Purple Martins in Greater Victoria

Purple Martins (Progne subis) are the largest swallow found in North America. Western Purple Martins (Progne subis arboricola) breed along the western coast of North America from California to British Columbia and are genetically distinct from their eastern cousins, Progne subis subis. Western Purple Martins are a Species of Concern from California to Washington and a provincial Species at Risk (Blue-listed, Vulnerable) here in BC.

Purple Martins are neotropical migrants, like other members of the swallow family. They migrate from their wintering grounds in north and central South America to the United States and southern Canada each spring to breed during the summer months, returning south in the fall.

By 1949, Purple Martins had disappeared from the BC Lower Mainland and by 1985 there were only about 5 breeding pairs remaining on Vancouver Island. Now their numbers have steadily increased to over 1000 pairs, primarily as a result of nest boxes being built, installed, and maintained by volunteers at marine coastal locations around the Strait of Georgia.

Purple Martin Nesting Habits

Our western Purple Martins use individual nest boxes in loose clusters, while eastern Purple Martins prefer hanging gourds or condo-style apartment blocks.

Here in BC, they once nested in loose colonies in the cavities of old trees. Their numbers decreased due to loss of nesting habitat as well as severe competition for remaining natural nest cavities, particularly from introduced bird species such as House Sparrows and European Starlings.

Now Purple Martins mainly use nest boxes provided by people. They make very rustic nest structures using clamshells and large sticks lined with cottonwood leaves. These nest boxes are usually clustered together on groups of marine pilings near or on the water.

Purple Martins develop strong site fidelity to a particular location, especially if the sites are well maintained and the birds experience reproductive success.

  

BC Purple Martin Stewardship and Recovery Program

In 1985 a volunteer nest box program to rebuild the Purple Martin population on Vancouver Island was established, beginning with the installation of nest boxes at Cowichan Bay. These boxes at Cowichan Bay and others subsequently located around Esquimalt Harbour likely rescued the BC Purple Martins from extirpation. As their numbers slowly increased, more nest boxes were installed at various suitable locations around the Strait of Georgia.

 

In 2002 the Georgia Basin Ecological Assessment and Restoration Society (GBEARS) assumed responsibility for the nest box program and it was named the BC Purple Martin Stewardship and Recovery Program. GBEARS has provided overall co-coordination and scientific direction, monitoring and management of the program.

There are currently around 1,500 nest boxes located in the Lower Mainland/Fraser Valley area and on the eastern coast of Vancouver Island. Approximately 150 volunteers are now actively involved in this recovery program, including many individuals, First Nation groups, naturalist and conservation groups, corporations, universities, as well as federal, provincial, regional and municipal government departments.

Each year nestlings that are 10-days old and older are banded at most of the BC colonies with a coloured, alpha-numeric band on one leg and an aluminum US Fish and Wildlife band on the other. The Purple Martins experience a fledge rate of 2-3 young per nest.

  

 

When martins return from South America in the spring a spotting scope is used to read the bands on about 300 previously banbirds. This provides a representative random sample of 20-30% of the BC population. This unique, long term banding study provides valuable information about the BC Purple Martin population. This is important to understand the changes taking place in the species due to variations in nesting success, fledgling production, and the overall progress of the recovery program.

Greater Victoria’s Purple Martin colonies are monitored as part of the BC Purple Martin Stewardship and Recovery Program which is coordinated by Bruce Cousens and Charlene Lee in Nanaimo.

RPBO and Purple Martins

In 2014 a number of RPBO members assumed responsibility for the Purple Martin nest box colonies in the Greater Victoria area. Prior to that Tom Gillespie, a long time RPBO member, had worked in the recovery program in Victoria on an informal basis, in affiliation with GBEARS. Tom was devoted to this project until his final days, banding almost 400 Purple Martin nestlings in the summer of 2013.

Tom Gillespie banding a nestling

Wallis Moore Reid is now the Regional Coordinator for the South Island population of Purple Martins. John Costello is in charge of nest box building and maintenance. Daniel Donnecke has taken on the task of reading and recording the band numbers of returning adult birds. These are just a few of the people who are involved in Greater Victoria.

 

John and Wallis preparing the nest boxes for 2015

2014 Results

The BC Purple Martin population continues to grow. In 2014 a total of 1060 pairs nested at 74 marine and 6 freshwater sites – 110 more pairs than last year! There are 13 active Purple Martin colonies in the South Island region. Last summer Wallis Moore Reid banded 467 nestlings. Some of the more active sites in this area were: Tod Inlet (122 nestlings banded), West Bay Marina (95 nestlings banded), and the Institute of Ocean Sciences on Patricia Bay (89 nestlings banded).

It is encouraging to see how a species can recover thanks to the dedicated effort and cooperation of both individuals and groups. The Purple Martin, once near extirpation in this region, now has a strong “wing”-hold. There is every reason to hope that these birds will continue to flourish, thanks to everyone who has helped, and continues to help, make this such a successful project.

There is much more information about the Purple Martin program on the GBEARS website.

http://georgiabasin.ca/puma.htm

Purple Martin Conservation Association

http://www.purplemartin.org/

Iridescence in Hummingbirds

Iridescence, a striking hallmark of hummingbirds, is a remarkable feather colouration actually produced by structure rather than pigment. The appearance of colour in birds is created by either pigment or feather structure, and sometimes a combination of the two. Iridescence is actually produced by the reflection of microscopic structural features on the feather surface. This dazzling display of shimmering colour that at different angles becomes a complete absence of colour is one of the signature characteristics of hummingbirds. How is it produced and what is its purpose?

Rufous Hummingbird

Anna's Hummingbird

The most common example of iridescent colouration is the changeable rainbow colouration seen in oily puddles on pavement. How do the layers of oil and water create all these colours? Here is a somewhat technical explanation of how this works: As light reaches the surface of the oil, some light is immediately reflected from the surface and some light passes into the oil. The light that passes into the oil slows down and becomes compressed because the oil has a higher density than air. Some of this light then reflects off the bottom of the oil layer and then moves back to the surface. Then at the surface this light from the bottom meets the light reflected from the surface. These two light waves can be “out of phase” (the peaks and troughs do not match up), meaning they cancel each other out; however some wavelengths will be in synch and can be amplified, displaying a variety of colours. This process of cancellation and amplification results in a brilliant colour display which changes according to the angle of observation, i.e. how we are positioned in relation to the oil slick as well as the angle of the sun as it hits the surface.

Iridescent feathers in birds produce their colours in a similar fashion to oil slicks. Below is a diagram which shows how sunlight plus angle of observation plus light wavelengths interact to produce vivid, dull or black colour. Light hitting the feathers may bounce back from any one of the layers and it adds together with light bouncing back from other layers. If the light waves add up, the observer sees bright, flashing colour. If they cancel each other out, the feathers appear black. If they are slightly out of synch, then one sees a duller colour.

  

The feather structures which create iridescent colours in hummingbirds are very complex, with multiple layers of air bubbles. In typical hummingbird iridescent colouration there are eight to ten layers of feathers tightly stacked on top of one another. Amazingly, it is the combined reflections from inner and outer surfaces of the air bubbles in the feather layers that create iridescent colours. This arrangement scatters and refracts light at a microscopic level and gives the feathers their shifting iridescence. The entire system is incredibly precise and uniform, creating what appears to be a consistent iridescent colour. This feather stacking will intensify and purify the resulting spectral colour, which explains why hummingbirds have possibly the most intensively iridescent feathers known in birds.

Black-chinned Hummingbird

Calliope Hummingbird

In hummingbirds these feather layers are arranged at a very specific angle so that the bounce-back of colour can be directional and targeted. This mechanism allows the hummingbird to give precise, ‘directional’ signals. The males, which are intensely iridescent, can deliberately signal rivals and attract females, while remain unobvious to predators. Females also have some iridescent feathers on their throats, which they use along with their tail feathers, to protect food resources in their area from other hummingbirds. This is particularly evident when they have a nest with young ones. It is believed that females may produce more iridescent throat feathers as they mature.

It is little wonder that hummingbirds are considered one of the most fascinating species of the avian world with their brilliant yet ephemeral iridescence, which is actually no ‘colour’ at all!

Anna's Hummingbird