.

Effects of Nestling Age and Brood Size on Nestling Care in the Bachman's Sparrow (Aimophila aestivalis)

-Effects of nestling age and brood size on parental food delivery and brood attention time were studied in the Bachman's sparrow (Aimophila aestivalis) in central Arkansas from 1983-1985. Nestlings received an increase in food mass with age because both parents increased the size of foods they delivered and because females increased the number of feeding trips and food items delivered. Males delivered a greater percentage of lepidopteran larvae to 0-2 day-old nestlings than to older nestlings. Nestling attentive time for both parents decreased with nestling age. Nestlings of large broods received approximately the same food mass as small brood nestlings because both parents increased the number of feeding trips and food items delivered. Brood size had no effect on the types of foods fed to nestlings. Small brood nestlings received more attentive time than large brood nestlings. Although females spent more time at the nest than males, they delivered roughly the same amount of food.

Group breeding in sea lions: pups survive better in colonies

Otariids are sexually dimorphic, polygynous and highly gregarious marine mammals. Females give birth and mate in large colonies during the annual breeding season. The effect of female grouping on reproductive success was studied by comparing female southern sea lions, Otaria byronia, raising pups in rookeries of hundreds of individuals, and in solitary mating pairs of one male and one female, at a distance from traditional breeding places. Only 1 of 143 pups born to gregarious females at Punta Norte, Peninsula Valdés, Argentina, died before the end of the breeding season, as opposed to 60% (34) of 57 pups born from solitary mating parirs. The main causes of pup death were infanticide by conspecific young males, and starvation, following mother-pup separation and failure to reunite. Pups in colonies were more protected from harassment by subordinate males and were readily found by mothers returning from feeding trips Females benefit from group breeding through increased survival of their pups.

SEXUAL DIMORPHISM IN NEWBORN SOUTHERN SEA LIONS

AbstractMale southern sea lion, Otaria byronia, pups born at Peninsula Valdés, Argentina, were significantly heavier (13.7 ± 1.6 kg, n = 37 vs 12.3 ± 1.4 kg, n= 38) and longer (0.82 ± 0.04 m, n= 29 vs. 0.79 ± 0.03 m, n= 29) than females. The rate of mass and length gain during the first month of life did not differ between the sexes (males: 0.21 kg/d, 0.003 m/d; females: 0.20 kg/d, 0.004 m/d). Sex differences in pup body size were not reflected in female nursing behavior, attendance patterns, and duration of feeding trips. These results suggest that southern sea lion mothers invest more energy in sons than in daughters during gestation, a difference consistent with the importance of large body size to the reproductive success of males in a polygynous species.