At first glance, it seems unlikely that there is a connection between the abundance of white-tailed deer and the long-term documented decline of many songbirds. But let’s take a closer look.
Amazingly enough, deer used to be scarce, with low populations nationwide prior to 1900. Their populations rebounded once restrictions on hunting were put in place and now they are incredibly abundant, making this perhaps one of the most successful wildlife conservation efforts ever.
Perhaps now the deer are even too abundant.
The existence of a browse line like the one shown in the accompanying photograph from Waskosim’s Rock Reservation is due to deer browsing. Such browse lines are widespread across the Island and the rest of North America. Browse lines on the low-nutrition junipers suggest that the deer have already eaten all of the more nutritious plants within their reach. So what happens when even the juniper branches are out of their reach?
That deer may starve to death when they reach high population levels has been well documented. The best known example of starvation occurred in the 1920s on the Kaibab Plateau north of the Grand Canyon. The deer population there exploded after the first ever restrictions on hunting them (bag limits and seasons) were put in place, and after wolves were intentionally eradicated. Browse lines appeared in those woodlands followed by large numbers of deer starving to death. This pattern has been repeated in many locations across North America.
Whether browse lines are present or not, there are numerous thoroughly documented examples of superabundant deer causing plants to become very rare. One of the nearest examples comes from the Appalachian Mountains, where several species of lady’s slippers have disappeared and are now only found on cliffs, the tops of large boulders and in areas that have been fenced to keep deer out. Perhaps deer browsing can explain why our pink lady’s slippers are now so much less common than they were 40 years ago.
But wait, this is a bird column! Haida Gwai is an archipelago of islands off the west coast of British Columbia. The larger islands have deer at densities approaching 50 per square mile (the estimated density of deer on the Vineyard), and these islands are “moss-covered parks” with virtually no understory vegetation and much reduced populations of songbirds, insects and pollinators. Deer have not reached the smaller and more remote islands, where the vegetation is a “verdant jungle,” and the native species have not declined.
The deer have consumed important parts of the songbird habitats, insects and pollinators. Any species wanting to use low shrubbery and other ground-level vegetation are out of luck because deer have eaten those components. Numerous other studies have documented similar patterns.
So it seems likely that superabundant deer can be added to the long list of potential causes of declining bird populations. These declines have been noticed by most birders, and are well documented for 39 per cent of the species that breed in Massachusetts. Some species have population declines of as much as 75 per cent since 1966.
Other more well-known causes contributing to these declines include direct mortality due to depredations by feral cats, collisions with man-made things (windows, power lines, and cars), habitat loss, invasive species and, last but not least, nest predation.
It is late March and more and more of the bird world is preparing for the coming breeding season. Listen in the early morning and hear the chorus of bird song getting louder every week as more individuals start singing. This is happening because days are getting longer, even though we seem to be stuck in a pattern of rain/snow storms.
Bob Woodruff reports interesting behavior in three long-tailed ducks that were close to the shoreline at State Beach. It seems that two males were competing for the attention of a female; they were chasing and attacking each other both underwater and in short flights as the female swam along the shoreline. Such courtship and aggressive behavior is expected at this time of the year as most ducks are pairing up now in anticipation of their upcoming arctic breeding season.
Sarah Carr and her children were excited to hear and then see two screech owls on March 21 as they left a cavity in her Lambert’s Cove yard. They photographed one of the owls sitting in that cavity the next day. Since it is spring and they generally start nesting in April, they may be searching for an appropriate nesting cavity.
And although it seems early, Joe Jims found and photographed a broken eggshell about the size of a quarter in his yard on March 24. Luanne Johnson guesses that it is a mourning dove egg, as it is the right color and size, and these doves will start nesting early.
We know barn owls nest early, too. Suzan Bellincampi reports that as of March 21 there are five eggs in the barn owl nest in the barn at Felix Neck.
Bird sightings unrelated to nesting activity are also of interest.
Perhaps the most exciting sighting of the week is Ken Magnuson’s finding of a second-year bald eagle over Edgartown Great Pond on March 22. Eagles live on the Connecticut River and at Quabbin Reservoir and, as the eagle flies, we are just around the corner. How come we do not see eagles more frequently?
Also exciting is the first report of a tree swallow, observed by Patrick Best, Margaret Curtin and Nancy Weaver as it flew over the fresh-water, presumably feeding on some early-hatching insects, at the Head of the Lagoon on March 23. A pair of osprey were sitting atop the chimney of the Pumping Station building.
Frank and Vasha Brunelle observed 135 bufflehead on Lagoon Pond near the Martha’s Vineyard shipyard on March 27. This is the largest flock they have observed in the past several years.
Tim Johnson found some harlequin ducks at Squibnocket on March 24, and they were still there the next day when Jeff Bernier found them and noted that they remained close to shore even though there were numerous people walking along the beach. Usually these ducks are more skittish and retreat further offshore when people arrive. Purple sandpipers were also present on the large off-shore boulders.
Lanny McDowell photographed a common loon that is beginning to change into its breeding plumage. Has anyone heard loons yodeling yet? We will hear bits and pieces of their haunting song before they head to their breeding grounds. He also reports some exciting bird news from Cape Cod. An adult male king eider was photographed at the Sandwich end of the Cape Cod Canal on March 21. Wouldn’t it be nice if he ventured over here?
Nelson Smith observed a female northern harrier flying low over the marsh on the Sengekontacket Pond side of Bend-in-the-Road Beach in Edagrtown on March 22.
And finally, I observed a first winter black-legged kittiwake flying in the middle of Vineyard Sound on March 20, as I was travelling to Woods Hole. Its undulating flight pattern, repeatedly swooping from high up to just above the water, is what caught my eye even when it was quite a way from the ferry. Fortunately, it flew closer so I could identify it.
There are lots of birds around, so please get out looking for them, and be sure to report your bird sightings to the Martha’s Vineyard bird hotline at 508-645-2913 or email firstname.lastname@example.org.
Robert Culbert leads guided birding tours and is an ecological consultant living in Vineyard Haven.