Growth and morphology of nestling Hooded crows Corvus corone cornix, a sexually dimorphic bird species

The growth and morphology of nestling Hooded crows, Corvus corone cornix , were studied at Trondheim, Central Norway, during 1980 and 1981. The sexual size dimorphism of the nestlings developed while they were in the nest, but was less pronounced than that of the juvenile birds. Female young grew relatively faster than the males. The size variation of the morphological characters studied was greater in the males than in the females, during the entire nestling period. The order of development of the different morphological characters seemed to be adapted to the needs of the nestlings during the nestling period. Growth of the bone and bill characters was the highest priority, body weight and feather characters the lowest. In general, the sizes of the different morphological characters were highly intercorrelated, particularly those that developed at the same time during the growth period. In the favourable breeding season of 1981, the nestlings were larger than in the unfavourable season of 1980. The high priority characters of the males increased more in size than did those of the females, and the low priority characters of the females increased more in size than did those of the males. About 75% of the nestlings could be correctly sexed from their external morphological characteristics. The findings support the view that the parental cost of rearing a male offspring is greater than that of a female.     

Reproduction in a population of the hooded crow Corvus cornix

Nest density was stable during the 8-year study period. The mean clutch size was 4.3, and the production of fledglings was 2.0 per pair. Incubation started, on average, when there were still two eggs to be laid and lasted for 18 days. Few eggs were lost but 23% of all broods of nestlings were lost to predators. Single nestlings in a brood were not lost to predators but often starved to death, this applied to 25% of all nestlings. A large proportion of the nestlings were probably infected by Syngamus tracheae , and some of these succumbed during the first weeks after fledging. A comparison with other studies of crow populations shows that the major causes of breeding failure are different in different populations. The causes of variation in breeding success between populations are discussed, especially considering the role of nonbreeding crows.     

Ontogeny of heart rate in embryonic and nestling crows (Corvus corone and Corvus macrorhynchos)

The developmental patterns of mean heart rate (MHR) and instantaneous heart rate (IHR) were investigated in embryos and chicks of altricial Corvuscorone and Corvus macrorhynchos. The MHR of embryos increased linearly with time from 250 beats · min⁻¹ at mid-incubation to 290 beats · min⁻¹ in hatchlings. MHR during the pipping period was maximal, but only marginally higher than in hatchlings. MHR was stable at about 290–300 beats · min⁻¹ during the 1st week after hatching. Spontaneous heart rate (HR) decelerations and accelerations were found in embryos and chicks, disturbing the baseline HR with increasing frequency during development. However, the IHR accelerations developed later and were less frequent than in precocial species. IHR and body temperature decreased during mild cold exposure (23–25 °C) and IHR accelerations were reduced in nestlings during the 1st week. We suggest that the development of parasympathetic control of HR in crows occurs at 60% of incubation, similar to precocial embryos, but sympathetic control may be delayed and suppressed in contrast to precocial embryos. Accepted: 3 March 1999     

Effects of social facilitation for locating feeding sites by cattle in an eight-arm radial maze

A study was conducted in an eight-arm radial maze to determine if cattle with various foraging experiences could facilitate location of feeding sites by other cattle. Heifers assigned as "followers" (n=24) were initially trained to expect straw at the end of each arm. Initial training of heifers assigned as "leaders" (n=12) differed based on the three following treatments:(1) no-experience, (2) barley in the same two arms, and (3) barley in two arms but locations changed daily. During training, leaders with barley in fixed locations foraged more efficiently by traveling to fewer (P<0.05) arm ends to find barley than leaders in the variable treatment. After training, two followers were placed in the maze with a leader, and barley was available in two arms. Leaders facilitated the location of barley by followers. In 61% of the occasions that followers first found barley, leaders were at the feeding site. Eighty-one percent of followers later located barley without leaders in the maze. Followers with experienced leaders did not find barley consistently more often than heifers with inexperienced leaders. Cattle can apparently learn feeding site locations from other animals, but additional research is needed to evaluate the behavioral mechanisms that influence social facilitation during foraging.     

Breeding biology of rooks (Corvus frugilegus L.) in Hawke's Bay,New Zealand

Abstract

Three rookeries in Hawke's Bay were studied during 1966–68. First or replacement clutches were started between 26 August and 23 October. First clutches averaged 4.3 eggs and replacements 3.7 eggs. The mean size of first clutches varied between years from 4.1 to 4.6 eggs. Incubation took 17–18 days. Most losses occurred around hatching, when about 40% of the eggs or young were lost. Incubated eggs and small nestlings incurred losses of 20% and 10% respectively, and all nestlings older than 10 days survived to at least 20 days. On average, 1.4 young were reared per nest in which eggs were laid; successful nests averaged 2.2 young. First clutches averaged 1.3 young (2.4 per successful first clutch). During the season, mean clutch size declined from 4.2 to 3.5, the mean number of young hatched declined from 2.0 to 0.6 per clutch, and the mean number of young fledged from all clutches declined from 1.3 to 0.4 per clutch. Mean nestling weight increased with age from 14 g on the first day after hatching to 360 g on the 19th day. The causes of egg and nestling mortality and the adaptiveness of clutch size are discussed.     

Food of the rook (Corvus frugilegus L.) in Hawke's Bay,New Zealand

Abstract

Throughout a year gizzards from 160 adult and juvenile rooks and 105 large young in rookeries were collected from Hawke's Bay. The main foods were invertebrates (especially Diptera larvae and Coleoptera adults) during the warmer months and walnuts and acorns in autumn and winter. When these foods were scarce cereals were taken, mainly from stubble. Other important food items were carrion, earthworms, peas, grass, and clover. Foods fed to young rooks were similar to those eaten by adults except that the young were fed more striped dung fly (Hybopygia varia) larvae (P < 0.025) and fewer blow fly (Calliphoridae) larvae (P < 0.025).     

Behavioral tactics among rats in a radial maze

The experiments were carried out on rats of Wistar (W) and Krushinsky-Molodkina (KM) lines, differing in the level of task performance in conditions of multiple choice of food sources in a 12ray radial symmetrical maze. It is shown that in the radial maze, the rats of both lines use a number of behavioural tactics. To determine the influence of changes of environmental spatial characteristics while preserving the main experimental strategy--never revisit the places of reinforcement,--on the peculiarities of tactics manifestations maze modifications were elaborated. Besides the environmental procedure was changed. Under all conditions the rats of W line solved the task. According to the situation, they either preserved former tactics or developed some new ones. The rats of KM line could not solve the task in changed conditions. In most sessions, appearance or absence of given tactics was not adequate to new conditions. The presence of the necessary tactics not always facilitated the task solving. Thus, for the realization of adequate reactions, the presence of necessary tactics is not sufficient: their "tuning" is needed depending on situation. The possibility is supposed of genetic determination of rats ability to some tactics. However, it is emphasized, that tactics are not strongly fixed, as their realization depends on environmental conditions.     

The characteristics of the morphological structure of the endbrain in the hooded crow (Corvus corone cornix L.) and in the rock dove (Columba livia) in relation to their development of elementary reasoning activities]

The number of neurons in the endbrain [correction of forebrain] of two avian species--carrion crows and rock pigeons--was assessed. It was shown that the higher development of reasoning activity of crows is associated with greater number of cells in evolutionary new fields of hyperstriatum and greater number of cell complexes than in pigeons.     

Formation of linear dominance relationship in captive jungle crows (Corvus macrorhynchos): implications for individual recognition

Jungle crows (Corvus macrorhynchos) flexibly change their social forms depending on their age, time of the day, and the season. In the daytime, paired adults behave territorially and unpaired subadults form small flocks of ten birds, whereas at night hundreds of birds roost together. In the breeding season, pairings remain in their nest all day. This fission-fusion raises questions about the underlying social structure and the cognitive capability of jungle crows. In this study, dyadic encounters were used to investigate dominance relationships (linear or non-linear) and the underlying mechanisms in captive jungle crows. Fourteen crows were tested in 455 encounters (i.e., 5 encounters per dyad), and a stable linear dominance relationship emerged. Sex and aggressiveness were determinants as individual characteristics for dominance formation. Males dominated females, and more aggressive individuals dominated less aggressive ones. Aggressive interactions in dyads occurred primarily during the first encounter and drastically declined during subsequent encounters without any signs of a confidence effect. These results suggest that, in captive jungle crow, a linear form of dominance is intrinsically determined by sex and aggressiveness and maintained extrinsically by memories of past outcomes associated with specific individuals, implying individual recognition.     

Analysis of kinetics of consecutive metabolic cerebral activations induced by spatial discrimination testing, using (14C)-glucose, in an eight-arm radial maze in mice

Regional mapping of relative (14C)-glucose (GLU) uptake was analyzed in Balb/c mice at 3 time intervals (5 min., 1 hr., 3 hrs.) after either the first (Day 1) or the last (Day 9) daily sessions of a spatial discrimination testing procedure in an eight-arm radial maze. On Day 1, increased labelling was found 5 min. post-training in subcortical, hippocampal and cortical regions. Decreased GLU uptake was observed 1 hr. later in the same regions, followed at 3 hrs. post-training by a retarded activation in the above areas and particularly in thalamic and cortical structures. On Day 9, there was only an early (5 min.) post-training increase in metabolic activity followed by a subsequent monotonic decrease over 3 hrs. post-training period.     

Intestinal spirochetes isolated from wild-living jackdaws, hooded crows and rooks (genus Corvus): provisionally designated "Brachyspira corvi" sp. nov

Intestinal spirochetes of genus Brachyspira are commonly isolated from mammalian and avian hosts, and several species have been reported to cause enteric disease in pigs and birds. Except for a previous publication on three isolates from corvid birds (order Passeriformes, family Corvidae, genus Corvus), of which two are further studied in this paper, no other reports exist on Brachyspira spp. of passerine birds. In this study, cloacal and intestinal swabs of small and large intestines were collected from 116 corvid birds of three species, i.e. jackdaws (Corvus monedula), hooded crows (Corvus corone cornix) and rooks (Corvus frugilegus), from four separate geographical locations in Sweden. Isolates were obtained by selective culture from 43 of 116 birds. All isolates were weakly hemolytic, indole-negative and lacked hippurate cleavage capacity. Examination by light microscopy did not indicate association with enteric disease in necropsied birds. Pure spirochete cultures were obtained by serial dilution and subculture, and selected isolates were analyzed by PCR (n=14), randomly amplified polymorphic DNA (RAPD) (n=14), and sequencing of the almost complete 16S rRNA (n=14), and partial nox genes (n=4). Positive reactions were noticed by PCR targeting a hexa-T segment of the 16S rRNA gene, which has been previously reported as a signature characteristic of Brachyspira pilosicoli. By 16S rRNA gene sequencing, the isolates formed a separate cluster related to genus Brachyspira, but not consistent with any presently recognized or proposed Brachyspira sp. The sequence similarity of the 16S rRNA gene among the isolates from corvid birds was 99.7-100%. Compared to 16S rRNA gene sequence data from all presently recognized and several proposed Brachyspira spp. the sequence similarity of the isolates from corvid birds varied between 94.1 and 96.5%. In a radial tree based on nox gene sequences, all four analyzed isolates from corvid birds formed a separate cluster. By RAPD analysis, the banding patterns of the isolates differed from all type strains of Brachyspira spp. Based on the results presented in this paper, we propose that the described isolates from corvid birds belong to a novel species within genus Brachyspira, with the provisional name "Brachyspira corvi" (cor'vi. L gen. n. corvi, of a crow).     

Contextual control of rats' foraging behaviour in a radial maze

This study demonstrated that with experience rats were able to discriminate the background contextual cues in order to foraging correctly in an eight-arm radial maze if the background contexts signaled to the rats which of two bait patterns was in effect in that context. Four of the eight arms were context-dependent: two arms were baited in the "night" context, while the other two were baited in the "daytime" context. The remaining four arms were context-independent: three of them were never baited, while the remaining one was baited in both contexts. The rats gradually began to avoid the arms that were uniquely baited in the other context, suggesting a contextual or conditional control of arm selection. Interestingly, these rats also showed better performance in avoiding the never-baited arms, compared with control rats. Namely, disambiguating the incentive values of the four arms by contextual cues collaterally facilitated the context-independent arm performance. Another interesting finding of the present study is that the rats did not visit the always-baited arm earlier than the arms uniquely baited in that context.     

Conditioning of Fasciation by Gibberellin and Genotype in Cotton (Gossypium hirsutum L.)

The round-leafed mutant cotton line L-501 developed fasciation of the upper stem when field grown in Central Asia. Fasciation co-segregated with the mutant gene for round leaves In. ^l Fasciation developed at the flowering stage, but removal of floral buds did not prevent fasciation. Fasciation in L-501 could be inhibited by the gibberellin (GA) biosynthesis inhibitor chlorocholine chloride or by fusicoccin. GA₃ application in the field induced fasciation in the mutant's parental line L-463, which has five-lobed leaves and does not normally develop fasciation. Fasciation did not develop in either line, even after GA₃ treatment, in UK glasshouse conditions. Received June 17, 1998; accepted January 25, 1999     

Human-like, population-level specialization in the manufacture of pandanus tools by New Caledonian crows Corvus moneduloides

The main way of gaining insight into the behaviour and neurological faculties of our early ancestors is to study artefactual evidence for the making and use of tools, but this places severe constraints on what knowledge can be obtained. New Caledonian crows, however, offer a potential analogous model system for learning about these difficult-to-establish aspects of prehistoric humans. I found new evidence of human-like specialization in crows' manufacture of hook tools from pandanus leaves: functional lateralization or 'handedness' and the shaping of these tools to a rule system. These population-level features are unprecedented in the tool behaviour of free-living non-humans and provide the first demonstration that a population bias for handedness in tool-making and the shaping of tools to rule systems are not concomitant with symbolic thought and language. It is unknown how crows obtain their tool behaviour. Nevertheless, at the least they can be studied in order to learn about the neuropsychology associated with early specialized and/or advanced population features in tool-making such as hook use, handedness and the shaping of tools to rule systems.     

Differential calls by Carrion and Hooded Crows (Corvus corone corone and C. c. cornix) in the Alpine hybrid zone

Spectrograms of calls given by Carrion and Hooded Crows in the Italian Alpine hybrid zone have been tested for differences between the two subspecies by univariate and multivariate techniques. Vocalizations of the two Crows are similar and composed of 2–15 caws, each usually made up of two harmonics, separated by short intervals. However, one-way ANOVA and discriminant analysis showed that they were differentiated with respect both to temporal and frequency parameters. We suggest that differences in vocalizations reflect mostly the phylogenetic divergence between Hooded and Carrion Crows. The results are in keeping with previous ecological, morphological and molecular data and would confirm that the present designation of the two Crows as distinct subspecies is correct. Differences in vocalizations, together with others regarding ecology and behaviour, may result in assortative mating and homotypic flocking and, therefore, may contribute to reinforcement of the reproductive isolation between the Carrion and the Hooded Crow in the Alpine hybrid zone.     

Muscle temperature in free-swimming giant Atlantic bluefin tuna (Thunnus thynnus L.)

Muscle temperature was measured by telemetry in giant Atlantic bluefin tuna whilst the tuna were free-swimming in large pounds. Muscle temperature tended to remain steady at about 24°C; water temperature ranged from 9 to 17°C. Muscle temperature was much less variable than stomach temperature in these fish. Muscle temperature varied less than 3°C whereas stomach temperature varied by as much as 14°C.     

Ovarian activity is differentially regulated across the breeding season in immature compared with adult American crows (Corvus brachyrhynchos)

American crow (Corvus brachyrhynchos) reproduction is seasonal. While photoperiod alters reproductive physiology and behavior in nesting adults, whether seasonal photoperiod changes alter ovarian activity in nonnesting adult and immature birds was not known. Ovarian follicular composition was examined in immature and nonnesting adult crows. Birds were divided into groups reflecting daylight hour exposure when captured: 12L, 12:30L, 13:30L, and 14L, representing early-, progressing-, peak-, and postbreeding seasons in southern California. Adult ovarian mass peaked in 13:30L and then decreased 65% by 14L. In contrast, immature ovarian mass peaked in 12L and decreased 58% by 14L. Whereas no change in adult follicle composition occurred, primordial follicle numbers increased 42%, and previtellogenic follicles increased 86% in immatures, resulting in an overall follicle number increase in immatures by 13:30L and 14L. Adult atretic follicles declined 68% by 14L, while immature atretic follicle numbers remained constant. Adult apoptotic transferase-mediated dUTP nick end labeling (TUNEL)-positive follicle numbers remained constant until a 52% decrease occurred in 13:30L. TUNEL-positive follicles declined 58% by 12:30L among immatures. These data are the first to demonstrate that follicular composition is differentially regulated between nonnesting adult and immature American crows. Seasonal ovarian activity alterations in nonbreeding adults may serve to prime individuals for potential mating.