The diurnal and seasonal changes in the number of white-bellies in the colony and its coastal water area were studied in 2001 and 2002. on Buldyr Island, as well as in 2004 on St. Paul Island, where their numbers are 10–12 and 34 thousand, respectively (Byrd, Day, 1986, Sowls et al., 1978). It should be noted that there are no and never were land-based predators on Buldyr Island, while the endemic Predlovsk blue arctic fox (Vulpes lagopus pribilofensis).
On Buldyr Island, white-bellied birds nest mainly in talus overgrown with herbaceous vegetation. Since the lush vegetation on the slope of the Northwest Ridge (52 ° 22′24 ″ N, 175 ° 52′44 ″ E), where there is a large colony of white-bellied, did not allow counting birds on its surface, then for collecting data on the dynamics of the number of birds in 2001 on the water, a registration area was laid. On this site, the social relationships of birds nesting on the slope were noted. Its boundaries were huge stones protruding from the water, the distance between which was 380 m. Birds were counted in a strip about 150 m from the water's edge. The point from which the survey was carried out was on a steep slope at an altitude of about 30 m above sea level. m.
In 2001, during the breeding season, censuses were carried out in three five-day series: May 28– June 1 (incubation period), June 21–25 (end of incubation - the very beginning of chick hatching), and July 14–18 (chick rearing period). All birds present at the site were counted during the entire period of their activity: in the morning from pre-dawn twilight until all birds left the site, i.e. until 13-15 hours, and in the evening from 20:00 until dark, when the silhouettes of the birds were difficult to distinguish against the background of the water surface. In addition to these three series of counts, the white belly was counted for another 18 days, of which 7 counts fell on the incubation period, and 11 - during the period of feeding the chicks. These counts were carried out only during the morning (7: 00–15: 00) and evening (22: 00–24: 00) peaks of bird activity in the colony.
In 2002, the site remained within the same boundaries as in 2001. This year, during the entire morning activity (6: 00–15: 00), white belly counts were carried out on June 14 and 24 (incubation period) and July 14 and 27 (period of feeding chicks). In addition, only during the morning peak of bird activity (8: 00–12: 00), 9 more counts were carried out, 5 of which occurred during the incubation period, and 4 - during the rearing period.
On St. Paul Island, field studies were carried out on May 19 – August 13, 2004. Belobryushek was taken from the Tourist Point Cape (57 ° 09′28 ″ N, 170 ° 23′21 ″ W). Here, on both sides of the cape, a site with a total length of 450 m was laid. Birds were counted both on the cliffs of the colony and in the coastal water area at a distance of 150 m from the water's edge. The point from which the bird counts were carried out was at a height of 7–8 m above sea level. m. Morning counts began at 7:00 and lasted until 15:00, evening began at 14:30 and lasted until 22:00. In the pre-incubation period, three morning and two evening counts were carried out, during the incubation period - six morning and six evening counts, and during the feeding period, six morning and nine evening counts. Morning and evening counting days alternated.
We received the weather forecast for ships operating in this water area by radio communication or looked at the Internet. The Beaufort scale was used to estimate the wind strength during the counts. Observations on Buldyr Islands in 2002 and St. Paul were carried out on days when the wind force was less than 12.5 m / s (25 knots).
White-bellies at all sites were counted visually using 8 × binoculars every 15 min.
The total duration of counts in 2001 was 263 hours 45 minutes, in 2002 - 68 hours 30 minutes, and in 2004 - 240 hours 45 minutes.
I determined the breeding chronology of white-bellied belly-bellies on Buldyr Island by examining the nesting chambers on the reproductive sites, which were established to monitor the breeding success of this species.During the entire breeding season, the nesting chambers were examined once every five days. Often only the date of hatching of the chicks was known. In this case, I calculated the median of the dates of hatching and from this I calculated the date of oviposition, taking the incubation duration equal to 35 days (Sealy, Bedard, 1973, Jones et al., 2001). On the island of St. Paul, the white-bellied nests along the cliffs, the lava flows forming these cliffs are dotted with hard-to-reach voids. The length of their “burrows” was significant, which did not allow direct observations of the chronology of the breeding period. Therefore, to determine the stages of the breeding season, I used indirect data: birds feeding their chicks carry food in a throat pouch, which is clearly visible during counts. The dates when such birds began to be recorded during the counts, I took as the beginning of the hatching period. Consequently, before this time there was an incubation period, and after that there was a period of feeding the chicks. As well as on Buldyr Island, the time of the beginning of the incubation period was also calculated.
Numerical data in the text are presented as follows: X ± SD, the amount of data is given in brackets. To compare the samples, the Mann-Whitney Z-test was used.
The article gives administrative summer time: for Buldyr Island - Hawaiian-Aleutian Standard Time (UTC –10), for St. Paul Island - Alaska Standard Time (UTC –9). It should be noted that on Buldyr Island astronomical (solar) time differs from administrative time by about 3 hours, and on St. Paul Island - by 2 hours, i.e. the corresponding number of hours must be subtracted from the administrative time adopted in a given area. For example, the sunrise, astronomical time, on Buldyr Island on June 25 fell at 3:55 am, which corresponds to 6:55 am administrative time.
According to the data obtained at the productive sites, the white-bellied beetles began to lay eggs in late May – early June, and hatching occurred in late June – early July. In 2001, the brooding period lasted from May 25 (the beginning of field work) to July 1, the median period of hatching of chicks. The period of feeding chicks, respectively, covered the period from July 2 to the gathering of chicks. In 2002, the median egg-laying period was 2 June and hatching was 4 July.
On St. Paul Island, the first white-bellied chicks hatched around July 10, therefore, the incubation period lasted from June 4 to July 10, and after this date there was a period of feeding the chicks.
On Buldyr Island, two peaks of activity were noted in white-bellies during the day, both in the colony and in the coastal water area. One of the parents, incubating an egg or heating a small chick, spends the night in the nest, and the other in the sea. In the predawn twilight, birds in flocks of 2–10 individuals begin to fly into the water area of the colony. First, they gather far from the coast, and then swim closer to the colony. During incubation, the number of birds in coastal waters increases until about 7:00. Then the birds from the water begin to move to the colony to change their partner in the nest. The number of birds on the water in front of the colony stabilizes at 8: 00–9: 30. Later, at the beginning of the second half of the day, the number of birds gradually decreases until their full dispersal from the coastal water area. In the evening, the first birds on the water near the colony appear at 19: 00–20: 00. At this time, in contrast to the first half of the day, the white-bellied birds never come close to the shore. Their number reaches its peak shortly before dark, which occurs at about 23:00, and then the number of birds decreases slightly. Later, when it is no longer possible to see the birds, a certain number of birds are still present on the registration site, which could only be judged by their voices coming from there.
The average number of white-bellied chicks on the survey site on Buldyr Island during incubation and feeding of chicks in 2001 (The graph shows the data of all counts, the incubation period lasted from May 28 to July 1, the feeding period lasted from July 2 to July 29).
During the feeding of the chicks, the birds arrived at the site later than during the incubation period, and the peak abundance occurs at 9: 00–11: 30, while during incubation - at 7: 00–10: 00. The number of birds visiting the survey site during the evening peak of activity gradually decreased as the breeding season developed.
Immature birds, which were determined by the shape of the beak and worn plumage, began to visit the colony at the very end of the incubation period. At this time, the number of birds on the counting site increased and reached its peak in the first half of the chick rearing period. The average number of birds present at the site during the peak in 2001, during the nestling period (271.3 ± 94.3 (SD)) was significantly higher than during incubation (169.5 ± 141.2 (SD), Mann – Whitney test Z = 6.89 n = 373, P <0.01). In the second half of the nestling period, the number of birds visiting the site dropped sharply. Only the birds that fed their chicks remained in the colony, and non-breeding birds and birds that failed to reproduce stopped arriving.
Both diurnal and seasonal dynamics of the abundance of white-bellies in 2002 on Buldyr Island was similar to that observed in 2001. Birds were present in the coastal water area both in the morning and in the evening with the same tendency for the peak of abundance to shift to a later one. time during the feeding period.
On St Paul's Island, before the eggs were laid, the number of white-bellies visiting the colony peaked in the first half of the day. The peak of the number of birds on the water near the colony preceded their peak on the rocks.
Average number of white bellies on the registration site in the Tourist Point colony on St. Paul Island in 2004 (Data presented: Arrival - 3 morning and 2 evening counts, Incubation - 6 morning and 6 evening counts, Feeding - 6 morning and 9 evening counts ).
With the development of the breeding season, when birds began to incubate eggs, both in the colony and in the coastal water area of the white belly could be seen for a longer time than in the pre-incubation period, and the peak of their abundance, which was observed only on land, shifted closer to the second half. day. On the water, the number of birds varied widely, with a tendency to decrease at the end of the day. At the end of the incubation period, only a small evening peak was noted.
While feeding the chicks, the birds were present at the colony throughout the day with two peaks in abundance: a small morning and a large evening.
Observations have shown that weather conditions strongly influence the number of birds present at the counting site. Strong winds lead to a decrease in the number of white-bellies in the coastal water area. On windy days, the birds left the site earlier than usual. On such days, both in the morning and in the evening, the birds, avoiding the surf, were farther from the coast than usual. In gusts of 25–30 m / s and more, there were almost no birds on the site, except for a few individuals that left the coastal water area, sometimes without even landing on the water. Even if the day following the storm was quiet, there were fewer birds on the site than usual.
Influence of wind speed on the number of white-bellied beetles at the counting site on Buldyr Island in 2001 (wind speed according to the forecast on May 29, 17–18 m / s, on May 30, 12–13 m / s).
Among the auklets, excluding the Lesser Auklet (Aethia pygmaea) (Byrd, Williams, 1993, Gaston, Jones, 1998, Zubakin, Konyukhov, 1999, Pshenichnikova et al., 2017), in the white belly in different parts of its nesting range, the greatest diversity of diurnal dynamics of population in the colonies is observed. In the south of the white-bellied range, on the Commander and Aleutian Islands, located in the southern part of the Bering Sea, both morning and evening peaks are expressed (Mikhtaryants, 1978, Konyukhov, 2002, Konyukhov, Juk, 2001). On Buldyr Island, a two-peak pattern of bird activity in the colony and adjacent water area persists throughout the breeding period, from the arrival of birds in the colony in spring to the gathering of chicks in the fall.In the northern part of the Bering Sea (the northern limit of the distribution of the white belly) and in the Gulf of Alaska (the eastern limit of the distribution of the species), birds gather on the surface of the colony and in the adjacent water area only in the morning, from dawn to noon (Sealy, Bedard, 1973; Konyukhov, 1993, Hatch , 2002). On Talan Island, in the Sea of Okhotsk, the white-bellied birds also have a pronounced morning peak, and the birds spend less time in the colony than in the coastal water area (Harding et al., 2002). On the Pribylov Islands in the central part of the Bering Sea, the situation with the dynamics of the number of birds in the colony is the most interesting. Depending on the stage of the reproductive period, the pattern of bird activity in the colony occupies an intermediate position between one- and two-peak daily activity. As noted above, at the beginning of the breeding season, before oviposition, birds were present in the colony and the adjacent water area only in the first half of the day, i.e. the same as in the north and east of the species range. During the incubation period, the peak of the abundance was noted only on land, but there is a general tendency towards a decrease in the number of birds, both on land and on water, in the second half of the day. The absence of a peak in water abundance is most likely caused by a disturbance factor. Northern fur seals, which in groups and one by one moved between the feeding areas and a nearby bachelor rookery, periodically scared the white-bellies and they flew away from the registration area. This rookery fills with seals in mid-June, just during the incubation and feeding of chicks with white-bellies. The formation of a small peak in the evening at the end of the incubation period is probably due to the fact that in some nests the chicks have already hatched and the parents brought them food.
During the nestling period, a small morning peak was formed mainly by birds that brought food to the nestlings. These birds, as a rule, sat right in front of the entrance to the nest and disappeared in it, remaining on the surface of the land for a minimum time. After feeding the chick, they immediately flew into the sea. The birds were not marked individually, but since the parents remain in the nest with the chick only for the first 3-5 days of its life (unpublished data), it is likely that during the entire feeding season of chicks, excluding its very beginning, the bird that arrived with food and left the nest a few minutes later was, I believe, the same one, and not her partner, who continued to remain in the nest. The evening peak during this period was probably formed by both birds feeding the chicks and birds not participating in breeding: immature and unsuccessful adults. When in the second half of the nestling period, birds that do not feed the nestlings leave the colony, this peak disappears. An explanation has not yet been found for such a variety of circadian rhythms in the belly belly in different parts of its range. Perhaps further research will shed light on its causes.
As noted above, strong winds significantly reduced the number of birds visiting the survey site. In a similar way, strong winds suppressed the activity of the frogs in the colony (Konyukhov, 2010). The influence of the wind could be expressed in two ways. The wind is stronger than 25 m / s simply blows the birds off the surface of the colony. But the main reason, probably, is that it, causing strong waves, mixes the surface layer of the sea and destroys the zones of stratification of water masses, where the white belly bears feed. Birds need more time to get full to get scattered food, and they may be starving during this time. This assumption is supported by the fact that on the day following the end of the storm, fewer birds were counted on the counting site than usual. A similar effect of windy weather was noted for both the great auklet and the Pacific guillemot in Chukotka, where the growth of chicks was suspended due to lack of food (Konyukhov, 1997).
All the features of the biology of the species described above should be taken into account when conducting monitoring surveys.
If the counts are being conducted for the first time in a given area, then first it is necessary to determine the time of day when the number of birds in the colonies of a given region is maximum, and it is during this period to carry out the count.
The accounting site should have pronounced boundaries, which will make it possible to obtain comparable data from year to year.
Since the daily changes in the number of white-bellies on the sites under consideration were minimal during the incubation period, it is advisable to count birds during this period as well.
As mentioned above, the number of white-bellies in the colonies decreases with an increase in wind speed; at a wind speed of 12.5 m / s (25 knots) and higher, the activity of birds on the colony surface is almost completely suppressed. Consequently, counts should not be carried out on days with such a wind force, as well as on the day after a storm, when the number of birds in the colony and adjacent water area is less than on normal days.
I am sincerely grateful to the staff of the Alaska Maritime National Wildlife Refuge for the opportunity to work on Buldyr and St. Paul Islands, for financial and technical support for the research, and E.K. Litvin, S.P. Kharitonov and V.A. Zubakin - for valuable comments during the preparation of the article for publication. Valuable comments from the reviewer helped to improve the quality of this publication. These studies were carried out within the framework of the Russian-American agreement in the field of environmental protection.