Energy relations of winter roost-site utilization by American goldfinches (Carduelis tristis)

Summary American goldfinches (Carduelis tristis) were observed roosting in Colorado blue spruce (Picea pungens), which comprised part of a mixed stand of conifers. Their winter roost-sites were distally situated among the most densely-needled branches on the leeward sides of these trees. Heated and unheated taxidermic goldfinch mounts were placed within these sites and at the same height in an adjacent clearing. The radiative and convective characteristics of these locations were monitored simultaneously and compared to predicted power requirements of live goldfinches (based on laboratory calibration of heated mounts) and operative temperatures (T _e ; based on body temperatures of unheated mounts). The winter roost-sites significantly reduced radiative and convective heat exchanges between goldfinches and the environment. Based on body composition data for winter goldfinches, all but two birds sampled could endure a 15-h roost period at average overnight T _e 's as low as-40°C. In contrast, if these birds were prevented from feeding the following day, only 30% could survive the imposition of a 39-h fast at average T _e 's of-2°C. Winter roost-site selection may be more constrained by thermoregulatory considerations in small birds than in larger species.     

Coccidial infection does not influence preening behavior in American goldfinches

Preening behavior in birds is important for the maintenance of thermoregulatory and ornamental functions of plumage. It has been repeatedly demonstrated that birds trade off time between plumage maintenance and other activities. However, the condition-dependent constraints of preening remain virtually unstudied. Here, we present the first experimental test of the hypothesis that intestinal parasite infection impairs preening activity. We studied male American goldfinches (Spinus tristis), a species with carotenoid-based plumage coloration. Following pre-alternate (spring) molt, we manipulated the health of males by infecting some birds with Isospora spp. coccidia and keeping others free of the infection. Although the goldfinches increased preening throughout the captive period, we found no significant effect of coccidial treatment on preening behavior. The effect of coccidia on plumage maintenance may be more pronounced under natural conditions where birds have limited access to food and engage in more activities that might limit time available for preening.     

Carotenoid pigments in male American goldfinches: what is the optimal biochemical strategy for becoming colourful?

Studies of brilliant carotenoid‐based coloration in birds have traditionally centred on the role that these colours play in attracting mates. More recently, biologists have begun to take a biochemical approach to understanding the types of pigments found in feathers and how these relate to the expression of ornamental coloration. Nevertheless, surprisingly few studies have assessed the types and amounts of carotenoids present in the diet or blood of animals in relation to season, sex, condition or sexually attractive colour traits, particularly for wild birds. It is conceivable not only that the total concentration of pigments available is an important predictor of sexual attractiveness and mate quality, but also that specific pigments vary among individuals and play more important physiological and pigmenting roles than others. We investigated the carotenoid content of blood and feathers in wild‐caught, yellow‐pigmented male American goldfinches (Carduelis tristis) throughout the year to determine the optimal biochemical strategy for becoming colourful. We found that birds acquired two main yellow hydroxycarotenoids (lutein and zeaxanthin) from the diet during both moulting and non‐moulting periods. Blood concentrations of both pigments changed significantly over time, with moulting birds accumulating higher levels of both lutein and zeaxanthin, but proportionally more zeaxanthin, than non‐moulting birds. Moulting birds that acquired more lutein and more zeaxanthin in blood deposited a higher concentration of carotenoid pigments (canary xanthophylls A and B) into plumage and acquired more colourful feathers. In sum, these results indicate that (a) the types of dietary carotenoids available across seasons do not change in American goldfinches, (b) seasonal fluctuations in plasma‐carotenoid signatures may result from differences in dietary access or pigment processing, and (c) the best biochemical strategy for becoming a colourful, wild male goldfinch is to accumulate as many dietary/blood pigments as possible during moult. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 273–280.     

The influence of carotenoid acquisition and utilization on the maintenance of species-typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis).

Birds display a tremendous variety of carotenoid-based colors in their plumage, but the mechanisms underlying interspecific variability in carotenoid pigmentation remain poorly understood. Because vertebrates cannot synthesize carotenoids de novo, access to pigments in the diet is one proximate factor that may shape species differences in carotenoid-based plumage coloration. However, some birds metabolize ingested carotenoids and deposit pigments that differ in color from their dietary precursors, indicating that metabolic capabilities may also contribute to the diversity of plumage colors we see in nature. In this study, we investigated how the acquisition and utilization of carotenoids influence the maintenance of species-typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis). We supplemented the diet of captive goldfinches with red carotenoids to determine whether males, which are typically yellow in color, were capable of growing red plumage. We also deprived cardinals of red dietary pigments to determine whether they could manufacture red carotenoids from yellow precursors to grow species-typical red plumage. We found that American goldfinches were able to deposit novel pigments in their plumage and develop a striking orange appearance. Thus, dietary access to pigments plays a role in determining the degree to which goldfinches express carotenoid-based plumage coloration. We also found that northern cardinals grew pale red feathers in the absence of red dietary pigments, indicating that their ability to metabolize yellow carotenoids in the diet contributes to the bright red plumage that they display.     

Individuality in Problem Solving: String Pulling in Two Carduelis Species (Aves: Passeriformes)

The research reported here was designed to study the individual peculiarities of birds in solving a problem. Goldfinches Carduelis carduelis and siskins C. spinus were tested with the string‐pulling task: sitting on a perch from which a small food container is suspended by a string the test bird had to lift the container, using the bill to pull the string stepwise up and a foot to hold it, and repeat that until they could reach the food. Fifty‐two goldfinches and 29 siskins raised under controlled conditions were tested individually. Three groups became apparent: ‘inventors’ (23% of goldfinches; 62% of siskins) solved the problem by themselves; ‘imitators’ (25% of goldfinches; 10% of siskins) succeeded after seeing a performing conspecific; ‘duffers’ (52% of goldfinches, 28% of siskins) did not succeed either way. The species – but not the sexes – differed significantly in string‐pulling ability. The results of our experiments indicate that string pulling is an acquired combination of innate behaviour elements. An individual's string‐pulling competence may depend on prior experience of handling branchlets, on trial‐and‐error learning and on social learning (emulation). However, some individuals succeeded without these facilitating factors, while others did not succeed at all despite all of them present. Although functionally and motivationally related to feeding, the learned string pulling is often shown as a playful activity without an obvious reward.     

Likeability of Garden Birds: Importance of Species Knowledge & Richness in Connecting People to Nature

Interacting with nature is widely recognised as providing many health and well-being benefits. As people live increasingly urbanised lifestyles, the provision of food for garden birds may create a vital link for connecting people to nature and enabling them to access these benefits. However, it is not clear which factors determine the pleasure that people receive from watching birds at their feeders. These may be dependent on the species that are present, the abundance of individuals and the species richness of birds around the feeders. We quantitatively surveyed urban households from towns in southern England to determine the factors that influence the likeability of 14 common garden bird species, and to assess whether people prefer to see a greater abundance of individuals or increased species richness at their feeders. There was substantial variation in likeability across species, with songbirds being preferred over non-songbirds. Species likeability increased for people who fed birds regularly and who could name the species. We found a strong correlation between the number of species that a person could correctly identify and how connected to nature they felt when they watched garden birds. Species richness was preferred over a greater number of individuals of the same species. Although we do not show causation this study suggests that it is possible to increase the well-being benefits that people gain from watching birds at their feeders. This could be done first through a human to bird approach by encouraging regular interactions between people and their garden birds, such as through learning the species names and providing food. Second, it could be achieved through a bird to human approach by increasing garden songbird diversity because the pleasure that a person receives from watching an individual bird at a feeder is dependent not only on its species but also on the diversity of birds at the feeder.     

The throat badge as a status signal in juvenile male willow titsParus montanus

Summary Status signalling in juvenile male Willow TitsParus montanus was studied by observing the outcome of interactions of birds with different size of their black throat badge, and by manipulating the size of their badge. The bird with the largest throat badge was the dominant one in all dyads studied (N=25), and the relative rank position of the males was positively correlated with the size of their badge. The badge size explained about 95% of the variation in the birds' dominance rank. When confronting juvenile males with a stuffed Willow Tit mounted close to a feeder placed in an aviary, there was found a negative correlation between the size of the badge of the males and the time from they were released till they visited the feeder. After subordinate birds from seven earlier dyads got their throat badge artificially increased, the originally dominant bird reacted submissively and tried to avoid the bird with a larger dyed badge, that temporary had increased its rank position. Our data support the status signalling hypothesis.

---

Zusammenfassung Durch Beobachtung von Interaktionen zwischen jungen Männchen der Weidenmeise (Parus montanus) mit schwarzem Kehlfleck unterschiedlicher Größe und durch experimentelle Veränderung der Kehlfleckgröße wurde untersucht, ob durch den Kehlfleck der Dominanzstatus eines Vogels signalisiert wird. In allen untersuchten Paarvergleichen war der Vogel mit dem größten Kehlfleck dominant (N=25); die relative Rangposition eines Männchens war mit der Kehlfleckgröße positiv korreliert. Kehlfleckgröße erklärte 95% der Variation in der Rangstellung. Wurden junge Männchen mit einem Stopfpräparat konfrontiert, das in einem Käfig nahe der Futterstelle montiert war, ergab sich eine negative Korrelation zwischen der Kehlfleckgröße der Versuchsmännchen und dem Intervall zwischen ihrem Einsetzen in den Käfig und dem Besuch der Futterstelle. Nachdem die Kehlflecke von unterlegenen Männchen in sieben der Paarversuche künstlich vergößert worden waren, reagierte das vorher dominante Männchen unterwürfig und versuchte den Vogel mit dem durch Färbung vergrößerten Kehlfleck zu meiden, der dadurch vorübergehend seine Rangstellung verbesserte. Unsere Ergebnisse unterstützen die status signalling-Hypothese.

     

The relationship between social status and resting metabolic rate in great tits (Parus major) and pied flycatchers (Ficedula hypoleuca)

The oxygen consumption of great tits (Parus major) in winter flocks and of male pied flycatchers (Ficedula hypoleuca) in breeding condition, was measured. Resting metabolic rate was significantly correlated with dominance rank, as expressed by the width of the breast-stripe in the great tits and the darkness of the plumage on the head and back, or date of pair-formation, in males of the pied flycatcher. Individuals with the highest metabolic rates were the most dominant ones. Similarly, heart weight, relative to body weight, in dominant great tits was greater than that in lower-ranking birds.     

Subordinates Must Wait

Direct advantages for dominant Mexican jays, Aphelocoma ultramarina, were investigated at an artificial food source. The time birds spent waiting to gain access to the food was used to test the prediction that access time and its variance would increase with a decrease in status. The number of feedings/h was also recorded to determine if, as a consequence of longer ‘wait’ times, these declined with a decline in status.     

Perch height predicts dominance rank in birds

Dominant individuals within animal groups will frequently place themselves in the most beneficial position for maximal protection against predation. Higher perches are generally associated with reduced predation risk in birds, so we predicted that dominant birds will preferentially place themselves on higher perches. We tested this by determining the dominance hierarchy in two populations of captive birds (Homing Pigeons Columba livia and Great Cormorants Phalacrocorax carbo), and relating rank within the dominance hierarchy to observed perch height preferences. We found that perch choice was significantly repeatable in pigeons, and that more dominant individuals of both species selected higher perches. As well as facilitating early detection of and escape from potential predators, higher perches are also likely to facilitate the display of aggression to other group members.     

Habitat Quality, Social Dominance and Dawn Chorus Song Output in Black-Capped Chickadees

Individuals that settle in poor habitats may reduce resource investments in various life history traits; for example, resources may be withheld from costly advertisement signals. There may be geographic variation in advertisement levels that correspond with habitat quality; however, this is poorly documented and it is unclear whether such habitat effects have consequences for the function of mate‐choice signals within habitats. We examined song output of male black‐capped chickadees (Poecile atricapillus) during the dawn chorus in two contrasting habitats (mature forest vs. young forest) known to differ in quality. Dominance rank is indicative of phenotypic quality in this species and was assessed during the preceding winter. We measured the song output of males participating in the dawn chorus during the nesting/egg laying period. Males living in young forest had reduced song output; however, a habitat–rank interaction term showed that dominant birds accounted for most of this difference. This suggests that signal reliability might be lost in poor habitats. We generate several hypotheses to explain these findings.     

Seasonal variation in pectoralis muscle and heart myostatin and tolloid-like proteinases in small birds: a regulatory role for seasonal phenotypic flexibility?

Seasonally variable environments produce seasonal phenotypes in small birds such that winter birds have higher thermogenic capacities and pectoralis and heart masses. One potential regulator of these seasonal phenotypes is myostatin, a muscle growth inhibitor, which may be downregulated under conditions promoting increased energy demand. We examined summer-to-winter variation in skeletal muscle and heart masses and used qPCR and Western blots to measure levels of myostatin and its metalloproteinase activators TLL-1 and TLL-2 for two small temperate-zone resident birds, American goldfinches (Spinus tristis) and black-capped chickadees (Poecile atricapillus). Winter pectoralis and heart masses were significantly greater than in summer for American goldfinches. Neither myostatin expression nor protein levels differed significantly between seasons for goldfinch pectoralis. However, myostatin levels in goldfinch heart were significantly greater in summer than in winter, although heart myostatin expression was seasonally stable. In addition, expression of both metalloproteinase activators was greater in summer than in winter goldfinches for both pectoralis and heart, significantly so except for heart TLL-2 (P = 0.083). Black-capped chickadees showed no significant seasonal variation in muscle or heart masses. Seasonal patterns of pectoralis and heart expression and/or protein levels for myostatin and its metalloproteinase activators in chickadees showed no consistent seasonal trends, which may help explain the absence of significant seasonal variation in muscle or heart masses for chickadees in this study. These data are partially consistent with a regulatory role for myostatin, and especially myostatin processing capacity, in mediating seasonal metabolic phenotypes of small birds.     

Effects of insect damage on photosynthesis,transpiration and SO2 uptake by sycamore

Summary The bilberry (Vaccinium myrtillus L.), is the dominant plant in the field layer of many boreal forests in northern Sweden. It is utilized by several herbivorous insect larvae as food (i.e. Lepidoptera: Geometridae, Tortricidae and Hymenoptera: Symphyta). Total density of insect larvae was 63% lower where birds had access to larvae compared to exclosures. Larvae with a feeding behaviour which exposes them to birds (geometrids and sawflies) showed a pronounced reduction in density when exposed to bird predators. Density of larvae with a concealed feeding behaviour (tortricids) was unaffected by birds. The frequency of larval damage to bilberry annual shoots was significantly higher in areas where larval density was high due to exclusion of birds. I concluded that birds have the potential to heavily modify the interaction between bilberry and insect larvae.     

Direct benefits of social dominance in juvenile crayfish

Crayfish are known for their innate aggressiveness and willingness to quickly establish dominance relationships among group members. Consequently, the formation of dominance hierarchies and the analysis of behavioral patterns displayed during agonistic encounters have mostly been tested in environments that provide no immediate resources besides space. We tested the hypothesis that social hierarchy formation in crayfish serves to determine access to future resources. Individuals within groups of three juvenile crayfish were allowed to form a social hierarchy in a featureless environment before a single food resource was presented. Higher dominance indices were significantly correlated with increased access to the food. The highest ranked crayfish spent more time in contact with the food than did medium-ranked and lowest ranked crayfish, and crayfish of medium rank spent more time in contact with the resource than did lowest ranked animals. The highest ranked crayfish consolidated their dominant status in the presence of food, indicated by a complete absence of any submissive behaviors during that period. The results of these experiments show that the disposition of crayfish to engage in fighting and formation of a dominance hierarchy in a featureless environment serves to determine future access to an emerging resource, thereby entailing greater benefits for animals of higher social rank.     

Ornamental bill color rapidly signals changing condition

Ornamental bill color is postulated to function as a condition‐dependent signal of individual quality in a variety of taxonomically distant bird families. Most red, orange, and yellow bill colors are derived from carotenoid pigments, and carotenoid deposition in ornamentation may trade off with their use as immunostimulants and antioxidants or with other physiological functions. Several studies have found that bill color changes in response to physiological perturbations, but how quickly such changes can occur remains unclear. We tested the hypothesis that carotenoid‐based orange bill color of American goldfinches Spinus tristis responds dynamically to rapid changes in physiological stress and reflects short‐term changes in condition. We captured male and female goldfinches and measured bill color in the field and again under captive conditions several hours later. The following day, the captive birds were injected with either immunostimulatory lipopolysaccharide (LPS) or a control saline and changes in bill color were measured over a five day period. Yellow saturation of the bill decreased within 6.5 h between the field and captivity measures on the first day, presumably in response to capture stress. Over the longer experimental period, bill hue and luminance decreased significantly, whereas saturation significantly increased in both LPS and control groups. Bill hue and luminance decreased significantly more in birds treated with LPS than in control birds. Among LPS treated birds, individuals expressing high bill color at the beginning of the experiment lost more color than ‘low‐color’ birds, but still retained higher color at the end of the experiment, suggesting that birds that invest heavily in bill coloration are able to sustain high costs in the face of a challenge. Bill color change may have resulted from rapid reallocation of carotenoids from ornamentation to immune function. However, the complex shifts in bill color over time suggest that bill color may be influenced by multiple carotenoid compounds and/or changes in blood flow or chemistry in vessels just beneath the translucent keratinized outer layer of the bill. We conclude that bill color is a dynamic, condition‐dependent trait that strategically and reliably signals short‐term fluctuations in physiological condition.     

On the feeding and social behaviour of the laying hen

This paper describes a study of the influences of early husbandry conditions, social attraction and social rank on various aspects of the feeding behaviour of laying hens.Birds were raised in flocks of 10, 60 or 500. Groups of 3 birds, selected from flocks of the same size, were then housed in pens. Some groups consisted of hens raised in the same flock, and some of birds raised in different flocks. The feeding and agonistic behaviour of each group at each of 5 types of feeder was observed and compared with the behaviour shown when the birds had free access to a 1-m long food trough. Each of the 5 feeders offered the same area of feeding space, but differed in its partitioning and spatial distribution. One feeder had a single unpartitioned feeding space. The other 4 feeders had 3 partioned feeding spaces which were adjacent, or separated by distances of 10, 20 or 40 cm, respectively.For the 5 feeders, total feeding times and lengths of feeding bouts were greatest, and the number of feeding bouts least, when the feeding space was unpartitioned. Synchrony of feeding behaviour was low when the feeding space was unpartitioned or the partitioned spaces adjacent, but was comparable to that at the 1-m long food trough when the distance between partitioned feeding spaces was 10 cm or greater. When feeding space was partitioned, the likelihood that 2 birds would eat together at the same site increased with the distance between feeding space. Dominant birds always exhibited the longest feeding bouts and greatest total feeding times, but were less likely to feed in the same space as another bird, and exhibited less synchrony of feeding behaviour than subordinates. The size of the flock in which the birds were raised, and whether or not the birds in a group had been raised together or apart, had no clear effect on behaviour.These results indicate that, within the limits of this experiment, early husbandry conditions do not influence behaviour shown during feeding in later life, and that social attraction has a greater influence on the feeding behaviour of hens than is generally assumed. In view of this latter finding, it is postulated that in attempting to determine the requirements of laying hens for feeding space, attention must be paid to social attraction as well as to competition at the feeder.     

The Adaptive Significance of Batesian Mimicry in the Swallowtail Butterfly,Papilio polytes (Insecta,Papilionidae): Associative Learning in a Predator

Experiments were conducted to examine the adaptive significance of Batesian mimicry in the swallowtail butterfly, Papilio polytes, with its model, Pacbliopta aristolochiae, an alkaloidal butterfly. The female of Pap. polytes is polymorphic, whereas the male is monomorphic. Two forms of the female, f. polytes mimic and f. cyrus non-mimic, were used in these experiments. Naive birds, brown-eared bulbuls Hypsipetes amaurotis pryeri, were trained to take food from two feeders in captivity, and then were offered Pach. aristolochiae in one of the feeders. After experiencing an uncomfortable encounter with this species, the birds reduced the frequency of taking regular food from the feeder where the butterfly had been placed. This result suggests that the birds can learn not only the model itself but also the place where they have experienced it. Thereafter, the birds also came to avoid the mimetic form of f. polytes. It is suspected that wild predators behave in the same way. These findings imply that it is adaptive for the mimic to overlap its habitats and daily activity with those of the model species.     

Foraging and Calling Behavior of Carolina chickadees (Poecile carolinensis) in Response to the Head Orientation of Potential Predators

When animals detect predators they modify their behavior to avoid predation. However, less is known about whether prey species modify their behavior in response to predator body and behavioral cues. Recent studies indicated that tufted titmice, a small songbird, decreased their foraging behavior and increased their calling rates when they detected a potential predator facing toward a feeder they were using, compared to a potential predator facing away from that feeder. Here, we tested whether related Carolina chickadees, Poecile carolinensis, were also sensitive not just to the presence of a predator model, but to its facial/head orientation. Although chickadees are closely related to titmice, recent studies in different populations suggest chickadees respond to risky contexts involving predators differently than titmice. We conducted two field studies near feeders the birds were exploiting. In Study One, a mask‐wearing human observer stood near the feeder. In Study Two, a model of a domestic cat was positioned near the feeder. In both studies, the potential threatening stimulus either faced toward or faced away from the feeder. Chickadees avoided the feeder more in both studies when the potential predator was present, and showed strongest feeder avoidance when the potential predator faced toward the feeder. Chickadee calling behavior was also affected by the facial orientation of the potential predator in Study 1. These results suggest that, like titmice, chickadees exhibit predation‐risk‐sensitive foraging and calling behavior, in relation to facial and head orientation of potential threats. These small birds seem to attend to the likely visual space of potential predators. Sensitivity to predator cues like behavior and body posture must become more central to our theories and models of anti‐predator behavioral systems.     

Impact of Environmental Disturbance on the Stability and Benefits of Individual Status within Dominance Hierarchies

Changes in environmental conditions affect social interactions and thus may modify an individual's competitive ability within a social group. We subjected three‐spined sticklebacks, Gasterosteus aculeatus, housed in groups of four individuals, to environmental perturbations to assess the impact on dominance hierarchy stability. Hierarchy stability decreased during increased turbulence or lowered water levels (‘simulated drought’) whereas control hierarchies became more stable in a constant environment. The dominant individual either became more aggressive and remained dominant during the environmental manipulation or was usurped by a lower rank member. Only simulated drought affected rates of aggression where levels of aggression were higher after the water level was dropped which may be the result of an increased encounter rate in these conditions. When there were large size differences between the group members, the dominant individual performed the greatest amount of aggression and ate the largest proportion of food and there was little aggressive behaviour from the lower ranks. In groups of similar‐sized individuals, aggression was much higher. The benefit of being dominant was to gain weight over the experimental period whereas ranks 2 and 3 lost weight. The lowest rank, 4, actually gained weight over the experimental period. This study suggests that it would benefit an individual to be dominant, highly aggressive and gain weight or be submissive, avoid aggressive interactions and, by sneakily obtaining access to food, also gain weight. Altering environmental conditions has a profound effect on social behaviour in this study.     

The effect of dietary carotenoid access on sexual dichromatism and plumage pigment composition in the American goldfinch

We investigated potential dietary and biochemical bases for carotenoid-based sexual dichromatism in American goldfinches (Carduelis tristis). Captive male and female finches were given access to the same type and amount of carotenoid pigments in the diet during their nuptial molt to assess differences in the degree to which the two sexes incorporated ingested pigments into their plumage. When birds were fed a uniform, plain-seed diet, or one that was supplemented with the red carotenoid canthaxanthin, we found that males grew more colorful plumage than females. HPLC analyses of feather pigments revealed that male finches incorporated a higher concentration of carotenoids into their pigmented feathers than females. Compared to females, males also deposited significantly more canary xanthophyll B into feathers when fed a plain-seed diet and a greater concentration and proportion of canthaxanthin when fed a carotenoid-supplemented diet. These results indicate that sex-specific expression of carotenoid pigmentation in American goldfinches may be affected by the means by which males and females physiologically utilize (e.g. absorb, transport, metabolize, deposit) carotenoid pigments available to them in the diet.