Continued Declines in 2009 Sacramento CA Martin Population

[Daniel Airola]

Martins are nearly done breeding here this year, so we have close-to-final population information. For those who don't know, I monitor 10-12 colonies that breed annually in elevated freeways and overpasses in urban Sacramento. This population is the last remnant of a once widespread population in the Central Valley, which was otherwise eliminated following starling arrival here in the late 1960s.

This year's population declined again, for the 5th consecutive year. This year we had 68 pairs, down 18% from 83 pairs last year. Overall, the population has declined by 61% from the 173 pairs we had as a high population in 2004.

Our annual adult survival, based on detailed monitoring of color-banded birds was only 50%. Our population model predicts the level of decline we observed with this relatively low rate of survival. Our models says we need about 65% annual adult survival to sustain a population. Relatively low reproduction last year (2.1 young per nesting pair) also may have contributed to this year's decline.

The ultimate causes of the decline are not certain. Dry conditions over the last few years may have played a role. Also, we experience a lot of train, truck, and car mortality, which may be intensifying as Sacramento focuses on "infill" development to reduce climate effects, traffic, etc.

Our 2009 reproductive monitoring is not quite completed, but current number look like it has been a better year, with about 3.2 young produced per nest.

Once again, we were unable to attract martins to use nest boxes away from sources of urban mortality. The boxes have been up for 2 seasons now with decoys and a dawnsong player. Presumably the population is not productive enough to encourage a lot of new colonists to seek out a new nesting substrate away from existing colonies. We put some boxes up near bridge colonies to allow birds to get familiar with them, but have had no takers. Contrary to our fears, however, the boxes have not been innundated by house sparrows.

We are also conducting a pilot survey of the status of about 40 other colony sites throughout Northern CA, but nesting occurs later at many of these sites than in hot Sacramento. I'll report later on this study.

[John Miller]

Dan

Keep up your work. Wish we knew some way to encourage martins to go to those boxes. I belive I've read the boxes do seem to work at other lcoations in California and look forward to further reports.
John M

[Daniel Airola]

Hi John -

Yes, Stan Kostka has had good success initiating a nest box program at Shelter Cove, Humboldt County, along the forested north coast region of California. We've had several recent articles on this PMCA-supported program in recent PM Update issues.

Transition to nest boxes is easier in the forested area at Shelter Cove than in hotter, more developed Sacramento perhaps for several reasons.

There are few starlings and house sparrows in forested area, while they are abundant in Sacramento, which is dominated by agriculture and development. As a result, in Shelter Cove we can put nest boxes right next to natural snags where martins are nesting. In Sacramento, boxes placed near urban colonies have always been overrun by house sparrows and martins have never transitioned. So we have had to put the boxes further away from developed area where the martins are now, and this decreases the chances that martins will find them. House sparrow control is problematic on public lands in urban areas, where all martins nest.

Second, although we don't have a lot of data yet to support this, coastal martin populations seem more healthy, but also more limited by nest sites. As an example, we have seen new bridges on the coast colonized by multiple martin pairs within a few years. In Sacramento, the population is declining, and yet nest sites in the bridges number in the thousands. So the martins are traditionally tied to these nest sites (which also are quite different in appearance from nest boxes), and because of the abundance of sites, the birds have little immediate incentive to search out new sites.

So what we appear to have in Sacramento is a "sink" habitat that attracts birds but does not produce enough young each year to sustain itself. If the cause for decline is dry weather and resulting insect foods, perhaps we will see a turnaround; recent information suggests that the El Nino weather phenomenon is returning, which brings us wetter weather. If the cause of decline is vehicle collisions to adults, then we just have to work and hope that martins can make it into starling-secure boxes in non-urban areas before they disappear altogether here.

Thanks for you interest.