We all know that spring has sprung…but what was our cue? Maybe it was the 85 degree days in February or the orange blossoms or the scrub-jays nesting – but what cue did the jay’s use to know that it was time to breed?
Dr. Reed Bowman, Director of the Avian Ecology Program at Archbold Biological Station, explained that “We’ve studied the nesting of Florida Scrub-Jays for nearly 50 years and the start of the breeding season varies from year to year, sometimes by as much as 4 or 5 weeks. The dilemma for all birds is that they must decide when to begin breeding often a month or more before they begin raising nestlings – so how do they make sure that food availability is peaking at the same time as the very hungry and fast-growing nestlings are demanding it? The first cue for birds is day length, the hours of daylight relative to darkness. As spring nears, days get longer and that gets the birds hormones going. They might begin courtship, maybe search for a nest site, even begin building a nest, but they are still waiting for another, secondary cue. We know food is one cue because birds with access to supplemental food breed earlier than birds without.”
Dr. Bowman and teams of interns, students, and assistants studied scrub-jays in suburban habitat in the Placid Lakes subdivision. They found the suburban jays bred at the same time each year, but usually weeks before the birds at nearby Archbold. The suburban birds had a predictable and plentiful food supply, including peanuts and bird seed provided by local homeowners, thus when days got longer, suggesting it was time to breed, the birds already ‘knew’ that food was available. Of course, this posed a problem for suburban jays later in the year because jays can’t raise healthy nestlings on a diet of peanuts and bird seed, but that’s another story.
During the 1970s, jays at Archbold had access to cracked corn provided for them at the Station’s main campus. Sure enough they bred much earlier during that decade. Bowman stated “After supplemental food was removed in 1980, the jays bred almost 4 weeks later than the average for the previous decade. Without access to human-provided foods, jays have to depend on other cues. Certainly one is weather.” Bowman’s research team found that the start of the breeding season coincided with the El Nino – La Nina cycle – breeding was earlier during the warm and dry winters of a La Nina cycle, much like this year. Warm winters usually means earlier flowering and the emergence of insects on which the jays feed their young.
Since 1980, the jays at Archbold have begun breeding slightly earlier. It still varies from year to year, but the trend is earlier and earlier, suggesting that jays are perceiving the appropriate cues earlier. However, Bowman cautioned that “if insect abundance doesn’t also occur earlier, eventually the jays could start nesting too early and find themselves with nests full of gaping mouths and nothing to feed them.” Guess we will have to study these birds for another 50 years!