The results of 11 years (2003–2013) monitoring activities, including estimation of number and gender structure of waterfowl on the Lake Khanka, are presented. The accounting work (50 days) took place in the first decade of April, in the period of mass spring migration of migratory birds. About 682,270 birds are registered. The comparison of the species composition and the ratio of the major groups of waterfowl of the two periods — 2003–2009 and 2010–2013 are given. The most minority group of migratory birds is Cygnus — less than 0.1% of all registered birds. More than 10,000 specimens of geese were accounted (17.7% of registered birds). The maximum number of birds was registered in 2008, the minimum number was registered in 2011. In all years of monitoring the part of Anas formosa was the largest among migratory birds — from 42 to 80% of all registered birds. The Anser albifrons dominates among all Ansers — about 50–80% of all identified species of Ansers. For the first time of all years of the ornithological investigations of the Prikhankayskaya lowland the gender structure of Anas was identified by visual estimates and photo data. The sample was 28.9 thousand birds. The average proportion of males for all years (2003–2013) was 58.9%, the maximum was recorded for Authya ferina (70.2%) and Authya foligula (70.3%).
Migratory birds; Spring migration; Waterfowl; Species structure; Gender structure
As a habitat for waterfowl, Lake Khanka is included into the list of wetlands of international importance (Ramsar Convention). Anseriformes is one of the most mass group among other birds of this location, its largest number can be seen during spring migration. At this time well pronounced ways of transit migration cross the lake, it is a place for long-term feeding stops. Such stops are used to refill birds' energy supplies, which is necessary for further migration and coming breeding season.
In Russian literature special attention is paid to quantitative and qualitative characteristics of Anseriformes' spring migration on the Lake Khanka (Polivanova, 1971, Polivanov, 1975, Gluschenko and Bocharnikov, 1990, Gluschenko and Bocharnikov, 1995, Gluschenko et al., 1995, Gluschenko et al., 2005, Gluschenko et al., 2008, Gluschenko et al., 2008, Gluschenko et al., 2013 and Gluschenko and Mrikot, 2000). In this paper we are presenting more detailed data collected on this question in 2010–2013 years. We also compare obtained results with the similar ones for the period of 2003–2009, which were published earlier (Bocharnikov et al., 2010).
Current work summarizes 11 years of monitoring of this important for the region birds' group and to some extent the whole period of observation since 1987 year.
The main observations during all these years were conducted in the places of Anseriformes' mass accumulation in the Russian part of the Khanka Lake according to methodology, which we described earlier (Gluschenko et al., 1995).
Depending on a year observation took time from 3 to 6 days mostly during the first decade of April (in a period recommended for hunting of waterfowl, basically in locations, where hunting is strictly prohibited) (Table 1).
Terms of spring surveys of Anseriformes on the Lake Khanka in 2003–2013 years.
|Year of observation||Terms of conducted surveys||Number of observing days|
During these days of observation we visited the key places of ducks' and geese' spring stops. According to expert estimation based particularly on multiple aerial surveys, which we held in the Prikhankayskaya lowland in recent times, we took into account from 40 to 80% of various species of ducks and geese crowded at the period of survey in the Russian sector of Khanka. But the main locations of swans' stops were always out of our focus. Birds of this genus were registered only by chance and sporadic, so such observations don't reflect the whole way of their migration through Lake Khanka. While planning the work we set 3 main goals: following the perennial dynamics of ducks and geese population; reveal a percentage between numbers of different species of ducks and geese; study a gender structure in spring populations of ducks.
As mentioned earlier, we have already published the results of annual surveys for the period of 2003–2009 years (Bocharnikov et al., 2010). Thus in current paper we are presenting data only for the last 4 years (from 2010 till 2013), when in sum we registered almost 170 thousand of Anseriformes from 23 species (Table 2).
|Registered specimens||%of the group||Registered specimens||%of the group||Registered specimens||%of the group||Registered specimens||%of the group|
|Anas carolinensis||0||0||1||< 0.1||0||0||0||0|
|Anas falcata||4||< 0.1||63||0.4||16||0.05||393||3.24|
|Anas strepera||0||0||21||0.1||2||< 0.01||23||0.19|
|Anas querquedula||1||< 0.1||13||0.1||2||0.01||4||0.03|
|Aythya fuligula||3||< 0.1||507||3.4||0||0||296||2.44|
|Bucephala clangula||17||0.2||329||2.2||1||< 0.01||275||2.27|
|Mergellus albellus||1||< 0.1||141||0.9||1||< 0.01||67||0.55|
|Duck (species not identified)||1121||10.3||71,221||70.2||2155||9.74||76,760||83.28|
|Total number of ducks||10,947||81.8||86,332||89.6||32,389||96.03||88,901||86.51|
|Total number of Anser||2408||18.1||9990||10.4||1340||3.97||13,865||13.49|
|Total number of swans||12||0.1||13||< 0.1||2||< 0.1||1||< 0.1|
In total for the whole period of annual surveys in 2003–2013 years we registered more than 628 thousand of Anseriformes of 26 species. Among them there were 19 species of ducks, 5 species of geese and 2 species of swans (Table 3).
|2003–2009 years||2010–2013 years||2003–2013 years|
|Total of registered specimens||Average number of specimens per season||%of the group||Total of registered specimens||Average number of specimens per season||%of the group||Total of registered specimens||Average number of specimens per season||%of the group|
|Anas carolinensis||0||0||0||1||0.3||< 0.01||1||0.1||< 0.01|
|Anas strepera||59||8.4||< 0.1||46||11.5||0.07||105||9.5||0.05|
|Aythya ferina||58||8.3||< 0.1||63||15.8||0.09||121||11||0.05|
|Aythya baeri||1||0.1||< 0.1||0||0||0||1||0.9||< 0.01|
|Aythya marila||0||0||0||9||2.3||0.01||9||0.8||< 0.01|
|Duck (species not identified)||206,493||29,499||55.1||76,760||19,190||69.20||283,253||25,750.3||61.05|
|Total number of ducks||375,049||53,584.9||81.77||141,993||22,225.3||88.78||517,042||42,177.3||82.29|
|Anser anser||4||0.6||< 0.1||0||0||0||4||0.4||0.02|
|Total number of Anser||83,395||11,913.6||18.18||27,603||6900.8||11.21||110,998||10,090.7||17.67|
|Total number of swans||202||28.9||0.05||28||6.5||0.01||230||20.7||0.04|
Ducks was the prevailing group of birds according to the species diversity (19 species) and overall abundance, they made up 82% of total met Anseriformes. At the same time ducks–geese ratio varied significantly from year to year; swans were met rarely and not every year, they made up only 0.04% of total Anseriformes. The minimum difference between numbers of ducks and geese was registered in 2007, when the ducks were only 1.6 times more than geese (60.9% of the total). The maximum difference was observed in 2012, we registered 24.2 times more ducks than geese (96% of the total). The sum total of duck and geese also varied yearly (Fig. 1). Absolute minimum registered in 2010 (about 13 thousand of specimens) was approximately 12 times lower than absolute maximum registered in 2008 (about 160 thousand of specimens).
Dynamics of ducks' and geese' populations on the Lake Khanka in early spring (based on survey data of 2003–2013 years).
Under such interannual dynamics it is difficult to determine the exact trend of Anseriformes numbers during spring migration on the Lake Khanka. However using our conditional division of all observation period into 2 groups — first 7 years (from 2003 till 2009) and last 4 years (from 2010 till 2013), we determined that the mean population of the last period, as it seen in Table 3, was 1.5 times lower (42.4 thousand of specimens comparing to 65.5 thousand of specimens per season). Yearly average rate of all observation seasons was a bit more than 57 thousand of Anseriformes. Besides this, according to our expert estimate from 25 to 300 thousand of Anseriformes (around 100 thousand in average) had been visiting Russian part of the Lake Khanka and adjusted territories of the Prikhankayskaya lowland in early spring every year. For the period of 1987–1991 years this rate was 160 thousand of specimens in average, for 1994–2003 years — 180 thousand of specimens (Gluschenko et al., 2005). Some growth in numbers at the turn of the millennium can be easily explained by significant increase of Anas formosa population, which was at the state of the depression during 1987–1991 years. We compared our obtained results with the data for the last quarter of the XX century and revealed that the total number of Anseriformes on the Khanka Lake during spring season decreased 1.7 times.
Within all 11 seasons of observation, discussed in current paper, A. formosa was the most numerous species among other birds of considered group. Almost all the time this species made up more than a half of all registered ducks, which were distinguished to species. Part of the A. formosa among other ducks average 79.5% (81.2% of the Anas genus), varying in different years: from 43.3% in 2005 to 95.2% in 2010 ( Fig. 2).
Contribution of Anas formosa, ducks from Anas genus and all other left species of ducks into forming of early-spring duck population on the Lake Khanka (based on survey data of 2003–2013 years).
Thus the numbers of the majority species of Anseriformes decreased many fold for the past quarter of the century. But the overall stock of the Anseriformes was compensated to some extent at the expense of abrupt growth of A. formosa population. It should be noted that A. formosa is listed for the second category in the Russian Red Data Book (2001), in the Red Data Book of Primorsky Krai (2005) and in the Red List of IUCN. Among other ducks, which are mentioned in a Red Books, during our early-spring surveys we met Aix galericulata and Aythya baeri. Their summary contribution to a total number of ducks is quite small (varied from 0.1 to 0.7%), mostly made up by A. galericulata. This species is rather common in Primorsky Krai, but in spring it can't find here suitable stations (in summer season during molt relative population of A. galericulata is slightly higher).
A. baeri was registered only once during past 11 spring seasons (on 6 of April in 2005 we observed a single male). We didn't register this species on the Prikhankayskaya lowland even during breeding period in spite of special search organized in 2012 year in places of his breeding in the recent times (Gluschenko et al., 2013). At the same time, his nesting stations now are occupied by Aythya ferina, which was firstly registered breeding on the Lake Khanka in 2004 ( Gluschenko et al., 2005). A. ferina progressively increases in numbers both in summer and migration seasons.
During the period of study we registered 5 species of geese within the spring migration. Anser albifrons and Anser fabalis turned out to be the most numerous, their summery part in different years was from 98.3 to 100% of the total number of geese distinguished to species. Three more species of geese were identified in a quite small quantity and irregularly — Anser erythropus, Anser сygnoides and Anser anser.
It should be mentioned, as we stated earlier (Gluschenko et al., 1995), during geese surveys conducted in such conditions, some underestimation of A. erythropus took place, because this species is almost indistinguishable from another and most numerous species — A. albifrons. But the real number of A. erythropus' specimens migrating through the Khanka Lake can hardly differ significantly from the data presented in Table 3. It is proved by mass photo shooting of geese, which we are conducting simultaneously with visual observations. Attentively analyzed photo data never revealed even 1 specimen of A. erythropus.
It must be emphasized that in the second half of XIX century A. erythropus was mentioned in spring on the Khanka Lake as common or even numerous species, often prevailing over other species of passing geese ( Przewalski, 1870 and Shulpin, 1936). For the first quarter of XX century A. erythropus was given as small or rare species. Later A. erythropus was met here irregularly and in a very limited quantity: in the second half of the past century according to approximate estimates it made up 3–5% of the whole number of migrating geese during spring migration on the Lake Khanka ( Gluschenko and Mrikot, 2000 and Gluschenko et al., 2005). Basing on data discussed in current paper, during 2003–2013 years A. erythropus average 0.24% of the total number of geese identified till species. And if in 2003–2009 years its part made up about 0.4%, during following 4 seasons this species wasn't registered at all.
Undoubtedly, the main migration of A. erythropus take place in later terms, but certain specimens and groups migrate in a first half of April. Moreover, catastrophic decrease of this species' population registered for the valley of Razdolnaya River, too, where, according to survey data of Shulpin (1936), mass flight of A. erythropus was located near Ussuriysk (ex-Voroshilov). In terms of our observations, conducted in 2003–2007 years in the valley of Razdolnaya River in surroundings of Ussuriysk (during the whole spring season, not only in early spring), A. erythropus was registered as rare migrating species, which made up only 0.8% of all geese determined to species ( Gluschenko et al., 2008A).
The ratio of A. albifrons and A. fabalis varies widely from year to year ( Fig. 3), but in vast majority cases during surveys the first species prevailing significantly with the average for all 11 spring seasons equal 78.6% among all geese determined to species.
Population ratio of the main geese species on the Lake Khanka in early spring (based on survey data of 2003–2013 years).
A lot of followers of spring duck hunting most of the time appeal to unequal sex ratio, as the males are dominating in spring, so it seems possible to remove “extra” males without doing any harm to population. But such male “surplus” has a positive influence on population (Mikhantiev and Selivanova, 2005). Basing on observations after duck species, which are definitely not nesting on the Lake Khanka, we registered their active lekking (Fig. 4), dividing into pairs and treading (Fig. 5) within the spring migration. Thus males' capture during this period has some negative impact on further course of females' reproduction, who lost their chosen during migration sexual partner.
Lekking of Bucephala clangula during the spring migration on the Lake Khanka (8 of April, 2013).
Photo by Korobov D.V.
Treading of Mergellus albellus during the spring migration on the Lake Khanka (18 of April, 2012).
Photo by Korobov D.V.
Without going into details of the obvious substantial harm, caused to Anseriformes by todays way of spring hunting in Russia, including the Lake Khanka, we conducted a study on gender structure of their populations during the first half of the spring migration; the sample exceeds 30 thousand of specimens (Table 4).
|Species||2003–2009 years||2010–2013 years||Total|
|Amount of sampling||Male %||Amount of sampling||Male %||Amount of sampling||Male %|
|Total number of Anas||13,077||60.7||11,626||57.6||24,703||59.2|
|Total number of diving ducks||1727||57.9||2478||56.1||4211||56.8|
As follows from Table 4, numerical superiority of males in early-spring period is typical for all species of Anas and most other species of ducks with the average of 17.8%. Among ducks of Anas genus the number of males was exceeding females 1.45 times in average, with a maximum of 1.86 times for Anas querquedula and minimum of 1.37 times — for A. formosa. For majority of diving ducks, such as A. galericulata, Aythya sp. and others we also registered marked dominance of males. But some species of Merganser are described with a reversed situation, first of all, Mergellus albellus, in whose small spring population females are prevailing considerably. It must be noted, that dominance of females in spring population of M. albellus is also registered in Tomsk Priobye. Nevertheless we should take into account that the first-year males of M. albellus in spring may look like a females from a distance. This fact can distort the results of surveys a bit.
It also should be mentioned, that conducting such observations in early-spring time distorts a bit the real ratio of genders, too. It happens because among ducks, as well as other groups of birds, adult males are prevailing at the beginning of migration, and females and first-year males mostly migrate slightly later. We documented this fact for the valley of Razdolnaya River where we observed a substantial male dominance for Mergus merganser during March (from 60 to 67.1%). But for the first 5 days of April the numbers of males and females were balanced, and in a later time we registered explicit prevalence of females, the part of males at the end of the migration made up 17.4–40.7% ( Gluschenko et al., 2008B). This regularity explains the maximum numbers of males in early-spring populations of A. querquedula, A. ferina and Aythya fuligula, who migrate much later than other species of ducks.
The total number of Anseriformes during the spring migration on the Lake Khanka decreased more than 1.5 times for the last 25 years.
Ratio between populations of various species of ducks has been changing considerably since the end of the past century. This is a consequence of abrupt population growth of A. formosa, who is making up 80% of all ducks. Besides increasing of A. formosa, population growth of A. ferina is obvious, too.
The number of A. erythropus decreased extremely; A. baeri as well as Anser cygnoides and A. anser almost completely disappeared from the group of migrating and nesting birds of the Lake Khanka.
Imbalance in gender structure during early spring is typical for the majority of duck species. Males are dominating, but this doesn't fully reflect the real structure, because such phenomenon connected with earlier migration of males than females. Thus, current imbalance can't be accepted as justification for spring hunting of “extra” males. Considerable harm, brought by spring hunt is also evident because during spring migration ducks choose a partner and tread actively.