Lincoln sparrow
by Laura Brandon, Boreal Educator
After completing a very cool and wet Spring Migration Monitoring season, the Lesser Slave Lake Bird Observatory has begun our MAPS (Monitoring Avian Productivity and Survivorship) program which is a continent-wide project coordinated by the Institute of Bird Populations that studies breeding bird populations in order to better conserve them and their habitats. By banding at these sites over the breeding season, we can estimate the amount of adult birds returning to their summer habitats to breed, as well as the number of young birds successfully leaving their nests. Unfortunately, the persistent rain and chilly temperatures are creating some challenging conditions for breeding songbirds this season and we suspect that some pairs have lost their nests.
By mid-June, we can expect to see many birds either sitting on eggs in their nest or busily feeding freshly- hatched chicks. Instead, our banders are observing very few fledglings in the field for this time of year. Mother birds can typically protect their eggs or hatchlings from short periods of rain, but it becomes more difficult in persistent wet and cold conditions. Insects are less active in cold weather, which makes it particularly difficult for birds who rely on insects caught in flight to find food. Instead, they must spend more time and energy foraging away from their nests. During long bouts of rain, a mother bird has a tough decision to make. Does she continue to incubate her eggs and risk running out of food for herself, or does she leave the nest to forage to maintain her own body heat and strength. Even leaving the nest for a few minutes in cold damp weather can be disastrous for eggs or hatchlings. Fortunately, we’re still fairly early in the breeding season, so many birds should be able to re-nest if their first nest failed.
Brood patch on a female Lincoln sparrow
We have been seeing signs that many species are already re-nesting, like increased singing in new locations, shifting territories and well-developed “brood patches”. After a mother bird has finished laying her eggs, she loses all the feathers on her breast and belly, blood flow increases to the area, and her skin becomes swollen with fluid. Birds have feathers for insulation to keep their body heat in, but these same feathers also keep heat away from eggs or hatchlings. This brood patch acts like a tiny hot water bottle and enables the mother bird to effectively transfer her body heat to her babies in the nest. Since females typically do the majority of the incubating, only the mama birds will develop brood patches in most species. However, in some species like woodpeckers, both the male and female take turns incubating, so they both develop brood patches!
Observing these breeding characteristics in the field is a reminder that birds are incredibly resilient. They fly thousands of kilometres to breed in the boreal forest and they will do everything in their power to produce young. While the wet weather may have ruined their first attempt, we’re optimistic that we will be seeing more baby birds in the forest very soon. Keep your fingers crossed for warmer days ahead!
