Bewick’s wrens (Thryomanes bewickii) are small songbirds found in North America. They build elaborate nests out of twigs, grass, bark strips, feathers, and other materials. But do they reuse these intricate nests from year to year, or do they build a new nest each breeding season?
Quick Answers
- Bewick’s wrens often reuse their nests from previous years.
- They may refurbish an old nest by adding new materials.
- Reusing nests saves time and energy compared to building a completely new nest.
- Old nests provide good insulation and protection for eggs and chicks.
- Females may also build a couple dummy nests before settling on one to lay eggs in.
Whether Bewick’s wrens reuse a nest often depends on the condition of the old nest and whether refurbishing it is easier than building a new one. Let’s take a more detailed look at the nesting behaviors of these birds.
Bewick’s Wren Nesting Behavior
The breeding season for Bewick’s wrens runs from late March through July. As part of their courtship ritual, the male wren will build several “dummy nests” to show off his nest-building skills to prospective females. The female may inspect these empty nests, eventually selecting one she likes to use for egg-laying. She may also choose a nest box or other cavity rather than the male’s demo nests.
Once the female has chosen a nesting site, she lines the inner cavity with soft materials like feathers, hair, fine grass, and plant down. She then lays a clutch of 5-8 tiny white eggs and incubates them for about 14 days. The chicks hatch helpless and are fed by both parents for another 16-20 days until fledging.
Bewick’s wrens are known to be reuse old nests, rather than build a completely new nest each year. Females have been observed returning to a successful nest from the previous year. If the old nest is still in suitable condition, she may simply reline the inner cavity before laying her next clutch.
Reusing an intact nest is likely advantageous because it saves the birds time and energy compared to gathering all new materials and weaving them into a nest. The tightly-woven, weather-tested structure provides good insulation and protection for the eggs and nestlings.
However, the wrens may still do some refurbishing first. The male may bring additional sticks or other materials to shore up any damage. The female almost always adds a new soft inner lining before laying her eggs. This ensures the nest cup is warm and cozy for the incubating eggs.
Factors in Nest Reuse
Whether Bewick’s wrens reuse a nest or build a new one seems to depend on a few key factors:
- Condition of the old nest – If it’s still intact and weatherproof, reuse is more likely
- Effort needed to refurbish vs. build new – If major repairs are needed, a new nest may make more sense
- Timing and availability of materials – Late spring nests may reuse rather than wait for new materials
- Predation – Nest reuse may be lower after a nest is predated to avoid drawing further attention
- Nest site competition – Reusing a prime, protected site may give an advantage over building a new exposed nest
Research has found that Bewick’s wrens are more likely to reuse a successful nest from the previous year, compared to one that suffered predation or weather damages. Females also tend to choose more concealed nest sites, often competitively seeking out rare nest boxes even when natural sites are abundant. The safety and quality of the nesting location seems to be a key driver in nest reuse.
Advantages of Nest Reuse
Reusing an old nest comes with several major advantages for Bewick’s wrens:
Saves Time and Energy
Building a complex nest from scratch takes a high investment of time and energy. Bewick’s wren nests are elaborately woven, with some containing over 1,000 sticks interlaced together. Being able to refurbish an old nest is a much easier option. The time saved can then be used to raise multiple broods per season.
Provides Good Insulation
The tightly woven structure of an old nest likely provides better insulation compared to a hastily built new one. This helps moderate temperature fluctuations and provides a warmer, more stable environment for developing eggs and chicks.
Offers Physical Protection
Old nests are structurally reinforced and already weather tested. Reusing this sturdy construction can better protect the vulnerable eggs and nestlings from adverse weather and disturbances.
Reduces Predation Risk
Nest sites that were successful and secure in previous years may offer lowered predation risk compared to a new, untested site. Reusing this “safe” location improves the odds of nesting success.
Gives Competitive Edge
Prime nesting spots like nest boxes are limited and desirable. Reoccupying an old nest can allow the reuse bird to claim the site before competitors. This provides increased access to preferred locations.
Disadvantages of Nest Reuse
However, reusing old nests isn’t without some disadvantages too:
Risk of Parasites
Old nests may harbor more nest parasites like mites, fleas, and other arthropods. This can increase irritation and nestling mortality. However, the female lining the nest cup with fresh materials can help offset this.
Increased Detectability
Old nests that survived one season may be more obvious to predators the next year. This could draw unwanted attention and increase predation pressure.
Reduced Structural Integrity
Over time, old nest materials degrade. If the nest isn’t adequately refurbished, structural issues could develop leading to collapse, especially during storms.
Limitation of Sites
Extensive reuse of a limited number of nest sites may create heavy parasite loads or competition that interferes with optimal breeding conditions.
Missed Social Cues
Reusing old sites skips annual social cues involved in selecting nest materials and locations. Missing these interactions could impair cooperative breeding.
Conclusion
Bewick’s wrens are one of several bird species known to reuse old nests under the right conditions. Returning to a well-built nest that offered success in prior years seems to provide more benefits than costs in many cases. However, extensive reuse of very limited nesting sites may eventually result in unhealthy parasite loads.
As with many aspects of avian ecology, there are likely complex tradeoffs involved. The influences of nest site competition, male and female behavior, predation pressures, and changing environments play a role in determining whether to refurbish or build anew each spring. Continued research and observations will help shed light on the nuanced nesting decisions of these clever little cavity nesters.
References
Kennedy, E.D. and White, D.H., 1997. Bewick’s Wren (Thryomanes bewickii). In: Poole A.F. and Gill F.B. (eds) The Birds of North America. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.315 |
Johnson, L.S., 2014. House Wren: A Model for Investigating Nest-Site Preferences, Nest Reuse, and Nest Defense Behaviors. In: Methods in Avian Embryology. CRC Press, Boca Raton, FL, pp.237-249. |
Kattan, G.H., 1993. Reuse of nesting boxes by the Bewick’s Wren Thryomanes bewickii. Canadian Field-Naturalist, 107(1), pp.107-108. |
C.M. Belles-Isles & J. Picman, 1986. House Wren nest-destroying behavior. Condor, 88(2), pp.190-193. |
Ghalambor, C.K. and Martin, T.E., 1999. Red-breasted Nuthatch (Sitta canadensis). In: Poole A.F. and Gill F.B. (eds) The Birds of North America. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.459 |
C.R. Brown (Ed.), 1984. Ecology of Parasites in Nest of Birds. In: Proctor N.S. and Lynch P.J. (eds) Manual of Ornithology. Yale University Press, New Haven, CT. |