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Tag Archive | "watch and law"

Cowbirds stand, watch, and lay


Ranger Steve’s Nature Niche | By Ranger Steve Mueller

Ranger Steve

By chance I discovered a Horned Lark nest in a prairie. The location was not distinctive but I memorized vegetative stems nearby so I could watch from a distance. I obscured myself as best I could and waited.

I first found the nest when I almost stepped on it and the lark flew off. I was able to return to the nest area for several days to determine if the young would survive to fledge. The second day a couple inches of snow covered the area but the young were protected and kept warm by the mother. 

Many hazards such as cold, wind, precipitation, insect parasites, predators, and vertebrate parasites make nest survival difficult. Brown-headed Cowbirds are non-native vertebrate parasites in our region that moved in after forest clearing. Perhaps they thrived in southwestern Michigan where some open prairies existed. 

Male Brown-headed Cowbirds have beautiful shiny feathers covering the body that provides iridescence. In contrast the head is a rich chestnut brown and the bill is fairly thick that serves well for crushing prairie seeds and insects. The females are dull gray with a behavior unique from most birds.

They stand, watch, and lay. The cowbirds followed bison in the prairie and fed heavily on insects stirred by the large mammals. Nomadic bison moved great distances. This behavior presented a problem for birds staying in one place while the animals stirring up food kept moving. 

Cowbirds developed an adaptation to stay with moving mammals but it prevented them from incubating eggs in a stationary nest. Moving a nest is not an option. The nomadic adaptation cowbirds developed allowed them to watch other birds to determine their nests locations. 

If you tried to find a bird nest during breeding season, you have discovered your success rate is low compared to the number of nests produced. If nests were easily found there would be few birds in existence. 

When I watched for the lark to feed her young, I usually did not see her return. I observed her leaving. She would land 25 feet or more away and sneak through the dead mat of winter vegetative stems to the nest, feed her young and fly away. She was adept at not revealing the nest location on approach. 

Cowbirds staying with roaming mammals found success by laying an egg in other birds’ nests and abandoning them. The new foster parent most often will incubate and rear the new sibling. Interestingly, baby cowbirds sometimes push nest young from their nest or because cowbirds are larger other young do not get adequate food and starve. This can be disastrous for the species parasitized. 

When following a mammal herd, the cowbird stands watching birds approach their nests. After a bird leaves its nest, the cowbird quickly flies in, lays an egg and departs. Like other birds, it takes about 24 hours for the bird to produce an egg. To survive the new egg must be fertilized before the shell develops. 

During the breeding the season, a cowbird can produce more than 30 eggs that might survive to fledge. The species being parasitized will usually have a clutch of 5 or fewer eggs. Several species will have two clutches a year so they might produce 8 to 10 young. It is unusual for more than one or two young to survive to the next breeding season. If more successful, bird populations increase but when less successful they decline. 

Cowbirds moved into altered Michigan nature niche habitats after forest clearing and nesting success for native birds declined for many species. This trend continues and is a reason many people do not appreciate cowbirds. Many prairie species have adaptations that help them survive nest parasitism that forest birds have not developed. Forest bird survival often depends on large contiguous forest stands because cowbirds do not enter to the deep interior. They thrive near forest edges and in open areas.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net – Ody Brook Nature Sanctuary, 13010 Northland Dr. Cedar Springs, MI 49319 or call 616-696-1753.


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