Interspecific interference between Green and Gray Woodpeckers in Moscow region: long-term studies during 1984–2007. - V.S. Friedmann. - Berkut. 18 (1-2). 2009. - P. 77-125.
Long-term interaction between populations of both species in Moscow region were traced during 1984–2007 years. Clear negative correlation between number changes and distribution area dynamics were registered. In XX century four times the cycles of mutual exclusion of these woodpeckers were registered; our observations apply to fourth cycle, all others were reconstructed on literature data. Cycle of long-term interaction between Picus species began from increasing of number of Gray Woodpecker with spreading its distribution area to the south and south-west. During this, Gray Woodpeckers suddenly settle near Green Woodpecker demes, often on the territories of second species, in its typical habitats a.o. The expansion of Grey Woodpeckers in 1989–1994 lead to swift decline of Green Woodpecker population in Moscow region. Green Woodpeckers leave the territories in which this Gray Woodpeckers settled (part of this territory was used jointly by pairs of two species). On all the places, in which Green and Gray Woodpeckers population interact during 1989–1994, first species cease nesting in own demes and vanish in this district. Interestingly, that the Grey Woodpeckers don’t stay too long on the territories, from which they «ejected» Green Woodpeckers pair. After 1–3 seasons inhabitancy P. canus leave all of this and stop their nesting in this districts, too. In this years (1995–1998) a minimum number of Green Woodpeckers population was registered in our region. The number and distribution area of Gray Woodpecker population reduce to levels existing before the growth. Simultaneously completely discrimination between habitats of both species has set in. Green Woodpeckers inhabit now only narrow belt of floodplains habitats. There are «bands» of alder tickets or willows in floodplains of small rivers, or«patches» of oak forests – in floodplains of larger rivers. The nest territories of Gray Woodpeckers now are confined solely to large woodlands on the plains, consists pine-birch forests with specks of spruce, aspen or oaks. Strict habitat differentiation between two Picus species initially is distinctive for their settlements on the Meshcherskaya lowland (floodplains of rivers Klyazma, Nerskaya, a.o) only, but after 1999 get typical for all remained Green Woodpecker populations. Now the habitats of two Picus species are separated as much as possible, even they live side by side, as on the floodplains of rivers on Meshchera. At the beginning our observations, in 1984–1986, the spectrum of species sufficiently exceed. The number of Green Woodpecker rehabilitate slowly through 10–15 years after Gray Woodpecker’s departure from former P. viridis territories and former habitats. The source of restoration is a big invasion from southern and southern-west populations which are remained better. Also, our research showed the equilibrium system with two species populations, interacting one with other in heterogenic environment. Population growth and distribution area spreading of P. canus lead to decline of P. viridis populations, and vice versa, and afterwards the initial state restore. It is important to emphasize, that cycling restoration the equilibrium between this species was showed in Moscow region, where Gray and Green Woodpeckers inhabit jointly long ago. In central and western Europe Gray Woodpecker appear relatively not long ago and actively settle in new places. Here the population interaction between P. canus and P. viridis often finish by the extinction of second species or big declining their populations. This article analyses some evidence in favour that the interspecific competition between these species exists and cyclic equilibrium between both is described with our model. Possible mechanisms of competitive exception will be analised in separated article. [Russian].
Key words: Picus canus, Picus viridis, Moscow region, competition, number, distribution, habitat.
Address: V.S. Friedmann, Laboratory of ecology and nature conservation, biological faculty, Moscow university, Leninskiye gory, 1/12, 119992 Moscow, Russia; e-mail: wolf17@list.ru.