Introduction

As noted in Part 1of the Bat Protection Program Report, Part 2 of the report was intended to address activities such as the demolition of the existing bridge, and monitoring of the colony during the construction period. Unfortunately, Sacramento County was unable to secure the necessary regulatory agency permits to allow construction to go forward and it appears that demolition and the construction period will be delayed until spring 2003. This delay created a need to increase our efforts at making the temporary bat homes as successful as possible. Every year that the bats are displaced from their bridge habitat, the potential of a decline in their reproductive success increases. Considering that the initial population at the bridge was estimated by Bat Conservation International (BCI) staff at about 30,000 or more individuals, there is concern that the replacement habitat does not totally fulfill their habitat needs. In 2001, there may have been as many as 10,000 bats at the various locations in the bridge, and in the bat houses, however, accurate estimates of the population was not possible. There were newspaper accounts of numerous bat populations in surrounding areas such as the south Sacramento Kaiser Hospital, which is about 13 miles north of the project site. It is unknown if these are ‘our’ bats displaced by the loss of acceptable habitat.

Accounts reported in Part 1 of the Bat Protection Report ended in the summer of 2000. From mid-summer until the bats migrated out, only bat house 2 was used. It was estimated that up to 1,000 bats were present in house 2 as late as October 14, 2000. Bat guano was observed under houses 1 & 3, but no bats were observed during the day. No bats or guano were observed on the TNC property (bat houses 4-6) during the 2000 season. Both Mexican free tails and big brown bats were observed on the bridge as late as November 7, 2000. At that time there were still about 250 bats in house 2. By November 29, 2000 all bats were absent from the site.

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Winter 2001

During the winter months of 2001 the netting was repaired and an attempt was made to caulk all crevices within the entire bridge. The County crew caulked crevices on each side of the bridge and within each span. At least 200, 24-ounce cans of caulking were used. It looked foolproof. Exclusion nets remained in place from bent 1 to bent 15. By early March all exclusion methods for the season were complete. There were reports of bats arriving in other places nearby south Sacramento locations, but no bats were noted at the bridge site. The year 2000 bat monitoring results reported in Part 1 of the Bat Report were shared with both Mark Kiser at BCI and Marvin Maberry of Maberry Center (the bat house manufacturer) to get feedback on our bat protection techniques. They suggested that the roofs of two of the houses be painted black to increase the temperatures in these houses.

In April 2001 the roofs of houses 2 and 5 were painted black. The black paint on house 5 was extended 2 feet down from the roof. Dunn and Edwards flat black paint was used.

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Spring 2001

In early April, guano is observed at bat houses 1 & 2, and under the bridge at the creek crossing. This is a favorite hunting area for the bats. The guano appears to be from night roosting. There were no bats present in the bridge or at the bat houses. An evening visit to the bridge revealed bats flying around the creek. No bats are observed emerging from the bridge or the bat houses. Their point of origin is undetermined. Temperatures are still cool ranging from low 50’s to mid-60’s.

By late April the weather was in the mid-70’s. Approximately 30-50 bats are noted in both bat house 2 and in bat house 3. Guano is observed under house 1. Bats are observed roosting in the northern end of the bridge where caulking is absent.

In June it was estimated that there are several hundred bats in the bridge. Guano is observed below bridge openings ¾ inch or smaller. They can also be heard in various bridge locations where they cannot be seen. The population in bat houses 2 and 3 is estimated to be about 200 bats each. Both big brown bats and Mexican free tails are observed using the bridge and occupying the houses.

In late June, bat pups can be seen in the bridge crevices. The population in the houses has decreased to about 50 individuals in house 3, and 2 individuals are in house 2.

By mid-July, it is estimated that a few thousand bats occupy the bridge. Hundreds of free-tail pups and big brown pups were observed. The bats have taken up space that is both tiny (small rotted areas used to enter the hollow areas under the bents) and larger spans that have not been used in previous years. Mixed groups of big browns and Mexican free-tails are occupying space that may be up to a foot wide. Conservative estimates indicate that there are about 50 bats in house 1, at least 500 bats in house 2 and more than 1,000 bats in house 3. It is impossible to get an accurate count due to the height of the bat houses and the way the bats are stacked up in the slats. An evening visit in mid-August detected flying juveniles.

In early September the bats have moved completely out of house 2, however there is an inch of guano under the house. The even distribution pattern of guano beneath the house suggests that bats were using the entire structure including the center slats before they vacated. The slats are warped and the netting is sagging. It is unknown what caused the bats to leave, however there are large yellow jacket nests on the outside of the house. Wasps are also observed inside the bat houses

One bat was observed in house 4 at the TNC on September 5, 2001.

On September 26, 2001, bats were noted in the center slats of house 3 for the first time. Several thousand bats occupy each slat of house 3. There are more than 3,000 bats in house 1 (estimate by Bob Wisecarver). A wren nest was seen in house 3.

On a side note, it is interesting that Bob Wisecarver has erected a bat house at a nearby residence. He reports there are 700-800 bats in that house. This is an increase over last year’s population. There are also 360 linear feet of bat guano under the Alta Mesa Bridge. That is the first bridge in Sacramento County to have bat habitat built in. It has taken over 2 years for the bats to return and fully occupy the habitat created in that bridge.

On October 4, 2001, all bat houses and the entire bridge was inspected for the presence of bats and no bats were observed. It appears that they have migrated out of the area even though the daily ambient temperature has been 100 degrees the past week.

After sharing the results of the 2001 season with Bob Wisecarver, Marvin Maberry and Mark Kiser it was decided that modifications should be made to the houses to increase their internal temperatures. It was postulated that a ‘wind chimney’ effect might keep the temperatures cool by allowing air to circulate in from the bottom of the bat house, up the middle and out the vents.

Temperature data loggers and instructions were sent to DERA courtesy of the BCI North American Bat House Research Project. On October 15, 2001 the data loggers were installed in bat house 1, house 6 and under the bridge. These loggers ran for two weeks and were removed and returned to BCI on October 29, 2001. BCI will review the results of the temperature and offer additional recommendations. Any further modifications to the existing bat houses will be completed prior to the 2002 bat season, which begins in March 2002.

After the data loggers were placed in the houses, the vents on all the houses were sealed. In addition, the roof of house 1 was painted black. House 6 on the TNC property was modified with a new sloped cover over the bottom of the bat house. The data logger placement and the bottom cover to house 6 are shown in Attachment B. At this time the bottom cover has been attached with screws. Hinges will be added before the bats return to allow easy access for clean out of bat guano and other maintenance.

In addition to the above modifications, Marvin Maberry graciously donated a “La Casa” bat home to Sacramento County that was installed midway between bat house 1 and 2. La Casa is one of the most successful bat houses that Maberry Centre builds. It can accommodate 2000 freetail bats. A description of La Casa is in Attachment C.

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Plan for 2002 Season

It is unknown at this time whether bridge demolition and construction will commence during the 2002 season. If regulatory agency permit delays continue, the trestle bridge may not be demolished next year. In any event, exclusion efforts will continue. If construction does occur, we want to be prepared to demolish the bridge without affecting the bat colony. If demolition does not occur, the bats a continual effort will be made to encourage bat habitation in the houses.

Winter repairs to the bridge (additional netting and caulking as necessary) and any further modifications to the bat houses will be done in the early months of 2002. Monitoring will commence with the arrival of the bats in March.

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Part 3 - 2003 Season

After the bats have left the bridge area next October, Part 3 of the bat report will be prepared.

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