First Observation of polyterritorial polygyny in Pine Warbler (Dendroica pinus)

Posted by: Mark Andrew Conboy.

Male passerines typically maintain a single territory throughout the breeding season which is used concurrently for foraging and breeding. Polyterritoriality, the maintenance of two or more territories, has been observed in numerous species of North American passerines (Ford 1996) but is far less common than the maintenance of a single territoriality. Some species split aspects of their life histories between polyterritories, where a primary territory is used for breeding and a secondary territory is used only for foraging. In other cases polyterritories are maintained by polygynous males and both territories are used for breeding activities. In cases of polyterritorial ploygyny males defend two or more disjunctive territories in which they pair with separate females and usually provision broods in each of those territories.

Figure 1. Pine Warbler (Dendroica pinus). Photo: Mark Andrew Conboy. Click on photo to see a larger version.

Here I report what appears to be the first case of polyterritorial polygyny documented for the Pine Warbler (Dendroica pinus; Figure 1). General knowledge of Pine Warbler territoriality is limited but to date polyterritoriality has apparently not been documented. Similarly the mating system of Pine Warblers is unknown but is assumed to be socially monogamous as in other Dendroica wood-warblers (Rodewald et al 1999). Field observations of banded birds from 12 territories in Eastern Ontario confirm that most pine warblers are monoterritorial and socially monogamous but I found one male that was polyterritorial and polygynous.

I captured, colour-banded and mapped the polyterritories of an after second year male (Pyle 1997) Pine Warbler in May 2008 at QUBS. This Pine Warbler had two disjunctive territories in each of which I observed him singing, delivering food to a nest and interacting with a different female. The primary territory (the one used more frequently by the male) had an area of 19 562 m2 and the secondary territory had an area of 5369 m2. The minimum distance between the two territories was 398 m (Figure 2).

Figure 2. Map illustrating the first documented case of polyterritorial polygyny in the Pine Warbler. The location is the north end of the Cape-Sauriol Environmental Studies Area at the Queen’s University Biological Station.

Polyterritories are in part characterized by the male singing in multiple territories but not in between them. In some cases territories of other males are interspersed between the primary and secondary territories. Other times there is an expanse of unsuitable habitat between the polyterritories putting them out of hearing and visual range (Ford 1996). In the present case I found there was a zone of unsuitable habitat (i.e. lacking mature eastern white [Pinus strobus] and red [P. resinosa] pines) between the primary and secondary territories. As expected this zone of unsuitable habitat was not occupied by other territorial male Pine Warblers. The male behaved territorially (singing and chasing conspecifics and yellow-rumped warblers [D. coronata]) in both his primary and secondary territories, but I did not observe these behaviours in the zone between territories.

Male song is the primary means by which territories are established and defended by Dendroica wood-warblers. The male was observed singing on both territories. I broadcasted locally recorded Pine Warbler songs to test the responsiveness of the male to conspecific song in both territories. A 10 min playback was broadcasted in the primary and secondary territories twice during the field season, five days apart. In the primary territory the male responded by descending out of the canopy to within 2 m of the speaker. He counter-sang and overlapped his song with the playback. He also gave a variety of call notes, characteristic of aggressive encounters in Pine Warblers. In the secondary territory the male did not approach the speaker and counter-sang only from the canopy. He maintained a distance of 10 m from the speaker even when playback was preformed directly below the nest. I also broadcasted playback in the zone between the primary and secondary territories. I played a recording of conspecific song one time at each of two points after the territories were fully mapped. I received no response to the playback between the two territories. Of course a null response does not entirely preclude the possibility that the male was present but simply did not respond to the playback. However, my field crew and I traveled in the area between the primary and secondary territories regularly and did not detect any Pine Warblers singing in the area. Given the aggressive nature of the species and ease with which I regularly elicited response with playback from territorial males, and our failure to detect the male during hours of field work in the zone between territories, it is probable the male’s territorial behaviours were confined to the two mapped areas and excluded the space between.
The difference in response to playback between territories may be representative of the degree of parental investment that the male was willing to make in each territory. Aggressive interactions between male Pine Warblers were commonly observed on our study site. Costs associated with chases and counter-singing may be sufficient to discourage males from engaging in overtly aggressive territorial defence on secondary territories where parental investment in offspring may be limited to begin with. Male American Redstarts (Setophaga ruticilla) make fewer foraging trips to nests in their secondary territories than their primary territories, indicating reduced parental investment (Secunda and Sherry 1991). I observed males provisioning nests on both territories, but did not measure feeding rates so I could not directly quantify male parental investment.

Although polyterritorial polygyny has a received only limited study among wood-warblers, it has been documented in at least five other wood-warbler species: Yellow Warbler (Dendroica petechia) (Spector 1991; Ford 1996), Black-throated Blue Warbler (D. caerulescens) (Petit et al 1988), Kirtland’s Warbler (D. kirtlandii) (Walkinshaw 1983), Prairie Warbler (D. discolor) (Nolan 1978), and American Redstart (Secunda and Sherry 1991). This behaviour could also be present in other species. It is suspected in Common Yellowthroat (Geothylpis trichas) (Stewart 1953), Tennessee Warbler (Vermivora peregrine) (Lein in Ford 1996), Yellow-rumped Warbler (D. coronata), Chestnut-sided Warbler (D. pensylvanica) and Black-throated Green Warbler (D. virens) (Kendeigh 1945). Because our knowledge of territoriality in general is limited, there is still ample opportunity to discover new cases of polyterritoriality or other novel territorial strategies among wood-warblers, including numerous species at QUBS.


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