Category Archives: Breeding/Nesting

Female American redstart uses old red-eyed vireo nest

Posted by: Ann McKellar

Figure 1. Female American redstart building a nest. Photo: Carla Crossman

American redstarts (Setophaga ruticilla) are long-distance migratory warblers that typically begin arriving in the Opinicon region in early May. A female will pair with a male, inspect their shared territory, and then build a nest over several days. But as the breeding season progresses and nests continue to be depredated, a female can typically build new nests more quickly, sometimes managing to build an entire nest in as little as a day in late June and July. Redstart nests are usually built at the junction of three branches (also known as a crotch), often on the main trunk of a small tree or on skinnier branches of a larger tree. This type of structure allows support for the small cup nest, and a female will often be found placing her breast in various crotches before deciding where to build. When nest-building, female redstarts begin by laying down a base of spider web, and subsequently attach various materials, which can include bark strips, grasses, leaves, and lichens, to build up the walls of the nest. The final stage involves lining the inside of the cup, which is often done with feathers and mammal hairs.

On June 30, 2010, I observed a female American redstart laying down spider web in a crotch of a small sugar maple near Rock Lake

Figure 2. Female American redstart (tail visible) incubating on an old red-eyed vireo nest. Photo: Ann McKellar

Lane. I returned the next day, expecting to find the nest well on its way to completion. Instead, I found that the previous day’s nesting attempt had been abandoned, although the female still appeared to be building a nest somewhere nearby, as I saw her carrying nesting material. Puzzled, I continued to search for the female’s new nest for the next few days, without any luck. Finally, on July 6, I found the same female incubating three eggs in what appeared to be an old red-eyed vireo’s (Vireo olivaceus) nest. Red-eyed vireos construct their nests suspended from a fork or from two lateral twigs, and they are very different in appearance from the smaller, more secure-looking redstart nests. I was very surprised by this discovery, but after some research, I found that the use of old or deserted nests of other species, although not common, has been described previously in American redstarts. Verdi Burtch (1898) reported an American redstart female using an old red-eyed vireo’s nest that she had freshly lined, and Alfred Otto Gross noted in Bent (1953) three cases in which a red-eyed vireo’s nest was used by an American redstart female, one in which a yellow-throated vireo’s (Vireo flavifrons) nest was used, and one in which a nest started and abandoned by a yellow warbler (Dendroica petechia) was used.

Figure 3. Red-eyed vireo nest, used by an American redstart female. Photo: Ann McKellar

The redstart-vireo nest was ultimately depredated four days later, perhaps partly due to its conspicuousness. At this point I collected the nest in order to observe it more closely. The redstart had indeed used the foundation of a hanging red-eyed vireo nest, but had added some of her own lining material, which explains why I saw her with material on July 1. I suspect that the she was becoming desperate at such a late stage of the breeding season (two of her previous nests had already been depredated) and, giving up on starting a third nest from scratch, she decided to quickly re-line the already-constructed vireo nest.


  1. Bent, A.C. 1953. Life histories of North American wood warblers. Dover Publishers: New York, New York, USA.
  2. Burtch, V. 1898. Curious nesting of the American redstart. Auk 15: 332.

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.


  1. Ford, N.L. 1996. Polyterritorial polygyny in North American passerines. Journal of Field Ornithology 67(1): 10-16.
  2. Howe, R.W. 1979. Distribution and behaviour of birds on small islands in northern Minnesota. J. Biogeog. 6: 379–390.
  3. Kendeigh, S.C. 1945. Nesting behaviour of wood warblers. Wilson Bulletin 57: 145-164.
  4. Nolan, V, Jr. 1978. The ecology and behaviour of the prairie warbler, Dendroica discolor. Ornithological Monographs 26: 1-595.
  5. Petit, K.E., Dixon, M.D. and Holmes, R.T. 1988. A case of polygyny in black-throated blue warbler. Wilson Bulletin 100: 132-134.
  6. Pyle, P. 1997. Identification guide to North American birds, Part 1: Columbidae to Plocediae. Slate Creek Press, Bolinas.
  7. Rodewald, P.G., Withgott, J.H. and Smith, K.G. 1999. Pine warbler (Dendroica pinus). The Birds of North America (Poole, A., editor.). Ithaca: Cornell Lab of Ornithology.
  8. Secunda, D.A. and Sherry, T.W. 1991. Polyterritorial polygyny in the American redstart. Wilson Bulletin 103: 190-203.
  9. Spector, D.A. 1991. The singing behaviour of yellow warblers. Behaviour 117: 29-52.
  10. Stewart, R.E. 1953. A life history of the yellow-throat. Wilson Bulletin 65: 99-115.
  11. Walkinshaw, L.H. 1983. Kirtland’s warbler: the natural history of an endangered species. Cranbrook Institute of Science Bulletin 58.

Nest building consistency in Yellow Warblers.

Consistency in an individual animal’s behaviour is a curious observation. If an animal shows a consistent behaviour, this suggests that the behaviour is not mediated by immediate environmental cues, and may suggest that the behaviour is heritable to some degree. In the summer of 2008, former Queen’s University undergraduate student Allie Patrick, investigated consistency in nest building behaviours of Yellow Warblers (Dendroica petechia) at the Queen’s University Biological Station (QUBS).

Photo shows two nests constructed by the same individual for eight different female Yellow Warblers. Nests constructed by the same female are arranged vertically. Note the similarity of nests constructed by the same female and the diversity of nests constructed by different females.

It is fascinating to think that the diversity of Yellow Warbler nests and the materials used to construct them is not at all random and that individual females actively seek-out and gather specific materials. This is readily seen in the photos, where one female Yellow Warbler lined her nests almost exclusively using duck feathers (nest pair on far left), while another used fluffy cattail (Typha spp.) pappus (second from the left). Using specific materials is not limited to the nest lining. Some females incorporated pieces of Common Mullein (Verbascum thapsus) leaves (third from the left) throughout the nest cup, and others used almost exclusively dry grasses and bark fibers (fourth from the left). To some degree breeding location will influence the availability of nesting materials; in some locations there may be no Common Mullein, while in others there may be no cattail pappus. However, many of these females nested within the same marsh (and therefore should have had access to similar materials), yet they built distinctive nests. Distinctive nests constructed by females in close proximity to each other suggests that, in addition to location, individual females show a preference for specific materials when constructing their nests.

These eight nests represent a small sample of the diversity of Yellow Warbler nests within the breeding population at QUBS in southeastern Ontario. As seen in the photos, the population-level variation in Yellow Warbler nests is impressive, yet nest building behaviour at the individual level may be much less variable. – Posted by Vanya Rowher

Early nesting mourning dove.

Dead Mourning Doves
The two dead nestling mourning doves (Zenaida macroura) collected form the earliest nest on record for this species in the Kingston Region. Photo: Mark Andrew Conboy.

Mourning doves (Zenaida macroura) are among our some of the earliest breeding birds often with eggs being laid by mid to late April (Weir 2008). Doves and pigeons produce protein rich crop “milk” to feed their nestlings. The milk is produced by both sexes and may allow doves and pigeons to breed very early in the year, when resource scarcity makes it impossible for most other species to nest. Here I report an exceptionally early nesting attempt by mourning doves at QUBS.

On April 17, 2010 I found a mourning dove nest 30 m north of the intersection of the Cataraqui Trail and the Old Bedford Road. The nest was built 2.1 m above the ground in an eastern redcedar (Juniperus virginiana). The nest contained two dead nestlings. The nestlings were not warm but were still soft and blood that was on the legs of both birds and near the cloaca of one bird was still wet to the touch. I suspect that the nestlings could not have been dead for very long. One adult flushed directly from the nest so was still likely brooding and a second adult flushed from the ground about 4 m away. There was half of a morning dove eggshell on the ground immediately below the nest.
The earliest egg date for mourning dove in the Kingston region is April 14 and earliest brood date is May 13 (Weir 2008). The typical incubation period for mourning doves is 14 days (Otis et al 2008). I estimated the age of the nestlings to be about 8 days old (Hanson and Kossack 1957). Based on the estimated age of the nestlings I suggest that the first egg date for this nest would be March 27. This is 19 days earlier than the previous earliest record for the Kingston region. In the southern part of their range mourning doves may breed at any time of year (Otis et al 2008), but in Ontario breeding normally occurs during April, May and June (Peck and James 1983). The earliest egg date for mourning doves breeding in Ontario that I could locate is March 19 (Peck and James 1983). – Posted by Mark Andrew Conboy


  • Hanson, H.C. and Kossack, C.W. 1957. Methods and criteria for aging incubated eggs and nestlings of the mourning dove. Wilson Bulletin 69: 91-101.
  • Otis, D.L., Schulz, J.H., Miller, D., Mirarchi, R.E. and Baskett, T.S. 2008. Mourning dove (Zenaida macroura), In The birds of North America Online (Poole, A. editor). Cornell Lab of Ornithology.
  • Peck, G.K. and James, R.D. 1983. Breeding birds of Ontario: nidiology and distribution volume 1: nonpasserines. Royal Ontario Museum.
  • Weir, R.D. 2008. Birds of the Kingston region, 2nd edition. Kingston Field Naturalists.

Coping with cowbirds: Yellow Warblers stack nest.

Brown-headed Cowbirds (Molothrus ater) are brood parasites that lay their eggs in the nests of many species of birds. Most birds that are parasitized by cowbirds accept the egg(s) and raise the chick as their own. However, some species of birds, like American Robins, recognize cowbird eggs and readily eject them from their nest. To do this, birds typically use their beak to toss the foreign egg from their nest. Birds whose beaks are too small to grasp the cowbird egg must use a different strategy to get rid of it.

Yellow Warblers (Dendroica petechia) are one such species. As an alternative to ejecting eggs, females often build a second nest directly on top of their existing nest, burying the cowbird egg along with some of their own eggs. In these pictures, you can see a Yellow Warbler nest that was parasitized by a cowbird and the subsequent nest constructed in response to the cowbird egg. This nest was found in 2008 in a Hawthorn bush surrounded by scrubby open fields and scattered farms, which provide excellent habitat for cowbirds. In an extreme case, a single Yellow Warbler built five consecutive nests, one on top of the other, all in response cowbird parasitism.

– Post by Vanya Rohwer –