Effects of artificial foods on the blood chemistry of the Australian magpie

Abstract Bird feeding on residential property is a popular activity throughout Western countries. Advocates insist the practice is beneficial, while opponents maintain that it can result in a wide range of negative outcomes including malnutrition. The biological effects of ‘backyard feeding’ were studied in Australian magpies Gymnorhina tibicen during the non‐breeding season in 1999 in the Greater Brisbane and the Lockyer Valley regions, south‐east Queensland, Australia. Six magpie populations were selected and 70 birds were individually tagged for identification. The birds were provided with processed foods, 20–40 g per bird daily. To monitor the effects of the food, blood chemistry and body mass (BM) were used as indices. Significant effects were observed in BM and plasma cholesterol (PC), showing strong sensitivity to food provisioning. Significant effects on PC and uric acid were found only when birds were fed dog sausage. Results suggest that blood PC levels in magpies are readily influenced by, probably, the lipids present in food, and that the type of food can affect blood PC levels. These effects may occur widely among fed magpies if the influence that we demonstrated at plasma level can be generalized. Following the free‐ranging study, six magpies were captured and subjected to a 6‐day captive experiment to determine whether the selected foods had the potential to alter the birds’ blood chemistry. It was found that all of the foods, when provided ad libitum, influence at least two of the three blood parameters (PC and non‐esterified fatty acids). Due to its popularity, wildlife feeding will continue. To make wildlife‐feeding activities truly sustainable, there is a need for further studies. This study clearly demonstrated that the physiology of wild magpies can be affected by ‘backyard feeding’.     

Provision of supplementary food for wild birds may increase the risk of local nest predation

In countries such as the UK, USA and Australia, approximately half of all households provide supplementary food for wild birds, making this the public's most common form of active engagement with nature. Year‐round supplementary feeding is currently encouraged by major conservation charities in the UK as it is thought to be of benefit to bird conservation. However, little is understood about how the provision of supplementary food affects the behaviour and ecology of target and non‐target species. Given the scale of supplementary feeding, any negative effects may have important implications for conservation. Potential nest predators are abundant in urban areas and some species frequently visit supplementary feeding stations. We assess whether providing supplementary food affects the likelihood of nest predation in the vicinity of the feeder, by acting as a point attractant for potential nest predators. We provided feeding stations (empty, peanut feeder, peanut feeder with guard to exclude potential nest predators) in an area of suburban parkland in the UK and monitored the predation rate of eggs placed in artificial nests located at distances that replicated the size of typical suburban gardens. Nest predators (Magpies Pica pica, Grey Squirrels Sciurus carolinensis) were frequent visitors to filled feeders, and predation caused by Magpies, European Jays Garrulus glandarius and Grey Squirrels was significantly higher when nests were adjacent to filled feeders. The presence of a feeder guard did not significantly reduce nest predation. As supplementary feeding is becoming increasingly common during the breeding season in suburban habitats, we suggest that providing point attractants to nest predators at this time may have previously unconsidered consequences for the breeding success of urban birds.     

Supplementary feeding increases Common Buzzard Buteo buteo productivity but only in poor‐quality habitat

Temporal heterogeneity in the effects of food supply during the breeding season on the productivity of the Common Buzzard Buteo buteo was investigated in a supplementary feeding experiment. Pairs were fed artificially (1) before egg‐laying, (2) after chicks hatched and (3) continuously throughout the season, and compared with (4) unfed controls. Pairs fed before egg‐laying had marginally larger clutches than those not fed, but lay date, egg volume and weight, brood size and hatching success were unaffected. Territorial quality had far greater effects, with pairs nesting in low‐quality habitats (bog, scrub and semi‐natural grassland) laying later and having lower hatching success, smaller broods and fewer fledglings than those in more productive agricultural landscapes. Supplementary feeding after egg hatching neutralized the negative effect of poor habitat, resulting in fed birds having significantly more fledglings. This study emphasizes the importance of food availability when provisioning chicks in suboptimal habitats and has implications for the success of diversionary feeding in reducing game losses to Buzzards.     

The effect of food supplementation on the reproductive success of Black-billed Magpies Pica pica

The effect of supplementary food on the reproductive success of Black-billed Magpies Pica pica was studied in an urban habitat in the city of Edmonton, Alberta, Canada. We provided supplementary food (pelleted dog food) regularly from August 1986 to June 1988 in a feeder situated outside all known magpie territories. Magpies using the supplementary food showed (i) an advancement of 7 days in the initiation of laying, (ii) no increase in clutch-size, (iii) higher survival of nest contents (eggs and young) during a spring snow storm, (iv) an increase in rate of nestling weight gain, and (v) an increase in fledging success. Supplementary food did not prompt the fed pairs to select nest sites nearer the feeder in 1988 than in 1987. The feeder did not affect the breeding density because the nearest neighbour distances of fed magpies did not differ from unfed magpies in either year, nor did they differ between the two years for either fed or unfed magpies. This study provided evidence that magpies frequently renest even if their initial nests fail after the eggs hatch—a practice that has been reported to be absent or rare in other studies. Although brood reduction was equally frequent in the nests of food-supplemented and control pairs, the actual number of nestlings disappearing from the former (1.56 per nest) was significantly smaller than that from the latter (2.60 per nest), suggesting that the availability of food plays a major role in magpie reproductive success.     

Plasticity of Noddy Parents and Offspring to Sea-Surface Temperature Anomalies

Behavioral and/or developmental plasticity is crucial for resisting the impacts of environmental stressors. We investigated the plasticity of adult foraging behavior and chick development in an offshore foraging seabird, the black noddy (Anous minutus), during two breeding seasons. The first season had anomalously high sea-surface temperatures and ‘low’ prey availability, while the second was a season of below average sea-surface temperatures and ‘normal’ food availability. During the second season, supplementary feeding of chicks was used to manipulate offspring nutritional status in order to mimic conditions of high prey availability. When sea-surface temperatures were hotter than average, provisioning rates were significantly and negatively impacted at the day-to-day scale. Adults fed chicks during this low-food season smaller meals but at the same rate as chicks in the unfed treatment the following season. Supplementary feeding of chicks during the second season also resulted in delivery of smaller meals by adults, but did not influence feeding rate. Chick begging and parental responses to cessation of food supplementation suggested smaller meals fed to artificially supplemented chicks resulted from a decrease in chick demands associated with satiation, rather than adult behavioral responses to chick condition. During periods of low prey abundance, chicks maintained structural growth while sacrificing body condition and were unable to take advantage of periods of high prey abundance by increasing growth rates. These results suggest that this species expresses limited plasticity in provisioning behavior and offspring development. Consequently, responses to future changes in sea-surface temperature and other environmental variation may be limited.     

A SOCIO-ECOLOGY OF MAGPIES PICA PICA

The behaviour and ecology of unmarked Magpies Pica pica living in the Cotswolds were investigated over 18 months. The spacing of nests was significantly more regular than random and breeding pairs defended territories throughout the year. In winter pairs occasionally left territories to feed with non-breeding birds which flocked throughout the year.
Magpies in flocks had a higher averiage feeding rate than birds alone or in pairs. Aggression rates in flocks increased as birds fed closer together and as food patches became richer.
Agonistic interactions between Crows Corvus corone and Magpies were common; Crows frequently dominated Magpies in disputes over food, and Crows also ate Magpie eggs and young. Single Magpies were most often chased by Crows while Magpies in flocks were able to feed longer in the presence of Crows.
Differences in fledgling success among breeding pairs were related to the location of nests; Magpie pairs breeding near Crow nests suffered higher rates of agonistic encounters with Crows and also produced fewer fledglings than did Magpies breeding at greater distances from Crow nests. Magpie nests were located nearer human habitations than were Crow nests.     

The effects of food abundance on breeding performance and adult time budgets of Guillemots Uria aalge

The breeding performance, food fed to chicks and adult time budgets of Guillemots Uria aalge were examined in a year of high and a year of low food availabiIity. There was no difference between the 2 years in reproductive success, although the rate of chick feeding, chick weight and fledging success were greater in the year of high food availability. On average, chick prey items were larger in the poor food year, but this was insufficient to compensate for the lower feeding frequency. Chick feeding frequency did not differ between days in the good year but did increase later in the season in the poor food year. Compared with the high food availability year, adult Guillemots in the year of low food availability spent much less time resting at the breeding colony. and their foraging trips were twice as long. Foraging birds tended to make several successive trips before resuming brooding duties from their mates when food supplies were good, but in the low food availability year single trips were the norm. These results demonstrate that predators experiencing reduced food supply may mitigate the effects on their reproductive output by shifting their time allocation such that more time is available for foraging.     

Effects of opportunistic predation on anti-predator behavioural responses in a guild of ground foragers

We studied factors that affect prey selection by a generalist predator that opportunistically attacks prey species, and the associated inter- and intra-specific responses of prey to this type of predation. Our model system was a guild of ground-foraging birds that are preyed upon by magpies (Pica pica) during the breeding season. We found that magpies attacked up to 12 species during three consecutive breeding seasons. The overall capture success was estimated to be 4.9%. Magpies tended to attack from the air, targeting solitary prey, either on the ground or flying. Inter-specific prey responses to the risk of magpie predation included a reduction in the mean number of species occupying a foraging patch when magpies were present and a decrease in the distance between heterospecific neighbours. Intra-specific responses to magpie predation varied between species that were subject to different attack rates. Preferentially attacked prey enhanced their risk responses (increase in scanning time and scanning rate in the presence of magpies) relative to those species attacked in proportion to their abundance (increase only in scanning rate with magpies). Species attacked infrequently, relative to their abundance, showed no antipredator response. The probability of being attacked, rather than mortality rate, appears to be the factor to which prey species respond.     

The social organization of non-breeding Magpies Pica pica

The social behaviour of non-breeding individuals in a colour-marked population of Magpies was studied. In early autumn most non-breeders began to forage in a common area, the 'Non-breeding Flock Area'. A few individuals remained on their natal territories away from the flock area as solitary non-breeders. Most non-breeders were first-year birds, but some were second years or adults which no longer held a territory. Birds foraged in groups, their food intake rate differing with both group size and location. It appeared that the area in which birds foraged had a significant effect on food intake rate; foraging groups tended to form at sites rich in food. There was a dominance hierarchy amongst non-breeders; an individual's foraging behaviour, survivorship and chances of breeding were status dependent, with subordinates feeding less in groups and being less likely to survive and breed. Solitary individuals' chances of breeding were similar to those of high status birds, although their survivorship to breeding age may have been lower. Non-breeding Magpies are compared with non-breeders of other species and the factors which may influence their social behaviour are discussed. It is suggested that remaining as a solitary non-breeder is a viable alternative to becoming a low-status flock member for some birds.     

Inter-annual variation in provisioning behaviour of Southern Rockhopper Penguins Eudyptes chrysocome chrysocome at Staten Island, Argentina

Understanding the relationship between reproductive performance and food availability requires knowledge about many different variables, including such factors as the length of incubation shifts, provisioning rates and patterns, as well as how variability in these factors affects reproductive output. To examine some of the most important aspects of parental investment, we studied the provisioning behaviour and patterns of adult Southern Rockhopper Penguins Eudyptes chrysocome chrysocome breeding at Staten Island, Argentina. We investigated foraging trip duration, provisioning rates and chick survival using adult foraging patterns. Our results show that Rockhopper Penguins had clear sex-specific differences in their provisioning behaviour. Females provision chicks throughout chick rearing. By contrast, males provision chicks only during the crèche stage and at a slightly lower rate than females during this period. Foraging trips increased in length as the breeding season progressed. Rockhopper Penguins from Staten Island performed longer trips throughout the breeding season than do other species of Eudyptes at several other locations. Our results also show differences in parental investment between years that were related to differences in chick survival. We suggest that this was most likely to be related to female rather than male foraging behaviour as only females showed inter-annual differences in their provisioning rates.     

Are corticosterone levels a good indicator of food availability and reproductive performance in a kittiwake colony?

We evaluated the use of corticosterone to gauge forage availability and predict reproductive performance in black-legged kittiwakes (Rissa tridactyla) breeding in Alaska during 1999 and 2000. We modeled the relationship between baseline levels of corticosterone and a suite of individual and temporal characteristics of the sampled birds. We also provided supplemental food to a sample of pairs and compared their corticosterone levels with that of pairs that were not fed. Corticosterone levels were a good predictor of forage availability in some situations, although inconsistencies between corticosterone levels and reproductive performance of fed and unfed kittiwakes suggested that this was not always the case. In general, higher corticosterone levels were found in birds that lacked breeding experience and in birds sampled shortly after arriving from their wintering grounds. All parameters investigated, however, explained only a small proportion of the variance in corticosterone levels. We also investigated whether corticosterone, supplemental feeding, year of the study, breeding experience, body weight, and sex of a bird were able to predict laying, hatching, and fledging success in kittiwakes. Here, breeding experience, year of the study, and body weight were the best predictors of a bird's performance. Corticosterone level and supplemental feeding were good predictors of kittiwake reproductive performance in some cases. For example, corticosterone levels of birds sampled during the arrival stage reliably predicted laying success, but were less reliable at predicting hatching and fledging success. Counts of active nests with eggs or chicks may be more reliable estimates of the actual productivity of the colony. Supplemental feeding had strong effects on kittiwake productivity when natural forage was poor, but had little effect when natural forage was plentiful.     

Foraging behaviour and prey size of the painted stork

The foraging behaviour of painted stork Mycteria leucocephala was studied during 2004–2006 at 14 different sites in the Delhi region, India. Observations were recorded on 131 individuals, including 29 juvenile birds using a video camera. Recordings were also made at the nesting colony in Delhi zoo to study the prey sizes regurgitated to nestlings. The results confirm that the painted stork is a tactile forager and exclusively piscivorous. Foraging group size ranged from 1 to 18 individuals. Per 5 min foot stirring rates in the vegetated habitats were significantly higher than in non-vegetated habitats. The attempt rate and feeding rate in the breeding season were significantly higher than that in the non-breeding season. Prey sizes taken in the breeding season were significantly smaller than those taken in the non-breeding season. About 80% fish fed to the chicks were smaller than 10 cm. Young chicks were offered smaller prey compared with older chicks. The variations in foraging parameters are discussed in relation to habitats and their conservation in the Delhi region.     

Sensitivity of breeding parameters to food supply in Black-legged Kittiwakes Rissa tridactyla

We fed Herring Clupea pallasi to pairs of Black-legged Kittiwakes Rissa tridactyla throughout the breeding season in two years at a colony in the northern Gulf of Alaska. We measured responses to supplemental feeding in a wide array of breeding parameters to gauge their relative sensitivity to food supply, and thus their potential as indicators of natural foraging conditions. Conventional measures of success (hatching, fledging and overall productivity) were more effective as indicators of food supply than behavioural attributes such as courtship feeding, chick provisioning rates and sibling aggression. However, behaviour such as nest relief during incubation and adult attendance with older chicks were also highly responsive to supplemental food and may be useful for monitoring environmental conditions in studies of shorter duration. On average, the chick-rearing stage contained more sensitive indicators of food availability than prelaying or incubation stages. Overall, rates of hatching and fledging success, and the mean duration of incubation shifts were the most food-sensitive parameters studied.     

Components of productivity in black-legged kittiwakes Rissa tridactyla: response to supplemental feeding

In contrast to the high productivity of black-legged kittiwakes in Britain, kittiwakes at many colonies in Alaska have failed chronically to reproduce since the mid 1970s. To determine if food is limiting productivity and, if so, at what stages of nesting food shortages are most severe, in 1996 and 1997 we supplementally fed kittiwakes nesting on an abandoned building. The effects of feeding were stronger in 1997 than in 1996, possibly because naturally occurring prey were of poorer quality in 1997. Consumption of supplemental herring declined as egg laying approached then increased slowly during incubation and more rapidly after hatching. All of the six components of productivity we studied were improved by supplemental feeding to some degree. Supplemental food did not significantly alter laying success in either year, although fed pairs bred at slightly higher rates than unfed pairs in 1997, the poorer food year. In 1996 and 1997, extra food noticeably increased clutch size and hatching success, but significantly so only in 1997. Fledging success and productivity were substantially augmented by feeding in both years. Fed pairs fledged twice as many chicks per nest as did unfed pairs in 1996 and three times as many in 1997. Fed and unfed pairs lost most of their potential productivity through the inability to hatch eggs, and secondarily because of their poor success at raising chicks. The benefits of supplemental feeding did not carry over from one stage of breeding to another. Pairs cut off from supplemental food after laying or hatching performed similarly to pairs that had not been previously fed. This study provides benchmark values of breeding performance attainable by kittiwakes in Alaska under optimal conditions. These values are comparable to highly productive colonies in Britain and suggest that differences in life-history characteristics between Pacific and Atlantic breeding populations are primarily controlled by food supply.     

Predation by Australian magpies (Gymnorhina tibicen) on pasture invertebrates: Are non-territorial birds less successful?

Diet composition and prey intake rates of Australian magpies in a New Zealand population were investigated to determine whether flocking, non-territorial birds were less successful predators of pasture invertebrates than territorial birds. Time-activity budgets showed that flock magpies foraged throughout the day during February and March, indicative of a prey shortage at that time. Prey abundance was therefore measured in the autumn months but there was no evidence of a large quantitative difference in the food supply of flock and territorial magpies. Significantly fewer invertebrates were collected from pitfall traps in the flock foraging area, but these were counterbalanced by significantly more scarab beetle larvae and more flying insects, obtained by sweep-netting. When compared with territorial magpies, flock birds exhibited similar peck rates, prey intake rates, and earthworm intake rates. While there were qualitative differences in the diets of flock and territorial magpies, determined by faecal analysis, five of seven prey items analysed were captured in the same relative proportions by the flock and territorial birds. Earthworms exceeded their relative availability in the diets of flock birds, and more scarab larvae were found in the diets of territorial magpies. Non-territorial magpies were therefore no less successful than territorial birds during the autumn, and it is suggested that the function of flocking behaviour may eventually be discovered through consideration of why non-territorial birds never occur as solitary individuals, rather than emphasizing comparisons with territorial magpies.     

Effects of winter food provisioning on the phenotypes of breeding blue tits

Throughout the Western World, huge numbers of people regularly supply food for wild birds. However, evidence of negative impacts of winter feeding on future reproduction has highlighted a need to improve understanding of the underlying mechanisms shaping avian responses to supplementary food. Here, we test the possibility that carry‐over effects are mediated via their impact on the phenotypes of breeding birds, either by influencing the phenotypic structure of populations through changes in winter survival and/or by more direct effects on the condition of breeding birds. Using a landscape‐scale 3‐year study of blue tits (Cyanistes caeruleus), we demonstrate the importance of nutritional composition of supplementary food in determining carry‐over effect outcomes. We show that breeding populations which had access to vitamin E‐rich foods during the previous winter were comprised of individuals with reduced feather carotenoid concentrations, indicative of lower pre‐feeding phenotypic condition, compared to fat‐fed and unfed populations. This suggests that supplementary feeding in winter can result in altered population phenotypic structure at the time of breeding, perhaps by enhancing survival and recruitment of lower quality individuals. However, supplementation of a fat‐rich diet during winter was detrimental to the oxidative state of breeding birds, with these phenotypic differences ultimately found to impact upon reproductive success. Our findings demonstrate the complex nature by which supplementary feeding can influence wild bird populations.     

Foraging behaviour and habitat partitioning of two sympatric cormorants in Patagonia, Argentina

Radiotelemetry was used to assess the distribution and diving behaviour of Rock Shags Phalacrocorax magellanicus and Red-legged Cormorants Phalacrocorax gaimardi breeding in sympatry, and Rock Shags breeding in isolation. When breeding in sympatry there was little overlap in the foraging locations of the two species, with the highest densities of each species separated by 10 km. Red-legged Cormorants fed significantly closer to the breeding colony than did Rock Shags and undertook shorter foraging trips, making almost twice as many foraging trips per day as Rock Shags. Rock Shags breeding in isolation had a shorter foraging range than the birds breeding in sympatry with Red-legged Cormorants and foraging trip duration was significantly shorter. However, the number of feeding trips per day was similar between areas of sympatry and allopatry. Differences in the foraging ecology of Rock Shags in areas of sympatry and allopatry may be due to interspecific competition, which forces niche differentiation. The distance between foraging sites, the speed of movement of the prey, a species tendency to move into prey-depleted areas and the length of the breeding season (during which the birds are constrained to be in the same area) may play critical roles in determining the extent to which differential area use by competitors is a strategy that benefits both parties.     

Sexual,Seasonal and Group Size Differences in the Allocation of Time between Vigilance and Feeding in the Greater Rhea,Rhea americana

We studied the effect of sex and group size on the proportion of time a greater rhea, Rhea americana, allocates to vigilance and feeding during the breeding and the non-breeding seasons. We analysed 175 records of focal animals that were feeding alone or in groups of 2 to 26 birds. In both seasons, males spent more time in vigilance and less time in feeding than females. Both sexes spent more time in vigilance and less time in feeding during the breeding season. Sexual and seasonal differences in vigilance were the result of different mechanisms. Males had shorter feeding bouts than females but there were no sexual differences in the length of the vigilance bouts. On the contrary, seasonal differences were the result of males and females having longer vigilance bouts during the breeding season but there were no seasonal differences in the length of the feeding bouts. During the non-breeding season, individual vigilance was higher in rheas foraging alone than in groups. In this case, solitary birds had longer vigilance and shorter feeding bouts than birds foraging in groups. We discuss the possible effect of intragroup competition and food availability on the allocation of time between feeding and vigilance in this species.     

Space utilization by a cormorant (Phalacrocorax carbo L.) colony in a multi-wetland complex in relation to feeding strategies

In this study, we investigated the response of inland breeding cormorants Phalacrocorax carbo to a complex spatial configuration of feeding habitats in relation to social and individual feeding strategies. The numbers of feeding trips outside the colony site (Lake Grand-Lieu, western France), where only solitary fishing is used by cormorants, and the number of birds fishing on the lake where social fishing predominates were investigated during the breeding season and compared with the fledging period. From the investigation of feeding trip traffic, we identified three major habitats used by cormorants in the vicinity of the colony site (< 25 km around the colony site) that accounted for 94.1 of the IN flights and 92.0% of the OUT flights (n = 1745 arrivals and 2404 departures respectively), and notably one area that accounted for 58% of total flights although it is the furthest away. No fundamental change in the relative significance of these feeding grounds for solitary fishing cormorants was found throughout the breeding season, even in a between-years comparison (1996-2001), in contrast to what has often been found elsewhere. Although the peak of foraging activity in the surrounding habitats and also within the lake waters largely coincided with the time when the majority of young had fledged, the index of cormorant numbers (ratio between bird numbers at a given time and that for a baseline date) on the lake remained at a high level until late August compared to movements outside the lake, as a result of regular social fishing (84.9 +/- 4.0% of fishing numbers). From these findings, we discuss factors governing the selection of feeding grounds throughout the breeding season in relation to energy considerations, feeding strategies and food resources.     

Foraging movements of the Shy Albatross Diomedea cauta breeding in Australia; implications for interactions with longline fisheries

Satellite telemetry was used to identify the foraging zones of Shy Albatrosses Diomedea cauta breeding at two sites off Tasmania, Australia (Albatross Island in western Bass Strait and Pedra Branca to the south) to assess their level of interaction with longline fisheries. Adult birds from both colonies fed locally both in and outside the breeding season. Breeding birds from Albatross Island foraged over the Australian continental shelf or slope waters off northwest Tasmania, while those from Pedra Branca foraged between the colony and the southeastern edge of the continental shelf. The distances travelled by the birds and the duration of their foraging trips varied during the breeding cycle and tended to decrease as eggs approached hatching. Adults which were tracked near the end of the breeding season (March-April, n = 7 birds) deserted their chicks prematurely, and while dispersing further than incubating or brooding birds, they remained over the continental shelf and slope waters off southeast Australia. Home range analyses indicated 41% overlap between foraging zones of birds during successive breeding stages. Dispersal during the postbreeding period extended the foraging zones with less overlap between individuals (10% for Albatross Island and 19% for Pedra Branca). The recent contraction of the Japanese Southern Bluefin Tuna longline fishery to the south and east coasts of Tasmania has resulted in extensive overlap with adult Shy Albatrosses from Pedra Branca, but appears to pose a minimal threat to adult birds from Albatross Island. Coupled with the concomitant increase in the Australian domestic tuna longlining industry, adult Shy Albatrosses from southern Tasmania (Pedra Branca and the Mewstone) are vulnerable to incidental capture through out their annual cycle.