Fall Trees & Birds

Nature Watch
October 2008

By Susan Benson,
CNHM Director of Education

Are the pines dying? When did the hummers last leave the feeders? These are some of the questions that have filtered into the Museum in the last two weeks. Read on for more answers.

Using the term “evergreen” to describe our conifers is not quite right. It is normal for some needles on our area’s conifers to fall off the trees. This occurrence, called fall needle drop, is a loss of the oldest and innermost needles shed from our pines, spruce and fir. Some fear that this is a disease, insect, or other warning sign, but is natural this time of year. Pines shed their oldest needles in the fall, and white pines usually shed their needles every two years. Sometimes the needle drop occurs in a short period of time, rapidly browning and falling, and other years, it’s almost unnoticeable because the discoloration happens over a longer time period. Environmental stress conditions can also affect this event, as root stress from extended dry periods, excess soil moisture, or poorly drained soils can impact this phenomenon, creating a greater needle loss. By the end of the needle drop, the trees may look bare, having lost approximately a third of their needles, and if the current season’s needle growth was a good one, there can be a greater fall needle drop. The needles on the tips of the branches are the newest growth, and if they were brown, this would be a larger concern and indication that something might be wrong with a particular tree.

What is happening in the bird world? Yellow-rumped warblers and sparrows are still migrating through. Migrating raptors and geese are still observable as is the occasional thrush in the forest. The ruby-throated hummingbirds appear to be gone. As requested in a previous article, last day reports came into the Museum from several people: September 16, September, 13, September 13, September 15 - all observed in the Cable area. Another report from Cable shared the past three year’s data: 2006, September 9; 2007, September 8; 2008, September 13. Thanks to those who shared this information! Ruby-throats do not do well in temperatures below the mid-20s (F), so this, mixed with the photo-period (shortening day length,) sends them south. A larger contributing factor driving migration is when there is the greatest food abundance. Banding studies have shown that those we saw in mid-September were not necessarily the same individuals we saw throughout the summer. Stumpy and the others we may have named at our feeders (this name comes from one of the Cable bird reports) might already be gone. The number of birds migrating south could be double that of the spring migration with the addition of immature birds. The immature have no memory of past migrations, and so follow an urge to gain weight and fly; once their flight is established the first time, it is possible that this becomes the route that bird retraces throughout its life. Some recommendations for those of us who have hummingbird feeders are to keep them out two weeks past the last day sighted, just in case there is a later migrant looking for food. At the same time, it is suggested to not keep your feeders out in conditions where they might freeze.

Earlier in the week it was raining pine needles. Today the sun shines. Our glorious fall weather and events continue. Get outdoors and enjoy it more, and please email any unusual observations to info@cablemuseum.org.

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 13470 County Highway M or on the web at http://www.cablemuseum.org/ to learn more about exhibits and programs.