An Unusual Year at English Boom. Stan Kostka, September 2004
photo: English Boom at low tide; middle photo: Installing nestboxes at English
Boom; bottom photo: English Boom at dusk;
all photos by Stan Kostka
2004 was an unusual year for the Purple Martin colony on the north end of Camano Island. The site, known as English Boom, is an unimproved county park on Skagit Bay, where the English Lumber Company built log rafts destined for Seattle and Everett sawmills many years ago. Some of the wooden pilings driven into the intertidal area of the bay to secure the rafts remain, and in April of 2000, nestboxes were placed on those pilings. Individual boxes are spread out to form a loose cluster along some 600 feet of shoreline. Distances between cavities range from a couple feet to over 100 feet, not unlike what might be found in a natural setting, such as a stand of dead trees used by a variety of primary cavity nesters over several seasons. Five pairs of martins nested the first year, the northernmost known active breeding location in Washington state at that time. Nestboxes were added in 2001 and 2002, for a current total of 15 cavities.
Background : Martins in the maritime Northwest did not widely use nestboxes until after the late 1970s and early 80s, when efforts to rescue a perceived remnant population began. The arrival of European starlings into the region during the 1940s coincided with the beginning of a noted decline in martin numbers. At that time, virtually all martins nested in “wild” unmanaged sites; tree cavities, various holes in or ledges on buildings, or anywhere some kind of nestsite could be found, in other words, all the places starlings and house sparrows nest today . By the mid 1970s, few known pairs of martins remained, some on buildings, and some nesting in holes in old wooden marine pilings similar to those at English Boom. Clusters of single nestboxes were installed at known breeding locations, in an attempt to mitigate a perceived cavity shortage caused by increasing numbers of starlings. The nestboxes were successful, others were installed over the years, and martin populations increased. Compared to known numbers in the late 1970s, Western Washington today has a relatively large and growing martin population, the overwhelming majority of known pairs in nestboxes [and gourds] on interior marine waters.
During 2000 and 2001, starlings were actively controlled at the new English Boom martin colony, and the colony size more than doubled the second year, from five to 11 pairs.
2002 was a busy spring, and less starling control was done. More of my time was spent installing clusters of martin nestboxes elsewhere in nearby counties, traveling throughout the Puget Sound Basin observing other martin colonies, scoping birds for leg bands, and searching for unknown breeding sites. That year, a pair of starlings slipped by me at English Boom. However, martins used the starling nest later that same season, and the size of the colony increased by one pair, from 11 to 12.
2003 was an exceptionally good year for martins in the Northwest, with unseasonably warm dry weather spring and summer. Martins colonized several new nestbox sites to the north of English Boom, in Skagit and Whatcom counties, and on Whidbey Island. Suddenly my martin schedule was overwhelmed, with much more data to collect, and a greatly expanded banding circuit. Starlings nested at English Boom again in 2003, and again martins used the old starling nest. In the end, 11 pairs of martins nested. Some of the martins at the other new sites were also using old starling nests, simply lining them with green leaves. Three of five new martin colonies in 2003 had a pair or two of starlings already nesting in them when colonized by martins, and all five sites also had tree swallows in some of the boxes.
2004 was much the same as 2003 with excellent weather, and an increase in martins. Numbers of pairs went up dramatically at some of the new sites, with reports of martins at other new sites with which I was not involved, elsewhere in Washington and British Columbia. With the knowledge of so many martins at so many new sites, my concern for the individual birds at English Boom waned somewhat, and the time seemed right for some experimentation. Although the negative impact of starlings on martin populations is commonly accepted , and reported widely in the literature , it has never been, to the best of my knowledge, specifically documented in a western colony. Here was an opportunity for some data. No active starling control, and I expected pairs of martins would probably decrease from the previous year. By the end of the 2004 season, those 15 nestboxes saw 22 nesting attempts (nest with eggs) by starlings, tree swallows, and martins.
The results were most surprising:
Contents of all nestboxes were checked ten times, 24 April thru 13 July. (Partial checks were done on additional occasions, later in July and August, primarily to band martin young. )
The earliest two checks, 24 April and 9 May, found two starling nests with eggs, and two starling nests without eggs. Also found were four tree swallow nests lined with feathers, one with eggs. Four other boxes had partial nests, characteristics of which indicated tree swallows as well, but they had not advanced to the point of being lined with feathers. Tree swallows were observed perching at some of these boxes, and based on my observations at other sites, a pair of tree swallows will build multiple nests. I am told starlings do not build multiple nests. (?) No nest building by martins had been observed at these early dates, although two boxes contained what appeared to be the beginning of martin nests. Martins were first observed at the site April 8, and were roosting in several boxes. On May 26, a minimum of 23 martins were counted. 27 martins were perched at the site in the evening on June 11. (In perfect hindsight, those 27 martins [and others uncounted, or yet to arrive] represented perhaps 13 or more pairs. However, only 9 cavities remained unoccupied by starlings and tree swallows). The nearest [known] martin colonies are about 15 miles north and south of English Boom.
Five nest checks 26 May through 15 June uncovered a bizarre pattern of starling eggs being lost and replaced, starling young being lost, tree swallow eggs being lost and not replaced, and tree swallow young dying and disappearing. Although there are raccoons at English Boom, there were no indications they or any other climbing predator had gotten to the nests. Almost all pilings have climbing predator guards, and there was no sign of climbing attempts, ie muddy scratch marks on the sheet metal wraps. The nests were intact, only the eggs or young were gone. (One clutch of four martin eggs also disappeared , but much later in early August, the last clutch initiated on 21 July.)
On June 2 an ASY male martin was observed in the entrance of a box that previously had tree swallow eggs. He was singing, and a female martin was on the porch. Neither martin was paying much attention to the tree swallow that was harassing them. Upon nest inspection, no tree swallow eggs remained. At another box that held a starling nest with eggs, several martins were ganging up on a starling, eventually driving it away. The martins then began to apparently fight among themselves for the box. The starling eventually did return, but when I checked the box, only two of its five eggs remained.
June 11 was bad news for the tree swallows. One box had 4 dead young near the entrance, partially covered with new nesting material, and the nestcup now had green leaves. Two other boxes had martin nests built on top of the tree swallow nests. From a fourth box I removed one dead tree swallow young, and the remaining four nestlings appeared weak. (There had been some showers and cool days recently, but nothing as bad and prolonged as weather associated with tree swallow mortality in past years. ) Almost immediately upon raising that last box, an SY male martin perched on it, and was soon joined by an SY female. Both birds were banded, and were pretty much ignoring the tree swallow that was buzzing and scolding them. During the process of scoping the bands, I flushed the martins from that box four times, and each time they returned almost immediately. Shortly I read the bands and headed back to my truck. What happened next really surprised me. One of the martins entered the box, remained inside for quite some time, and came out with tiny bits of what appeared to be feathers stuck to its bill. I went back, lowered the box again, and sure enough one of the tree swallow young had been pecked, and was laying partially out of the nestcup from where I had observed it shortly before. Three days later on June 14, only two tree swallow young remained in that box, both dead near the entrance, partially covered with new nesting material.
By mid July, only two nesting attempts by starlings were successful, and both were likely replacement clutches. One of the starling nests only fledged one young from five eggs. Three eggs disappeared before they hatched, and one never hatched. SY martins later used that nest. None of the tree swallows fledged young. Martins used all four nests that originally had tree swallow eggs or young, even though some tree swallows remained near their lost nesting cavities for some time. Whether or not these tree swallows were the ones displaced I cannot say with certainty, but it seem reasonable to assume. In the end, 14 pairs of martins nested in 15 nestboxes, two more pairs than the previous year.
I’m not sure what to make of this event. Am not totally surprised that the martins displaced the tree swallows. Have seen this happen in the past, and it happened this year at another colony as well. But only one nest at a time, never multiple nests at one site in one season as happened this year at on Camano Island.
The disappearing starling eggs are the real mystery. Is it possible that a cavity seeking martin will remove starling eggs from a nest? Are some martins beginning to adapt to starling presence? What else could be going on that benefited the martins?
Perhaps two unusually warm and dry breeding seasons has been the factor, here, approaching the northern end of their western range. If so, then has the role of starlings in West Coast martin decline been somewhat overplayed, and was martin decline likely influenced moreso by adverse weather, in combination with starling arrival, which reduced the availability of cavity clusters for a colonial species, cluster types that would have already been scarce in a non-managed setting; loose cavity clusters, that allow early returning ASY martins to establish themselves at a colony site, in spite of the fact that some starlings and tree swallows are already nesting there. Such a weather scenario might play here, but doesn’t seem to explain the same decline that has occurred in California.
Or, are starlings experiencing a decline, either regionally or locally, for whatever reasons, at the same time martins are rebounding? During the decades when nestboxes were being installed for martins, much of the lowland agricultural areas that supported the initial post 1940s starling explosion in the region have been developed for non ag uses. Many dairy farms disappeared, and that trend continues today. Could interspecific dynamics at a breeding location be determined to some extent by numbers of each species? Perhaps a few pairs of martins could be displaced by many tree swallows and starlings, but this years events at English Boom indicate a few pairs of starlings and tree swallows are not likely to displace many pairs of highly colonial nest site seeking martins, especially when weather is good, martin numbers are up, and cavities are limited at a historically productive breeding location.
Will see just how out of the ordinary this has been next year, when again no active starling control will happen at English Boom. (Rectangular starling resistant entrances will remain on the nestboxes, a design starlings seem to defeat regularly, and the boxes will stay up and open all winter, as they have since installation. )
Stan Kostka, © September 2004.