Status and Occurrence of Acorn Woodpecker (Melanerpes formicivorus) in British Columbia
by Rick Toochin
Read the full article, with photos and tables, here.
Introduction and Distribution
The Acorn Woodpecker (Melanerpes formicivorus) is a common woodpecker of montane woodlands from southern Washington State (localized along the Columbia River at the town of Lyle), northwestern Oregon, south throughout California, with 2 localized populations in the Baja Peninsula in Mexico, Arizona, New Mexico, West Texas, and western Mexico through the highlands of Central America to the northern Andes in Colombia (Koenig et al. 1995, Wahl et al. 2005). Throughout its range, this species is closely associated with Oak Trees (genus Quercus) and is most commonly found in Pine-Oak Woodlands (Koenig et al. 1995). It is probably best known for its highly social habits and unique method of storing acorns in specialized trees known as storage trees or granaries, although colonial living and acorn storage are not characteristic of all populations (Koenig et al. 1995). This is generally a sedentary species, but at least one population, located near the Huachuca Mountains in southeastern Arizona, regularly migrates annually (Stacey and Bock 1978) although irregular migrations occur elsewhere when local acorn crops fail (Koenig et al. 1995). The Acorn Woodpecker is an accidental species to British Columbia and records could reflect either birds searching for acorns due to crop failure or a possible range expansion north (Koenig et al. 1995, Toochin et al. 2014, see Table 1). There is one accepted record by the Alberta Bird Records Committee of a bird photographed near Sundre, Alberta from July 1-9, 2006 (Hudon et al. 2008) There are no records for Alaska (West 2008, Gibson et al. 2012) or Idaho (IBRC 2011).
Occurrence and Documentation
The Acorn Woodpecker is an accidental species in British Columbia with only 7 Provincial records of which 5 have occurred in the past 4 years (Toochin et al. 2014, see Table 1). Five records involve adult females with one record not giving the sex of the bird and the first record being identified as a male might actually have been a female (D. Bastaja Pers. Comm., Toochin et al. 2014, see Table 1). When groups of Acorn Woodpeckers exhaust their food stores they will often abandon their normal territories and wander in search of other food sources (Koenig et al. 1995). If there is a small local failure in acorns, birds will leave their normal territory to search for food in nearby areas not far from the territory of origin where they will likely return the following spring (Koenig et al. 1995). If the crop of acorns has a more extensive or massive crop failure, this can lead to birds permanently leaving an area with the results in the disappearance of an entire population (Koenig et al. 1995). It is in these “flight years” when birds are found out of range and out of normal suitable habitats (Koenig et al. 1995). The recent records in British Columbia are likely the result of a lack of food stores forcing birds to wander, but could also be the result of birds looking to expand their range northward. It is also possible that since female birds in the Melanerpes family of woodpeckers are known to wander in order to look for suitable nesting habitat as the males look after the young at the nest that there could be some sort of range extension happening (Koenig et al. 1995). So these occurrences could be the result of both factors. In the past 4 years, there have been two separate years of records were birds showed up together during the same time period (Toochin et al. 2014,see Table 1). There were 3 birds seen in 2010 and 2 birds found in 2012 (Toochin et al. 2014, see Table 1). There have been four different birds found between the dates May 17 – May 28 (Toochin et al. 2014, see Table 1). All but one was identified as an adult female. These birds were found in Princeton, Manning Provincial Park, Merritt and Hope (Toochin et al. 2014, see Table 1). The first 2 records for the province were both June records with 1 bird found in Maple Ridge and another found near Oliver (Toochin et al. 2014, see Table 1). The only other provincial record is of a female that successfully wintered in Abbotsford in 2010-11 (Toochin et al. 2014, see Table 1). So far this species tends to turn up in the southern interior which makes perfect sense because this region has the most similar preferred habitat that Acorn Woodpeckers like to live in. The Abbotsford bird wintered in a hazelnut farm and had plenty of nuts to eat over the winter months. According to Wahl et al. (2005) the population in southern Washington is small but stable so birds coming into British Columbia might not necessarily be coming from this population but from farther south where there have been droughts and massive forest fires between the years 2010-2013 (M. Meredith pers. comm.). As it stands right now, the Acorn Woodpecker is an eruptive species that likely occurs as a result of food shortages rather than a true range expansion, but hopefully in time as more records accumulate, it will be possible to see what is actually happening with this species in the province. It would be wonderful to see this magnificent looking woodpecker breeding in the southern interior of the province. Observers should particularly watch bird feeders and areas of mixed Pine and Oak Trees for the signs that this species is around. If a tree or telephone pole is riddled with holes that have acorns in them, then there is an Acorn Woodpecker nearby.
