Carrol Henderson

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Oriole Migration Update: May 21, 1998

Today's Report Includes:

Final Oriole Migration Map & Data

Winter and Breeding Range
Map by
Macalester College

Final Migration Map
(Compare with Spring, 1997)

Spring Songbird Migration Summary
A Most Unusual Year

This spring has been one of the warmest ever recorded, how has this affected migratory birds?

Early migrants, such as robins, returned much earlier than usual. However, neotropical migrants were mostly on schedule--or even a little behind. Since birds in the tropics have absolutely no way of knowing in advance what the weather is going to be like when they arrive in North America, they don't depend on weather cues. Instead, cues such as daylength and where the stars are in the sky tell them it's time to leave their wintering grounds.

Fires & Drought on Songbird Wintering Grounds
This season has been unusual in other ways, too. Mexico and Central American countries have suffered serious drought conditions. Mexico's Environment Secretary, Julia Carabias, reported that this is the worst drought in 70 years and that there are presently 10,000 fires burning in that country. For birds preparing to migrate, these conditions have stressed their bodies right when they needed to put on fat to fuel their journey north. Enormous fires have been burning out of control in Central America and Brazil--so enormous that smoke from them is now reaching Florida and Texas. These fires have been destroying millions of acres of critical tropical habitat, and probably outright killing millions of birds as well.

For more information about fires in Mexico, Central and South America see:

Migrants Silently Zip By
Meanwhile, in response to the mild temperatures, trees in the US and Canada leafed out much earlier than normal. Birders who associate the arrival of warblers with leaf-out became concerned as hardly any warblers, tanagers, orioles, or other migrants could be found. Many people have been talking about an eerie, silent spring, fearful that bird numbers are declining below a safe level.

Fortunately, many of these fears are unfounded. Canadian birders are now finding plenty of neotropical migrants already on their territories in the north, and have been writing reassuring notes on the bird chat lines on the internet.

Clear nights in many parts of the continent during the peak of migration must have allowed birds to fly greater distances more easily, and enormous numbers of them simply zipped by unnoticed.

The early leaves made it hard for birders to see migrants this spring, perhaps giving the impression they weren't there. In addition, migrating songbirds don't like to spend a lot of time in trees with advanced leaf-growth. Here's why: Moth and butterfly eggs hatch out right as tiny new leaves are first opening. Plant tissues have cell walls, but newly-emerging leaves are soft and tender because they haven't developed these protective cell walls yet, making them much easier for tiny baby caterpillars to digest. Warblers and other little songbirds eat huge quantities of these tiny caterpillars. This year small migrants found other sources of insects, and the early leaf-out may even have made them rush north faster than normal to find these tiny caterpillars.

Breeding Back into Balance?
Although huge numbers of birds survived the drought, fires, and hazards of the journey, many did not. So, when the lucky survivors arrive on their breeding grounds, they won't have as much competition as normal. They will have more insects to feed their babies, so each pair will raise more babies on average than usual. This will help them bring back their numbers fairly quickly. But we can help them recover faster. Here are some projects you might try to help the neotropical migrants in your area.

Unpave the Way for Wildlife

Big City Buildings--Lights Out Please!

Starlight or City Lights?
Navigating primarily by the the stars, night-migrating birds become disoriented by city lights. But the city of Toronto's "Fatal Lights Awareness Program" (FLAP) is helping migratory songbirds by turning down the lights.

Link to FLAP Story

Journey North
Year End Evaluation
Please share your thoughts

This is the FINAL Oriole Migration Update.