Michael W. Collopy
Bio: Michael W. Collopy is an academic researcher from University of Michigan. The author has contributed to research in topics: Paternal care & Nest. The author has an hindex of 2, co-authored 2 publications receiving 115 citations.
TL;DR: The division of labor between the sexes of Golden Eagles during breeding is quantified and these activities to the food consumption of nestlings are related to theories of sexual size dimorphism and parental investment.
Abstract: -A field study of Golden Eagles (Aquila chrysaetos) nesting in and near the Snake River Birds of Prey Area was conducted during 1977-1979. Patterns of parental care differed between female and male eagles during incubation and chick rearing; males consistently captured more food throughout all phases of brood rearing (1.2 vs. 0.6 prey/day), while females typically fed and tended the offspring. During the 7th through 9th week of chick rearing, when the food requirements of nestlings were greatest, the female contributed 43% of the prey biomass. No differences were observed in mean daily capture rates between 1978 and 1979 or between parents of one-chick broods and parents of two-chick broods. Although there were no differences between the sexes in the mean weight of prey captured, there were significant differences among pairs, suggesting differences in prey availability or hunting ability. The daily food consumption of eaglets increased as chick rearing progressed and peaked between the 7th and 9th week. Comparisons between eaglets in different-sized broods revealed that individuals in multiple-chick broods received more food from adults than those in one-chick broods. Late in chick rearing, however, those chicks competing with siblings for food had lower consumption rates. Received 24 February 1984, accepted 1 May 1984. THE general nesting biology of Golden Eagles (Aquila chrysaetos) has been described by many naturalists (e.g. MacPherson 1909, Gordon 1927, Bent 1937). Several studies also have been conducted specifically on territory size (Dixon 1937), molt (Jollie 1947), and growth (Sumner 1929, 1933). More recently, research on Golden Eagles has focused on diet and food requirements (e.g. Fevold and Craighead 1958, McGahan 1967, Mollhagen et al. 1972) and nesting success (e.g. Smith and Murphy 1973, U.S.D.I. 1979). Although these studies contributed greatly to our understanding of eagle biology, none has described the relationship between nestling food consumption and parental care. In this paper, I quantify the division of labor between the sexes of Golden Eagles during breeding and relate these activities to the food consumption of nestlings. The size and total biomass of prey delivered to young by male and female eagles also are considered in relation to theories of sexual size dimorphism and parental investment. STUDY AREA AND METHODS The study was conducted along the Snake River Canyon and surrounding upland desert plateau south ' Present address: School of Forest Resources and Conservation, 118 Newins-Ziegler Hall, University of Florida, Gainesville, Florida 32611 USA. of Boise, Idaho. This 195,063-ha area, known as the Snake River Birds of Prey Area (BPA), is administered by the Bureau of Land Management and lies within the Great Basin semidesert scrub biome (Whittaker 1975). The major vegetation types in the area include big sagebrush (Artemisia tridentata) associations, grasses (Poa and Bromus spp.), and shadscale (Atriplex confertifolia). Approximately one-fifth of the BPA is cultivated. A more detailed description of the vegetation can be found in U.S.D.I. (1979) and Collopy (1980). Incubation data were collected in 1977-1979 from 11 nesting attempts. Weekly observations at each site were made from a prominent location 150-750 m from the nest, and the amounts of time each parent spent incubating or brooding were recorded. Instances of male eagles providing prey to females when relieving them from incubation also were recorded. Data during the nestling period were collected at the same four nest sites in 1978 and in 1979. Daylong observations at each study site were made once every 6 days from blinds 15-40 m away. Photographs showing unique plumage characteristics of the breeding adults in 1978 and in 1979 revealed that the same individuals nested at the same sites in both years. The sex of parents was determined from these photographs, from size differences, and from behavior. I identified parents during each nest visit by using these unique plumage characteristics and by comparing photographs of adults taken during each visit. Adults away from the nest were monitored by a second observer, so when identification of the parent on the nest seemed uncertain it was confirmed by accounting for the location and sex of its mate. For a detailed description of nestling diet and nest 753 The Auk 101: 753-760. October 1984 This content downloaded from 18.104.22.168 on Sun, 27 Mar 2016 07:03:43 UTC All use subject to http://about.jstor.org/terms 754 MICHAEL W. COLLOPY [Auk, Vol. 101 observation and visitation procedures see Collopy (1983a). Parental care of nestlings involved both sheltering and feeding. Sheltering activities included brooding and shading, and both are discussed in this paper. Both the delivery of prey to the nest and its consumption by nestlings were considered feeding activities. The parental care of each adult was analyzed in relation to the age of its offspring. Following each observation period, I measured the body weight and foot-pad size (tip of hallux to tip of middle toe on extended foot) of the chicks (Kochert 1972). Determination of the sex of each chick was made late in the nestling period when size dimorphism became obvious. All prey delivered to the nest during each observation period were identified to species and assigned to a size class. The estimated proportion of the carcass delivered and sex of the eagle delivering the prey also were recorded. I calculated prey biomass delivered to nests from the estimate of the proportion of the carcasses delivered and the species' weights (Steenhof 1983). A series of experiments on the food consumption and growth energetics of captive Golden Eagle chicks was conducted concurrently with this study (Collopy 1980). These feeding trials were designed to monitor the consumption rates of eaglets presented blacktailed jackrabbit (Lepus californicus) food ad libitum and to quantify their growth rates. Because of permit restrictions, the birds were tested only between the ages of 11 and 57 days old. Following the experiments, they were returned to foster eagle nests in the wild, from which they all successfully fledged. During the feeding trials, it was apparent that one meal each day was much larger than all others and that it represented the maximum quantity a chick that age could consume. I quantified this relationship for the two female and two male eaglets tested by expressing the maximum meal size (Y, grams) as a function of age (X, days): female: Y = -99.96 + 12.31X; R2= 0.87, P < 0.0001; male: Y = -20.76 + 7.68X; R2= 0.85, P < 0.0001. Following each meal, the percentage of the crop of each wild nestling that was full was estimated, and the amount of food consumed was calculated. Statistical procedures used to analyze data included the Chi-square test, two-sample t-test, and analysis of variance (Remington and Schork 1970). Assumptions of the normality and equal variance of the statistical models were tested; percentage data were arcsine transformed before analysis whenever they were outside the interval between 30 and 70%. All means are reported with standard errors. RESULTS Incubation.-A total of 692 daylight hours (56 observation days) of data was collected at 11 Golden Eagle nests during incubation in 19771979. At the 10 sites that hatched young, female eagles spent a significantly greater portion of the day incubating (82.6 ? 1.6%) than males did (13.8 ? 1.8%) (t = -22.90, P < 0.0001). Eggs were left exposed only 3.7 ? 0.4% of the daylight hours. In addition to performing the majority of the daytime incubation, only females incubated at night. Overall, males relieved incubating females 2.1 ? 0.1 times daily and averaged 49.4 ? 4.7 min per incubation bout. Of the 111 male-initiated changeovers, 17 (15.3%) involved food transfers to the female on or near the nest. Eagle behavior away from the nest was not monitored systematically during incubation; females occasionally were observed foraging on their own, however, when males did not provide them with food. The unsuccessful eagle pair abandoned their nesting effort during the third week of incubation in 1978. The male incubated only once during my 23.4 h of daylight observations and did not deliver any food to his mate. The lower incubation time of the female (67.5% of daylight hours) and the greater exposure time of the eggs (31.6%) suggest that inattentiveness by the male may have forced the female off the nest to forage and ultimately to abandon her effort altogether. No direct evidence exists that the male who successfully bred at this site in 1977 died or was supplanted, but the lack of synchrony between the pair in 1978 suggests that a different male was present. Brooding/shading nestlings.-A total of 1,248 daylight hours (86 observation days) of data was collected during chick rearing at eight nests in 1978-1979. Chick rearing was defined as the period between the hatching of the first egg and the fledging of the last offspring. Although males regularly landed on nests to deliver prey, they were present only 0.6 ? 0.2% of the observation time. I observed a male brooding and feeding nestlings only once during the study. Clearly, the parental role of males during brood rearing was to provide food, because essentially no time was invested in brooding or feeding young. Several other workers who closely monitored parental behavior at the nest also reported that male eagles rarely brooded or fed young (Hunsicker 1972, Hoechlin 1974, Ellis 1979). This content downloaded from 22.214.171.124 on Sun, 27 Mar 2016 07:03:43 UTC All use subject to http://about.jstor.org/terms October 1984] Care and Feeding of Golden Eagles 755
TL;DR: For the purposes of this study, caching behavior was designated as any activity involved in storing or retrieving prey in any bird of prey species.
Abstract: Prey caching is documented for many birds of prey. A review of some raptor species which cache food was provided by Mueller (1974). Additional records of caching among falconiforms were reported by Roest (1957), Gullion (1965) and Balgooyen (1976). Prey caching has also been noted in many owl species (Allen 1924, Lockley 1938, Wallace 1948, Mossman 1955, Jansson 1964, Norburg 1964, Grant 1965, Ligon 1968, Catling 1972). For the purposes of this study, I designated caching behavior as any activity involved in storing or retrieving prey. Storage is that aspect of caching in which a food item is placed in a cache. Retrieval is that aspect of caching in which a stored food item is removed from a cache. Typical prey retrieving behavior which failed to produce a food item is called here an attempt to retrieve. Most accounts of caching by American Kestrels (Falco sparverius) are based on relatively few observations of wild or captive birds (Pierce 1937, Tordoff 1955, Roest 1957). Stendell and Waian (1968) observed a female kestrel store 17 prey items in one cache over a 40-day period. Balgooyen (1976) watched kestrels caching food during the breeding season. He discussed the advantages of caching food, especially during periods when inclement weather is common and
TL;DR: A corollary of provisioning offspring with food is a stable, relatively high metabolic rate, which ensures that parents can maintain a steady flow of food to the relatively few, "expensive" offspring.
Abstract: We limit our discussion of food storage, or caching, to the movement of potential food items from one location to another for eating at some later time. This activity occurs exclusively in those animals that bring food to their offspring, and not in those that bring their offspring to food (i.e. that lay their eggs near food in a favorable microhabitat). Provisioning offspring is limited taxonomically to mammals, most birds, and some Hymenoptera. Moving food to a favorable microhabitat was apparently the first transitional step in the evolution of more complex systems of provisioning offspring in hymenopterans (72). Although all species that cache food provision their offspring, the converse is not true. Relatively few of the animals that provision their young with food also cache food, and caching food has no obvious connection to the glandular secretion of milk, which probably initiated offspring provisioning in the evolutionary history of mammals. Repeated traveling from a foraging area to dependent young seems to precondition animals for caching food. One of the goals of our review will be to determine what other conditions among species of birds and mammals and their food favor the evolution of caching. We limit our discussion to birds and nonhuman mammals because of our own backgrounds and because experimental studies have recently been done on these vertebrates (4, 14, 20, 48a, 62, 10la, 103-105, 116, 117, 128), although earlier investigations started with wasps (121). A corollary of provisioning offspring with food is a stable, relatively high metabolic rate (even in the Hymenoptera), which ensures that parents can maintain a steady flow of food to the relatively few, "expensive" offspring
01 Jan 1981
TL;DR: For most animals, the environment is a complex of variables fluctuating with a distinct 24-hr periodicity as discussed by the authors, which is a direct consequence of the earth's rotation on its axis and of the periodic exposure of its surface to irradiation from the sun.
Abstract: For most animals, the environment is a complex of variables fluctuating with a distinct 24-hr periodicity. There are abiotic fluctuations as a direct consequence of the earth’s rotation on its axis and of the periodic exposure of its surface to irradiation from the sun. Foremost among the physical factors with a distinct 24-hr pattern are light and temperature and, in addition, water vapor pressure and wind in the terrestrial milieu, oxygen pressure and turbulence in the aquatic milieu. Secondarily, there are biotic variations, due to organisms on other trophic levels, such as food species, predators, and parasites, or on the same trophic level: competitors and reproductive mates. By the creation of such daily patterns, the earth’s rotation has profoundly affected the ecological complexity of animal communities. Only a few environments, such as deep caves and ocean abysses, are fairly constant throughout the day. Some are only temporarily constant, at least in some variables (e.g., when covered by insulating snow and ice), or are polar habitats at the summer and winter solstices.
TL;DR: Caching behaviour is interpreted as a circadian strategy allowing separate optimization of hunting-adjusted to prey availability-and eating-adaptive by retaining minimum body weight in daytime flight and by thermo-regulatory savings at night.
Abstract: 1. In an attempt to evaluate the importance of individual daily habits to a freeliving animal, foraging behaviour of kestrels was observed continuously for days in sequence in open country. Data obtained in 2,942 observation hours were used. Flight-hunting was the prominent foraging technique yielding 76% of all prey obtained. 2. Flight-hunting was impeded by rain, fog and wind speeds below 4 m/s and above 12 m/s (Fig. 3). Flight-hunting tended to be suppressed also in response to recent successful strikes and more generally by a high level of post-dawn accumulated prey (Figs. 4, 5). Flight-hunting had a tendency to be enhanced in response to recent unsuccessful strikes (Fig. 6). 3. Trapping results demonstrated a fine-grained daily pattern of common vole trap entries, with peaks at intervals of ca. 2 h (Figs. 7, 8). The interpretation of some of this pattern as representative of vole surface activity was supported by overall strike frequencies of kestrels hunting for voles (Fig. 9). 4. Detailed analysis of the behaviour of three individuals revealed significant peaks in hunting yield and frequency, coinciding with each other and with peaks in vole trapping (Fig. 11). It is suggested that the kestrels adjusted their flight-hunting sessions to times of high 'expected' yield. Vole activity peaks sometimes remained unexploited. 5. Meal frequencies culminated shortly before nightfall except in incubating females. The difference between the daily distributions of hunting and eating was due to some of the prey being cached in daytime and retrieved around dusk (Fig. 13). Caching behaviour is interpreted as a circadian strategy allowing separate optimization of hunting-adjusted to prey availability-and eating-adaptive by retaining minimum body weight in daytime flight and by thermo-regulatory savings at night. 6. Some kestrels showed remarkable constancy from day to day in the temporal distribution of specific behaviours (Fig. 16) and of spatial movements (Figs. 18, 19). In three 1-2 week sequences of observation analysed, flight-hunting frequency peaked 24 h after prey capture (Fig. 17). This is probably based on day to day correlations in flight-hunting frequency as well as on increased motivation for hunting in response to prey capture 24 h ago (Table 5). 7. In one individual with three distinct hunting areas, the tendency to return to an area again was maximal 24 h after prey capture in that area (Fig. 21, Table 6). A field experiment tested the effect of prey capture on the daily distributions of hunting and site choice in this individual (Fig. 22). A significant concentration of flight-hunting activity in the experimental feeding area was observed at the daily time of feeding (Fig. 23). Two alternative hypotheses are compatible with the result. Favoured is the one that the birds use "time memory" for the optimization of their daily patterns of flight-hunting and site choice. 8. By adjusting her daily flight-hunting to times of high yield, one kestrel saved 10-22% on her total time spent flight-hunting. Maximal efficiency, by concentration of all hunting activity in the hour of maximal yield, was not attained, presumably because of information constraints. The generality of the contribution of daily habits to survival is discussed.
01 Jan 1993
TL;DR: This chapter discusses four aspects of these animals' behavior: how stored food is recovered; the life history and social consequences of food storing; the economics of food caching and the decision making it involves; and the interrelations between food-storing animals and their food plants.
Abstract: Publisher Summary This chapter discusses four aspects of these animals' behavior: (1) how stored food is recovered; (2) the life history and social consequences of food storing; (3) the economics of food caching and the decision making it involves; and (4) the interrelations between food-storing animals and their food plants. The terms hourding, storing, and caching will be used as synonyms, and the material discussed is restricted to birds and mammals. Many invertebrates store food, and one well-studied instance is described in Heinrich. The chapter describes three animals: Acorn Woodpeckers (Melanerpes formicivorus), South Island Robin (Petroicu uustrulis), and Eastern Chipmunk (Tumias striutus) that illustrate the variation, which can occur in food storing. Storing food is an essential feature of the annual cycle of many animals, it is a prerequisite for successful breeding in some species, and has advanced the time of breeding in others. Finally, food-storing animals are used as agents of dispersal by a variety of plants.