Re: Why Aren't My Martins Back (Yet)?!
From: James R. Hill, III
Date: 3/12/02
Time: 12:23:26 PM
Comments
Basically, every year folks get all worried because their birds are either "late" or their numbers are down on any particular date, compared to previous years. However, our scout-arrival database shows that scout dates for most locations have varied by as much as 30+ days over the past 100 years. So, when you look at the 100-year record, there's no cause for concern. Be patient. Variation in the time of arrival is related to weather, age of birds, food supplies, population levels, molt phase, physical condition of the migrant, conditions on the wintering grounds, moon phase (possibly), etc. Total population numbers also go up and down each year. Weather, food supplies, parasites, predators, competition, poisons in the environment, diseases, human persecution, and collisions with manmade objects, all take their toll. However, at this particular date we don't know if migration is 10% complete or 50% complete at any given southern latitude. Therefore, it's way premature to be making judgments on population levels, I feel. The subadults aren't even back yet. If it turns out that population levels are down this year, it would most likely be because of poor over-winter survival in Brazil, likely weather related. However, we have no widespread reports of martin numbers being down in the US this year. We always get more reports of numbers being up, than we do of numbers being down. Bottom line, wait till migration is clearly 100% complete (usually June 1st) to make final population judgments. The Breeding Bird Survey http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa00.pl?06110 shows martin numbers on the increase, continent-wide. However, there are regional exceptions (Click on the state links). Numbers in Florida are on the decline. Why? Could it be drought (weather), increase in predator numbers, loss of habitat, loss of well-managed breeding sites, or pesticides reducing insect prey? Any or all of these could be responsible. All the more reason for folks in these areas to redouble their efforts to help martins, locally. Hope this will reduce some of the anxiety all landlords experience this time of year. It's too early to be worried about what the final numbers will be this year.
James R. Hill, III
Executive Director/Founder
Purple Martin Conservation Association
