Common Merganser nest building in Jackson County
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Charles Hundertmark
May 29, 2018, 12:01:59 PM5/29/18
to Cobirds
On the final day of a Denver Field Ornithologists field trip to North Park, the six remaining birders on the trip observed some interesting merganser behavior. We were at the bridge over the North Platte west of Cowdrey on JCR 6W. This may be the best place in the state to easily observe a Bank Swallow nest colony.
We were watching the swallows entering and leaving nest cavities in the large dirt bank, apparently in the nest building stage, and trying to spot the occasional Northern Rough-winged Swallow among the Bank Swallows. We were also listening the to Willow Flycatcher intermittently singing in the distance.
We finally turned our attention to Jean McClenathen’s observation that she had seen a large gray bird with reddish head disappear into the bank north from the colony. With many eyes trained on the general area described, we finally saw what turned out to be a female Common Merganser fly to the tall bank along the river. The bird would repeatedly fly up to the same spot on the bank, possibly a crevice, to work for a short while and fly off, returning again minutes later. She appeared to be excavating dirt from a crevice or cavity.
After a few minutes, we saw a second female fly up to the bank a short distance from where the first bird was working. The second merganser was clinging to the bank below a large cavity and appeared to be working on it.
Common Mergansers are cavity nesters, most often known to nest in tree cavities. However, they are sometimes known to nest on ledges or in dirt banks. In the second Colorado BB Atlas, Mitchel and Versaw observed, “Breeding in cliffs probably happens more frequently than records suggest.”
It appears that these two female mergansers were preparing nest cavities in the dirt bank.
Chuck Hundertmark
Lafayette, CO
We were watching the swallows entering and leaving nest cavities in the large dirt bank, apparently in the nest building stage, and trying to spot the occasional Northern Rough-winged Swallow among the Bank Swallows. We were also listening the to Willow Flycatcher intermittently singing in the distance.
We finally turned our attention to Jean McClenathen’s observation that she had seen a large gray bird with reddish head disappear into the bank north from the colony. With many eyes trained on the general area described, we finally saw what turned out to be a female Common Merganser fly to the tall bank along the river. The bird would repeatedly fly up to the same spot on the bank, possibly a crevice, to work for a short while and fly off, returning again minutes later. She appeared to be excavating dirt from a crevice or cavity.
After a few minutes, we saw a second female fly up to the bank a short distance from where the first bird was working. The second merganser was clinging to the bank below a large cavity and appeared to be working on it.
Common Mergansers are cavity nesters, most often known to nest in tree cavities. However, they are sometimes known to nest on ledges or in dirt banks. In the second Colorado BB Atlas, Mitchel and Versaw observed, “Breeding in cliffs probably happens more frequently than records suggest.”
It appears that these two female mergansers were preparing nest cavities in the dirt bank.
Chuck Hundertmark
Lafayette, CO
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