Philopatry and natal dispersal in a sedentary population of western marsh harrier

Dispersal is a key life-history trait because it influences population dynamics and population genetic structure. From a behavioural perspective, the study of natal dispersal requires some understanding of the mechanisms that affect individual movements, because movements of an animal form a path that is continuous throughout its life. Our aim was to investigate juvenile dispersal strategies in the western marsh harrier Circus aeruginosus , between fledging and first breeding attempt (from 1 to 4 years later, depending on the sex and individual). Using radio tracking, we monitored dispersing juvenile harriers and their home-range size variations within a sedentary population in central western France from 2001 to 2007. Juvenile dispersal strategy was mainly characterized by a very high natal philopatry (i.e. birds that remained within the study area) and short-distance dispersal. All but one bird (out of 39) remained within the study area between their first winter and their first spring, and 96.0% during their first spring. The distance moved at 2 years of age was significantly larger for males than for females (3800± sd 3593 m and 935± sd 481 m for seven males and six females, respectively), in contrast to most bird species studied so far. Home-range size was not sex biased and significantly decreased with age. In addition, non-breeding birds had larger home ranges (1603± sd 2128 ha) than breeders (349± sd 185 ha). Using data obtained from other populations, juvenile marsh harrier dispersal strategies appeared to be determined by migratory status (migratory birds dispersing farther) and demographic parameters (juvenile survival or fecundity).     

Natal dispersal and its consequences in Black Grouse Tetrao tetrix

Data on dispersal distances of juveniles are important for understanding the genetic structure of populations, population regulation processes and the effects of landscape ecology on metapopulation dynamics. We studied dispersal in juvenile Black Grouse Tetrao tetrix in the French Alps between 1990 and 1998, by radiotracking 39 young grouse captured in August or autumn in a study area of 836 ha. Natal dispersal occurred in two discrete phases, autumn (October) and spring (mid-April to early May), with periods of reduced mobility between. The mean distance travelled by females exceeded that of males in autumn but not in spring. The natal dispersal distance of females was greater than that of males, and resulted in 81% of females leaving the study area to nest 5–29 km from their site of capture. This emigration must have been compensated for by immigrants because the number of hens in the study area increased during the study. Males were more philopatric. By the summer after capture, only 9% had emigrated from the study area. Despite the longer dispersal distances of females, there was no difference in the survival functions of the sexes between the ages of 6 weeks and 13 months.     

Using recruitment age, territorial fidelity and dispersal as decisive tools in the conservation and management of peregrine falcon ( Falco peregrinus ) populations: the case of a healthy population in Northern Spain

Methods of evaluating population trends have recently received particular attention because of perceived declines in several species during the twentieth century. We have studied demographic traits of the peregrine falcon (Falco peregrinus) population in Bizkaia (Northern Spain) for 11 years. This species suffered a severe decline in the 1950s and 1960s and started to recover in the 1980s and 1990s, although the recovery trends differed between areas. In our study area the peregrine falcon density is one of the highest found in Spain. The frequency of juvenile breeders was 2.0%, the mean age at first breeding being 3.7 calendar years for males and 4.0 cy for females. The territorial fidelity was at least 3.4 years for males and 3.7 years for females. Females dispersed on average 80.5 km and males 51.8 km during their pre-breeding movements, whilst distance between birthplace and breeding territories was on average 108.5 km for females and 64.5 km for males. We studied the relationships between adult turnover, recruitment age, territorial fidelity and dispersal in a healthy population in order to establish population dynamics. A combination of these parameters, not just age at first breeding, could be used as a potential early warning signal indicating future changes, prompting their consequences to be evaluated. This approach could lead to the reclassification of the large-scale health of a population. Its utilization would allow resources to be directed into helping “ailing” subpopulations, detecting causes of decline, and developing adequate recovery strategies.     

Radio-telemetric monitoring of dispersing stag beetles: implications for conservation

Migratory movements of the endangered stag beetles Lucanus cervus (18 males, 38 females) were monitored radio-telemetrically for three reproductive periods (2003–2005). The aim of the study was to estimate the migratory range of free-ranging individuals as a measure of connectivity among neighbouring populations for future conservation measures. Miniature transmitters of c . 350 mg (battery life: 10–15 days) were attached externally to the pronotum. Transmitter/beetle mass ratio was 12.8% on average (7.1–28.0%). Male dispersal behaviour consisted of frequent flights directed to sites with reproductive females and rarely of on-ground movement. Total displacement distance recorded was up to 2065 m, the maximum distance of a single flight being 1720 m. Flights always began at elevated structures such as trees and shrubs and took place in an air temperature range of 11–27°C. Within this range, temperature did not influence flight distance. Female dispersal behaviour consisted mostly of a single flight, followed by mating and consequent ground movements towards oviposition sites. Total displacement distance recorded was up to 762.6 m, the maximum distance of a single flight being 701 m. Climatic constraints of flights were the same as in males. Modelling the dispersal behaviour suggests that about 1% of males are capable of maintaining gene flux among nest sites within a radius of about 3 km. However, the colonization of new nest sites depends on the dispersal ability of females and amounts to less than 1 km. Thus, isolated populations (distance to the next population greater than 3 km) have an increased probability of local extinction.     

Summer predation rates on ungulate prey by a large keystone predator: how many ungulates does a large predator kill?

Estimates of predation rates by large predators can provide valuable information on their potential impact on their ungulate prey populations. This is especially the case for pumas Puma concolor and its main prey, mule deer Odocoileus hemionus . However, only limited information on predation rates of pumas exist where mule deer are the only ungulate prey available. I used VHF telemetry data collected over 24-h monitoring sessions and once daily over consecutive days to derive two independent estimates of puma predation rates on mule deer where they were the only large prey available. For the 24-h data, I had 48 time blocks on female pumas with kittens, 43 blocks on females without kittens and 30 blocks on males. For the daily consecutive data, the average number of consecutive days followed was 51.5±4.2 days. There were data on five female pumas with kittens, five pregnant females and nine females without kittens. Predation rates over an average month of 30 days from the 24-h monitoring sessions were 2.0 mule deer per puma month for males (15.1 days per kill), 2.1 mule deer per puma month (14.3 days per kill) for females without kittens and 2.5 mule deer per puma month (12.0 days per kill) for pregnant females and females with kittens. For the consecutive daily data, females without kittens had an estimated predation rate of 2.1±0.14 mule deer per puma month (14.9±0.90 days per kill). Pregnant and females with kittens had predation rates of 2.7±0.18 and 2.6±0.21 mule deer per puma month, respectively (11.4±0.72 and 12.0±1.1 days per kill, respectively). Predation rates estimated in this study compared with those estimated by energetic demand for pumas in the study area but were lower than other field derived estimates. These data help increase our understanding of predation impacts of large predators on their prey.     

Postfledging dispersal in the endangered Lesser Kestrel Falco naumanni

Much is known about the breeding period of the threatened Lesser Kestrel, but little of the postfledging period. Here, I examine the postfledging dispersal of juvenile Lesser Kestrels, based on all ringing recoveries of Lesser Kestrels ringed as nestlings in Spain and recovered before September (migration) of the same year. Of 28 juveniles recovered, 19 (67.9%) dispersed and their median recovery distance was 210 km (range 41–578 km), with significantly northern directions. No difference was found in the dispersal distance between individuals ringed as nestlings in mid-north and mid-south Spain, nor was any correlation found between the recovery distance and ringing latitude. These findings for postfledging dispersal in juvenile Lesser Kestrels seem in accordance with predictions of a mental map hypothesis for homing, but they do not exclude food as a potential factor influencing such movements. However, these postfledging movements cannot be explained by the hypothesis of gathering information for identifying a future breeding site.     

Dispersal distances of juvenile radiotagged Red Grouse Lagopus lagopus scoticus on moors in northern England

Radio-transmitters were fitted on 146 juvenile Red Grouse Lagopus lagopus scoticus (116 hens, 30 cocks) to study the timing, frequency and distances of dispersal on managed grouse moors in northern England between 1999 and 2002. A third of the radiotagged birds were shot. Disturbance on shoot days meant that radiotagged birds were shot at points more than twice as far from the catch location as the points when they were last recorded alive. For birds that were shot, the distance from the catch location to the place they were shot was more than twice the natal dispersal distances of the survivors. Therefore, shot birds were excluded from the dispersal analysis. Juvenile hens dispersed significantly further (mean 861 m, range 50–4660 m) than juvenile cocks (mean 343 m, range 90–660 m). Dispersal distances were not related to predispersal Grouse densities at the catch area in summer or to Grouse densities in the following spring. The mean date of dispersal for juvenile hens was 6 October ± 4 days (se), with only one record of spring dispersal (14 March) of 1490 m.     

Development of chicks and predispersal behaviour of young in the Eagle Owl Bubo bubo

Little quantitative information on the development and behaviour of chicks and young is available for many species, despite the crucial importance of such data and the sensitivity of this stage in a bird's life. For Eagle Owls Bubo bubo , despite the large amount of scientific literature on this species, much basic information is lacking. This study provides a photographic and morphometric guide for age estimation of nestlings and fledglings, as well as data on the call behaviour of young, and patterns of movements during the post-fledging dependence period. The most remarkable event in chick development is the rapid increase in mass, and size gain, during the first 30 and 40–45 days, respectively. Because after this time morphometric differences become less evident, young-feather development is more useful for ageing. Patterns of chick call behaviour showed that the time spent calling increased with age and, from 110 days of age, chick vocalizations were usually uniformly distributed through the whole night and most synchronized at sunset and sunrise (the maximum recorded number of vocalizations per chick and per night was 1106 calls). During the post-fledging dependence period, radiotagged Owls moved widely, up to 1500 m from the nest after the age of 80–90 days. During such movements, the mean distance among siblings increased with age, from 168 m on average for juveniles less than 100 days old, to 489 m for those older than 100 days. Definitive dispersal started when young were about 150–160 days old. Information on chick call behaviour and movements is crucial for unbiased census and nest checking, as well as for the definition of young post-fledging areas. Knowledge of the latter is very important in terms of conservation and management (especially for those species that move largely around their nest before dispersal) owing to the high mortality that can occur during this period.     

New data on mortality,home range,and dispersal of red-legged partridges (Alectoris rufa) released in a mountain range

We tested the success, dispersal, and home range of 20 radio-tagged farm-reared red-legged partridges that were released into typical Mediterranean scrubland on a coastal mountain in southern Spain. Partridges were kept in two acclimatization pens separated by 1 km for 4 weeks. Mortality was 25% during the first 10 days, 51.9% at the end of the second month, and stopped by the 14th week after release. The overall survival rate was 20.6%. Mean dispersal distance was 832 m; home range (MPC 95%), 16.6 ha; and activity centers (Kernel 60%), 15.1 ha. Two released females paired with wild males and one of them successfully nested.     

Effects of experimental food supplementation on movements of juvenile northern goshawks (<Emphasis Type="Italic">Accipiter gentilis atricapillus</Emphasis>)

Food availability is thought to strongly influence the leaving phase of natal dispersal in animals with condition-dependent dispersal. We conducted a food supplementation experiment to determine the influence of extra food on the onset of dispersal and early dispersal movement patterns of 42 radio-tagged northern goshawks (Accipiter gentilis atricapillus) from 28 broods in north-central New Mexico during 1992 and 1993. We randomly assigned half of the broods each year as treatments and the other half as controls. Treatment broods were given supplemental food from hatching (late April) until mid-October. Control broods received the same visitation rate but no food. Birds were located approximately every 2 days from fledging until mid-October in 1992 and 1993. Timing of fledging and independence were not affected by the treatment. However, extra food significantly influenced post-fledging movements of juvenile goshawks. During the late fledgling-dependency period (>65 days of age until independence) control birds were located in the natal area (<2 km from nest tree) more frequently than supplemented birds. This pattern reversed after independence (approximately 82 days of age) when supplemented birds were located more frequently in the natal area than controls. After independence the control birds were never located in the natal area and by the end of September in both years the controls had all left the study area (study area boundaries were approximately 25 km from nest tree). Supplemented birds were never located outside of the study area for the duration of the experiment. We conclude that the control birds dispersed out of the study area and the supplemented birds remained. Since the experimentally fed juveniles remained near a known food source and the controls did not, our study demonstrates that food availability influences at least the first 4 months of post-fledging movement patterns in this population. These results also suggest individuals base dispersal decisions on knowledge of their environment at a local scale, which can influence juvenile recruitment.     

Timing and speed of migration in male, female and juvenile Ospreys Pandion haliaetus between Sweden and Africa as revealed by field observations, radar and satellite tracking

Breeding Ospreys were studied in southern Sweden and 13 birds were tracked by satellite telemetry on autumn migration to the African wintering grounds. This was supplemented with studies of migrating birds at Falsterbo and radar trackings from southern Sweden. Females generally left the nest site 2–3 weeks ahead of males and juveniles. Among males, failed breeders migrated significantly earlier than successful breeders. At Falsterbo, Ospreys passed in the order adult females (median 22 Aug), adult males (26 Aug) and juveniles (30 Aug). Birds tracked by radar achieved cross‐country speeds of 18–47 km/h. Most of our birds wintered in an area from The Gambia to the Ivory Coast, with one juvenile in Cameroon and one female in Mozambique. Ospreys spent on average 45 days travelling an average distance of 6742 km with no significant differences between sex and age categories. Between 0 and 44 days were used for stopovers en route. Females generally made more stopovers at northerly latitudes than males. Average speed on migration was 174 km/d, which is similar to speeds reported for other large raptors followed by satellite. Speed on travelling days was on average 257 km/d with males generally moving fastest. There was a clear tendency for lower speeds and more stopovers in Europe than during the crossing of the Sahara. Migratory activity generally took place between 8 a. m. and 5 p. m. local time and we have no indications of birds flying at night. With 9 hours travelling time the expected cross‐country speed, derived from the theory of thermal soaring flight and assuming thermal climb rates of 1–2 m/s, varies from 251 to 360 km/d, which is similar to the observed mean speed on travelling days. Even so, one male travelled 746 km/d between Sweden and Spain. Some Ospreys need a much larger fraction of travelling days than expected from theory, suggesting that they deposit fuel on the breeding grounds before departure. This is supported by a correlation between the observed fraction of days spent travelling and departure date. In late departing Ospreys, especially males and juveniles, a major part of the energy for migration is probably deposited on the breeding grounds.     

Post-juvenile dispersal of Hazel Grouse Bonasa bonasia in an expanding population of the southeastern French Alps

We studied the post-juvenile dispersal of 18 radiotagged juvenile Hazel Grouse Bonasa bonasia (14 males, four females) in an expanding population in the southeastern French Alps between 1998 and 2001. The mean dispersal distances between the capture sites of juveniles in September–October and the centre of the home range in the following spring was 4 km for males (range 0.1–24.9 km) and 2 km for females (range 0.2–5.6 km). The distances recorded for two long-dispersing males (15 and 24.9 km) are greater than those reported to date for Hazel Grouse. Using our radiotracking data, we interpret the pattern of range expansion that has been occurring since the 1950s around our study area. Barriers to dispersal included rocky ground and other alpine habitats above 2000 m and over 1 km wide, but Hazel Grouse did cross open agricultural land at lower elevation. Two patterns of dispersal movements were recognized in juveniles: erratic movements that led to settlement on or near the natal site, and direct movements to a new range relatively far from the natal area. We discuss the adaptive consequences of these different behaviour patterns.     

Age polyethism in the leaf-cutting ant Acromyrmex subterraneus brunneus Forel, 1911 (Hym., Formicidae)

Abstract  This study describes and quantifies the behavioural acts of two laboratory colonies of Acromyrmex subterraneus brunneus by investigating worker age polyethism. Twenty-nine behavioural acts were recorded during the 19-week observation period. Young individuals performed tasks inside the nest related to brood care and care for the fungus garden, whereas older individuals performed activities outside the nest such as foraging and activities in the waste chamber. The average longevity (±SD) was 108.21 ± 3.30, 109.15 ± 1.92 and 122.71 ± 1.55 days for large, medium and small workers, respectively. The small-sized workers presented a higher probability of reaching older age than large- and medium-sized workers. This study describes task switching according to age polyethism and the relationship of physical and temporal subcastes.     

Parental care and the transition to independence of Spanish Imperial Eagles Aquila heliaca in Doñana National Park, southwest Spain

The behaviour of five broods of radio-tagged Spanish Imperial Eagles Aquila heliaca adalberti was studied in Doñana National Park, Spain during the post-fledging period. The distance between perching sites and nest, the mean flight duration and distance, the percentage of time spent flying and the home range all increased exponentially with age. As the young got older, the parents spent less time in their vicinity. Young were not seen hunting, but depended on their parents for food. They begged and chased their parents throughout the post-fledging period, with higher intensity at the end. Nevertheless, the adults became progressively more reluctant to feed them, as reflected in the decrease in feeding frequency and in the number of approaching flights towards the young. At the end of the post-fledging period, adults often performed aerial displays and frequently chased their offspring. The age of independence of the different young studied varied between 123 and 145 days. The correlations between individual independence and the dates when the young were last fed by their parents, and when the highest intensity of parental aggressive behaviour occurred, were higher than correlations with the variables related to the maturation of flying. Therefore, it is suggested that parental 'meanness' and aggressive behaviour may be the factors determining the date of juvenile independence and dispersal from the home territory.     

千岛湖岛屿社鼠的扩散特征

2009年7月—11月,2010年3月—11月对千岛湖两个岛屿上的社鼠(Niviventer confucianus)种群进行标志重捕,通过分析扩散个体的性别、年龄及扩散距离等,探讨陆桥岛屿环境下社鼠的扩散特征。研究结果显示:岛屿环境下社鼠的扩散率为37.96%,不同季节社鼠的扩散率存在差异,社鼠倾向于在春季发生扩散,尤其是3月份,社鼠扩散个体数最多;对于整个捕获史而言,雌雄扩散个体数存在极显著的差异(x~2=12.542,df=1,P0.001),雄性个体更倾向于发生扩散;而在繁殖高峰期,当怀孕鼠存在时,雄性扩散数亦大于雌性,两者存在显著差异(x~2=4.504,df=1,P=0.034)。扩散个体体重的季节差异不显著;扩散与社鼠的年龄密切相关,社鼠更加倾向于在亚成年阶段发生扩散;另外,家群大小对社鼠扩散个体数量也有显著影响,家群越大,扩散个体越多;对扩散距离进行分析发现存在显著的性别差异(t=-9.229,df=50,P0.001),雌性个体的平均扩散距离为(282.97±16.14)m,显著大于雄性的(146.70±6.80)m,而扩散距离与年龄、体重、最大活动距离均无显著相关性。     

Irradiation does not affect field dispersal ability in the West Indian sweetpotato weevil, Euscepes postfasciatus

The effect of irradiation on the dispersal ability of males and females of the flightless West Indian sweetpotato weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae), a major sweet potato pest, was examined in the field using mark–release–recapture techniques. To evaluate the dispersal ability of the weevil, we released 7 619 weevils in two replicates (July and August 2007). Each replicate lasted 5 days from release to sampling and consisted of one weevil release and two weevil samplings. Thirty-two traps were placed in lines corresponding to eight compass directions and in four distance classes (8, 12, 16, and 20 m) in each replicate. We captured 709 (9.3%) weevils in the two replicates. Weevils dispersed at least 20 m from the release point in 2 days, regardless of sex or irradiation. Dispersal was strongly affected by wind direction, and in both replicates most weevils were recaptured in upwind directions. The mean dispersal distance for non-irradiated weevils was about 11 m per 2 days. Although there were some differences between sexes in recapture rate and dispersal distance, there was no consistent difference between irradiated and non-irradiated weevils in dispersal distance. We conclude that irradiation does not affect the dispersal ability of flightless E. postfasciatus in the field.     

Role of breeding and natal movements in lifetime dispersal of a forest‐dwelling rodent

The lifetime movements of an individual determine the gene flow and invasion potential of the species. However, sex dependence of dispersal and selective pressures driving dispersal have gained much more attention than dispersal at different life and age stages. Natal dispersal is more common than dispersal between breeding attempts, but breeding dispersal may be promoted by resource availability and competition. Here, we utilize mark–recapture data on the nest‐box population of Siberian flying squirrels to analyze lifetime dispersal patterns. Natal dispersal means the distance between the natal nest and the nest used the following year, whereas breeding movements refer to the nest site changes between breeding attempts. The movement distances observed here were comparable to distances reported earlier from radio‐telemetry studies. Breeding movements did not contribute to lifetime dispersal distance and were not related to variation in food abundance or habitat patch size. Breeding movements of males were negatively, albeit not strongly, related to male population size. In females, breeding movement activity was low and was not related to previous breeding success or to competition between females for territories. Natal philopatry was linked to apparent death of a mother; that is, we did not find evidence for mothers bequeathing territories for offspring, like observed in some other rodent species. Our results give an example of a species in which breeding movements are not driven by environmental variability or nest site quality. Different evolutionary forces often operate in natal and breeding movements, and our study supports the view that juveniles are responsible for redistributing individuals within and between populations. This emphasizes the importance of knowledge on natal dispersal, if we want to understand consequences of movement ecology of the species at the population level.     

Equal investment in male and female offspring in southern elephant seals

Sex ratio theory predictions concerning differential parental investment in offspring by sex were tested on southern elephant seals, Mirounga leonina , breeding at Península Valdés, Argentina. Females invested equally in sons and daughters, as reflected by the similar mass at birth (mean ± 1 S.D.) of 14 males (44.1 ± 6.5 kg) and 14 females (43.4 ± 3.8 kg), and similar mass at weaning of 52 males (131.5 ± 22.4 kg) and 38 females (131.4 ± 18.3 kg). There were also no sex differences in the rate of mass gain during nursing (males = 4.0 ± 0.9 kg/day; females = 3.9 ± 0.8 kg/day), rate of mass loss during the first month of post-weaning fast (males = 0.85 ± 0.19 kg/day; females = 0.92 ± 0.15 kg/day), mean age at weaning (males = 22.3 ± 1.6 days; females = 22.7 ± 1.7 days), and female nursing behaviour. Mother's size accounted for most of the variation in mass of pups at weaning. Mothers ranked as small, medium and large, weaned pups with a mean mass of 102, 130 and 145 kg, respectively. The sex ratio of weanlings did not differ from unity. These data are consistent with Fisher's (1930) sex ratio theory.     

Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.