This fall has been an interesting season for nuthatches here at Kiptopeke! We've had Red-breasted, White-breasted, and Brown-headed Nuthatches at the feeders this season. Many visitors have asked why they see Red-breasted Nuthatches some years and not others, and others have commented on the previous relative lack of Brown-headed and White-breasted Nuthatches on this part of the Eastern Shore. So what's going on here, you might ask? While all are varieties of nuthatches, the reasons for the appearance of these three species are different.
Red-breasted Nuthatches are an irruptive species - the same as the Blue Jays we've been witnessing in such huge numbers recently. As we noted previously when discussing the jays, irruptive species are birds that are highly dependent on eating certain cone or nut crops in the northern parts of their range during the winter. So, when these crops do poorly, nuthatches and others continue down into other areas where food may be more abundant. Irruptive species have famously erratic migration patterns. Unlike "regular" migrators, they don't have a set route or destination, but simply fly until they find food.
Irruption is a complex phenomenon with many factors, and its reasonings change from species to species. With Red-breasted Nuthatches and others, an interesting phenomenon known as masting has an effect on their particular brand of irruptive migration.
Masting trees - which include many conifer and nut trees - are those that produce cyclic bumper crops followed by periods of very low production (on a roughly every-other-year cycle). While there are likely many reasons for masting - nutritional supply, rainfall, etc. all factoring in - one particular reason the trees may have developed this production technique is as a species-level survival mechanism. Since seeds can't exactly get up and run away from seed-predators, trees developed another way to ensure all of their progeny wouldn't consistently be eaten up by a stable predator population. So, they developed a way to destabilize the predator population: instead of producing a consistent year-to-year crop, some years they flood the market - meaning there are way too many seeds for the seed-predator population to eat all of - while other years they dry it up, meaning there are either predator die-offs or - as is the case with the irruptive bird species - the seed-predators simply go elsewhere, leaving the little seedlings a chance to establish themselves. Keeping the seed-predator population a bit off-kilter is one key to their seedlings' survival - and is also what allows us to see Red-breasted Nuthatches down here!
The situation with Brown-headed Nuthatches is different. They are not an irruptive migrator like their Red-breasted cousin, but instead are year-round residents throughout Virginia. However, they have not been typical at Kiptopeke, with some records from the National Wildlife Refuge just south of us but not many within the park. According to Brian Taber, CVWO's President, he has only seen these nuthatches around the hawkwatch site perhaps 2 out of the 40 years he's been observing this area! His theory is that because there are more Loblolly Pines growing up between the Refuge and Kiptopeke, these little guys are being provided a habitat bridge and have decided to take up residence at Kiptopeke.
As for the White-breasted Nuthatches, we have not seen any of these little friends since the beginning of the season. But the fact that we saw any was apparently quite remarkable for this immediate area. While they are common throughout the rest of the state, they are very rare on the southern tip of the Eastern Shore, with Brian again saying he's only seen 2 or 3 at Kiptopeke over the years. These birds sometimes have "mini irruptions" south, and Brian has postulated that this could account for their appearance at the hawkwatch this year.
I hope you've enjoyed this view into our nuthatch movements at Kiptopeke Hawkwatch this season! We're still getting plenty of Brown-headed and Red-breasted Nuthatches at the feeders, so please come on by if you'd like to see them for yourself!
Happy birding!
Bridgett
