“An energetic simulation model for managing Steller’s eagle in
[The manuscript based on the preliminary report for the MacArthur Foundation]
the wildlife viewing, fishering and otherrecreational uses of important for eagle habitats are dramatically increasing in Kamtchatka Peninsula, Russian Far East. Many studies focus on single species and undertake to measure direct mortality, decreased reproductive success and reduced population in preferred habitats resulting from human activities. Here we focus on a more subtle, but perhaps more important effect of disturbance, the changes in temporal activity, foraging patterns, energetic balance and resource utilisation in endangered species -Steller's eagle. We described energy requirements of wintering and breeding Steller's eagle. The objective of our research is to obtain and present an energetics simulation model that provides information useful for the management of Steller's eagle population in disturbing areas of Kamtchatka.
1. Dayly Energy Budget (DEB) is necessary for surviving dayly energy portion found in an evolution process. In nature animals are aspire to save this balance constantly. So, any impacts from the environment, both, natural and artificial can increase ordecrease DEB. Been influensing for a long time these factors can be a dengerous for birds' survival.
2. Feeding behaviuor is a strategy which was formed in evolution under pression of natural selection for increasing the efficience of food utilisation and decreasing the energy loss . Basing on the species-specific feeding stereotype, bird select time of day, light, place, microhabitats, level of water in marine lagoon and river, which are optimal for feeding. If they do it, it is usefull for them. So, any artificial changing in a feeding stereotype decrease the efficiency of feeding. In a period of the year, which demands a high efficiency of feeding, such as wintering and breeding seasons, additional time spent for feeding or absence of possibilities to find alternative food source after disturbance can be dengerously for birds.
MATERIALS AND METHODS
Research was conducted at the two model areas: at the biggestsockey salmon spowning ground in Euroasia - Kuril lake and at thesmall choho and pink salmon spowning groung in eastern Kamtchatka. In accordance with the concepts, we investigated foraging patterns in a free living Steller's eagle in two different areas:
1. Plot near the boundary of Kronotskiy State Reserve ischaracterised by relatively high level of human activity wholeyear.
2. Kuril lake is characterised by the absence of regul preparing and eating salmon in compared with birds in a group
We censused birds along the feeding areas from observationpoints had been constracted specially for this goal. At winter time it was igloo-like small cabin standed at the salmon spowning ground creeks, at reproduction time it was watching tower that provided views of 100% of the study area and included both feeding and nest territory. We recorded age class, sex (when possible), location (on or off the river) and behaviour (feeding, standing, perching,flying, soaring) of each individual sighted. We determinedrelative food abundance weekly by recording the number, position (submerged, partly submerged, exposed) and degree of consumption of every carcass. From the watching point we recorded the use of feeding areas by eagles. Simultaneously any kinds of human activity was censused. We recorded time of day, number, frequency and effects on eagle of each visitors in areas where eagle habitate.
Kuril lake reseach station in winter was an "ideal" poligon where foraging patterns inthe absence of human activity was investigated. We conducted some field experiments to simulate human disturbance and estimate eagles's responce on. We recorded flight distances for 154 group of eagles atwinter, 46 at summer and 13 approach to the nest (table 4). Therewas no significant differences between avoidance distance insummer and winter. Randomly we conducted 5-10 disturbance, during which observer approuched the feeding areas on foot, snowcar or motoboat.We recorded the time that elapsed between flushing and subsequent reuse of the feeding area and distance from which eagles fly away, additionally time of relaxation and kinds of pedal activity of eagle was recorded. To document preference for open or intact carcasses, weconducted 103 trials of a choice experiment in which we providedpre-weighed open and intact carcasses. Then we recorded the number of bites taken from each carcass by eagles and reweighed salmon at the end of each observation period.
We constructed energetics simulation model that providesinformation useful for the management of Steller's eagle population. The model predicts salmon and consequence energy equivalent required fo wintering and breeding eagles. The model consist of 3 subtroutines:1) consumable biomass, 2)energy consumption, 3)activity cost. Model predicts the quantity of biomass that potentially is usable by eagle, determines requirements for and use by eagles of this biomass as influenced by activity demands and predicts population densities and carrying capasities of breeding and wintering areas.
Estimates of salmon comsumption (consumable biomass submodel) and energy consumption.
This parameter show the daily rate of salmon necessar for eaglein undisturbed model. We calculated the quantity of salmonconsumed by eagles as: S=(bird-minute of feeding)X(bites per bird-minute of feeding)X(grams consumed per bite). For eagles, the value of 78,5 g/min and 840 g day food consumption were estimated. Thus, eagle need 10.7 min feeding per day in average. In summer this rate increase to 3150 g/day and 40.1 min feeding due to necessaty to feed eaglets. Wet-matter energy of salmon prior to decomposition is 0.9 kcal/g (Stalmaster, Gessaman, 1982), or energy equivalent of 840g salmon is 756 kcal. So, one sockeye salmon (weight 3.5 kg)provide approximately 4.1 eagle-days, one chum salmon (4.5 kg) - 5 eagles-days.
Basal Metabolism Rate (BMR) meashured for wintering bald eagle is 2.77 cal/g/hour (Stalmaster, 1981). For 6.5 kg Steller's eagle, Dayly BMR is 432.2 kcal and 18.0 kcal/h. For flights (speeds are assumed to be 45 km/h, by Pennycvuick, 1972), 225 kcal/h was calculated as an estimate of the cost of flapping flight and 63 kcal/h for the cost of soaring flight.
All avoidance flights are flapping in character, therefore requiring 225 kcal/h. Total salmon biomass was consumed by eagles population inwinter was estimated. We calculated number of fish at all spownedgrounds when it was possible at the end of spowning. At thisperiod dayly rate of salmon consumption was about 3.5% of totalsalmon population. It is means that wintering population of 800 eagles consumed per winter about 15,000 salmon.
The activity costs subroutine calculates energy costs of eachkinds of natural activity, devided into the feeding, contactswith other birds, perching, comfort, orientation, flyght (active, soar), and avoidance behaviuor (flight, orientation) caused by human disturbance (table 1). For recalc time spent on some kinds of activity we used coefficients, computed in literature (Pennycuick, 1972, Dolnik, 1989) ). The amount of natural flights was derived by monitoring dailyactivities. Of the 24-hour day, 1,3% is spent in flapping flightand 3.7% in soaring and gliding flight. Most flight activityoccurs for gathering food (foraging flights) or to seek roosts (roosting flights) (table 2.) As possible to see, almost 34% of Dayly Energy Budget is spending on feeding activity. So, we can conclude, it is feeding the most weakest point in species ecological energetics. Probably feeding is the most vulnerable behaviuor in relation with human disturbance.
Foraging patterns in the absence of human activity.
Temporal patterns was differ in winter and summer season.here was no preferable time of day for feeding in winter.Differences were very high day after day. We could not find some regularity. Probably, it is depends on weather conditions, rate of saturation at previuos day, all food situation in area. In winter season on Kuril lake eagle formed feedingaggregation in salmon spowning grounds. Such aggregations, raise effectivness of feeding of individuals, which are formed such group. Single eagle spend much more time for seaching, preparing and eating salmon in compared with birds in a group. Thus, forming a group in a feeding areas is a special behavioural adaptation which one raise food consumption success of individuals in an extremal period of the year. In summer on a sea coast feeding activity was closelyconnected with water altitude - peak of activity was at low level of water and there was no some activity at flow (Fig 1).
Due to time of flow and ebb are changing day after day, eagle temporal activity are changing as well, but predictable.
Changing in foraging patterns due to human activitiy.
Human disturbance was effected on eagle in two ways:reduction of kinds of activity which are important fot survivaland direct increasing activity (and energy lost respectively) costs. There was no significant differences among different kinds of human activity on changes in foraging patterns. All of human activity has one result: disturbing eagle when they flew away from feeding station. But really human disturbance is a more complicated factor, which changes bird's behaviuor as a whole and include changes in foragin patterns: preferable time of day for foraging, refusal from feeding,necessity to search for a new feeding place, decrease the rate of food consumed (bites-minutes per feeding), refusal from captured prey. After a disturbance, eagles never back to the same feeding station and feeding groups, which increase feeding effectivness as itself, were destroyed.
Not commercy human activity like amateur fishers, tourists,crafters and forest guards was turned out unpredictable. Such disturbance was a very variety in a time of day, form of activity, level of disturbance, so there is no some law-governed nature of their effect on eagle. So, we can work out somenegative recommendation for such kinds of activity: what does NOT they MUST to do.
We constructed just model of eagle responce to human activity and can predict effects of energetics loss due to single disturbance. On the base of these data we can predict eagle behaviour: new searching for food, how much food they will need additionally, etc.
Unexpectedly for us was the data about commercy fishering activity, which has been expected as the most important factor of eagle's disturbance. The mutter is at the East coast of Kamtchatka eagles hunting at breeding season mostly in river estuaries. The same place commercy salmon fishers use. But their "temporal niches" were separated. It means that temporal patterns of eagle and fisher's activity are different. Eagle's activity is depends on low latitude of water in river estuary - ebb, when they are able to catch fish on a swallow. Fishermen are active at flow only, because they need water for boating. So, eagle's and fisher's "ecological niche" are separated due to different "ecological demands" to the environment (fig. 1).
Effects of disturbance on salmon consumption patterns.
This affects has different importance in a different feedingsituation. When there is abundance of food, the total amount ofsalmon consumed at the feeding station did not differ betweendisturbed and undisturbed day, because eagles were able to find alternative station for feeding. But the rate of each salmon consumption was changed. We estimate that eagle rate only 5.7% of the salmon consumed on disturbed days in contrast to 31% on undisturbed days (average mass of coho salmon in our areas is about 4.3 kg and sockeye salmon is about 3.5 kg), to take into consideration eagle's dayly salmon consumption, calculated as 840 g. It means that disturbed eagle lost their partially opened and comsumed fish and have to undertake new seach for food to obtane dayly food rate. Thus, totally they are able to find enough food, but for more high cost. To show a load on eagle due to human disturbance we calculated feeding effort (bird-minute of feeding per day) by eagles on undisturbed (n=45) and disturbed (n=12) days (table 5).
When food is scarce, situation was changed. At this time ofthe year available feeding areas are limited and far away onefrom another. So, been disturbed from feeding plot eagle either have to find alternative feeding plot or been waiting for a next day to feed at the same plot. It is not clear understandable, why eagles never back this day to feeding area after disturbance, we can consider this particular as a specific characteristics of their behaviuor. For us it is means, that the cost of human disturbance at the period of the year when food are scarce is very expensive for eagle: any way they loss either energy for a searching and transfering for another feeding area or they loss fool day without feeding. Cosequently, cost of disturbance is enormously increased.
Changing in foraging patterns due to human presence:
1. Direct influence: any kind of disturbance have resulted the encreasing of energy expendeture. This is extra energy and time loss. Average costs of direct avoidance activity of eagle due to single human disturbance was estimated as 128 kcal or in salmon biomass equivalent 142.5 g, which is about 17 percent of dayly salmon cosumption.
2. Indirect influence: loss of prey, necessity to undertake new search of food. Besides, birds lost energy and time spent to first prey. Totally energy cost of human disturbance we calculated as: total energy costs = energy loss of prey from which eagle was disturbed (81.3% of rate stealed is 176 g or 159 kcal, see table 5) + direct disturbance costs (128 kcal) + costs of replacment and new feeding (256 kcal) = 543 kcal or 70% of daily energy budget! Besides, we are not include in this formula costs of low effectivness of foraging single bird and extra time expence for a new search for food.
3. There is hazard does not find any food in summer period wheneagle's activity is closely arrange for certain time of day (ebbsand flows) and at another time of day prey either is not available or it is required much more time and energy for capturing.
4. Indirect influence of human activity due to changing offeeding group complement and feeding situation as whole: humandisturbance decrease total number of birds in group; relative number of single feeding birds is increased, that has result decresing efficiensy of food utilisation and expendetures of prey capturing is increasing. Besides, feeding situation is changed as whole, because that salmon, which were only partly eaten by solitary eagles is lost for them and were utilised by other birds crows, ravens and gulls.
Other words, in the absence of disturbance eagle utilised(not muddle up with digest) all captured food, but at thepresence of disturbance they loss much part of foun food (real percent of lost food depends on the moment of feeding when they were disturbed).
5. Accidents: this effects of human disturbance is unpredictableand depends on eagle's individually behaviuor particularies. They are: loss of living nest just after disturbance; killing ofthe eaglets and eggs in the nest by some predators like crows andravens which are not afraid people and do it when eagle areabsent at the nest due to human disturbance.
1. "Disturbance pattern" of Stellers' eagle behaviuor is described at this research. Human disturbance has a complicated influence on temporal and foraging patterns of eagle population, this influence is not limited just direct loss of energy due to disturbance and totally changes feeding situation in eagle habitats.
2. Foraging is the most expensive activity of eagle and we can expect the most high effect of human disturbance it is in a feeding areas.
3. Costs of disturbance on the nest is equal to one extra feeding and twice low then costs of disturbance in feeding area.
4. Managment implications. Based on the data about salmon spowning ground we can classifying any territory from the point of view it's significance for Steller's eagle.
For this areas we recommened instructions for recreational activity (both temporal and spatial), which include maximum distances of approuching to the feeding eagle, and to the nest, temporal activity during the day and seasons, etc.