Archive for December, 2014

The Tricolored Blackbird (Agelaius tricolor) is a bird both fascinating and beautiful. One of its unique characters is that it is found nowhere in the world except California and a small portion of Baja California. This alone makes it pretty special to anyone from California! The glossy, black male Tricolors can be identified by the thin slice of white just below the red on their shoulders. This distinguishes them from the similarly plumaged Red-winged Blackbird because the later has a slice of yellow below the red, or sometimes just red.

Tricolored Blackbirds form huge flocks of many tens of thousands of individuals. These are larger than any other bird species in North America today. They can get so big and so dense, that they blacken the sky. However, while these flocks are big, they only rank as the second largest flocks of North American birds ever. The Passenger Pigeon was another sky darkening bird which once formed even larger flocks. However, the Passenger Pigeon when extinct in 1914. There are actually several parallels to be drawn between the Passenger Pigeon and the Tricolored Blackbird. Some of these parallels may give rise to concerns about the long term survival of the Tricolored, but these parallels may also give us a chance to save the blackbird where we were unable to save the pigeon.

One of these parallels between the Tricolored Blackbird and the Passenger Pigeon is that they are both highly social and nest in huge colonies. Tricolored Blackbird nesting colonies sometimes get as large as 50,000 birds! This colonial breeding lifestyle is one the factors that is thought to have been the downfall of the Passenger Pigeon. Social cues can play very important roles in controlling when birds come into breeding condition. It may have been that Passenger Pigeons could only breed if they were surrounded by other Passenger Pigeons that were also breeding. As populations of Passenger Pigeon were decimated by market hunting, the colonies may have fallen below some critical threshold where even though there were many individuals left alive, there were not enough to trigger each other into breeding. This would have resulted in practically no young birds being hatched and the total collapse of what was the most numerous bird species in the western hemisphere. The fact that Tricolored Blackbirds also only breed in very large colonies suggests that they may also need the social cues of having many breeding neighbors in order to reproduce. This makes the Tricolored Blackbird at risk of the same fate as the Passenger Pigeon.

Another parallel between the two species, that goes hand in hand with large numbers required to breed, is that the breeding colonies occupy a fairly small area. All those birds pile in to relatively small patches of suitable freshwater marsh habitat in the central valley. These patches of habitat are more and more often agricultural lands such as rice fields and the feed fields for dairy cows. This high density in a small area is one of the reasons that Passenger Pigeons were so profitable to hunt. Market hunters could go to a colony and bring down tremendous numbers of birds in a very short time. While not hunted, small and concentrated breeding colonies is a problem for the Tricolored Blackbird because nestlings are usually not ready to fly when harvest time comes around. As many as 20,000 nests were destroyed when a single 10 acre rice field was harvested.

These characteristics have contributed to a dramatic decline in Tricolored Blackbird numbers over the last two decades including a particularly sharp drop in the last six years from an estimated population of 395,000 in 2008 to a population of 145,000 in the 2014 breeding season. This severe drop has led the U.S. Fish & Wildlife Service to grant this species temporary status as Endangered under the Endangered Species Act. This temporary listing, the first of its kind, means that the Tricolored Blackbird will be treated as a fully listed species but only for six months with the potential for a six month extension after that. This is to help protect the breeding colonies into and through the 2015 breeding season. If numbers respond well in 2015, it seems likely that this will provide impetus to list the species permanently.

Only time will tell if we have been able to learn the lessons taught by the Passenger Pigeon at so high a cost. The Tricolored Blackbirds surely hope that we have.

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