Breeding success in Brent in relation to individual feeding opportunities during spring staging in the Wadden Sea

Brent Geese Branta bernicla individually marked with inscribed leg rings were intensively watched from permanent towers on the saltings of the island Schiermonnikoog in the Dutch Wadden Sea during the spring staging period April- May 1982 when 3,000 used the area. By observing geese on plots with enhanced vegetation (biomass, protein content) as a result of fertilizer treatment, it was found that individuals on the improved sites fought more and walked more slowly. The position of the marked individuals in relation to the total feeding minutes accumulated by the flock as the group grazed past the tower was determined by making use of a radial system of counting plots. Individuals tended to be consistent in their relative timing in the grazing sequence, and the highest rate of interaction and lowest pacing rate was found just behind the leading edge of the flock, in the second quartile of feeding minutes, and by inference birds in this sector experienced the best feeding conditions. Status of the males (proportion of interactions won) was highest for individuals habitually in this sector, and observation of the same birds in the fall revealed the highest incidence of breeding success (pairs accompanied by young) for this group. A number of measures reflecting a good food supply (low pace rate, highest percentage feeding times, and highest number of bites per step) were found to correlate positively with male status supporting the conclusions from the grouped data presented in relation to the grazing sequence. Though a causal relation cannot be proved from such correlations, we interpret these findings to indicate that males of high status can provide their mates with enhanced feeding opportunities, resulting in accumulation of more body reserves in the spring, and a heightened probability of successful breeding. Females subsequently found to prove successful had a larger proportion of Triglochin maritima in their spring diet but a larger sample of droppings will be needed to substantiate this hint of a difference of diet in birds of the same flock

Breeding success in Brent in relation to individual feeding opportunities during spring staging in the Wadden Sea

Brent Geese Branta bernicla individually marked with inscribed leg rings were intensively watched from permanent towers on the saltings of the island Schiermonnikoog in the Dutch Wadden Sea during the spring staging period April- May 1982 when 3,000 used the area. By observing geese on plots with enhanced vegetation (biomass, protein content) as a result of fertilizer treatment, it was found that individuals on the improved sites fought more and walked more slowly. The position of the marked individuals in relation to the total feeding minutes accumulated by the flock as the group grazed past the tower was determined by making use of a radial system of counting plots. Individuals tended to be consistent in their relative timing in the grazing sequence, and the highest rate of interaction and lowest pacing rate was found just behind the leading edge of the flock, in the second quartile of feeding minutes, and by inference birds in this sector experienced the best feeding conditions. Status of the males (proportion of interactions won) was highest for individuals habitually in this sector, and observation of the same birds in the fall revealed the highest incidence of breeding success (pairs accompanied by young) for this group. A number of measures reflecting a good food supply (low pace rate, highest percentage feeding times, and highest number of bites per step) were found to correlate positively with male status supporting the conclusions from the grouped data presented in relation to the grazing sequence. Though a causal relation cannot be proved from such correlations, we interpret these findings to indicate that males of high status can provide their mates with enhanced feeding opportunities, resulting in accumulation of more body reserves in the spring, and a heightened probability of successful breeding. Females subsequently found to prove successful had a larger proportion of Triglochin maritima in their spring diet but a larger sample of droppings will be needed to substantiate this hint of a difference of diet in birds of the same flock

High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study

1. Given the allometric scaling of thermoregulatory capacity in birds, and the cold and exposed Arctic environment, it was predicted that Arctic-breeding shorebirds should incur high costs during incubation. Using doubly labelled water (DLW), daily energy expenditure (DEE) during incubation was measured in eight shorebird species weighing between 29 and 142 g at various sites in the Eurasian and Canadian High Arctic. The results are compared with a compilation of similar data for birds at lower latitudes. 2. There was a significant positive correlation between species average DEE and body mass (DEE (kJ day−1) = 28·12 BM (g)^0·524, r^2 = 0·90). The slopes of the allometric regression lines for DEE on body mass of tundra-breeding birds and lower latitude species (a sample mostly of passerines but including several shorebirds) are similar (0·548 vs 0·545). DEE is about 50% higher in birds on the tundra than in temperate breeding areas. 3. Data for radiomarked Red Knots for which the time budgets during DLW measurements were known, indicated that foraging away from the nest on open tundra is almost twice as costly as incubating a four-egg clutch. 4. During the incubation phase in the High Arctic, tundra-breeding shorebirds appear to incur among the highest DEE levels of any time of the year. The rates of energy expenditure measured here are among the highest reported in the literature so far, reaching inferred ceilings of sustainable energy turnover rates.

Dark-bellied Brent Geese Branta bernicla bernicla, as recorded by satellite telemetry, do not minimize flight distance during spring migration

Nine Dark-bellied Brent Geese Branta bernicla bernicla were equipped with satellite transmitters during spring staging in the Dutch Wadden Sea in 1998 and 1999. The transmitters (in all cases less than 3% of body mass) were attached to the back by a flexible elastic harness. One juvenile female was tracked to the Yamal peninsula in 1998. Eight adult males were selected from a single catch of 75 to span the range of body mass observed on the date of capture (11 May 1999) and all but the lightest individual completed the first lap of the migratory flight to the White Sea, Russia, according to the time schedule normal for this species. Six birds were successfully tracked to Taymyr for a total distance averaging 5004 km (range 4577-5164) but judging from later movements none bred (although 1999 was breeding year). Although the routes chosen during spring migration were closely similar; none of the tagged birds migrated together. On average the geese used 16 flights to reach their summer destinations on Taymyr. The longest uninterrupted flights during the first half of the journey (Wadden Sea to Kanin) covered 1056 km (mean of seven adult males, range 768-1331), while the corresponding value for the second half of the migration (Kanin-Taymyr) was only 555 km (mean of six adult males). Only 7% of total time during spring migration was spent in active flight, as contrasted to c. 80% at long-term stopovers. Overall average travelling speed was 118 km/day (range 97-148). Including fattening prior to departure the rate of travel falls to 62 km/day (range 49-70), in keeping with theoretical predictions. Routes followed deviated from the great circle route, adding at least 700 km (16%) to the journey from Wadden Sea to Taymyr, and we conclude that the coastal route is chosen to facilitate feeding, drinking and resting en route instead of minimizing total flight distance

Continuous time resource selection analysis for moving animals

1.Resource selection analysis (RSA) seeks to understand how spatial abundance covaries with environmental features. By combining RSA with movement, step selection analysis (SSA) has helped uncover the mechanisms behind animal relocations, thereby giving insight into the movement decisions underlying spatial patterns. However, SSA typically assumes that at each observed location, an animal makes a 'selection' of the next observed location. This conflates observation with behavioural mechanism and does not account for decisions occurring at any other time along the animal's path. 2.To address this, we introduce a continuous time framework for resource selection. It is based on a switching Ornstein‐Uhlenbeck (OU) model, parameterised by Bayesian Monte Carlo techniques. Such OU models have been used successfully to identify switches in movement behaviour, but hitherto not combined with resource selection. We test our inference procedure on simulated paths, representing both migratory movement (where landscape quality varies according to season) and foraging with depletion and renewal of resources (where the variation is due to past locations of the animals). We apply our framework to location data of migrating mule deer (Odocoileus hemionus) to shed light on the drivers of migratory decisions. 3.In a wide variety of simulated situations, our inference procedure returns reliable estimations of the parameter values, including the extent to which animals trade‐off resource quality and travel distance (within 95% posterior intervals for the vast majority of cases). When applied to the mule deer data, our model reveals some individual variation in parameter values. Nevertheless, the migratory decisions of most individuals are well‐described by a model that accounts for the cost of moving and the difference between instantaneous change of vegetation quality at source and target patches. 4.We have introduced a technique for inferring the resource‐driven decisions behind animal movement that accounts for the fact that these decisions may take place at any point along a path, not just when the animal's location is known. This removes an oft‐acknowledged but hitherto little‐addressed shortcoming of stepwise movement models. Our work is of key importance in understanding how environmental features drive movement decisions and, as a consequence, space use patterns