In the last post, I discussed the hopeful prediction that this winter will bring irruptive finches into Maine based on seed production to our north. So far, those prognosticators are looking good. Pine Siskins are common across the state now. Evening Grosbeaks are putting on a better show than they have in many years. Pine Grosbeaks have been reported from scattered locations. I know of several Common Redpoll reports, including some from York County. Bring ‘em on!
I’ll devote today’s column to some recent research on Tufted Titmice published in the Wilson Journal of Ornithology this year. This species has been expanding northward in the state, starting in the 1970s. Titmice are pretty well established in the southern half of the state now. Double-digit counts of the species are common on Christmas Bird Counts as far north as Skowhegan, Bangor and Orono.
The expansion into Maine is a continuation of the northward expansion into southern New England that started around 1940. Prof. Sylvia Halkin and John Correia at Central Connecticut State University recently published a paper in which they explored the interactions between Black-capped Chickadees and Tufted Titmice. Both are members of the family Paridae and have similar diets and foraging styles. One might rightly expect the two species would compete. Has the arrival of titmice altered the behavior of the chickadees?
The researchers studied the two species in three forest tracts and at one feeding station. In the forested sites, they recorded the portions of trees where individuals of each species foraged. Chickadees spent more time in the outer, upper portion of the canopy than the titmice. Other portions of trees were equally attractive to the titmice.
Chickadees spent more time foraging in bushes than the titmice. On the other hand, titmice spent much of their time foraging on the ground; chickadees rarely spent time there.
A titmouse is twice as heavy as a chickadee. Perhaps, titmioce have a harder time foraging on the thin branches of the outer upper canopy. The larger size of the titmice may make it easier for them to feed on the bigger branches of the canopy. At any rate, the two species seem to be partitioning food resources by feeding in different sub-habitats.
At the feeding station, the titmice were clearly dominant. Both species visited the feeder, took a single seed and then left. When a bird was at the feeder, an approaching bird had the choice of waiting or challenging the bird at the feeder. Chickadees waited for both other chickadees and titmice more often than they challenged them. Titmice usually waited for other titmice but tried to displace chickadees. The titmice were always successful in challenging chickadees and usually won challenges against other titmice.
The birds had the choice of safflower seeds, black oil sunflower seeds with the shell intact and black oil sunflower seeds with the shell removed. All three types of food were taken but titmice preferred the safflower seeds and the chickadees preferred the shelled sunflower seeds.
The study results indicate that differences in foraging sites and food preference may mitigate competition between the two species. The authors point out that competition might be more severe in more northerly areas like Maine where our colder winters require greater food consumption.
Wieteke Holthuijzen reports on eavesdropping by Veeries on Tufted Titmice in New York. Veeries are active participants in the dusk chorus. Their songs and calls can attract predators in the twilight.
Tufted Titmouse give a distinct alarm call (the seet call). Holthuijzen tested the notion that Veeries might use titmice alarm calls to modify their vocalization rate at dusk. By playing recordings of the titmouse alarm, she found that Veeries did not change their song output but did increase their own call notes, acting as secondary informants to other Veeries about danger in the vicinity.