The jump point is usually May first, across the majority of the United States (including MA). While fertilization earlier than that using organics isn't going to cause a problem, there's no real reason to. The lawn doesn't need it if you winterized. If you didn't winterize, a weak fertilization when growth resumes might not be a bad idea. Half rate on Milorganite or around 7 to 8 pounds of soybean meal per thousand will do it fine. Then feed normally May 1-May 20th. But it also wouldn't be an error to just wait for May. The grass will manage. Time between fertilizations...variable. Post May, I won't feed until August again. The grass doesn't need summer fertilization. Although again, done organically, it's not a problem. It's just not strictly necessary. Fall is the season to hit it hard. I feed monthly August to October, which starts to release three weeks post feeding. After that, winterize when it's time and call it a year. Southern grasses will differ as their growth tendencies differ. Northern lawns are more cyclic. Feeding like that means you never run out of nitrogen and rarely, if ever, see signs that the lawn can use a feeding (if you do, it happens in late April when you're already thinking about it anyway).

Up, up and not away!

Glad to hear the bird was ok. There is a good bit of information on how to help an injured bird on the Bird Watching forum, it is at the top of the forum.

I'm glad your bird problem turned out to be seasonal but just in case you ever face this problem again (or any bird infestation problem) I thought it might be helpful to just mention a different angle on this. The problem is not that the birds are pooping (or whatever they're doing) in your pool. That is simply a symptom of your real problem: that your environment is attractive to birds. If you really want to keep birds from being destructive to your property you have to make it so that your land is a place they don't want to hang out on in the first place. There are a lot of different approaches to this but yes, stopping the food supply is one of them. Another would be the mylar balloons someone else mentioned up above. There are also specialized bird scare balloons with 'eyes' that follow the birds wherever they fly as well as holographic tape. These incorporate movement so they are usually more affective than static decoys. There are other senses to attack as well: taste/smell, touch, and hearing. Birds hate methyl anthranilate (a chemical derived from concord grapes that has long been used for grape flavoring)--it gives them a similar sensation to what we feel when we encounter bleach. This comes in commercially available sprays. Also, there are sticky gels, netting, or spike strips that keep birds from roosting on certain surfaces. Lastly, there are sound devices that utilize recordings of predators/distress calls that scare birds away. For a partially or fully enclosed area you could use an ultrasonic device as well (one that can't be heard by humans but is annoying to birds and bats). Make sure that you switch up whatever you use from time to time. If you use balloons, move the location (but always keep it near where the birds are nesting). If you're using a sound device change the interval between effects, try to randomize the effects being used. Also, using the products together in a synergistic way will create a more effective and longer-lasting reaction. I'm glad to hear that no one has mentioned killing or injuring the birds...don't do that. As mentioned before that would be reacting to the symptoms rather than truly solving the problem. Furthermore, it would be very easy to accidentally tamper with one of the MANY birds protected by the Migratory Bird Act of 1918 (and then you'd be in big trouble). Just a side note: be careful when cleaning up the bird poop. Birds can transmit over 60 diseases to humans. Some of them are fatal. Bird dropping particles can be unknowingly inhaled and lead to serious health problems. Good luck in your future bird encounters! Here is a link that might be useful: click for examples, case studies and FAQs about bird pest control