![\"\"](\"https:\/\/featheredphotography.com\/blog\/wp-content\/uploads\/2019\/05\/cowbird-and-savannah-sparrow-8989-ron-dudley.jpg\" "\\"cowbird-and-savannah-sparrow-8989-ron-dudley\\"")
<\/p>\nThe difference in size isn’t always this extreme but it can be even more dramatic than some of the examples I’ve included here.<\/p>\n
Brown-headed Cowbirds are North America’s best known brood parasites, meaning they lay their eggs in the nests of other species which essentially forces the host species to raise their young for them. My readers and I have discussed the process and results of brood parasitism in previous posts but today’s edition of Feathered Photography will focus on the visual size difference between the young cowbirds and their “adoptive parent” species.<\/p>\n
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The adult Savannah Sparrow on the left had just stuffed a large insect into the bill of the fledgling cowbird on the right. The cowbird is in the process of swallowing it as the sparrow waits to feed it another smaller insect that isn’t easily seen in its bill. I have other photos that show the actual food transfer but with this side view of the cowbird we get a better feel for the difference in size between parasite and host.<\/p>\n
It’s one thing to read that the average weight of the two species as adults is 20 grams vs 44 grams but to actually see that difference in size really drives it home. Imagine the number of insects the relatively small “parent” sparrows would have to deliver in order to raise a youngster of this size. It exhausts me just to think about it.<\/p>\n
But in the case of some other host species the task would be even more daunting.<\/p>\n
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![\"\"](\"https:\/\/featheredphotography.com\/blog\/wp-content\/uploads\/2019\/05\/cowbird-and-orange-crowned-warbler-6222-ron-dudley.jpg\" "\\"cowbird-and-orange-crowned-warbler-6222-ron-dudley\\"")
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This Orange-crowned Warbler host is delivering an insect to the fledgling cowbird it’s raising. Adult Orange-crowned Warblers average only 9 grams in weight so the cowbird it is raising will be nearly 5 times heavier (larger) as an adult than its adoptive parent.<\/p>\n
The size difference between parasite and host isn’t always this dramatic. Over 220 host species have been reported as parasitized by cowbirds, ranging in size up to 150 gram meadowlarks.<\/p>\n
I know from previous blog posts on this subject that many of my readers dislike cowbirds because of their parasitic habits but personally I lean in another direction. Their parasitic ways evolved naturally and then their range expanded because of the effects of humans on the landscape.\u00a0I have no problem with natural behaviors and we can only blame ourselves for causing cowbirds to expand their range and find many new host species they didn’t naturally coevolve with.<\/p>\n
Most of any “blame” rests squarely on our shoulders.<\/p>\n
Ron<\/p>\n
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<\/p>\n","protected":false},"excerpt":{"rendered":"
The difference in size isn’t always this extreme but it can be even more dramatic than some of the examples I’ve included here.<\/p>\n